**2. Rare earth elements occurrence**

The rare earth elements (REE) are an unusual group of metallic elements with unique properties: chemical, catalytic, magnetic, metallurgical and phosphorescent which consists of seventeen elements belonging to lanthanides. The lanthanide group includes rare earth elements with the atomic number (Z) from 57 to 71 which are: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). Yttrium (Y) and scandium (Sc) belonging to the scandium subgroup are grouped with rare earth elements because of their similar physicochemical properties (Spedding & Daane, 1961; Powell, 1964; Gschneidner, 1981; Stasicka, 1990)

Generally, lanthanide elements with low atomic numbers are more abundant in the earth crust than those with high atomic numbers. Those with even atomic numbers are two to seven times more abundant than the adjacent lanthanides with odd atomic numbers. The lanthanide elements traditionally have been divided into two groups: the light rare earth elements group (LREEs) which contains elements from lanthanum to europium (Z from 57 to 63) and the heavy rare earth elements group (HREEs) which contains elements from gadolinium to lutetium (Z from 64 to 71). Although yttrium is the lightest rare earth element, it is usually grouped with the HREEs to which it is chemically and physically similar (Kumar, 1994; Robards et al. 1998; Moustafa & Abdelfattah, 2010).

The geochemical studies have revealed that rare earth elements are actually not rare at all. Rare earth elements as the lithophilous ones occur mainly as phosphates and silicates. Due to their chemical similarity, lanthanides occur side by side in the scattered form in about 200 own minerals or as admixtures in the minerals of other elements. They occur in the crust of the earth in higher concentrations than Bi, I and Ag. For example, cerium, which is the most abundant and its average amount is equal to 6.010-3% occurs in higher concentrations than Sn, Pb, Co and Mo. Thulium the least abundant of them (4.810-5%) is still more abundant than the platinum group metals (PGM). As for spread in the earth crust scandium occupies position 31 (2.210-3%) and occurs in higher concentrations than Pb, Cu and Ag, whereas the average content of yttrium is 3.310-3%.

102 Ion Exchange Technologies

hydroxoethyl)ethylenediamine-N,N,N'

concentration of rare earth(III) elements.

**2. Rare earth elements occurrence** 

agents as: ethylenediaminetetraacetic acid (EDTA), iminodiacetic acid (IDA), N'

Particular attention is also paid to separation and removal of rare earth(III) elements nitrate complexes by means of frontal analysis from the polar organic solvent-H2O-HNO3 on anion exchangers of various types. The affinity series of rare earth(III) elements nitrate complexes depends on the kind of functional groups, kind of the skeleton, porosity of skeleton, cross linking degree of anion exchanger skeleton as well as kind and concentration of polar organic solvent, concentration of nitric acid, addition of another organic solvent and

In the paper the research on the applicability of different types of anion exchangers for the separation of rare earth elements in the presence of the complexing agents IDA, HEDTA and CDTA will be presented. The effect of the addition of a polar organic solvent (methanol, ethanol, acetone, 1-propanol, 2-propanol) on separation of rare earth(III) elements in such system will be also discussed. The examples of the removal of rare earth(III) elements nitrate

The rare earth elements (REE) are an unusual group of metallic elements with unique properties: chemical, catalytic, magnetic, metallurgical and phosphorescent which consists of seventeen elements belonging to lanthanides. The lanthanide group includes rare earth elements with the atomic number (Z) from 57 to 71 which are: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). Yttrium (Y) and scandium (Sc) belonging to the scandium subgroup are grouped with rare earth elements because of their similar physicochemical

Generally, lanthanide elements with low atomic numbers are more abundant in the earth crust than those with high atomic numbers. Those with even atomic numbers are two to seven times more abundant than the adjacent lanthanides with odd atomic numbers. The lanthanide elements traditionally have been divided into two groups: the light rare earth elements group (LREEs) which contains elements from lanthanum to europium (Z from 57 to 63) and the heavy rare earth elements group (HREEs) which contains elements from gadolinium to lutetium (Z from 64 to 71). Although yttrium is the lightest rare earth element, it is usually grouped with the HREEs to which it is chemically and physically

The geochemical studies have revealed that rare earth elements are actually not rare at all. Rare earth elements as the lithophilous ones occur mainly as phosphates and silicates. Due to their chemical similarity, lanthanides occur side by side in the scattered form in about 200 own minerals or as admixtures in the minerals of other elements. They occur in the crust of the earth in higher concentrations than Bi, I and Ag. For example, cerium, which is the most

complexes from the polar organic solvent-H2O-HNO3 will also be presented in detail.

properties (Spedding & Daane, 1961; Powell, 1964; Gschneidner, 1981; Stasicka, 1990)

similar (Kumar, 1994; Robards et al. 1998; Moustafa & Abdelfattah, 2010).

cyklohexanediaminetetraacetic acid (CDTA) in lanthanides separation.



There are known abort 250 rare earth element minerals of which 10-20 are found to be useful and only 5 practically applicable. Over 90% of the world's economically recoverable rare earth elements are found in primary mineral deposits i.e. in bastnaesite ores which are located in China and at Mountain Pass in California (USA) (Fig.1). Monazite deposits in Australia, South Africa, China, Brazil, Malaysia, India and Russia are the second largest concentrations of rare earth elements. Concerns over radioactive hazards associated with monazites because of thorium presence and high costs associated with its disposal have nearly eliminated it as a rare earth element source in the USA. Additional rare earth elements reserves and resources are found in Colorado, Idaho, Montana, Missouri and Utah. HREEs dominate in the Quebec-Labrador (Strange Lake) and Northwest Territories (Thor Lake) areas of Canada. There are high-grade deposits in Bayan Obo, Inner Mongolia, China and lower-grade deposits in South China provinces providing a major source of the HREEs. The areas considered to be attractive for rare earth elements development include also Karonga, Burundi and Wigu Hill in Southern Tanzania.

1 Mountain Pass, USA; 2 Pajarito Mountain, USA; 3 Gallinas Mountains, USA; 4 Iron Hill, USA; 5 Bald Mountain, USA; 6 Bear Lodge, USA; 7 Pea Ridge, USA; 8 Green Cove Springs, USA; 9 Carolina placers, USA; 10 Lemhi Pass, USA; 11 Snowbird, USA; 12 Rock Canyon Creek, Canada; 13 Hoidas Lake, Canada; 14 Thor Lake, Canada; 15 Elliot Lake, Canada; 16 Strange Lake, Canada; 17 IIimaussaq complex, Greenland; 18 Araxa, Brazil; 19. Barro do Itapirapua, Brazil; 20 Lovozero and Khibina complexes, Russia; 21 Tamazeght complex, Morocco; 22 Bou Naga, Mauritania; 23 Nile Delta and Rosetta, Egypt; 24 Etaner, Nambia; 25 Okorous, Namibia; 26 Steenkampskraal , South Africa; 27 Zandkopsdrif, South Africa; 28 Plinesberg Complex, South Africa; 29 Naboomspruit, South Africa; 30 Palabora, South Africa; 31 Richards Bay, South Africa; 32 Kangankunde, Malawi; 33 Congolone, Mozambique; 34 Karonge, Burundi; 35 Chavara, India; 36 Amba Dongar, India; 37 Orrisa, India; 38 Perak, Malaysia; 39 Maoniuping/Dalucao, China; 40 Bayan Obo, China; 41 Weishan, China; 42 Xunwu/Longnan, China; 43 Dong Pao, Vietnam; 44 Eneabba, Australia; 45 Jangardup, Australia; 46 Mount Weld, Australia; 47 Brockman, Australia; 48 Nolans Bore, Australia; 49 Mary Kathleen, Australia; 50 Olympic Dam, Australia; 51 WIM 150, Australia; 52 Dubbo Zirconia, Australia; 53 Fraser Island, Australia.

**Figure 1.** The rare earth deposits (http://www.bgs.ac.uk/research/highlights/2010 /rare \_earth\_elements.html).

As for their distribution in the environment and in living organisms it should be stressed that they are found, as mentioned above, in the earth crust in a relatively wide range (Hedrick, 1993; Hedrick, 1995). Moreover, they are found in the North Atlantic Ocean waters in very low concentrations. The predominant species are carbonates, such as La2(CO3)3 with the concentration 0.002-0.005 ppb in the case of La(III), Ce(III) and Nd(III) and from 4 to 20 times less in the case of other lanthanides. The studies of the pathways of La(III), Ce(III), Th(IV) and Sm(III) from the soil to plants and farm animals show that sorption and soil abundance decrease in the following order: Ce(III) > La(III) > Th(IV) > Sm(III) (Linsalata, et al. 1986). The levels of lanthanides in healthy human tissues have been reported as follows: liver 0.005 µg/g of ash, kidney 0.002 µg/g, lung 0.004 µg/g, bones 0.2-1.0 µg/g (Goering, et al. 1991).

In the paper by Du & Graedel (2011) the first quantitative life cycles (for the year 2007) for ten rare earth elements: La(III), Ce(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III) and Y(III) were presented. In the charts it was shown that after extraction from ores using different separation processes the mixed rare earth element concentrates are produced. Thereafter, they are separated from each other into individual rare earth element compounds (i.e., oxides, chlorides, fluorides). The compounds are converted into pure metals or alloys and further transformed into intermediate products. Purification of metals is by electrolysis or vacuum reduction. Production of alloys is either by direct co-reduction of the rare earth element compounds or by melting and casting of metals. The intermediate products are manufactured into final goods. When the products containing rare earth elements are discarded at the end-of-life (EOL), the quantity of rare earth element material in use is lost unless recycling occurs. The idea of generic scheme for the REE cycle is presented in Fig.2. Losses of rare earth elements occur at five points in the cycles: mining, separation, fabrication, manufacturing, and waste management. The authors also emphasize that recycling of rare earth elements is challenging and it appears possible for metallurgical applications, automobile catalysts, magnets in wind turbines and automobiles, in which REEs are used in fairly large quantities.

**Figure 2.** The generic scheme of REE cycle (Du & Graedel, 2011)
