ð4Þ

#### 6.3. Catalytic activity of ruthenium

Ruthenium acts as a catalyst in many reactions. In the olefin metathesis, the carbene and alkylidene complex of Ruthenium act as a catalyst. In Fischer Tropsch reaction (Eq. 5), Ruthenium also acts as a catalyst [16]. Fischer Tropsch reaction is a reaction in which liquid hydrocarbons are formed as a product of reaction between hydrogen and carbon monoxide. Decomposition process of ammonia also employs Ru as catalyst [17]. Ru also catalyzes group of reactions called "borrowing hydrogen reactions". Borrowing hydrogen reaction is a reaction where two atoms of hydrogen are transferred to the catalyst to covert alcohol to carbonyl. The same reaction occurs in the conversion of alcohol to alkenes [5, 17].

Ruthenium carbonyl complex catalyzes the conversion of primary alcohol to aldehydes and secondary alcohol to aldehydes and ketones in the presence of a co-oxidant N-methylmorpholine-N-oxide (NMO) [8]. Ruthenium acts as a unique catalyst in oxidation reaction because of its varying oxidation state that ranges from �2 to +8 [6].

show the solubility in polar solvents (dichloromethane and acetone) and are insoluble in nonpolar solvents (aspentane and hexane). It is stable in air and shows diamagnetic nature with

Properties and Applications of Ruthenium http://dx.doi.org/10.5772/intechopen.76393 383

Figure 2. Structure of (p-cymene) ruthenium (II) 2-(naphthylazo)phenolate complexes.

the +2 oxidation state [6, 10].

Figure 3. Structure of Tris (bipyridine) ruthenium (II) chloride.

#### 7. Ruthenium complexes

In recent years, there has been remarkable growth and evaluation in the field of coordination and organometallic chemistry of Ru. Many publications have appeared recently on the formation of Ru-based complexes and their applications in such areas as medicine, catalysis, biology, nanoscience, redox and photoactive materials. These developments can be related to the fact that Ru has the unique ability to exist in multiple oxidation states. Examples of these complexes and various applications of Ru are reviewed in the following sections.

#### 7.1. Development of half-sandwich para-cymene ruthenium (II) naphthylazophenolato complexes

Ruthenium (II)-arene complex has a structure of three-legged piano stool with a metal at the center in a quasi-octahedral geometry which is occupied by byan arene complex. 2-(naphthylazo)phenolate ligands reacts with chloro-bridged (g6-p-cymene) ruthenium complex [{(g6-pcymene)RuCl}2(l-Cl)2] in methanol having molar ratio 1:1 at room temperature leads to formation of monomeric ruthenium(II) complexes. The formed complexes (Figure 2)

Figure 2. Structure of (p-cymene) ruthenium (II) 2-(naphthylazo)phenolate complexes.

ð4Þ

ð5Þ

6.3. Catalytic activity of ruthenium

382 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

7. Ruthenium complexes

complexes

Ruthenium acts as a catalyst in many reactions. In the olefin metathesis, the carbene and alkylidene complex of Ruthenium act as a catalyst. In Fischer Tropsch reaction (Eq. 5), Ruthenium also acts as a catalyst [16]. Fischer Tropsch reaction is a reaction in which liquid hydrocarbons are formed as a product of reaction between hydrogen and carbon monoxide. Decomposition process of ammonia also employs Ru as catalyst [17]. Ru also catalyzes group of reactions called "borrowing hydrogen reactions". Borrowing hydrogen reaction is a reaction where two atoms of hydrogen are transferred to the catalyst to covert alcohol to

Ruthenium carbonyl complex catalyzes the conversion of primary alcohol to aldehydes and secondary alcohol to aldehydes and ketones in the presence of a co-oxidant N-methylmorpholine-N-oxide (NMO) [8]. Ruthenium acts as a unique catalyst in oxidation reaction because

In recent years, there has been remarkable growth and evaluation in the field of coordination and organometallic chemistry of Ru. Many publications have appeared recently on the formation of Ru-based complexes and their applications in such areas as medicine, catalysis, biology, nanoscience, redox and photoactive materials. These developments can be related to the fact that Ru has the unique ability to exist in multiple oxidation states. Examples of these complexes and

7.1. Development of half-sandwich para-cymene ruthenium (II) naphthylazophenolato

Ruthenium (II)-arene complex has a structure of three-legged piano stool with a metal at the center in a quasi-octahedral geometry which is occupied by byan arene complex. 2-(naphthylazo)phenolate ligands reacts with chloro-bridged (g6-p-cymene) ruthenium complex [{(g6-pcymene)RuCl}2(l-Cl)2] in methanol having molar ratio 1:1 at room temperature leads to formation of monomeric ruthenium(II) complexes. The formed complexes (Figure 2)

carbonyl. The same reaction occurs in the conversion of alcohol to alkenes [5, 17].

of its varying oxidation state that ranges from �2 to +8 [6].

various applications of Ru are reviewed in the following sections.

show the solubility in polar solvents (dichloromethane and acetone) and are insoluble in nonpolar solvents (aspentane and hexane). It is stable in air and shows diamagnetic nature with the +2 oxidation state [6, 10].

Figure 3. Structure of Tris (bipyridine) ruthenium (II) chloride.

#### 7.2. Development of functionalized polypyridine ligands for ruthenium complexes

Polypyridine are coordination complexes containing polypyridine ligands such as 2,2<sup>0</sup> bipyridine, 1,10-phenanthroline and 2,2<sup>0</sup> ,60 200-terpyridine. Polypyridines are multi-denated ligands which are responsible for characteristics property of metal complex they formed. Some of complexes show the characteristics of absorption of light by a process called metal-to-ligands charge transfer (MLCT). This said property of metal complex is due to the change in substituent to the polypyridine moiety. Among the polypyridine ligands for ruthenium complexes the mostly studied complex is Tris (bipyridine) ruthenium (II) chloride (Figure 3). It is a red crystalline salt having a hexahydrate form. Tris (bipyridine) ruthenium (II) chloride salt is prepared when aqueous solution of ruthenium trichloride reacts with 2,2<sup>0</sup> -bipyridine in the presence of reducing agent hypo-phosphorus acid. In this reaction Ru(III) gets reduced to Ru(II) [18].

glands. In treatment of medullary thyroid carcinoma (MTC), determination of calcitonin level plays an important role. The process of determination of calcitonin level involves one step sandwich assay method. This method is carried out in two incubation steps. Each incubation process takes 9 min each. In first incubation, 50 microliters of sample of biotinylated monoclonal human calcitonin specific antibody and monoclonal human calcitonin specific antibody labeled with ruthenium complex are incubated. This incubation leads to formation of sandwich like complex where human calcitonin is carrying both biotinylated and ruthenylated complex. After the first step, second incubation step is done where streptavidin-coated microparticles is added. Streptavidin-coated microparticle makes complex with biotin. After the incubation step, measurement is done. For measurement, the mixture of incubation is aspirated into measuring cells and micro particles of mixture are magnetically attracted to the surface of electrode. After that the unbound particles are removed. Voltage is applied on to the electrode and induction of chemi-lumiscent emission is done and after that

Properties and Applications of Ruthenium http://dx.doi.org/10.5772/intechopen.76393 385

• Folate is the main constituent of synthesis of DNA. It is also essential for formation of red blood cells. Deficiency of folate leads to megalobalstic anemia. Deficiency of folate is estimated by determination of folate level in erythrocytes as well as serum. Ruthenium plays an important role in Elecys folate RBC assay in estimating folate deficiency in RBC. The process involved in folate determination is competition principle. This process involves three steps incubation method. In first incubation step folate pretreatment reagent is added which leads to release of folate from its binding sites (erythrocytes). In the second incubation step, Rulabeled folate binding protein is added which makes complex with the sample. In the third incubation step streptavidin bounded microparticles are added which get attached to unbound sites of ruthenium-labeled folate binding protein. The whole complex is bound to solid phase via streptavidin and biotin. For measurement, the mixture of incubation is aspirated into measuring cells and microparticles of mixture are magnetically attracted to the surface of electrode. After that the unbound particles are removed. Voltage is applied on to the electrode and induction of chemi-lumiscent emission is done and after that the

• Ruthenium is also employed in detection of cyclosporine by Elecsys cyclosporine assay. Determination of cyclosporine is an important aspect for management of liver, kidney, heart lungs and bone marrow transplant patients receiving cyclosporine therapy [12].

History of medical science shows metals like gold has always been used for medicinal purpose. Though it is known that metals may have beneficial effect for health, but the exact mode of

• Immunosuppressant: Immunosuppressant is drug used to suppress hyperactivity of body's immune system. An immunosuppressant Cyclosporin A which has wide application in treatment of disease like anemia and psoriasis eczema has shown side effects such as nausea, renal diseases, and hypertension. To modify the action of Cyclosporin A,

activity remains unknown. Ruthenium also has been applied in treatment [21].

the response is studied with photomultiplier [12].

response is studied with photomultiplier [12].

8.2.2. Applications in treatment

#### 8. Applications of ruthenium

Ruthenium has a wide variety of application in diverse fields. Few of the applications of Ruthenium are listed below.

#### 8.1. General applications

Ruthenium finds application both in electronic industry and chemical industry. In electrical industry it is used in manufacturing of electronic chips [19]. Chemically it is used in the form of anodes for chlorine production in electrochemical cells [20]. Ruthenium is used as a hardener when it is mixed with other metals to form alloy. This characteristic of ruthenium is used in the preparation of jewelry of palladium [18, 20]. When Ruthenium forms alloy with titanium it improves its corrosion resistant property. Ruthenium alloys also find application in manufacturing of turbines of jet engines [17]. Fountain pen nibs also contain Ru tips. Ruthenium has also application in therapy. For instance 106 isotope of Ru has application in radiotherapy of malignant cells of eye [11]. RuO4 is used in criminal investigations as it reacts with any fat or fatty substance having sebaceous pigments to give black or brown coloration due to formation of ruthenium dioxide pigments [12].

Ruthenium complexes tend to absorb light rays of visible spectrum. This property of ruthenium finds application in manufacturing solar cells for production of solar energy. [16] Ruthenium vapor get deposited on the surface of substrate and has magneto-resistive property. This property of Ru is used in making a layer or film on hard disk drives [12].

#### 8.2. Biomedical applications

#### 8.2.1. Applications in diagnosis

• Ruthenium is used for determination of calcitonin level in blood. This determination is helpful in diagnosis and treatment of diseases related to thyroid and parathyroid

glands. In treatment of medullary thyroid carcinoma (MTC), determination of calcitonin level plays an important role. The process of determination of calcitonin level involves one step sandwich assay method. This method is carried out in two incubation steps. Each incubation process takes 9 min each. In first incubation, 50 microliters of sample of biotinylated monoclonal human calcitonin specific antibody and monoclonal human calcitonin specific antibody labeled with ruthenium complex are incubated. This incubation leads to formation of sandwich like complex where human calcitonin is carrying both biotinylated and ruthenylated complex. After the first step, second incubation step is done where streptavidin-coated microparticles is added. Streptavidin-coated microparticle makes complex with biotin. After the incubation step, measurement is done. For measurement, the mixture of incubation is aspirated into measuring cells and micro particles of mixture are magnetically attracted to the surface of electrode. After that the unbound particles are removed. Voltage is applied on to the electrode and induction of chemi-lumiscent emission is done and after that the response is studied with photomultiplier [12].


#### 8.2.2. Applications in treatment

7.2. Development of functionalized polypyridine ligands for ruthenium complexes

,60

bipyridine, 1,10-phenanthroline and 2,2<sup>0</sup>

384 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

this reaction Ru(III) gets reduced to Ru(II) [18].

8. Applications of ruthenium

of ruthenium dioxide pigments [12].

8.2. Biomedical applications

8.2.1. Applications in diagnosis

Ruthenium are listed below.

8.1. General applications

reacts with 2,2<sup>0</sup>

Polypyridine are coordination complexes containing polypyridine ligands such as 2,2<sup>0</sup>

ligands which are responsible for characteristics property of metal complex they formed. Some of complexes show the characteristics of absorption of light by a process called metal-to-ligands charge transfer (MLCT). This said property of metal complex is due to the change in substituent to the polypyridine moiety. Among the polypyridine ligands for ruthenium complexes the mostly studied complex is Tris (bipyridine) ruthenium (II) chloride (Figure 3). It is a red crystalline salt having a hexahydrate form. Tris (bipyridine) ruthenium (II) chloride salt is prepared when aqueous solution of ruthenium trichloride

Ruthenium has a wide variety of application in diverse fields. Few of the applications of

Ruthenium finds application both in electronic industry and chemical industry. In electrical industry it is used in manufacturing of electronic chips [19]. Chemically it is used in the form of anodes for chlorine production in electrochemical cells [20]. Ruthenium is used as a hardener when it is mixed with other metals to form alloy. This characteristic of ruthenium is used in the preparation of jewelry of palladium [18, 20]. When Ruthenium forms alloy with titanium it improves its corrosion resistant property. Ruthenium alloys also find application in manufacturing of turbines of jet engines [17]. Fountain pen nibs also contain Ru tips. Ruthenium has also application in therapy. For instance 106 isotope of Ru has application in radiotherapy of malignant cells of eye [11]. RuO4 is used in criminal investigations as it reacts with any fat or fatty substance having sebaceous pigments to give black or brown coloration due to formation

Ruthenium complexes tend to absorb light rays of visible spectrum. This property of ruthenium finds application in manufacturing solar cells for production of solar energy. [16] Ruthenium vapor get deposited on the surface of substrate and has magneto-resistive property. This

• Ruthenium is used for determination of calcitonin level in blood. This determination is helpful in diagnosis and treatment of diseases related to thyroid and parathyroid

property of Ru is used in making a layer or film on hard disk drives [12].


200-terpyridine. Polypyridines are multi-denated


History of medical science shows metals like gold has always been used for medicinal purpose. Though it is known that metals may have beneficial effect for health, but the exact mode of activity remains unknown. Ruthenium also has been applied in treatment [21].

• Immunosuppressant: Immunosuppressant is drug used to suppress hyperactivity of body's immune system. An immunosuppressant Cyclosporin A which has wide application in treatment of disease like anemia and psoriasis eczema has shown side effects such as nausea, renal diseases, and hypertension. To modify the action of Cyclosporin A,

complex is made with Ru(III). Ruthenium cyclosporin complex gives a stable compound which results in an inhibitory effect on T lymphocyte proliferation [22].

the ability to bind to the DNA and inhibits its replication as well as protein synthesis. Ruthenium has low aqueous solubility which was the only drawback of it. This drawback was countered by using dialkyl sulfoxide derivative of ruthenium. The mechanism of action of ruthenium as an anticancer agent is that it causes apoptosis of tumor cells by acting at

Properties and Applications of Ruthenium http://dx.doi.org/10.5772/intechopen.76393 387

• Radiation therapy: in cancer treatment radiotherapy has also been used. Radiation therapy becomes beneficial only when it is proximal to the cancerous cell. The agents used in radiation therapy are called radio sensitizers. To increase the proximity to cancerous cells radio sensitizers' complexes with ruthenium are used as Ru has the affinity to bind to

• Photodynamic therapy: it is a therapy where chemicals and electromagnetic radiations are used. In this therapy chemicals are targeted on the cancerous cell, these chemicals become cytotoxic when they interact with electromagnetic radiation. In this therapy Ruthenium find its application as it increases the access of these chemicals to the cancer-

• Action on cancerous mitochondria: mitochondria are the power house of any cell. This makes it a potential target for anticancer therapy. Ruthenium red is a type of ruthenium which is used to stain mitochondria. Mitochondrial surface has some calcium entity on it. When ruthenium red is added, it reacts with this calcium and stains the mitochondria. Ruthenium red also has tumor inhibiting activity. However, ruthenium red is not prefer-

• Effect on metastasis: metastasis is the ability of cancerous cell to spread in the body by lymphatic or circulatory system. A tumor cell more than 1 mm in size requires additional blood supply to spread in the body. Formations of new blood vessels are called angiogenesis. Drugs which act as anti-metastasis many inhibit this action. Ruthenium complexes anti-metastatsis drug namely NAMI-A does the same action by binding to the mRNA and production of denatured protein which gets accumulated on the surface of tumor making a hard film and prevents any blood supply to the tumor cell. This action inhibits the metastasis. Ruthenium has additional benefit that it easily crosses any cell so the reach of

Ruthenium with atomic number of 44 and symbol Ru was discovered by Russian chemist Karl Klaus (1796–1864). In earth's crust, it is quite rare, found in parts per billion quantities, in ores containing some of the other platinum group metals. It is silvery whitish, lustrous hard metal with a shiny surface. The ability of Ru to exist in many oxidation states is an important property of this rare element which plays an important part in its applications. Ruthenium readily forms coordinate complexes and these complexes have their applications in diverse fields such as medicine, catalysis, biology, nanoscience, redox and photoactive

DNA level. Apoptosis is a controlled destruction of cells [17, 18].

ably used clinically as it has major side effects [20, 22].

DNA easily [18, 19].

ous cells [20, 21].

the drug increases [23, 26].

9. Summary and conclusions


#### 8.2.3. Applications of Ruthenium in cancer research

• Anti-carcinogenic activity: cancer or carcinoma is a stage where body cells undergo uncontrolled proliferation and having invasiveness and metastatic property. To treat carcinoma, drug therapy aims at inhibiting synthesis of cancerous protein as well as inhibiting DNA replication. In market there are drugs such as Cisplatin which uses platinum as anticancer agent. Though platinum has shown better results in treatment of cancer but in some cancers, platinum is unable to show positive results. This shortcoming of Platinum made way for use of Ruthenium as a new entrant in treatment of cancer. Ruthenium shows

the ability to bind to the DNA and inhibits its replication as well as protein synthesis. Ruthenium has low aqueous solubility which was the only drawback of it. This drawback was countered by using dialkyl sulfoxide derivative of ruthenium. The mechanism of action of ruthenium as an anticancer agent is that it causes apoptosis of tumor cells by acting at DNA level. Apoptosis is a controlled destruction of cells [17, 18].


#### 9. Summary and conclusions

complex is made with Ru(III). Ruthenium cyclosporin complex gives a stable compound

• Antimicrobial action: antimicrobial drugs are drugs that inhibit microbial growth in human body. Ruthenium complex has its effectiveness against wide range of parasitic diseases. Microbial strains which are exposed to a certain kind of antimicrobial therapy become resistant to that drug. The resistance develops because the microbes mutate themselves against the organic compound of the drug. But with the formation of complex with certain metals the effectiveness of the drug increases as the microbes are unable to deal with the metal part of the organometallic complex of drug. In case of Chloroquine, Plasmodium species develops résistance against it, whereas when Chloroquine is

• Antibiotic action: antibiotics are drugs which are made from one particular microorganism and act on the other microorganism. Synthetic antibiotics are also nowadays made in laboratory. Antibiotic exhibit their action by entering the cell of microbes and targeting any vital biosynthetic pathway. Ruthenium has upper edge if it gets complexes with synthetic antibiotics. Ruthenium being a metal has better tendency to bind to the cellular component similar to Iron. When an organic moiety gets bind to a metal ion, at that time sharing or delocalization of cations between the two moieties occurs. The change in charges among the component of drug increases the permeability of cellular component in favor of drug. For example, Thiosemicarbazone shows a remarkable increase in its

• Inhibitory effect on nitric oxides: nitric oxide is a cellular component which is produced by many cells. The main physiological role of nitric oxide is to produce vasodilation. Nitric oxide does this action my increasing cellular level of cyclic-guanosine 3<sup>0</sup>

• Anti-carcinogenic activity: cancer or carcinoma is a stage where body cells undergo uncontrolled proliferation and having invasiveness and metastatic property. To treat carcinoma, drug therapy aims at inhibiting synthesis of cancerous protein as well as inhibiting DNA replication. In market there are drugs such as Cisplatin which uses platinum as anticancer agent. Though platinum has shown better results in treatment of cancer but in some cancers, platinum is unable to show positive results. This shortcoming of Platinum made way for use of Ruthenium as a new entrant in treatment of cancer. Ruthenium shows

monophosphate (CGMP) which is a secondary messenger in the physiological system. Over production of nitric acid can cause many disorders associated with respiratory system such as tumor of respiratory system. It also causes severe hypotension on over production. It also causes gastric inflammatory disorders. Ruthenium has beneficial effect in treatment of over production of nitric oxides. When ruthenium is administered in complex form such as ruthenium poly amino carboxylates, excess nitric oxide present in blood binds to this complex readily and reduces ruthenium to form an unabsorbable

,50 -

which results in an inhibitory effect on T lymphocyte proliferation [22].

386 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

complexed with ruthenium, resistance does not develop [23].

activity due to formation of complex of Ru [24].

complex there by inhibiting its unwanted effects [25].

8.2.3. Applications of Ruthenium in cancer research

Ruthenium with atomic number of 44 and symbol Ru was discovered by Russian chemist Karl Klaus (1796–1864). In earth's crust, it is quite rare, found in parts per billion quantities, in ores containing some of the other platinum group metals. It is silvery whitish, lustrous hard metal with a shiny surface. The ability of Ru to exist in many oxidation states is an important property of this rare element which plays an important part in its applications. Ruthenium readily forms coordinate complexes and these complexes have their applications in diverse fields such as medicine, catalysis, biology, nanoscience, redox and photoactive materials. In biomedical fields Ru is used for diagnosis and treatment purpose. For example, Ru is used for determination of calcitonin level in blood which is helpful in diagnosis and treatment of diseases related to thyroid and parathyroid glands. Also, Ru plays an important role in Elecys folate RBC assay in estimating folate deficiency in RBC. Ruthenium cyclosporin complex gives a stable compound which results in an inhibitory effect on T lymphocyte proliferation which shows its immune-suppressant action. Ruthenium complex has its effectiveness against wide range of parasitic diseases. Ruthenium shows the ability to bind to the DNA and inhibits its replication as well as protein synthesis. This property helps in the treatment of cancer. This chapter gives a brief account of the various properties of Ru which are exploited for applications in the medical field. It is likely that in the coming years, further research will lead to even more useful applications of this miraculous element.

[6] Ablialimov O, Kędziorek M, Malinska M, Wozniak K. Synthesis, structure, and catalytic activity of new ruthenium(II) indenylidene complexes bearing unsymmetrical N-hetero-

Properties and Applications of Ruthenium http://dx.doi.org/10.5772/intechopen.76393 389

[7] Valente A, Garcia MH. Synthesis of macromolecular ruthenium compounds: A new approach for the search of anticancer drugs. Inorganics. 2014;2:96-114. DOI: 10.3390/

[8] Meija J. Atomic weights of the elements 2013 (IUPAC technical report). Pure and Applied

[9] Motswainyana WM, Ajibade PA. Anticancer activities of mononuclear ruthenium(II) coordination complexes. Advances in Chemistry. 2015:1-21. DOI: 10.1155/2015/859730

[10] Marx VM, Sullivan AH, Melaimi M. Cyclic alkyl amino carbene (CAAC) ruthenium complexes as remarkably active catalysts for ethenolysis. Angewandte Chemie, Interna-

[11] Singh SK, Pandey DS. Multifaceted half-sandwich arene-ruthenium complexes: Interactions with biomolecules, photoactivation, and multinuclearity approach. RSC Advances.

[12] Rezayee NM, Huff CA, Sanford MS. Tandem amine and ruthenium-catalyzed hydrogenation of CO2 to methanol. Journal of the American Chemical Society. 2015;137:1028-1031.

[13] Miyada T, Kwan EH, Yamashita M. Synthesis, structure, and bonding properties of ruthenium complexes possessing a boron-based PBP pincer ligand and their application for catalytic hydrogenation. Organometallics. 2014;33:6760-6770. DOI: 10.1021/

[14] Xian-Lan H, Liang Z-H, Zeng M-H. Ruthenium(II) complexes: Structure, DNA-binding, photocleavage, antioxidant activity, and theoretical studies. Journal of Coordination

[15] Corral E, Hotze CG, Den D. Ruthenium polypridyl complexes and their modes of interaction with DNA: Is there a correlation between these interactions and the antitumor activity of the compounds. Journal of Biological Inorganic Chemistry. 2009;14:439-448. DOI:

[16] Shoba C, Satyanarayana S. Synthesis, characterization, and DNA-binding properties of Ru (II) molecular "light switch" complexes. Journal of Coordination Chemistry. 2012;65(3):

[17] Sava G, Bergamo A. Ruthenium drugs for cancer chemotherapy: An ongoing challenge to treat solid tumours. Cancer Drug Discovery and Development. 2009;1:57-66. DOI:

cyclic carbenes. Organometallics. 2014;33:2160-2171. DOI: 10.1021/om4009197

Chemistry. 2016;88(3):265-291. DOI: 10.1515/pac-2015-0305

tional Edition. 2015;54:1919-1923. DOI: 10.1002/anie.201410797

Chemistry. 2011;64:3792-3807. DOI: 10.1089/dna.2009.0979

2014;4:1819-1840. DOI: 10.1039/C3RA44131H

DOI: 10.1021/ja511329m

10.1007/s00775-008-0460-x

10.1007/978-1-60327-459-3\_8

474-486. DOI: 10.1080/00958972.2011.649736

om500585j

inorganics2010096

## Author details

Anil K. Sahu<sup>1</sup> , Deepak K. Dash1 , Koushlesh Mishra<sup>1</sup> , Saraswati P. Mishra<sup>1</sup> , Rajni Yadav<sup>2</sup> and Pankaj Kashyap<sup>1</sup> \*

\*Address all correspondence to: pankajkashyap333@gmail.com

1 Royal College of Pharmacy, Chhattisgarh Swami Vivekanand Technical University, Raipur, Chhattisgarh, India

2 Columbia Institute of Pharmacy, Raipur, Chhattisgarh, India

#### References


[6] Ablialimov O, Kędziorek M, Malinska M, Wozniak K. Synthesis, structure, and catalytic activity of new ruthenium(II) indenylidene complexes bearing unsymmetrical N-heterocyclic carbenes. Organometallics. 2014;33:2160-2171. DOI: 10.1021/om4009197

materials. In biomedical fields Ru is used for diagnosis and treatment purpose. For example, Ru is used for determination of calcitonin level in blood which is helpful in diagnosis and treatment of diseases related to thyroid and parathyroid glands. Also, Ru plays an important role in Elecys folate RBC assay in estimating folate deficiency in RBC. Ruthenium cyclosporin complex gives a stable compound which results in an inhibitory effect on T lymphocyte proliferation which shows its immune-suppressant action. Ruthenium complex has its effectiveness against wide range of parasitic diseases. Ruthenium shows the ability to bind to the DNA and inhibits its replication as well as protein synthesis. This property helps in the treatment of cancer. This chapter gives a brief account of the various properties of Ru which are exploited for applications in the medical field. It is likely that in the coming years, further

research will lead to even more useful applications of this miraculous element.

, Koushlesh Mishra<sup>1</sup>

1 Royal College of Pharmacy, Chhattisgarh Swami Vivekanand Technical University, Raipur,

[1] Medici S, Peana M, Nurchi VM. Noble metals in medicine: Latest advances. Coordination

[2] Matthew G, Vander H. Targeting Cancer metabolism. A therapeutic window opens.

[3] Blunden BM, Rawal A, Stenzel MH. Superior chemotherapeutic benefits from the ruthenium-based anti-metastatic drug NAMI-A through conjugation to polymeric micelles. Mac-

[4] Pastuszko A, Niewinna K, Czyz M. Synthesis, X-ray structure, electrochemical properties and cytotoxic effects of new arene ruthenium(II) complexes. Organometallic Chemistry.

[5] Ivry E, Ben-Asuly A, Goldberg I, Lemcoff NG. Amino acids as chiral anionic ligands for ruthenium based asymmetric olefin metathesis. Chemical Communications. 2015;51:3870-

Chemistry Reviews. 2015;284:329-350. DOI: 10.1186/s13065-015-0126-z

Nature Reviews Drug Discovery. 2011;10:671-684. DOI: 10.1038/nrd3504

, Saraswati P. Mishra<sup>1</sup>

, Rajni Yadav<sup>2</sup> and

Author details

, Deepak K. Dash1

388 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

\*Address all correspondence to: pankajkashyap333@gmail.com

2 Columbia Institute of Pharmacy, Raipur, Chhattisgarh, India

romolecules. 2014;47:1646-1655. DOI: 10.1021/ma402078d

2013;14:745-746. DOI: 10.1016/j.jorganchem.2013.07.020

3873. DOI: 10.1039/C5CC00052A

\*

Anil K. Sahu<sup>1</sup>

Pankaj Kashyap<sup>1</sup>

Chhattisgarh, India

References


[18] Ang WH, Dyson PJ. Classical and non-classical ruthenium-based anticancer drugs: Towards targeted chemotherapy. European Journal of Inorganic Chemistry. 2006;20:4003- 4018. DOI: 10.1002/ejic.200600723

**Section 5**

**Metallurgy and Recovery**


## **Metallurgy and Recovery**

[18] Ang WH, Dyson PJ. Classical and non-classical ruthenium-based anticancer drugs: Towards targeted chemotherapy. European Journal of Inorganic Chemistry. 2006;20:4003-

[19] Daxiong H, Haiyan W, Nailin R. Molecular modelling of B-DNA site recognition by Ru intercalators: Molecular shape selection. Journal of Molecular Modeling. 2004;10:216-222.

[20] Gunanathan C, Milstein D. Bond activation and catalysis by ruthenium pincer complexes.

[21] Tönnemann J, Scopelliti R, Severin K. (Arene) ruthenium complexes with imidazolin-2 imine and imidazolidin-2-imine ligands. European Journal of Inorganic Chemistry. 2014;

[22] Mukherjee T, Ganzmann C, Bhuvanesh N, Gladysz JA. Syntheses of enantiopure bifunctional 2-guanidinobenzimidazole cyclopentadienyl ruthenium complexes: Highly enantioselective organometallic hydrogen bond donor catalysts for carbon-carbon bond forming

[23] Saez R, Lorenzo J, Prieto MJ, Font-Bardia M. Influence of PPh3 moiety in the anticancer activity of new organometallic ruthenium complexes. Journal of Inorganic Biochemistry.

[24] Clavel CM, Păunescu E, Nowak-Sliwinska P, Dyson PJ. Thermoresponsive organometallic arene ruthenium complexes for tumour targeting. Chemical Science. 2014;5:1097-1101.

[25] Adeniyi AA, Ajibade PA. An insight into the anticancer activities of Ru(II)-based metallocompounds using docking methods. Molecules. 2013;18:10829-10856. DOI: 10.3390/

[26] Zhang S, Ding Y, Wei H. Ruthenium polypyridine complexes combined with oligonucleotides for bioanalysis: A review. Molecules. 2014;19:11933-11987. DOI: 10.3390/molecule-

reactions. Organometallics. 2014;33:6723-6737. DOI: 10.3490/molecules200917274

Chemical Reviews. 2014;114:12024-12087. DOI: 10.1039/c3nj00315a

14:4287-4293. DOI: 18.5586/Inorg.Chem.9172442001

2014;136:1-12. DOI: 10.3390/molecules23010159

DOI: 10.3390/molecules200917244

molecules180910829

s190811933

4018. DOI: 10.1002/ejic.200600723

390 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

DOI: 10.1016/S0006-3495(96)79587-5

**Chapter 18**

**Provisional chapter**

**Extraction of Platinum Group Metals**

**Extraction of Platinum Group Metals**

DOI: 10.5772/intechopen.73214

About 80% of the worlds' reserves for platinum group metals (PGMs) are in South Africa's Bushveld Igneous Complex. Processing of PGM involves comminution, flotation, smelting, converting, base metals refinery and precious metals refinery. Due to increasing chrome content in the feed and the challenges associated with operating high chrome feed, alternative routes to smelting of PGM are being investigated. Some hydrometallurgical routes have been proposed. However, none of the reported potential routes have yet

Platinum group metals (PGMs) are a group of six elements, namely iridium (Ir), osmium (Os), platinum (Pt), palladium (Pd), rhodium (Rh) and ruthenium (Ru) [1, 2]. PGMs together with gold and silver are classified as noble or precious metals because of their high corrosion and oxidation resistance [1–3]. The world's reserves of platinum group metals/elements are estimated at 100 million kilogrammes, of which over 80% is contained in South Africa's Bushveld Igneous Complex [4]. Summary of the PGM reserves by country is shown in **Table 1** [5]. PGMs are used in a number of industrial processes and commercial applications including automotive, jewellery, electronics, dentistry, catalysts, needles, pivots, temperature measurements, special crucibles and investments amongst

**Keywords:** platinum group metals, chrome, smelting, UG2, Merensky

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

Bongephiwe Mpilonhle Thethwayo

Bongephiwe Mpilonhle Thethwayo

http://dx.doi.org/10.5772/intechopen.73214

**Abstract**

**1. Introduction**

others [5–7].

been commercialised.

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

**Provisional chapter**

## **Extraction of Platinum Group Metals**

**Extraction of Platinum Group Metals**

#### Bongephiwe Mpilonhle Thethwayo Bongephiwe Mpilonhle Thethwayo Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.73214

#### **Abstract**

About 80% of the worlds' reserves for platinum group metals (PGMs) are in South Africa's Bushveld Igneous Complex. Processing of PGM involves comminution, flotation, smelting, converting, base metals refinery and precious metals refinery. Due to increasing chrome content in the feed and the challenges associated with operating high chrome feed, alternative routes to smelting of PGM are being investigated. Some hydrometallurgical routes have been proposed. However, none of the reported potential routes have yet been commercialised.

DOI: 10.5772/intechopen.73214

**Keywords:** platinum group metals, chrome, smelting, UG2, Merensky

#### **1. Introduction**

Platinum group metals (PGMs) are a group of six elements, namely iridium (Ir), osmium (Os), platinum (Pt), palladium (Pd), rhodium (Rh) and ruthenium (Ru) [1, 2]. PGMs together with gold and silver are classified as noble or precious metals because of their high corrosion and oxidation resistance [1–3]. The world's reserves of platinum group metals/elements are estimated at 100 million kilogrammes, of which over 80% is contained in South Africa's Bushveld Igneous Complex [4]. Summary of the PGM reserves by country is shown in **Table 1** [5]. PGMs are used in a number of industrial processes and commercial applications including automotive, jewellery, electronics, dentistry, catalysts, needles, pivots, temperature measurements, special crucibles and investments amongst others [5–7].

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons


A typical mineralogy of the flotation concentrate blend is shown in **Table 2** [11]. Eksteen (2011) [8] has given the fractions of typical minerals in the UG2 and Merensky concentrates. The abundant gangue minerals in a typical PGM concentrate are orthopyroxene, talc, clinopy-

with cobalt (Co), copper (Cu), iron (Fe) and nickel (Ni) belong to the class of transition metals in the periodic table [6]. Geologically, PGM associates with base metal sulphides such as chal-

[3, 12, 13]. Troilite carries trace amounts of iridium, while chalcopyrite has trace amounts of Ru, Pd, Ir and Pt [13]. Gangue minerals associated with PGM-containing minerals are feld-

Typical process route for treating PGM ore with the approximate PGM grade in each process

The PGM ore is initially treated in primary and secondary crushers after which it is sent to rod and ball milling circuits. The milled PGM ore is treated using gravity separators and flotation cells; xanthate and dithiophosphate collectors are typical reagents used for flotation at a pH of

Typical composition of UG2 and Merensky flotation concentrate is shown in **Table 3** [14]. A typical PGM content in the flotation concentrate is in **Table 4** [9]. The UG2 concentrate has higher chrome content when compared to the Merensky as seen in **Tables 3** and **4**. UG2 also has higher PGM content than the Merensky concentrate. The concentrate from the flotation

To separate the PGM-rich sulphides from the gangue minerals, smelting is used. Rectangular six-in-line or circular three-electrode electric furnaces are typical in the PGM industry [12]. Smelting is a high-temperature process step where the sulphides (valuable minerals) are separated from the silicates (gangue minerals). Energy required for melting the concentrate is provided by Joule heating when an electric current is passed through the resistive bath [15]. The electrodes are used for electrical connections between the power supply and the bath. Graphite electrodes are inserted into the resistive bath such that when a current is applied

7.5–9 [1]. A sulphide-rich PGM concentrate is produced in the flotation cells [6].

cells is dried and smelted to separate the sulphides from the silicates [9].

through the electrodes, thermal energy is generated [6, 15].

S8

, PtS, Pt(AsS)2

) and pyrrhotite (Fe1−xS)

Extraction of Platinum Group Metals http://dx.doi.org/10.5772/intechopen.73214

Sb and elemental ruthenium [3, 7]. Noble metals together

, pyrite (FeS<sup>2</sup>

,

395

roxene and plagioclase [8]; other gangue minerals are <5% by mass [8].

), millerite (NiS), pentlandite (Fe,Ni)9

and Pd3

The principal sources of PGM are sulphide and arsenide minerals such as PtAs2

**3. Sources of PGM**

(Pt,Pd)S, (Pt,Pd,Ni)S, RuS2

is shown in **Figure 1** [1, 7, 9].

**4.1. Comminution**

**4.2. PGM ore smelting**

spar, biotite, plagioclase and pyroxene [12].

**4. PGM ore processing: an overview**

copyrite (CuFeS<sup>2</sup>

**Table 1.** World's reserves of PGM [5].

#### **2. Geology**

In South Africa, the PGM ore is mined in the western and eastern limb of the Bushveld Igneous Complex [8]. Within the Bushveld Igneous Complex, the Merensky reef, the Platreef and Upper Group 2 (UG2) reef are exploited for platinum production [1, 4, 9]. Merensky and Platreef have similar chemical and mineral composition [6, 10]. These reefs typically have fairly low contents of sulphides. UG2 differs from the two reefs in that it has low nickel and copper content [3]; compared to UG2, Merensky reef has higher amounts of chalcopyrite, pentlandite and pyrrhotite [8]. Chromite spinel can be up to 4% by mass in a UG2 concentrate, while a Merensky concentrate can have <1% by mass chromite spinel [8, 10].


**Table 2.** Sulphide and gangue mineralogy of a typical PGM concentrate [11].

A typical mineralogy of the flotation concentrate blend is shown in **Table 2** [11]. Eksteen (2011) [8] has given the fractions of typical minerals in the UG2 and Merensky concentrates. The abundant gangue minerals in a typical PGM concentrate are orthopyroxene, talc, clinopyroxene and plagioclase [8]; other gangue minerals are <5% by mass [8].

#### **3. Sources of PGM**

The principal sources of PGM are sulphide and arsenide minerals such as PtAs2 , PtS, Pt(AsS)2 , (Pt,Pd)S, (Pt,Pd,Ni)S, RuS2 and Pd3 Sb and elemental ruthenium [3, 7]. Noble metals together with cobalt (Co), copper (Cu), iron (Fe) and nickel (Ni) belong to the class of transition metals in the periodic table [6]. Geologically, PGM associates with base metal sulphides such as chalcopyrite (CuFeS<sup>2</sup> ), millerite (NiS), pentlandite (Fe,Ni)9 S8 , pyrite (FeS<sup>2</sup> ) and pyrrhotite (Fe1−xS) [3, 12, 13]. Troilite carries trace amounts of iridium, while chalcopyrite has trace amounts of Ru, Pd, Ir and Pt [13]. Gangue minerals associated with PGM-containing minerals are feldspar, biotite, plagioclase and pyroxene [12].

#### **4. PGM ore processing: an overview**

Typical process route for treating PGM ore with the approximate PGM grade in each process is shown in **Figure 1** [1, 7, 9].

#### **4.1. Comminution**

**2. Geology**

**Table 1.** World's reserves of PGM [5].

In South Africa, the PGM ore is mined in the western and eastern limb of the Bushveld Igneous Complex [8]. Within the Bushveld Igneous Complex, the Merensky reef, the Platreef and Upper Group 2 (UG2) reef are exploited for platinum production [1, 4, 9]. Merensky and Platreef have similar chemical and mineral composition [6, 10]. These reefs typically have fairly low contents of sulphides. UG2 differs from the two reefs in that it has low nickel and copper content [3]; compared to UG2, Merensky reef has higher amounts of chalcopyrite, pentlandite and pyrrhotite [8]. Chromite spinel can be up to 4% by mass in a UG2 concentrate,

Sulphide minerals

Gangue minerals

S8

– Ca(Mg, Fe)Si2

O6

O4

SiO4

O8 – CaAl2 Si2 O8

O3

while a Merensky concentrate can have <1% by mass chromite spinel [8, 10].

Alteration silicates Hydrated minerals

**Mineral Formula**

**Country PGM reserves (kg)**

United States 900 000 Canada 310 000 Russia 1 100 000 South Africa 63 000 000 Other countries 800 000 World total (rounded) 66 000 000

394 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

Chalcopyrite CuFeS2 Pentlandite (Fe, Ni, Co)9

Pyrite FeS2 Pyrrhotite Fe1 − xSx

Chromite spinel FeCr2

Pyroxenes (Mg, Fe)SiO3

Olivine (Mg, Fe)2

Plagioclase/feldspar NaAlSi3

Quartz SiO2 Haematite Fe2

**Table 2.** Sulphide and gangue mineralogy of a typical PGM concentrate [11].

The PGM ore is initially treated in primary and secondary crushers after which it is sent to rod and ball milling circuits. The milled PGM ore is treated using gravity separators and flotation cells; xanthate and dithiophosphate collectors are typical reagents used for flotation at a pH of 7.5–9 [1]. A sulphide-rich PGM concentrate is produced in the flotation cells [6].

Typical composition of UG2 and Merensky flotation concentrate is shown in **Table 3** [14]. A typical PGM content in the flotation concentrate is in **Table 4** [9]. The UG2 concentrate has higher chrome content when compared to the Merensky as seen in **Tables 3** and **4**. UG2 also has higher PGM content than the Merensky concentrate. The concentrate from the flotation cells is dried and smelted to separate the sulphides from the silicates [9].

#### **4.2. PGM ore smelting**

To separate the PGM-rich sulphides from the gangue minerals, smelting is used. Rectangular six-in-line or circular three-electrode electric furnaces are typical in the PGM industry [12]. Smelting is a high-temperature process step where the sulphides (valuable minerals) are separated from the silicates (gangue minerals). Energy required for melting the concentrate is provided by Joule heating when an electric current is passed through the resistive bath [15]. The electrodes are used for electrical connections between the power supply and the bath. Graphite electrodes are inserted into the resistive bath such that when a current is applied through the electrodes, thermal energy is generated [6, 15].

the concentrate zone can exceed the liquidus temperature of the sulphides. The silicate minerals melt when they reach the molten bath (concentrate-slag interface) [16]. The silicates and

The molten silicates and oxides form a fayalitic-forsteric slag layer, while the PGM-containing sulphides form a matte layer [16]. The specific gravity of matte ranges from 4.8 to 5.6, and that of slag ranges from 2.8 to 3.8 [6, 15]. Owing to the difference in specific gravities of matte and slag, the slag forms a top layer. Matte being denser than slag falls through the slag layer and settles underneath the slag. Matte consists of base metal sulphides (cobalt, copper, iron and nickel).

Operating temperature of matte and slag varies with the composition of the concentrate [8]. Typical smelter operating temperature for matte varies from 1380 to 1600°C, and that of slag

The molten slag and matte are tapped out of the smelter through the tap holes situated at the sidewall of the furnace. After tapping, the matte either can be fed directly to the converters as tapped or can be granulated before the conversion step; matte treatment varies with the producers.

Anglo American Platinum (Amplats), Impala Platinum (Implats) and Lonmin are three major producers of PGM in South Africa [9]. Typical compositions of matte from selected smelters are shown in **Table 5**. Matte from different smelters seems to have comparable amounts of major components (Cu, Fe, Ni and S). The slight difference is that the amount of iron in

Amplats matte is slightly higher than the iron in a Lonmin matte (**Table 5**).

sulphides are immiscible; upon melting they form two separate layers.

O3 0.6 3.0 0.3 Sulphur 15-20 4-6 10-15 USD value/tonne 14009 16526 7397

**Assay Merensky UG2 Platreef** PGM-4E 200 200 120 Pt-% of 4E 63.5 56.7 45.1 Pd 28.1 29.4 45.7 Rh 4.4 13.0 3.2 Au 4.0 0.9 6.0 Ir 0.6 1.6 1.0 Ru 6.8 9.6 3.5 Ni % 6.0 1.4 4.9 Cu 3.4 0.7 2.5 Co 0.15 0.05 0.2

Extraction of Platinum Group Metals http://dx.doi.org/10.5772/intechopen.73214 397

Matte serves as a collector for the PGMs [6, 7, 14].

**Table 4.** Typical content of a PGM flotation concentrate [9].

varies from 1500 to 1680°C [8].

Cr2

*4.2.1. Industrial PGM-furnace matte*

**Figure 1.** Typical process flow diagram for PGM ore processing [9, 12].


**Table 3.** Typical composition of Merensky and UG2 concentrate [14].

The PGM concentrate is introduced into the smelter through the feed ports situated on the furnace roof. The concentrate forms a thick bed (~400 mm) on top of the molten bath. The heat generated in the resistive bath causes the concentrate bed to melt gradually [8].

The operating temperature of the smelter at the concentrate zone can range from 600 to 900°C [16]. The liquidus temperature of base metal sulphides associated with PGMs is 850–875°C, whereas the liquidus temperature of the corresponding silicates is approximately 1350°C [16]. The sulphides in a PGM concentrate start melting at the concentrate bed since temperature at


**Table 4.** Typical content of a PGM flotation concentrate [9].

the concentrate zone can exceed the liquidus temperature of the sulphides. The silicate minerals melt when they reach the molten bath (concentrate-slag interface) [16]. The silicates and sulphides are immiscible; upon melting they form two separate layers.

The molten silicates and oxides form a fayalitic-forsteric slag layer, while the PGM-containing sulphides form a matte layer [16]. The specific gravity of matte ranges from 4.8 to 5.6, and that of slag ranges from 2.8 to 3.8 [6, 15]. Owing to the difference in specific gravities of matte and slag, the slag forms a top layer. Matte being denser than slag falls through the slag layer and settles underneath the slag. Matte consists of base metal sulphides (cobalt, copper, iron and nickel). Matte serves as a collector for the PGMs [6, 7, 14].

Operating temperature of matte and slag varies with the composition of the concentrate [8]. Typical smelter operating temperature for matte varies from 1380 to 1600°C, and that of slag varies from 1500 to 1680°C [8].

The molten slag and matte are tapped out of the smelter through the tap holes situated at the sidewall of the furnace. After tapping, the matte either can be fed directly to the converters as tapped or can be granulated before the conversion step; matte treatment varies with the producers.

#### *4.2.1. Industrial PGM-furnace matte*

The PGM concentrate is introduced into the smelter through the feed ports situated on the furnace roof. The concentrate forms a thick bed (~400 mm) on top of the molten bath. The heat

Merensky 1.6 2.2 0.3 2.1 22.3 18.2 3.2 9 41.4 100 - 250 UG2 5.0 2.4 2.9 0.8 12.6 21.0 1.7 3.6 44.0 300 - 600

**O3 Cu FeO MgO Ni S SiO2 PGM (g/t)**

The operating temperature of the smelter at the concentrate zone can range from 600 to 900°C [16]. The liquidus temperature of base metal sulphides associated with PGMs is 850–875°C, whereas the liquidus temperature of the corresponding silicates is approximately 1350°C [16]. The sulphides in a PGM concentrate start melting at the concentrate bed since temperature at

generated in the resistive bath causes the concentrate bed to melt gradually [8].

**Figure 1.** Typical process flow diagram for PGM ore processing [9, 12].

396 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

**O3 CaO Cr2**

**Table 3.** Typical composition of Merensky and UG2 concentrate [14].

**Al2**

Anglo American Platinum (Amplats), Impala Platinum (Implats) and Lonmin are three major producers of PGM in South Africa [9]. Typical compositions of matte from selected smelters are shown in **Table 5**. Matte from different smelters seems to have comparable amounts of major components (Cu, Fe, Ni and S). The slight difference is that the amount of iron in Amplats matte is slightly higher than the iron in a Lonmin matte (**Table 5**).


**5. Operational challenges facing PGM industry**

tions, the operating temperature limits the solubility of Cr<sup>2</sup>

• Formation of chromite spinels which are insoluble in slag.

of the slag and they lower the fluidity of the slag [19].

leads to the entrainment of matte in slag [8].

lowing actions have eased chromite problem in the smelters:

**5.1. Challenges associated with smelting high chromite concentrate**

tion of spinels on the hearth reduces the volume of the furnace [8].

O3

the solubility of Cr<sup>2</sup>

PGM melt [8].

lems in the furnace [19].

sion [16, 19].

South Africa is faced with increasing cost of electricity which has direct impact on the energyintensive processes such as smelting [1, 18]. South African PGM producers generally process a Merensky concentrate where available; otherwise, the Merensky and UG2 concentrates are blended together to achieve the required feed composition for the smelter. In recent years, the depletion of the Merensky reef has forced the PGM producers to mine the UG2 reef that has up to 60% chromite. As a consequence, the concentrate from the floatation cells has high chrome content than the amount that the smelters are designed to handle. In reducing condi-

with numerous challenges owing to the treatment of a high chrome concentrate [9, 19].

The challenges associated with high chrome feed to the smelter are the following [19]:

• Chromite spinels have high melting points as such they increase the liquidus temperature

• Chromite spinels increase the overall temperature of the constituents (slag and matte) [8]. • When the matte temperature is above the liquidus temperature of the slag freeze-lining, the matte dissolves the freeze-lining; this leads to corrosion of the refractories by corrosive

• There are FeO- and CrO-based spinels; the proportion of Fe and Cr in the spinel may vary, as such there are spinels that are heavier than the matte, while other spinels are slightly lighter than matte. Spinels which are denser than matte settle on the hearth; the accumula-

• Spinels with intermediate density form a 'mushy' layer at the slag-matte interface; this

• High chrome decreases electrical conductivity of the bath leading to electrical control prob-

• Higher chrome levels affect the matte temperatures during conversion step (matte temperatures above 1355°C have been observed); this causes damage to the refractory lining. Cold dope (revert) is normally used to lower the temperature of the matte during conver-

A number of approaches have been investigated to deal with the chrome problem. The fol-

O3

in slag is limited to 1.8% by mass. As such the smelters have battled

in a typical slag. At 1450–1650°C

Extraction of Platinum Group Metals http://dx.doi.org/10.5772/intechopen.73214 399

**Table 5.** Typical chemical composition of industrial matte from selected smelters (% by mass) [12].


**Table 6.** Typical chemical composition of industrial slag from different smelters (% by mass) [12].

#### *4.2.2. Industrial PGM-furnace slag*

Gangue minerals associated with PGM-containing minerals are feldspar, biotite, plagioclase and pyroxene ([Ca,Na]Al1–2Si3–2O8 ) [12]. During smelting these gangue minerals form a slag that is a silicate rich phase. Typical composition of a PGM-furnace slag from different smelters is shown in **Table 6** [12]. The oxide compounds in Amplats and Lonmin-Merensky slag are comparable; Lonmin-UG2 slag has higher Cr2 O3 , CaO and MgO; and its FeO content is significantly lower when compared to that of the slag from Amplats and Lonmin-Merensky ore.

#### **4.3. Converting**

After smelting, the furnace matte is treated in Pierce-Smith converters or Ausmelt process where iron sulphide is oxidised to ferrous oxide and sulphur is oxidised to sulphur dioxide [9]. Sulphur dioxide is removed as an off-gas, and iron oxide is removed as a fayalitic slag. The slag phase of the converter contains significant amounts of entrained PGM and is recycled to the smelting furnace to recover the entrained PGM. The converter matte is cooled, milled and treated in base metals refinery (BMR) [1, 9].

#### **4.4. Purification**

Typical hydrometallurgical processes used for PGM purification are as follows: dissolutionprecipitation (pressure oxidation leach), solvent extraction and ion exchange and molecular recognition technology [17]. Pressure oxidation leach is a typical hydrometallurgical process used to separate base metals from the PGM residue. The base metals are leached, while the PGMs remain in the residue. The PGM residue is sent to a precious metal refinery where various solution extraction and precipitation methods are used to separate individual metals [1]. Solvent extraction is another method by which PGMs can be separated from the base metals [7].

## **5. Operational challenges facing PGM industry**

South Africa is faced with increasing cost of electricity which has direct impact on the energyintensive processes such as smelting [1, 18]. South African PGM producers generally process a Merensky concentrate where available; otherwise, the Merensky and UG2 concentrates are blended together to achieve the required feed composition for the smelter. In recent years, the depletion of the Merensky reef has forced the PGM producers to mine the UG2 reef that has up to 60% chromite. As a consequence, the concentrate from the floatation cells has high chrome content than the amount that the smelters are designed to handle. In reducing conditions, the operating temperature limits the solubility of Cr<sup>2</sup> O3 in a typical slag. At 1450–1650°C the solubility of Cr<sup>2</sup> O3 in slag is limited to 1.8% by mass. As such the smelters have battled with numerous challenges owing to the treatment of a high chrome concentrate [9, 19].

#### **5.1. Challenges associated with smelting high chromite concentrate**

The challenges associated with high chrome feed to the smelter are the following [19]:

• Formation of chromite spinels which are insoluble in slag.

*4.2.2. Industrial PGM-furnace slag*

and pyroxene ([Ca,Na]Al1–2Si3–2O8

**4.3. Converting**

**4.4. Purification**

comparable; Lonmin-UG2 slag has higher Cr2

**Al2**

398 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

**O3 CaO Co Cr2**

**Table 5.** Typical chemical composition of industrial matte from selected smelters (% by mass) [12].

**Table 6.** Typical chemical composition of industrial slag from different smelters (% by mass) [12].

treated in base metals refinery (BMR) [1, 9].

Gangue minerals associated with PGM-containing minerals are feldspar, biotite, plagioclase

Amplats-Waterval 3.3 6.4 0.1 0.8 0.1 31.0 15.0 0.2 0.5 46.0 Lonmin-Merensky 2.0 9.8 0.1 1.2 0.1 28.0 19.0 0.2 0.0 44.0 Lonmin-UG2 3.9 13.0 0.0 2.4 0.1 9.2 22.0 0.1 0.0 47.0

Amplats-Waterval 0.5 0.5 9.0 41.0 17.0 27.0 Lonmin-Merensky/UG2 0.5 0.2 9.7 37.0 17.0 28.0 Lonmin-UG2 0.5 0.3 9.8 35.0 17.0 28.0

that is a silicate rich phase. Typical composition of a PGM-furnace slag from different smelters is shown in **Table 6** [12]. The oxide compounds in Amplats and Lonmin-Merensky slag are

O3

nificantly lower when compared to that of the slag from Amplats and Lonmin-Merensky ore.

After smelting, the furnace matte is treated in Pierce-Smith converters or Ausmelt process where iron sulphide is oxidised to ferrous oxide and sulphur is oxidised to sulphur dioxide [9]. Sulphur dioxide is removed as an off-gas, and iron oxide is removed as a fayalitic slag. The slag phase of the converter contains significant amounts of entrained PGM and is recycled to the smelting furnace to recover the entrained PGM. The converter matte is cooled, milled and

Typical hydrometallurgical processes used for PGM purification are as follows: dissolutionprecipitation (pressure oxidation leach), solvent extraction and ion exchange and molecular recognition technology [17]. Pressure oxidation leach is a typical hydrometallurgical process used to separate base metals from the PGM residue. The base metals are leached, while the PGMs remain in the residue. The PGM residue is sent to a precious metal refinery where various solution extraction and precipitation methods are used to separate individual metals [1]. Solvent extraction is another method by which PGMs can be separated from the base metals [7].

) [12]. During smelting these gangue minerals form a slag

**O3 Cu FeO MgO Ni S SiO2**

**Co Cr Cu Fe Ni S**

, CaO and MgO; and its FeO content is sig-


A number of approaches have been investigated to deal with the chrome problem. The following actions have eased chromite problem in the smelters:

• Deep electrode immersion operating at high power densities causes sufficient mixing which keeps the solids in suspension [8, 21], but high power densities adversely affect the refractory life. To minimise the effect of high power input on the refractory life of the sidewall lining, the phase voltage is increased without increasing the current levels [19].

Graphite blocks have increased the service life of the waffle copper coolers through the formation of a protective layer. However, high infiltration of melt is still observed at the matte-slag tidal zone. This is a challenge that still needs to be addressed; currently, conventional bricks or monolithics are used at lower sidewall of the PGM smelter refractory. It is desired to extend the graphite blocks to the lower sidewall of the PGM smelter refractory wall against the matte zone [25]. It is envisaged that using carbon-based refractory at the hot face of the matte zone (lower sidewall) will improve the service life of the furnace lining in

Extraction of Platinum Group Metals http://dx.doi.org/10.5772/intechopen.73214 401

The PGM industry faces challenges with increasing chrome content in the feed and premature failure of refractory lining in the smelter. Alternative ways to process the PGM have become attractive due to the challenges associated with the conventional smelting process [1, 18]. A hydrometallurgy (Kell) process has been probed as an alternative to smelting PGM. The Kell process has three stages: stage 1 is the leaching of base metal sulphides in an acidic sulphate medium (pressure oxidation); stage 2 is roasting of the residue from stage 1; and stage 3 is atmospheric leaching of PGMs in a chloride media. The leached precious metals are further treated in refineries to recover metals [18]. Other hydrometallurgical routes have been discussed in Ref. [1]. These hydrometallurgical processes have advantages over the smelting process since they reduce the operating costs drastically [1]. However, the alternative hydro-

In this chapter, an overview of PGM processing has been presented. The conventional smelting process has challenges with high chromium feed, premature failure of refractory lining and increased operating cost associated with increasing cost of electricity in South Africa. The Kell process is an alternative way to process a PGM concentrate, and it has a number of advantages such as less energy consumption, less energy cost, less electricity consumption,

emissions and no restriction on chrome content of feed. Other hydrometallurgical

metallurgical routes of processing PGMs have not yet been commercialised [1].

routes have been investigated, but none has been commercialised yet.

PGM smelters [25].

**7. Conclusions**

less CO2

**Author details**

Bongephiwe Mpilonhle Thethwayo

Address all correspondence to: 77mpilot@gmail.com

University of Johannesburg, Johannesburg, South Africa

**6. Opportunities in PGM processing**


#### **5.2. Premature failure of refractory lining**

Due to high operating temperatures (1350 to >1600°C) [8] associated with PGM smelting, the smelter has to be lined with refractories at the hot face. To prolong the service life of the refractories, sufficient cooling of the refractories is required at the cold face of the refractory wall. Copper waffle coolers are typically used in the cold face of the refractories to extract heat away from the refractories [24]. Due to high operating temperature and corrosiveness of the PGM melt, premature failure of the waffle copper coolers has been experienced in PGM smelters [24] in the upper sidewall region. Failure of waffle copper coolers causes explosions, loss of production and costs associated with furnace rebuild. The failure of waffle copper coolers was preceded by the consumption of conventional refractory bricks (MgO<sup>x</sup> -CrOx ) which were used to form the furnace lining. The refractory brick (MgO<sup>x</sup> -CrOx ) had low resistance to chemical attack by liquid PGM melt. To prevent the occurrences of copper cooler failures, conventional bricks have been replaced by the graphite blocks in recent designs of PGM smelter refractory walls [25]. Graphite blocks are only applied at the hot face of the upper sidewall (against the concentrate and the slag zone).

With the graphite block lining, a frozen protective skull forms at the hot face of the refractory. The formation of the protective skull is attributed to the efficient cooling of the refractory wall by waffle coolers. The frozen skull is the melt that solidified due to the surface temperature of the graphite that was lower than the liquidus temperature of the melt [25].

Graphite blocks have increased the service life of the waffle copper coolers through the formation of a protective layer. However, high infiltration of melt is still observed at the matte-slag tidal zone. This is a challenge that still needs to be addressed; currently, conventional bricks or monolithics are used at lower sidewall of the PGM smelter refractory. It is desired to extend the graphite blocks to the lower sidewall of the PGM smelter refractory wall against the matte zone [25]. It is envisaged that using carbon-based refractory at the hot face of the matte zone (lower sidewall) will improve the service life of the furnace lining in PGM smelters [25].

#### **6. Opportunities in PGM processing**

The PGM industry faces challenges with increasing chrome content in the feed and premature failure of refractory lining in the smelter. Alternative ways to process the PGM have become attractive due to the challenges associated with the conventional smelting process [1, 18]. A hydrometallurgy (Kell) process has been probed as an alternative to smelting PGM. The Kell process has three stages: stage 1 is the leaching of base metal sulphides in an acidic sulphate medium (pressure oxidation); stage 2 is roasting of the residue from stage 1; and stage 3 is atmospheric leaching of PGMs in a chloride media. The leached precious metals are further treated in refineries to recover metals [18]. Other hydrometallurgical routes have been discussed in Ref. [1]. These hydrometallurgical processes have advantages over the smelting process since they reduce the operating costs drastically [1]. However, the alternative hydrometallurgical routes of processing PGMs have not yet been commercialised [1].

#### **7. Conclusions**

• Deep electrode immersion operating at high power densities causes sufficient mixing which keeps the solids in suspension [8, 21], but high power densities adversely affect the refractory life. To minimise the effect of high power input on the refractory life of the sidewall lining, the phase voltage is increased without increasing the current levels [19]. • Some producers stopped recycling the converter slag to the furnaces since the converter

• The flux addition in the furnace was discontinued since lower CaO levels increased the

• The control of furnace inputs and control of furnace parameters (power, furnace availabil-

• Another innovation able to manage chrome-rich ores is the ConRoast process. This process involves removing and capturing sulphur from the concentrate prior to smelting in a DC arc furnace. Roasting a concentrate makes smelting more environmentally friendly; it also enables furnaces to accept any proportion of chromite, resulting in more efficient and cost-

Due to high operating temperatures (1350 to >1600°C) [8] associated with PGM smelting, the smelter has to be lined with refractories at the hot face. To prolong the service life of the refractories, sufficient cooling of the refractories is required at the cold face of the refractory wall. Copper waffle coolers are typically used in the cold face of the refractories to extract heat away from the refractories [24]. Due to high operating temperature and corrosiveness of the PGM melt, premature failure of the waffle copper coolers has been experienced in PGM smelters [24] in the upper sidewall region. Failure of waffle copper coolers causes explosions, loss of production and costs associated with furnace rebuild. The failure of waffle copper cool-

chemical attack by liquid PGM melt. To prevent the occurrences of copper cooler failures, conventional bricks have been replaced by the graphite blocks in recent designs of PGM smelter refractory walls [25]. Graphite blocks are only applied at the hot face of the upper sidewall

With the graphite block lining, a frozen protective skull forms at the hot face of the refractory. The formation of the protective skull is attributed to the efficient cooling of the refractory wall by waffle coolers. The frozen skull is the melt that solidified due to the surface temperature of


) had low resistance to


) which

ers was preceded by the consumption of conventional refractory bricks (MgO<sup>x</sup>

the graphite that was lower than the liquidus temperature of the melt [25].

were used to form the furnace lining. The refractory brick (MgO<sup>x</sup>

slag has high chrome content [19, 20].

effective platinum production [9, 23].

**5.2. Premature failure of refractory lining**

(against the concentrate and the slag zone).

solubility of the chromite in the slag [19, 20].

400 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

ity) are essential in controlling chrome content [19].

• Tapping out the intermediate layer intentionally [22]. • Decreasing the chromium input to the smelters [20].

• Selective reduction improves the solubility of chromium in the slag [20].

In this chapter, an overview of PGM processing has been presented. The conventional smelting process has challenges with high chromium feed, premature failure of refractory lining and increased operating cost associated with increasing cost of electricity in South Africa. The Kell process is an alternative way to process a PGM concentrate, and it has a number of advantages such as less energy consumption, less energy cost, less electricity consumption, less CO2 emissions and no restriction on chrome content of feed. Other hydrometallurgical routes have been investigated, but none has been commercialised yet.

#### **Author details**

Bongephiwe Mpilonhle Thethwayo Address all correspondence to: 77mpilot@gmail.com University of Johannesburg, Johannesburg, South Africa

#### **References**

[1] Safarzadeh MS, Horton M, Van Rythoven AD. Review of recovery of platinum group metals from copper leach residues and other resources. Mineral Processing and Extractive Metallurgy Review. 2018;**39**(1):1-17

[14] Liddell KS, McRae LB, Dunne RC. Process routes for beneficiation of noble metals from

Extraction of Platinum Group Metals http://dx.doi.org/10.5772/intechopen.73214 403

[15] Habashi F. Textbook of Pyrometallurgy. Canada: Métallurgie Extractive Québec; 2002.

[16] Eksteen JJ, Van Beek B, Bezuidenhout GA. Cracking a hard nut: An overview of Lonmin's operations directed at smelting of UG2-rich concentrate blends. Journal of the Southern

[17] Bezuidenhout GA, Eksteen JJ, Akdogan G, Bradshaw SM, De Villiers JPR. Pyrometallurgical upgrading of PGM-rich leach residues from the western platinum base metals

[18] Liddell K, Newton T, Adams M, Muller B. Energy consumptions for Kell hydrometallurgical refining versus conventional pyrometallurgical smelting and refining of PGM concentrates. In: The 4th International Platinum Conference, Platinum in Transition 'Boom or Bust'. Johannesburg, South Africa: The Southern African Institute of Mining

[19] Coetzee V. Common-sense improvements to electric smelting at impala platinum. Journal of the Southern African Institute of Mining and Metallurgy. 2006;**106**(3):155-164

[20] Hundermark RJ, Mncwango SB, de Villiers LPS, Nelson LR. The Smelting Operations of Anglo American's Platinum Business: An Update, Southern African Pyrometallurgy 2011. Johannesburg: Southern African Institute of Mining and Metallurgy; 6-9 March

[21] Liddell KS, Adams MD. Kell hydrometallurgical process for extraction of platinum group metals and base metals from flotation concentrates. Journal of the Southern

[22] Barnes AR, Newall AF. Spinel Removal from PGM Smelting Furnaces. Southern African Pyrometallurgy, 5-6 March 2006. Johannesburg, South Africa: Southern African Institute

[23] Jones RT, Geldenhuys IJ. The pros and cons of reductive matte smelting for PGMs.

[24] McDougall I, Eksteen JJ. Sidewall design to improve lining life in a platinum smelting furnace. In: International Smelting Technology Symposium (Incorporating the 6th Advances in Sulphide Smelting Symposium). Warrendale, PA: TMS (The Minerals,

[25] Thethwayo BM. Sulphidation of copper coolers in PGM smelters. [MSc thesis]. South

Merensky and UG-2 ores. Mintek Review. 1986;**4**:33-44

African Institute of Mining and Metallurgy. 2011;**111**(10):681-690

refinery through roasting. Minerals Engineering. 2013;**53**:228-240

African Institute of Mining and Metallurgy. 2012;**112**(1):31-36

and Metallurgy; 2010. pp. 181-186

of Mining & Metallurgy; 2006. pp. 77-88

Minerals Engineering. 2011;**24**(6):495-498

Metals & Materials Society); 2012. pp. 47-54

Africa: University of Pretoria; 2010

2011. pp. 295-307

pp. 237-242


[14] Liddell KS, McRae LB, Dunne RC. Process routes for beneficiation of noble metals from Merensky and UG-2 ores. Mintek Review. 1986;**4**:33-44

**References**

Metallurgy Review. 2018;**39**(1):1-17

402 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

Deposita. 2015;**50**(1):41-54

21-24 August 2005. pp. 147-178

**24**(7):676-687

525-534

Hayes Publishing CO; 2003. pp. 278-279

Institute of Mining and Metallurgy; 2008. pp. 5-9

review. Minerals Engineering. 2004;**17**(9):961-979

[1] Safarzadeh MS, Horton M, Van Rythoven AD. Review of recovery of platinum group metals from copper leach residues and other resources. Mineral Processing and Extractive

[2] Glaister BJ, Mudd GM. The environmental costs of platinum–PGM mining and sustainability: Is the glass half-full or half-empty? Minerals Engineering. 2010;**23**(5):438-450 [3] Xiao Z, Laplante AR. Characterizing and recovering the platinum group minerals – A

[4] Junge M, Wirth R, Oberthür T, Melcher F, Schreiber A. Mineralogical siting of platinumgroup elements in Pentlandite from the Bushveld complex, South Africa. Mineralium

[5] Jewell S, Kimball SM. Mineral Commodity Summaries 2015. U.S. Geological Survey. Reston, Virginia: CreateSpace Independent Publishing Platform; 2015;**196**:120-121

[6] Jones RT. An overview of Southern African PGM smelting, nickel and cobalt 2005: Challenges in extraction and production. In: 44th Annual Conference of Metallurgists, Calgary, Alberta, Canada: Canadian Institute of Mining, Metallurgy and Petroleum.

[7] Hayes PC. Process Principles in Minerals & Materials Production. 3rd ed. Australia:

[8] Eksteen JJ. A mechanistic model to predict matte temperatures during the smelting of UG2-rich blends of platinum group metal concentrates. Minerals Engineering. 2011;

[9] Cramer LA. What is your PGM concentrate worth? In: Third International Platinum Conference, 'Platinum in Transformation', Johannesburg, South Africa: South African

[10] Nell J. Melting of platinum group metal concentrates in South Africa. Journal of the

[11] Andrew NJ, van Beek B, Lexmond A, Zietsman JH. Effect of Feed Composition Fluctuations on a Platinum Furnace Energy Balance and Slag Temperature. The Southern African Institute of Minng and Metallurgy, Pyrometallurgical Modelling-Principles and

[12] Jones RT. Platinum smelting in South Africa. South African Journal of Science. 1999;**95**:

[13] Cabri LJ, Rudashevsky NS, Rudashevsky VN. Current approaches for the process mineralogy of platinum-group element ores and tailings. In: Ninth International Congress

for Applied Mineralogy ICAM. Geological Society of India. 2009. pp. 9-17

South African Institute of Mining and Metallurgy. 2004;**104**(7):423-428

Practices, Kempton Park, South Africa, 4-5 August 2014. pp. 117-126


**Chapter 19**

**Provisional chapter**

**Rare Earth Extraction from NdFeB Magnets**

**Rare Earth Extraction from NdFeB Magnets**

DOI: 10.5772/intechopen.70881

There is a considerable interest in the extraction of rare earths (RE) from NdFeB magnets in order to recycle rare earth elements. Although the wet process using acid is in practical use in the in-plant recycle of sludge, higher selectivity between rare earths and Fe at room temperature is desired. We have recently proposed a pretreatment of corrosion before the hydrochloric acid (HCl) leaching and the oxalic acid precipitation. Almost full recovery of rare earths can be achieved even at room temperature process. In practical extraction methods, employing wet processes, the discharge of waste acid solution is a problem that needs to be solved to reduce the environmental impact. We further present an encouraging demonstration of rare earth extraction from NdFeB magnet using a closed-loop HClbased process. Triple extraction has been conducted, and the recovery ratio of rare earths is approximately 50% in each extraction, which is reduced from almost 100% recovery in a one-shot extraction. Despite the reduced extraction efficiency, our method with a rather small number of procedures at almost room temperature is still highly advantageous in terms of cost and environmental friendliness. This study represents the initial step toward the realization of a closed-loop acid process in the recycling of rare earth

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.

Rare earths (RE) are widely consumed in polish, catalysts, rare earth magnets, and so on [1]. Due to the skewed distribution of production countries for RE, many countries depend on the imports from other countries. For example, in Japan, the amount of import of RE metals reached 6479 tons in 2014. The import price, severely depending on international markets, fluctuates widely. Japan is promoting the provisions such as development of alternative materials and the recycle of rare earths. Because the demand of NdFeB magnets has been growing rapidly in recent years because of their use in motors of electric vehicles, wind

Jiro Kitagawa and Masami Tsubota

Jiro Kitagawa and Masami Tsubota

http://dx.doi.org/10.5772/intechopen.70881

**Abstract**

elements.

**1. Introduction**

Additional information is available at the end of the chapter

**Keywords:** recycle, corrosion, closed-loop acid process

Additional information is available at the end of the chapter

**Provisional chapter**

## **Rare Earth Extraction from NdFeB Magnets**

**Rare Earth Extraction from NdFeB Magnets**

DOI: 10.5772/intechopen.70881

Jiro Kitagawa and Masami Tsubota Jiro Kitagawa and Masami Tsubota Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.70881

#### **Abstract**

There is a considerable interest in the extraction of rare earths (RE) from NdFeB magnets in order to recycle rare earth elements. Although the wet process using acid is in practical use in the in-plant recycle of sludge, higher selectivity between rare earths and Fe at room temperature is desired. We have recently proposed a pretreatment of corrosion before the hydrochloric acid (HCl) leaching and the oxalic acid precipitation. Almost full recovery of rare earths can be achieved even at room temperature process. In practical extraction methods, employing wet processes, the discharge of waste acid solution is a problem that needs to be solved to reduce the environmental impact. We further present an encouraging demonstration of rare earth extraction from NdFeB magnet using a closed-loop HClbased process. Triple extraction has been conducted, and the recovery ratio of rare earths is approximately 50% in each extraction, which is reduced from almost 100% recovery in a one-shot extraction. Despite the reduced extraction efficiency, our method with a rather small number of procedures at almost room temperature is still highly advantageous in terms of cost and environmental friendliness. This study represents the initial step toward the realization of a closed-loop acid process in the recycling of rare earth elements.

**Keywords:** recycle, corrosion, closed-loop acid process

#### **1. Introduction**

Rare earths (RE) are widely consumed in polish, catalysts, rare earth magnets, and so on [1]. Due to the skewed distribution of production countries for RE, many countries depend on the imports from other countries. For example, in Japan, the amount of import of RE metals reached 6479 tons in 2014. The import price, severely depending on international markets, fluctuates widely. Japan is promoting the provisions such as development of alternative materials and the recycle of rare earths. Because the demand of NdFeB magnets has been growing rapidly in recent years because of their use in motors of electric vehicles, wind

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

turbines, etc., the recycling of RE elements extracted from used magnets has become an important research area [2–5].

**2. Materials and methods**

We used two kinds of commercial NdFeB magnets (Niroku seisakusyo). The elemental component of one magnet (denoted as magnet (1)) according to the manufacturer is Nd:Fe:B:the other elements (Dy et al.) = 28:66:1:5 in wt%. The composition of the other magnet (denoted as magnet (2)) was checked by an energy-dispersive X-ray spectrometer equipped in a field emission scanning electron microscope (JEOL, JSM-7100F) and determined to be Nd1.6Pr0.6Fe14B. **Figure 1(a)** shows the process flow without a closed-loop acid process. A demagnetized and pulverized NdFeB magnet (1), weighing approximately 0.5 g, was immersed in 3% NaCl solution (300 mL) for 1 week. An air pump provided constant air flow to the solution to accelerate the corrosion.

Rare Earth Extraction from NdFeB Magnets http://dx.doi.org/10.5772/intechopen.70881 407

**Figure 1.** (a) Procedures for rare earth recovery from NdFeB magnet (1) without closed-loop acid process. (b) Procedures for rare earth recovery from NdFeB magnet (2) with closed-loop acid process. S, L, and IL denote the solid, liquid, and ionic liquid, respectively. In procedure (b), elements expected to be present in the solid or solution are denoted.

There are two main classes of recycling of RE: dry and wet processes. As for the dry process, the recovery of Nd metal has been demonstrated [6] by employing Mg acting as an extraction medium, which forms a low-viscosity liquid alloy with Nd. It has been reported that RE can be separated by a selective reduction and a distillation [7]. The large difference of vapor pressure between RECl2 and RECl3 is skillfully utilized, and the selection efficiency is highly improved. Recently, the difference of oxygen affinity between RE and transition metals has also received attention in that this difference is used as a RE separation. For example, the mixture with flux FeO·B<sup>2</sup> O3 is a promising method for high purity and high extraction ratio of RE oxide [8]. Thermal isolation of RE oxides from NdFeB magnets using carbon as a reducing agent has been reported [9]. However, many attempts based on the dry process proposed so far are still at the initial laboratory stage.

Development of ore dressing technologies has promoted wet process methods [10, 11], which have already been applied to recycling the sludge of in-plant scrap. After the acid leaching of scrap using HCl, HNO<sup>3</sup> , and H2 SO<sup>4</sup> , and the filtration of insoluble material mainly containing Fe, acid solution is reacted with oxalic or carbonic acid to form a precipitate containing RE elements. The calcined precipitate becomes RE oxides, which can be returned to the initial manufacturing process of NdFeB magnet. The roasting of NdFeB magnet [12–14] as a pretreatment improves the selectivity between rare earths and Fe, but the recovery ratio of RE is usually rather low with acid (especially HCl) leaching at room temperature. Nearly 100% recovery is achieved [12, 13] when HCl solution is heated to 80–180°C. In the acid leaching method for sludge [15], it is also necessary to heat the acid solution up to 80°C. We have recently proposed a pretreatment of corrosion [16] before the HCl leaching and the oxalic acid precipitation. In this method, the recovery ratio of Nd reaches 97% even when a room temperature process is used.

From the standpoint of sustainability and ecology, the main issue of the wet process is the discharge of waste acid solution. The recyclability of waste acid crucially depends on the efficient extraction of the constituent elements of the magnet from the used acid. One of the promising methods for Fe extraction involves a reaction with an ionic liquid [12, 17–20], which often possesses a high selectivity between rare earths and Fe. Trihexyl(tetradecyl)phosphonium chloride (Cyphos® IL101) is a well-characterized ionic liquid that can extract Fe3+ ions in HCl solution with no extraction of trivalent rare earth ions [12, 18]. A possible closed-loop acid process for roasted NdFeB magnet has also been proposed, and the elemental technologies are well investigated [12]. However, an actual demonstration with reuse of waste acid solution has not been performed.

In this study, we introduce the full recovery of rare earth from NdFeB magnet using a wet process with the pretreatment of corrosion but without a closed-loop acid process. After that we describe the detailed experimental results of multiple rare earth extraction in a closed-loop acid process [21].

#### **2. Materials and methods**

turbines, etc., the recycling of RE elements extracted from used magnets has become an

There are two main classes of recycling of RE: dry and wet processes. As for the dry process, the recovery of Nd metal has been demonstrated [6] by employing Mg acting as an extraction medium, which forms a low-viscosity liquid alloy with Nd. It has been reported that RE can be separated by a selective reduction and a distillation [7]. The large difference of vapor

improved. Recently, the difference of oxygen affinity between RE and transition metals has also received attention in that this difference is used as a RE separation. For example, the

RE oxide [8]. Thermal isolation of RE oxides from NdFeB magnets using carbon as a reducing agent has been reported [9]. However, many attempts based on the dry process proposed so

Development of ore dressing technologies has promoted wet process methods [10, 11], which have already been applied to recycling the sludge of in-plant scrap. After the acid leaching of

Fe, acid solution is reacted with oxalic or carbonic acid to form a precipitate containing RE elements. The calcined precipitate becomes RE oxides, which can be returned to the initial manufacturing process of NdFeB magnet. The roasting of NdFeB magnet [12–14] as a pretreatment improves the selectivity between rare earths and Fe, but the recovery ratio of RE is usually rather low with acid (especially HCl) leaching at room temperature. Nearly 100% recovery is achieved [12, 13] when HCl solution is heated to 80–180°C. In the acid leaching method for sludge [15], it is also necessary to heat the acid solution up to 80°C. We have recently proposed a pretreatment of corrosion [16] before the HCl leaching and the oxalic acid precipitation. In this method, the recovery ratio of Nd reaches 97% even when a room

From the standpoint of sustainability and ecology, the main issue of the wet process is the discharge of waste acid solution. The recyclability of waste acid crucially depends on the efficient extraction of the constituent elements of the magnet from the used acid. One of the promising methods for Fe extraction involves a reaction with an ionic liquid [12, 17–20], which often possesses a high selectivity between rare earths and Fe. Trihexyl(tetradecyl)phosphonium chloride (Cyphos® IL101) is a well-characterized ionic liquid that can extract Fe3+ ions in HCl solution with no extraction of trivalent rare earth ions [12, 18]. A possible closed-loop acid process for roasted NdFeB magnet has also been proposed, and the elemental technologies are well investigated [12]. However, an actual demonstration with reuse of waste acid solu-

In this study, we introduce the full recovery of rare earth from NdFeB magnet using a wet process with the pretreatment of corrosion but without a closed-loop acid process. After that we describe the detailed experimental results of multiple rare earth extraction in a closed-loop

is skillfully utilized, and the selection efficiency is highly

, and the filtration of insoluble material mainly containing

is a promising method for high purity and high extraction ratio of

important research area [2–5].

pressure between RECl2

mixture with flux FeO·B<sup>2</sup>

scrap using HCl, HNO<sup>3</sup>

temperature process is used.

tion has not been performed.

acid process [21].

and RECl3

O3

406 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

, and H2

SO<sup>4</sup>

far are still at the initial laboratory stage.

We used two kinds of commercial NdFeB magnets (Niroku seisakusyo). The elemental component of one magnet (denoted as magnet (1)) according to the manufacturer is Nd:Fe:B:the other elements (Dy et al.) = 28:66:1:5 in wt%. The composition of the other magnet (denoted as magnet (2)) was checked by an energy-dispersive X-ray spectrometer equipped in a field emission scanning electron microscope (JEOL, JSM-7100F) and determined to be Nd1.6Pr0.6Fe14B. **Figure 1(a)** shows the process flow without a closed-loop acid process. A demagnetized and pulverized NdFeB magnet (1), weighing approximately 0.5 g, was immersed in 3% NaCl solution (300 mL) for 1 week. An air pump provided constant air flow to the solution to accelerate the corrosion.

**Figure 1.** (a) Procedures for rare earth recovery from NdFeB magnet (1) without closed-loop acid process. (b) Procedures for rare earth recovery from NdFeB magnet (2) with closed-loop acid process. S, L, and IL denote the solid, liquid, and ionic liquid, respectively. In procedure (b), elements expected to be present in the solid or solution are denoted.

The corroded sample was leached into HCl solution (100 mL) ranging from 0.1 to 0.3 mol/L, at room temperature. The insoluble material was calcined at 800°C for 5 h to obtain α-Fe<sup>2</sup> O3 . The solution after removal of the insoluble was reacted with 0.26 g oxalic acid. The precipitate after the reaction was also calcined at 800°C for 5 h to obtain cubic Mn2 O3 -type Nd2 O3 (c-Nd2 O3 ).

To examine the feasibility of closed-loop acid process, the process flow was modified as shown in **Figure 1(b)**. In this case, the corroded sample was leached in HCl solution (100 mL) with 0.2 mol/L or 0.5 mol/L for 1–2 h. After removal of the insoluble material, the solution was reacted with ionic liquid Cyphos® IL101 (HCl:ionic liquid = 4:1 in volume ratio), purchased from Sigma-Aldrich. The salting-out agent 10 mol/L NH4 Cl was added to the solution. The mixture underwent magnetic stirring at 750 rpm and 60°C for 10 min. Then, it was centrifuged at 2500 rpm for 10 min and split into each component. The HCl solution was reacted with oxalic acid.

Several samples, calcined at 800°C for 5 h in the air, were evaluated using a powder X-ray diffractometer (Shimadzu, XRD-7000 L) with Cu-Kα radiation. We employed an inductively coupled plasma atomic emission spectrometer (Shimadzu, ICPE-9000) to analyze the concentrations of Nd, Pr, Fe, and B dissolved in HCl or NaCl solution. The concentrations were determined by the working curves of standard Nd, Pr, Fe, and B liquids.

#### **3. Results and discussion**

The XRD pattern of corroded magnet (1) is shown in **Figure 2**, in which the XRD pattern of magnet (1) itself is also displayed. The main phase of magnet (1) is Nd2 Fe14B with additional minor phase of NdFe4 B4 . The XRD pattern of Nd<sup>2</sup> Fe14B completely disappears in the corroded magnet, partially containing the XRD pattern of γ-FeOOH denoted by the filled triangles. In order to investigate the origin of the rest of the diffraction peaks (open circles) in the corroded sample, we have corroded NdFeB magnet (1) by hydrogenating it at 600°C for 12 h under a high pressure of hydrogen. The hydrogenated sample [22], as shown in the bottom pattern of **Figure 2**, shows the decomposition into Nd hydride (NdH2 <sup>+</sup> <sup>x</sup> ) and α-Fe. Therefore, in each compound, the corrosion process would independently occur. The XRD pattern of corroded sample after the hydrogenation almost coincides with that of directly corroded magnet (1). Considering that α-Fe corroded into the Fe hydroxide (γ-FeOOH), a Nd hydroxide is probably responsible for the rest of the diffraction peaks (open circles) in the corroded sample. We note here that the NaCl concentration is not optimized. We simply suppose the sea water which is an abundant resource. The preliminary result using more concentrated NaCl solution (10%) also leads to the same results.

**Figure 4** shows the leaching time dependences of effective recovery ratio *R* of Nd through 0.1,

**Figure 2.** XRD patterns of corroded magnet, corroded sample after hydrogenation, and hydrogenated magnet. The employed magnet is magnet (1). The origin of each pattern is shifted by an integer value for clarity. Based partly on Ref. [16].

*<sup>R</sup>* <sup>=</sup> (Mass of Nd in Nd2 <sup>O</sup>3)/(Mass of Nd in magnet) <sup>×</sup> <sup>100</sup> (1)

For each HCl concentration, *R* increases with increasing leaching time, and approximately saturates, however exceeds 100% at some conditions. The excess above 100% would be due to

Next, we show the experimental results of rare earth extraction using the closed-loop acid process. The starting magnet is magnet (2) with the mass of approximately 0.5 g. The distribution of constituent elements in our method mentioned above is partially unknown. Thus, a one-shot extraction with 0.2 mol/L HCl and 0.26 g oxalic acid but with no use of ionic liquid was performed. **Table 1** shows the distribution of each ion in the NaCl solution after removal of the corroded sample and in the HCl solution after removal of precipitates produced by the reaction with oxalic acid. In the NaCl solution, only B is detected. A sufficient amount of oxalic acid can efficiently separate rare earths. A large amount of Fe stays in the HCl solution. The expected ion concentrations of the completely dissolved 0.5 g magnet are 1041 mg/L for Nd, 381 mg/L for Pr, 3527 mg/L for Fe, and 49 mg/L for B, respectively. The summation of the B concentrations in the two states listed in **Table 1** is not far from 49 mg/L. Then, approximately 30% of B can be separated by the NaCl solution, and the remaining B stays in the HCl solution. Approximately 60% of the Fe ions are contained in the insoluble material obtained

and/or incomplete filtration technique.

Rare Earth Extraction from NdFeB Magnets http://dx.doi.org/10.5772/intechopen.70881 409

O3

0.2, and 0.3 mol/L HCl leaching. *R* was obtained by the equation.

after HCl leaching. The recovery ratio of Nd (Pr) is 99% (97%).

the existence of impurity phases in c-Nd2

We checked the XRD pattern of insoluble material after HCl leaching of the corroded sample as shown in **Figure 3(a)**. The diffraction peaks match well with those of the XRD pattern of γ-FeOOH, which transforms into α-Fe<sup>2</sup> O3 through the calcination (see **Figure 3(b)**). **Figure 3(a)** supports that the Nd hydroxide would be selectively dissolved into HCl solution, in which Nd ions are generated. The oxalic acid precipitation was performed to recover Nd. The precipitate has been calcined and evaluated by XRD pattern, which is displayed in **Figure 3(b)** with the simulated pattern of c-Nd<sup>2</sup> O3 . The XRD patterns are well matched between the calcined precipitate and c-Nd2 O3 , suggesting the successful recovery of Nd in the form of Nd oxide.

The corroded sample was leached into HCl solution (100 mL) ranging from 0.1 to 0.3 mol/L, at

solution after removal of the insoluble was reacted with 0.26 g oxalic acid. The precipitate after

To examine the feasibility of closed-loop acid process, the process flow was modified as shown in **Figure 1(b)**. In this case, the corroded sample was leached in HCl solution (100 mL) with 0.2 mol/L or 0.5 mol/L for 1–2 h. After removal of the insoluble material, the solution was reacted with ionic liquid Cyphos® IL101 (HCl:ionic liquid = 4:1 in volume ratio), purchased from Sigma-

went magnetic stirring at 750 rpm and 60°C for 10 min. Then, it was centrifuged at 2500 rpm for

Several samples, calcined at 800°C for 5 h in the air, were evaluated using a powder X-ray diffractometer (Shimadzu, XRD-7000 L) with Cu-Kα radiation. We employed an inductively coupled plasma atomic emission spectrometer (Shimadzu, ICPE-9000) to analyze the concentrations of Nd, Pr, Fe, and B dissolved in HCl or NaCl solution. The concentrations were

The XRD pattern of corroded magnet (1) is shown in **Figure 2**, in which the XRD pattern of

magnet, partially containing the XRD pattern of γ-FeOOH denoted by the filled triangles. In order to investigate the origin of the rest of the diffraction peaks (open circles) in the corroded sample, we have corroded NdFeB magnet (1) by hydrogenating it at 600°C for 12 h under a high pressure of hydrogen. The hydrogenated sample [22], as shown in the bottom pattern

compound, the corrosion process would independently occur. The XRD pattern of corroded sample after the hydrogenation almost coincides with that of directly corroded magnet (1). Considering that α-Fe corroded into the Fe hydroxide (γ-FeOOH), a Nd hydroxide is probably responsible for the rest of the diffraction peaks (open circles) in the corroded sample. We note here that the NaCl concentration is not optimized. We simply suppose the sea water which is an abundant resource. The preliminary result using more concentrated NaCl solu-

We checked the XRD pattern of insoluble material after HCl leaching of the corroded sample as shown in **Figure 3(a)**. The diffraction peaks match well with those of the XRD pattern of

supports that the Nd hydroxide would be selectively dissolved into HCl solution, in which Nd ions are generated. The oxalic acid precipitation was performed to recover Nd. The precipitate has been calcined and evaluated by XRD pattern, which is displayed in **Figure 3(b)** with the

, suggesting the successful recovery of Nd in the form of Nd oxide.

O3

10 min and split into each component. The HCl solution was reacted with oxalic acid.

determined by the working curves of standard Nd, Pr, Fe, and B liquids.

magnet (1) itself is also displayed. The main phase of magnet (1) is Nd2

. The XRD pattern of Nd<sup>2</sup>

of **Figure 2**, shows the decomposition into Nd hydride (NdH2 <sup>+</sup> <sup>x</sup>

O3

Cl was added to the solution. The mixture under-

Fe14B completely disappears in the corroded

through the calcination (see **Figure 3(b)**). **Figure 3(a)**

. The XRD patterns are well matched between the calcined precipi-


O3 (c-Nd2 O3 ).

Fe14B with additional

) and α-Fe. Therefore, in each

O3 . The

room temperature. The insoluble material was calcined at 800°C for 5 h to obtain α-Fe<sup>2</sup>

the reaction was also calcined at 800°C for 5 h to obtain cubic Mn2

408 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

Aldrich. The salting-out agent 10 mol/L NH4

**3. Results and discussion**

B4

tion (10%) also leads to the same results.

γ-FeOOH, which transforms into α-Fe<sup>2</sup>

O3

simulated pattern of c-Nd<sup>2</sup>

O3

tate and c-Nd2

minor phase of NdFe4

**Figure 2.** XRD patterns of corroded magnet, corroded sample after hydrogenation, and hydrogenated magnet. The employed magnet is magnet (1). The origin of each pattern is shifted by an integer value for clarity. Based partly on Ref. [16].

**Figure 4** shows the leaching time dependences of effective recovery ratio *R* of Nd through 0.1, 0.2, and 0.3 mol/L HCl leaching. *R* was obtained by the equation.

$$R = \text{ (Mass of Nd in Nd}\_2\text{O}\_3\text{)} \text{(Mass of Nd in magnet)} \times 100\tag{1}$$

For each HCl concentration, *R* increases with increasing leaching time, and approximately saturates, however exceeds 100% at some conditions. The excess above 100% would be due to the existence of impurity phases in c-Nd2 O3 and/or incomplete filtration technique.

Next, we show the experimental results of rare earth extraction using the closed-loop acid process. The starting magnet is magnet (2) with the mass of approximately 0.5 g. The distribution of constituent elements in our method mentioned above is partially unknown. Thus, a one-shot extraction with 0.2 mol/L HCl and 0.26 g oxalic acid but with no use of ionic liquid was performed. **Table 1** shows the distribution of each ion in the NaCl solution after removal of the corroded sample and in the HCl solution after removal of precipitates produced by the reaction with oxalic acid. In the NaCl solution, only B is detected. A sufficient amount of oxalic acid can efficiently separate rare earths. A large amount of Fe stays in the HCl solution. The expected ion concentrations of the completely dissolved 0.5 g magnet are 1041 mg/L for Nd, 381 mg/L for Pr, 3527 mg/L for Fe, and 49 mg/L for B, respectively. The summation of the B concentrations in the two states listed in **Table 1** is not far from 49 mg/L. Then, approximately 30% of B can be separated by the NaCl solution, and the remaining B stays in the HCl solution. Approximately 60% of the Fe ions are contained in the insoluble material obtained after HCl leaching. The recovery ratio of Nd (Pr) is 99% (97%).

The preliminary experiment for a closed-loop process of HCl solution was performed using 0.5 mol/L HCl to reduce the experimental time. The oxalic acid mass was maintained at 0.26 g. Hereafter, the HCl solutions after removal of insoluble material in the acid leaching, after Fe extraction by the ionic liquid, and after removal of rare earths by oxalic acid precipitation are denoted state [I], [II], and [III], respectively (see also **Figure 1(b)**). **Table 2** shows the Nd, Pr, and Fe concentrations of these states during each cycle. In the first cycle, approximately 24% of rare earths are extracted together with Fe by the ionic liquid. Only Nd and Pr are separated by the reaction with the oxalic acid. In state [I] during the second cycle, the concentrations of Nd and Pr are approximately one-quarter of those during the first cycle, which means an

**Solution Nd (mg/L) Pr (mg/L) Fe (mg/L) B (mg/L)** NaCl after removal of corroded magnet ND ND ND 12.3 HCl after removal of oxalic acid precipitates 10.6 13.0 1480 28.6

The preliminary experiment suggested that the weight of oxalic acid needs to be adjusted. The weight of oxalic acid for a 0.5 g magnet, reproducing the initial concentrations of Nd and Pr in state [I] in the second cycle, has been searched as shown in **Figure 5**. The vertical axis shows the difference in Nd (Pr) ion concentration in state [I] between the first and second cycles, which is denoted as ▵c. A positive value for ▵c indicates a poor precipitation efficiency, and a negative value indicates an excess oxalic acid. For each element, ▵c linearly decreases with increasing weight of oxalic acid. A weight of 0.1675 g oxalic acid can reproduce the initial Nd (Pr) ion concentration of state [I] in the second cycle. The chemical equation for oxalic acid precipitation is.

If the starting magnet weight is 0.5 g, the ideal amount of oxalic acid is 0.1335 g. However, as shown in **Figure 5**, Nd and Pr would not fully precipitate for 0.1335 g of oxalic acid. To achieve sufficient precipitation, the amount of oxalic acid that is consumed must be 1.3 times larger.

> [II] 707 264 105 [III] 16.9 17.4 109

> [II] 231 99 132 [III] ND ND 134

**Cycle State of solution Nd (mg/L) Pr (mg/L) Fe (mg/L)** First [I] 929 346 2320

Second [I] 218 94 2770

The notations of solutions are defined in **Figure 1(b)**. ND means not detected. Based partly on Ref. [21].

**Table 2.** Distribution of Nd, Pr, and Fe in the preliminary experiment of a closed loop for HCl solution.

<sup>2</sup> (C2 <sup>O</sup>4) 3 + 3H2↑ (2)

Rare Earth Extraction from NdFeB Magnets http://dx.doi.org/10.5772/intechopen.70881 411

immediate precipitation due to excess oxalic acid in the previous cycle.

ND means not detected. Based on Ref. [21].

**Table 1.** Distribution of Nd, Pr, Fe, and B in the one-shot recovery process.

1.46 Nd3+ + 0.54 Pr3+ + 3H2 C2 O<sup>4</sup> → (Nd0.73 Pr0.27)

**Figure 3.** (a) XRD patterns of corroded magnet (1) and insoluble material after HCl (0.1 mol/L, 30 min) leaching and γ-FeOOH. (b) XRD patterns of insoluble material and oxalic acid precipitate in HCl solution. They were calcined in the air. The simulation patterns of α-Fe<sup>2</sup> O3 and c-Nd2 O3 are also shown. The HCl concentration is 0.2 mol/L, and the leaching time is 2 h. The origin of each pattern in (a) and (b) is shifted by an integer value for clarity. Based partly on Ref. [16].

Following the results of Ref. [12] which reported that salting-out agent NH4 Cl plays an essential role in full extraction of Fe by an ionic liquid, the dependence of extraction efficiency on NH4 Cl concentration was determined. Without NH4 Cl, the extraction efficiency of Fe is only 40%, increasing to 75% with 5 mol/L NH4 Cl and 95% for 10 mol/L NH4 Cl. In this experiment, we also found that B is fully extracted by the ionic liquid. We speculate that Cyphos® IL101 represented by C38H68ClP transforms into C38H68FeCl4 , after the incorporation of Fe3+ ions. Thus, the extraction efficiency of Fe severely depends on the Cl concentration, and the saltingout agent NH4 Cl is necessary to provide enough Cl ions.

**Figure 4.** Leaching time dependences of effective recovery ratio of Nd. The examined HCl solutions are 0.1, 0.2, and 0.3 mol/L. Based partly on Ref. [16].


**Table 1.** Distribution of Nd, Pr, Fe, and B in the one-shot recovery process.

Following the results of Ref. [12] which reported that salting-out agent NH4

O3

Cl is necessary to provide enough Cl ions.

Cl concentration was determined. Without NH4

O3

410 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

and c-Nd2

represented by C38H68ClP transforms into C38H68FeCl4

40%, increasing to 75% with 5 mol/L NH4

air. The simulation patterns of α-Fe<sup>2</sup>

NH4

out agent NH4

0.3 mol/L. Based partly on Ref. [16].

tial role in full extraction of Fe by an ionic liquid, the dependence of extraction efficiency on

**Figure 3.** (a) XRD patterns of corroded magnet (1) and insoluble material after HCl (0.1 mol/L, 30 min) leaching and γ-FeOOH. (b) XRD patterns of insoluble material and oxalic acid precipitate in HCl solution. They were calcined in the

time is 2 h. The origin of each pattern in (a) and (b) is shifted by an integer value for clarity. Based partly on Ref. [16].

we also found that B is fully extracted by the ionic liquid. We speculate that Cyphos® IL101

Thus, the extraction efficiency of Fe severely depends on the Cl concentration, and the salting-

**Figure 4.** Leaching time dependences of effective recovery ratio of Nd. The examined HCl solutions are 0.1, 0.2, and

Cl and 95% for 10 mol/L NH4

Cl plays an essen-

Cl. In this experiment,

Cl, the extraction efficiency of Fe is only

are also shown. The HCl concentration is 0.2 mol/L, and the leaching

, after the incorporation of Fe3+ ions.

The preliminary experiment for a closed-loop process of HCl solution was performed using 0.5 mol/L HCl to reduce the experimental time. The oxalic acid mass was maintained at 0.26 g. Hereafter, the HCl solutions after removal of insoluble material in the acid leaching, after Fe extraction by the ionic liquid, and after removal of rare earths by oxalic acid precipitation are denoted state [I], [II], and [III], respectively (see also **Figure 1(b)**). **Table 2** shows the Nd, Pr, and Fe concentrations of these states during each cycle. In the first cycle, approximately 24% of rare earths are extracted together with Fe by the ionic liquid. Only Nd and Pr are separated by the reaction with the oxalic acid. In state [I] during the second cycle, the concentrations of Nd and Pr are approximately one-quarter of those during the first cycle, which means an immediate precipitation due to excess oxalic acid in the previous cycle.

The preliminary experiment suggested that the weight of oxalic acid needs to be adjusted. The weight of oxalic acid for a 0.5 g magnet, reproducing the initial concentrations of Nd and Pr in state [I] in the second cycle, has been searched as shown in **Figure 5**. The vertical axis shows the difference in Nd (Pr) ion concentration in state [I] between the first and second cycles, which is denoted as ▵c. A positive value for ▵c indicates a poor precipitation efficiency, and a negative value indicates an excess oxalic acid. For each element, ▵c linearly decreases with increasing weight of oxalic acid. A weight of 0.1675 g oxalic acid can reproduce the initial Nd (Pr) ion concentration of state [I] in the second cycle. The chemical equation for oxalic acid precipitation is.

$$1.46\,\text{Nd}^{\text{+}} + 0.54\,\text{Pr}^{\text{+}} + 3\text{H}\_{2}\text{C}\_{2}\text{O}\_{4} \rightarrow \left(\text{Nd}\_{0\,\text{r}3}\,\text{Pr}\_{0\,\text{z}}\right)\_{2}\left(\text{C}\_{2}\,\text{O}\_{4}\right)\_{3} + 3\text{H}\_{2}\text{A} \tag{2}$$

If the starting magnet weight is 0.5 g, the ideal amount of oxalic acid is 0.1335 g. However, as shown in **Figure 5**, Nd and Pr would not fully precipitate for 0.1335 g of oxalic acid. To achieve sufficient precipitation, the amount of oxalic acid that is consumed must be 1.3 times larger.


**Table 2.** Distribution of Nd, Pr, and Fe in the preliminary experiment of a closed loop for HCl solution.

concentrations of Nd and Pr ions in state [I] are the same as those during the previous cycle. The recovery ratio of each element, calculated by eliminating the amount of element extracted by the ionic liquid, is approximately 50% in all cycles. **Figure 6** shows the XRD pattern of calcined insoluble material after HCl leaching in the second cycle. The simulated patterns

together with Fe. The XRD pattern in **Figure 6** supports the idea that the Nd and Pr elements, which are present in the same concentration as the ions in state [III], would enter insoluble

In our method, Cyphos® IL101 is rather expensive, and the regeneration of the ionic liquid by stripping Fe3+ is required to reduce the cost. We examined two stripping methods. The first one is the stripping using NaOH solution. After the reaction of the ionic liquid containing Fe3+

after the calcination. The ionic liquid was reacted with NaOH solution (1 mol/L) with a volume ratio of Cyphos® IL101:NaOH solution = 1:2.The calcined precipitate was checked by the XRD pattern, and it is shown in **Figure 7(a)**. The obtained pattern is in good agreement with the XRD

employment of ammonia solution, for which 100% stripping of Fe3+ has been already reported [23]. We roughly followed the reported recipe [23]. The yellow-colored ionic liquid containing Fe3+, which was obtained in the actual process flow, was reacted with the ammonia solution (approximately 3 wt.%) with a volume ratio of Cyphos® IL101:ammonia solution = 1:10.

**Figure 6.** XRD pattern of calcined insoluble material after HCl leaching in the second extraction. The simulated

patterns are also shown. The origin of each pattern is shifted by an integer value for clarity.

is expected to be precipitated, and Fe2

. The recovery ratio of Fe is estimated to be 17%. The second method is the

are also exhibited. Elemental Nd (Pr) is partially recovered

O3

Rare Earth Extraction from NdFeB Magnets http://dx.doi.org/10.5772/intechopen.70881 413

would be obtained

of Nd0.73Pr0.27FeO<sup>3</sup>

pattern of NaFeO<sup>2</sup>

Nd0.73Pr0.27FeO<sup>3</sup>

Based partly on Ref. [21].

and α-Fe<sup>2</sup>

O3

and α-Fe<sup>2</sup>

material in state [I] in the next cycle.

ions with NaOH solution, Fe(OH)<sup>3</sup>

O3

**Figure 5.** A plot of Δc vs. the weight of oxalic acid. Δc represents the difference in Nd (Pr) ion concentration after HCl leaching of corroded magnet between the first and second cycles. Based partly on Ref. [21].

From the preliminary experiments for the closed-loop process of HCl solution, we have obtained the conditions of 10 mol/L NH4 Cl and 0.1675 g oxalic acid for the recycling of 0.5 g magnet. **Table 3** shows the results of a demonstration of triple rare earth extraction from 0.5 g magnet with the closed loop of HCl solution. The HCl concentration was 0.5 mol/L to expedite the experiment. The concentrations of Nd and Pr ions are measured in states [I], [II], and [III]. In each cycle, 10–15% of Nd and Pr ions are extracted together with Fe ions by the ionic liquid, as in the preliminary experiment (see **Table 2**). Contrary to our expectation, 30–35% of Nd and Pr ions remain in solution after the oxalic acid precipitation. However, these ions apparently do not contribute to the rare earth concentrations of state [I] in the next cycle; the


The notations of the solutions are defined in **Figure 1(b)**. Based partly on Ref. [21].

**Table 3.** The distribution of Nd and Pr and the recovery ratio of each element in a triple rare earth extraction.

concentrations of Nd and Pr ions in state [I] are the same as those during the previous cycle. The recovery ratio of each element, calculated by eliminating the amount of element extracted by the ionic liquid, is approximately 50% in all cycles. **Figure 6** shows the XRD pattern of calcined insoluble material after HCl leaching in the second cycle. The simulated patterns of Nd0.73Pr0.27FeO<sup>3</sup> and α-Fe<sup>2</sup> O3 are also exhibited. Elemental Nd (Pr) is partially recovered together with Fe. The XRD pattern in **Figure 6** supports the idea that the Nd and Pr elements, which are present in the same concentration as the ions in state [III], would enter insoluble material in state [I] in the next cycle.

In our method, Cyphos® IL101 is rather expensive, and the regeneration of the ionic liquid by stripping Fe3+ is required to reduce the cost. We examined two stripping methods. The first one is the stripping using NaOH solution. After the reaction of the ionic liquid containing Fe3+ ions with NaOH solution, Fe(OH)<sup>3</sup> is expected to be precipitated, and Fe2 O3 would be obtained after the calcination. The ionic liquid was reacted with NaOH solution (1 mol/L) with a volume ratio of Cyphos® IL101:NaOH solution = 1:2.The calcined precipitate was checked by the XRD pattern, and it is shown in **Figure 7(a)**. The obtained pattern is in good agreement with the XRD pattern of NaFeO<sup>2</sup> . The recovery ratio of Fe is estimated to be 17%. The second method is the employment of ammonia solution, for which 100% stripping of Fe3+ has been already reported [23]. We roughly followed the reported recipe [23]. The yellow-colored ionic liquid containing Fe3+, which was obtained in the actual process flow, was reacted with the ammonia solution (approximately 3 wt.%) with a volume ratio of Cyphos® IL101:ammonia solution = 1:10.

From the preliminary experiments for the closed-loop process of HCl solution, we have

**Figure 5.** A plot of Δc vs. the weight of oxalic acid. Δc represents the difference in Nd (Pr) ion concentration after HCl

magnet. **Table 3** shows the results of a demonstration of triple rare earth extraction from 0.5 g magnet with the closed loop of HCl solution. The HCl concentration was 0.5 mol/L to expedite the experiment. The concentrations of Nd and Pr ions are measured in states [I], [II], and [III]. In each cycle, 10–15% of Nd and Pr ions are extracted together with Fe ions by the ionic liquid, as in the preliminary experiment (see **Table 2**). Contrary to our expectation, 30–35% of Nd and Pr ions remain in solution after the oxalic acid precipitation. However, these ions apparently do not contribute to the rare earth concentrations of state [I] in the next cycle; the

**Cycle State of solution Nd (mg/L) Pr (mg/L) Recovery ratio of Nd (%) Recovery ratio of Pr (%)**

First [I] 971 370 50 47

leaching of corroded magnet between the first and second cycles. Based partly on Ref. [21].

Second [I] 980 406 49 50

Third [I] 919 410 61 56

**Table 3.** The distribution of Nd and Pr and the recovery ratio of each element in a triple rare earth extraction.

The notations of the solutions are defined in **Figure 1(b)**. Based partly on Ref. [21].

[II] 818 311 [III] 328 136

[II] 836 357 [III] 352 156

[II] 842 360 [III] 280 130

Cl and 0.1675 g oxalic acid for the recycling of 0.5 g

obtained the conditions of 10 mol/L NH4

412 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

**Figure 6.** XRD pattern of calcined insoluble material after HCl leaching in the second extraction. The simulated Nd0.73Pr0.27FeO<sup>3</sup> and α-Fe<sup>2</sup> O3 patterns are also shown. The origin of each pattern is shifted by an integer value for clarity. Based partly on Ref. [21].

safe processes. Since B is harmful, its separation is highly desired. Our method has achieved 30% B separation, whereas the other methods do not report a clear B separation. If a closedloop acid process with a high recovery ratio of rare earths is realized, our method is promising because each step except Fe extraction by ionic liquid is performed at room temperature. This condition and the rather simple procedures lead to a safe and low-cost recovery process. In addition, the peculiar feature of B separation in our method is environmentally friendly.

Rare Earth Extraction from NdFeB Magnets http://dx.doi.org/10.5772/intechopen.70881 415

Rare earth extraction methods based on acid leaching are entering the stage of practical use. To address the issue of rather low selectivity between rare earths and Fe at the room temperature acid-process, we have proposed the pretreatment of corrosion. Our method has improved the selectivity, and rare earth recovery ratio, in one-shot extraction, reaches to almost 100% even at room temperature. For sustainability and environmental considerations, the recyclability of waste acid solution is one of the central issues in rare earth recycling, and this has not been well investigated. In this work, we have experimentally determined the recovery ratio of rare earth elements in our method with the closed-loop acid process. This ratio is approximately 50%, reduced from almost full recovery in a one-shot extraction. Although the recovery ratio is rather low at the present stage, our encouraging result should lead to rapid advancement of

The demonstration of closed-loop process for HCl solution indicates that the precipitation by oxalic acid is not sufficient, although the amount of oxalic acid is larger than the ideal amount calculated using the chemical formula of precipitation. To increase the recovery ratios of rare earth elements, if the amount of oxalic acid is increased, it will result in a reduced recovery ratio in the second cycle, as deduced from **Table 2**. Thus, a trade-off between the number of rare earth extractions and the recovery ratio of rare earths might exist for the present precipitation condition. The main cause of the reduced recovery ratio is the insufficient ionization of oxalic acid. The degree of ionization of oxalic acid strongly depends on the pH of the solution. The ionization concentration generally increases with increasing pH, and the full ionization of oxalic acid with an ideal weight of 0.1335 g would be realized. Another issue to be considered is the partial rare earth extraction by the ionic liquid. If the oxalic acid precipitation process is performed before the process of Fe3+ extraction by the ionic liquid, only rare earth elements would be separated due to the high selectivity between rare earths and Fe under oxalic acid precipitation. Thus, the issue would be resolved by reversing the sequence of the

two processes. As shown in **Figure 6**, unassigned peaks of material other than α-Fe<sup>2</sup>

liquid from the HCl solution is difficult, which results in contamination of the calcined sample. Further improvement of the separation technique is needed to obtain a pure calcined sample.

are present in the XRD spectrum. In our study, complete separation of the ionic

O3 and

the study of recycling using a closed-loop acid process.

**4. Summary**

**5. Future directions**

Nd0.73Pr0.27FeO<sup>3</sup>

**Figure 7.** (a) XRD pattern of the calcined sample recovered from used Cyphos® IL101 reacted with NaOH solution. The simulated NaFeO<sup>2</sup> pattern is also presented. The origin of each pattern is shifted by an integer value for clarity. (b) XRD pattern of calcined sample recovered from used Cyphos® IL101 reacted with ammonia solution. The simulated α-Fe<sup>2</sup> O3 , Fe3 PO<sup>7</sup> , and C patterns are also presented. The origin of each pattern is shifted by an integer value for clarity. (Based partly on Ref. [21]).

The precipitate at the interface between the liquids was collected using a cellulose filter and calcined together with the filter in the air. **Figure 7(b)** shows the XRD pattern of the calcined sample recovered from used Cyphos® IL101. The figure also displays the simulated patterns of α-Fe<sup>2</sup> O3 , Fe3 PO<sup>7</sup> , and C. The experimental XRD pattern closely matches the superposition of simulated patterns. The sources of P and C atom contamination would be Cyphos® IL101 containing P and the cellulose filter, respectively. Despite the contamination due to our insufficient filtration technique, Fe can be stripped. Furthermore, the yellow-colored ionic liquid once again became transparent after Fe3+ stripping, which means the ionic liquid is regenerated.

Focusing on the one-shot recovery processes, a comparison between our method and other methods [12–15] based on the acid leaching mentioned in Introduction is shown in **Table 4**. The number of steps in the recovery processes and the rare earth recovery ratio of each method are similar. The roasting used in Refs. [12–14] would have a cost disadvantage. Although Ref. [15] does not employ roasting, HNO<sup>3</sup> has a disadvantage because waste discharge containing nitrate salt is severely controlled by law for environmental reasons. The acid leaching process in our method and in Ref. [14] is performed at room temperature, which means that these are


**Table 4.** Comparison between our method and other methods based on acid leaching in a one-shot recovery process.

safe processes. Since B is harmful, its separation is highly desired. Our method has achieved 30% B separation, whereas the other methods do not report a clear B separation. If a closedloop acid process with a high recovery ratio of rare earths is realized, our method is promising because each step except Fe extraction by ionic liquid is performed at room temperature. This condition and the rather simple procedures lead to a safe and low-cost recovery process. In addition, the peculiar feature of B separation in our method is environmentally friendly.

#### **4. Summary**

The precipitate at the interface between the liquids was collected using a cellulose filter and calcined together with the filter in the air. **Figure 7(b)** shows the XRD pattern of the calcined sample recovered from used Cyphos® IL101. The figure also displays the simulated patterns

**Figure 7.** (a) XRD pattern of the calcined sample recovered from used Cyphos® IL101 reacted with NaOH solution. The

, and C patterns are also presented. The origin of each pattern is shifted by an integer value for clarity. (Based

pattern of calcined sample recovered from used Cyphos® IL101 reacted with ammonia solution. The simulated α-Fe<sup>2</sup>

of simulated patterns. The sources of P and C atom contamination would be Cyphos® IL101 containing P and the cellulose filter, respectively. Despite the contamination due to our insufficient filtration technique, Fe can be stripped. Furthermore, the yellow-colored ionic liquid once again became transparent after Fe3+ stripping, which means the ionic liquid is regenerated.

Focusing on the one-shot recovery processes, a comparison between our method and other methods [12–15] based on the acid leaching mentioned in Introduction is shown in **Table 4**. The number of steps in the recovery processes and the rare earth recovery ratio of each method are similar. The roasting used in Refs. [12–14] would have a cost disadvantage. Although Ref.

nitrate salt is severely controlled by law for environmental reasons. The acid leaching process in our method and in Ref. [14] is performed at room temperature, which means that these are

950°C

separated

**Items Our method [16] [12] [13] [14] [15]**

Acid leaching temperature RT 80°C 180°C RT 80°C

Recovery ratio of rare earths (%) 97 100 100 100 94

**Table 4.** Comparison between our method and other methods based on acid leaching in a one-shot recovery process.

Acid HCl HCl HCl H2

, and C. The experimental XRD pattern closely matches the superposition

pattern is also presented. The origin of each pattern is shifted by an integer value for clarity. (b) XRD

has a disadvantage because waste discharge containing

Not separated Not

Roast at 750°C

separated

Sludge

O3 ,

Not separated

SO<sup>4</sup> HNO<sup>3</sup>

Roast at 500–1000°C

of α-Fe<sup>2</sup>

Fe3 PO<sup>7</sup>

> O3 , Fe3 PO<sup>7</sup>

simulated NaFeO<sup>2</sup>

partly on Ref. [21]).

[15] does not employ roasting, HNO<sup>3</sup>

Pretreatment Corrosion at RT Roast at

414 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

B separation 30% Not

RT means room temperature. Based partly on Ref. [21].

Rare earth extraction methods based on acid leaching are entering the stage of practical use. To address the issue of rather low selectivity between rare earths and Fe at the room temperature acid-process, we have proposed the pretreatment of corrosion. Our method has improved the selectivity, and rare earth recovery ratio, in one-shot extraction, reaches to almost 100% even at room temperature. For sustainability and environmental considerations, the recyclability of waste acid solution is one of the central issues in rare earth recycling, and this has not been well investigated. In this work, we have experimentally determined the recovery ratio of rare earth elements in our method with the closed-loop acid process. This ratio is approximately 50%, reduced from almost full recovery in a one-shot extraction. Although the recovery ratio is rather low at the present stage, our encouraging result should lead to rapid advancement of the study of recycling using a closed-loop acid process.

#### **5. Future directions**

The demonstration of closed-loop process for HCl solution indicates that the precipitation by oxalic acid is not sufficient, although the amount of oxalic acid is larger than the ideal amount calculated using the chemical formula of precipitation. To increase the recovery ratios of rare earth elements, if the amount of oxalic acid is increased, it will result in a reduced recovery ratio in the second cycle, as deduced from **Table 2**. Thus, a trade-off between the number of rare earth extractions and the recovery ratio of rare earths might exist for the present precipitation condition. The main cause of the reduced recovery ratio is the insufficient ionization of oxalic acid. The degree of ionization of oxalic acid strongly depends on the pH of the solution. The ionization concentration generally increases with increasing pH, and the full ionization of oxalic acid with an ideal weight of 0.1335 g would be realized. Another issue to be considered is the partial rare earth extraction by the ionic liquid. If the oxalic acid precipitation process is performed before the process of Fe3+ extraction by the ionic liquid, only rare earth elements would be separated due to the high selectivity between rare earths and Fe under oxalic acid precipitation. Thus, the issue would be resolved by reversing the sequence of the two processes. As shown in **Figure 6**, unassigned peaks of material other than α-Fe<sup>2</sup> O3 and Nd0.73Pr0.27FeO<sup>3</sup> are present in the XRD spectrum. In our study, complete separation of the ionic liquid from the HCl solution is difficult, which results in contamination of the calcined sample. Further improvement of the separation technique is needed to obtain a pure calcined sample.

#### **Acknowledgements**

This research was supported by the Matching Planner Program of the Japan Science and Technology Agency (JST). J.K. is grateful for the support provided by the Comprehensive Research Organization of Fukuoka Institute of Technology.

[10] Xie F, Zhang TA, Dreisinger D, Doyle F. A critical review on solvent extraction of rare

Rare Earth Extraction from NdFeB Magnets http://dx.doi.org/10.5772/intechopen.70881 417

[11] Yang Y, Walton A, Sheridan R, Güth K, Gauẞ R, Gutfleisch O, Buchert M, Steenari B-M, Gerven TV, Jones PT, Binnemans K. REE recovery from end-of-life NdFeB permanent magnet scrap: A critical review. Journal of Sustainable Metallurgy. 2017;**3**:122-149 [12] Hoogerstraete TV, Blanpain B, Gerven TV, Binnemans K. From NdFeB magnets towards the rare-earth oxides: A recycling process consuming only oxalic acid. RSC Advances.

[13] Japan Oil, Gas and Metals National Co., National Institute of Advanced Industrial Science and Technology, Tohoku Univ. Method of rare-earth extraction by acid leaching.

[14] Önal MAR, Borra CR, Guo M, Blanpain B, Gerven TV. Recycling of NdFeB magnets using sulfation, selective roasting, and water leaching. Journal of Sustainable Metallurgy.

[15] Rabatho JP, Tongamp W, Takasaki Y, Haga K, Shibayama A. Recovery of Nd and Dy from rare earth magnetic waste sludge by hydrometallurgical process. Journal of

[16] Kataoka Y, Ono T, Tsubota M, Kitagawa J. Improved room-temperature-selectivity between Nd and Fe in Nd recovery from Nd-Fe-B magnet. AIP Advances. 2015;**5**:117212

[17] Billard I. Ionic liquids: New hopes for efficient lanthanide/actinide extraction and separation? Handbook on the Physics and Chemistry of Rare Earths. 2013;**43**:213-273 [18] Hoogerstraete TV, Wellens S, Verachtert K, Binnemans K. Removal of transition metals from rare earths by solvent extraction with an undiluted phosphonium ionic liquid: Separations relevant to rare-earth magnet recycling. Green Chemistry. 2013;**15**:919-927

[19] Dupont D, Binnemans K. Recycling of rare earths from NdFeB magnets using a combined leaching/extraction system based on the acidity and thermomorphism of the ionic

[20] Parmentier D, Hoogerstraete TV, Metz SJ, Binnemans K, Kroon MC. Selective extraction of metals from chloride solutions with the tetraoctylphosphonium oleate ionic liquid.

[21] Kitagawa J, Uemura R. Rare earth extraction from NdFeB magnet using a closed-loop

[22] Kataoka Y, Kawamoto Y, Ono T, Tsubota M, Kitagawa J. Hydrogenation of Nd-Fe-B magnet powder under a high pressure of hydrogen. Results in Physics. 2015;**5**:99-100 [23] Wellens S, Hoogerstrete TV, Möller C, Thijs B, Luyten J, Binnemans K. Dissolution of metal oxides in an acid-saturated ionic liquid solution and investigation of the backextraction behaviour to the aqueous phase. Hydrometallurgy. 2014;**144-145**:27-33

Japanese Unexamined Patent Application Publication 2011; No. 2011-184735

Material Cycles and Waste Management. 2013;**15**:171-178

liquid [Hbet][Tf2N]. Green Chemistry. 2015;**17**:2150-2163

acid process. Scientific Reports. 2017;**7**:8039

Industrial and Engineering Chemistry Research. 2015;**54**:5149-5158

earths from aqueous solutions. Minerals Engineering. 2014;**56**:10-28

2014;**4**:64099-64111

2015;**1**:199-215

#### **Author details**

Jiro Kitagawa<sup>1</sup> \* and Masami Tsubota2

\*Address all correspondence to: j-kitagawa@fit.ac.jp

1 Department of Electrical Engineering, Faculty of Engineering, Fukuoka Institute of Technology, Fukuoka, Japan

2 Physonit Inc., Hiroshima, Japan

#### **References**


[10] Xie F, Zhang TA, Dreisinger D, Doyle F. A critical review on solvent extraction of rare earths from aqueous solutions. Minerals Engineering. 2014;**56**:10-28

**Acknowledgements**

**Author details**

Technology, Fukuoka, Japan

2000;**289**:2326-2329

2015;**1**:151-160

2017;**5**:6201-6208

manent magnet scraps by FeO-B<sup>2</sup>

2 Physonit Inc., Hiroshima, Japan

Jiro Kitagawa<sup>1</sup>

**References**

This research was supported by the Matching Planner Program of the Japan Science and Technology Agency (JST). J.K. is grateful for the support provided by the Comprehensive

1 Department of Electrical Engineering, Faculty of Engineering, Fukuoka Institute of

[1] Goonan TG. Rare earth elements—End use and recyclability. U.S. Geological Survey

[2] Tanaka M, Oki T, Koyama K, Narita H, Oishi T. Recycling of rare earths from scrap.

[3] Binnemans K, Jones PT, Blanpain B, Gerven TV, Yang Y, Walton A, Buchert M. Recycling

[4] Darcy JW, Bandara D, Mishra B, Emmert MH. Challenges in recycling end-of-life rare

[5] Rademaker JH, Kleijn R, Yang Y. Recycling as a strategy against rare earth element criticality: A systemic evaluation of the potential yield of NdFeB magnet recycling.

[6] Takeda O, Okabe TH, Umetsu Y. Recovery of neodymium from a mixture of magnet scrap and other scrap. Journal of Alloys and Compounds. 2006;**408-412**:387-390

[7] Uda T, Jacob KT, Hirasawa M. Technique for enhanced rare earth separation. Science.

[8] Bian Y, Guo S, Jiang L, Tang K, Ding W. Extraction of rare earth elements from per-

[9] Maroufi S, Khayyam R, Sahajwalla V. Thermal isolation of rare earth oxides from Nd-Fe-B magnets using carbon from waste tyres. ACS Sustainable Chemistry & Engineering.

flux treatment. Journal of Sustainable Metallurgy.

O3

Handbook on the Physics and Chemistry of Rare Earths. 2013;**43**:159-211

of rare earths: A critical review. Journal of Cleaner Production. 2013;**51**:1-22

Research Organization of Fukuoka Institute of Technology.

416 Noble and Precious Metals - Properties, Nanoscale Effects and Applications

Scientific Investigations Report. 2011;**2011-5094**:1-15

Environmental Science & Technology. 2013;**47**:10129-10136

earth magnets. JOM. 2013;**65**:1381-1382

\* and Masami Tsubota2 \*Address all correspondence to: j-kitagawa@fit.ac.jp


## *Edited by Mohindar Singh Seehra and Alan D. Bristow*

The use of copper, silver, gold and platinum in jewelry as a measure of wealth is well known. This book contains 19 chapters written by international authors on other uses and applications of noble and precious metals (copper, silver, gold, platinum, palladium, iridium, osmium, rhodium, ruthenium, and rhenium). The topics covered include surface-enhanced Raman scattering, quantum dots, synthesis and properties of nanostructures, and its applications in the diverse fields such as high-tech engineering, nanotechnology, catalysis, and biomedical applications. The basis for these applications is their high-free electron concentrations combined with high-temperature stability and corrosion resistance and methods developed for synthesizing nanostructures. Recent developments in all these areas with up-to-date references are emphasized.

Published in London, UK © 2018 IntechOpen © JoyTasa / iStock

Noble and Precious Metals - Properties, Nanoscale Effects and Applications

Noble and Precious Metals

Properties, Nanoscale Effects and Applications

*Edited by Mohindar Singh Seehra* 

*and Alan D. Bristow*