**4. Hydrometallurgical process of REE recovery**

In order to separate the individual REEs, at first they have to be recovered from the raw material such as REE ores or the WEEE, in hydrometallurgical process. The technological scheme of REE extraction from minerals usually consists of grinding and cracking mined ore, preliminary enrichment to produce mixed REO concentrates, and then further concentration, separation and purification of REE oxides. To concentrate the REE extracted from minerals, the methods such as flotation, gravity separation, electrostatic separation, or magnetic processes are used [2].

Various methods and solutions are used for the extraction of REE from solid materials. As lixiviants, inorganic acids, alkalines, electrolytes, and chlorine gas are used. The leaching reagent should be selected to fit specific characteristics of the source material, for example, acids are commonly used to extract REE from silicate ore mineral such as gadolinite, eudialite, and allanite, and the alkaline reagents and sulfuric acid are mainly used to leach REE from phosphate ore minerals like monazite and xenotime. Electrolyte solutions are used to extract of REE from ion adsorption clay deposits. The chlorination process can be used to treat majority of rare earth minerals.

The obtained solution is a mixture of various REE with other metals, present in the raw material. The separation of individual metals is one of the most major challenges in hydrometallurgy. Currently the solvent extraction is the most preferable method of purification due its continuous nature and possibility to handle large amounts of diluted post-leaching solution. Selection of the ligand used for forming the organic soluble metal-ligand complex can have profound effects on separation of metals and overall process efficiency and economics. Generally all three major classes of extractants: acidic, neutral, or basic extractants can be utilized for separating rare earths [29].

laptops [1]. The recovering and processing of the WEEE have become very important because of the huge amount of the collected WEEE in Poland and in the European Union. Only 25% of the mass of WEEE produced in the EU-27 is stored and processed, and the remaining 75% is not processed. In Poland, an overall of 1.48 kg per capita of WEEE was collected in 2008 and 4.39 kg per capita in 2014; it is roughly 168,900 tonnes of WEEE. In 2021 Poland will be obliged

Based on the data of the Chief Inspectorate for Environmental Protection (CIEP), Poland, there are a lot of Polish Organisation of Electrical and Electronic Equipment Recovery (OEEER), for example, Elektroeko, the European Recycling Platform, AURAEKO, Biosystem Elektrorecykling, CCR RELECTRA, Electro-System, DROP, and TOM, which are responsible for meeting the collecting and recycling obligations on behalf of enterprises [23]. In Poland, there are also a number of companies collecting and processing WEEE, which cooperate with companies belonging to OEEER, for example, Elektrorecykling Sp. z o.o. [24]**,** REMONDIS Electrorecycling Sp. z o.o.

A total of 168,932 tonnes of WEEE was collected in the country, including 159,756 tonnes (94.56%) from households and 9175 tonnes (5.44%) from other sources in 2014. The largest volume of this waste is composed of large household appliances, 79,562 tonnes (47.09%), and IT and telecommunication equipment (e.g., computers, laptops, mobile phones, etc.), 24,965 tonnes (14.72%). The smallest part is composed of wastes of automatic dispensers, 115 tonnes

In order to separate the individual REEs, at first they have to be recovered from the raw material such as REE ores or the WEEE, in hydrometallurgical process. The technological scheme of REE extraction from minerals usually consists of grinding and cracking mined ore, preliminary enrichment to produce mixed REO concentrates, and then further concentration, separation and purification of REE oxides. To concentrate the REE extracted from minerals, the methods such as flotation, gravity separation, electrostatic separation, or magnetic

Various methods and solutions are used for the extraction of REE from solid materials. As lixiviants, inorganic acids, alkalines, electrolytes, and chlorine gas are used. The leaching reagent should be selected to fit specific characteristics of the source material, for example, acids are commonly used to extract REE from silicate ore mineral such as gadolinite, eudialite, and allanite, and the alkaline reagents and sulfuric acid are mainly used to leach REE from phosphate ore minerals like monazite and xenotime. Electrolyte solutions are used to extract of REE from ion adsorption clay deposits. The chlorination process can be used to treat major-

The obtained solution is a mixture of various REE with other metals, present in the raw material. The separation of individual metals is one of the most major challenges in hydrometallurgy. Currently the solvent extraction is the most preferable method of purification due

[25], Baterpol S.A. [26]**,** and P.P.H.U. POLBLUME Zbigniew Miazga [27].

**4. Hydrometallurgical process of REE recovery**

to collect 11 kg per capita [23].

14 Lanthanides

(0.06%) [28].

processes are used [2].

ity of rare earth minerals.

The extraction step is always followed by scrubbing. The organic phase from extraction step is contacted with scrubbing solution in order to remove any undesirable solutes that are entrained in the organic solution and improve the purity of valuable elements. Typically scrubbing is carried out by using water, dilute acid, or base solution. It is worth to note that a relatively high amount of valuable metals may pass to the scrubbing solution. For this reason, it should be recycled back to extraction stage and mixed with the feed aqueous solution.

The metals extracted to the organic phase should then be stripped back to aqueous phase for further recovery. The stripping is the reverse operation to the extraction. As a stripping solution, typically concentrated acid, alkaline, or salt solutions are used. Likewise extraction, stripping may be performed in a one-stage, two-stage, or multi-stage process [30].

REE can be separated using ion-exchange techniques. The separation of lanthanides can be achieved by using the combination of chelating eluents that are selective for individual lanthanides with resins that is characterized by little selectivity. The other possibility is the extractions with the chemically modified resins; among them are resins coated with extractant [31].

Several REE can be separated basing on their redox properties [31]. The example is cerium and europium which have been isolated on an industrial scale using reduction-oxidation reactions. Cerium (III) was oxidized to +4 that forms sparingly soluble oxides or hydrates. The precipitate was separated to give pure cerium solid (99% of purity) and cerium free liquor. Europium was reduced to +2 and precipitated as sulfate from mixed rare earth elements solution. The purity of europium obtained in this way was >99%.

The industrial process of purification of lanthanum, gadolinium, terbium, and dysprosium uses fractional crystallization techniques. This method is based on the different solubility of rare earth bromate, nitrate, and sulfate complexes. A lot of repetition of crystallization is necessary to obtain pure metal. For example, the lanthanide with 99.98% purity was obtained from a mixture of REE with using ammonium nitrate after 16 repetitions of crystallization ([31], and references therein).

Summarized, the separation of REE is the most difficult aspect of their production. The expanding global demand of these metals is the reason for the intensive increase of research in this field.

## **5. Separation of REE from polish resources**

Initiating the nuclear power program in Poland generated interest in domestic uranium resources and the study of the recovery of uranium from Polish uranium ores [32, 33]. Most Polish uranium ores are black shale and sandstone-type deposits [34, 35]. Uranium is usually accompanied by other valuable metals, among them REE [36]. These metals could be recovered at the same time as uranium, to improve the economy of processing of low-grade uranium ores predominated in the country. The content of lanthanum in Polish ores is 31–62 ppm in dictyonema shales and 4–53 pm in Triassic sandstones. The studies performed in the scope of national projects have shown 66% efficiencies of leaching of La from dioctynemic shales by 10% H<sup>2</sup> SO4 at 80°C [36]. The leaching under elevated pressure (2, 3, 5, 7 bar) did not improve the efficiencies, however shortened the time of process from 8 to 2 hours. Zakrzewska-Koltuniewicz et al. developed the second-order regression models to predict the leaching efficiencies of valuable chemical elements. They carried out the statistically designed experiments to investigate the recovery of U, V, and Mo chemical elements and representative lanthanides like La and Yb from low-grade uranium ore using sulfuric acid as a leaching reagent [37]. Lanthanum can also be extracted from sandstones with high efficiency (80%) at temperature 60°C with 10% HCl [38].

used: precipitation and extraction in liquid-liquid systems with the participation of an organic phase as well as crystallization methods, among others [43, 44]. Results of this work confirmed higher efficiency of leaching lanthanides from phosphogypsum by the application of nitric acid (c.a. 90%) than sulfuric acid (c.a. 60%). However, in the case of using nitric acid, an

The possibility of recovery of REE from phosphogypsum stored in Wizów heap with simul-

[14]. The technology was examined at laboratory scale by the processing of 1 Mg/h of phosphogypsum. The technological flowsheet consisted of three steps: (i) leaching of lanthanide from the phosphogypsum using sulfuric acid at a concentration of 15%, (ii) crystallization

recrystallization of gypsum. In this way, insoluble high-quality anhydrite, phosphoric acid, and concentrate of rare earths concentrate containing more than 90% of oxides were products

The leaching of valuable metals from phosphogypsum stored in Wiślinka heap was also studied. The experiments were performed in laboratory scale. Lanthanum and other REEs were recovered with high efficiencies (**Figure 4**). Initially, the phosphogypsum was treated with 30% NaOH at 60°C, and then the solid residue was leached with 10% HCl at 60°C [12, 45].

Zielinski et al. studied the recovery of lanthanides from Kola apatite used for the phosphoric acid production in Polish phosphoric fertilizer factory [46]. It was found that a stage of the hydration of hemihydrate provides the best conditions for the recovery of lanthanides. In this stage for the removal of lanthanides, a solvent extraction has been applied and consequently a precipitation-stripping process for the removal of lanthanides from the solvent has been employed. As a result, a concentrate enriched with lanthanides has been obtained in which lanthanides were recovered with an efficiency of 80–85%. The similar results were obtained by the El-Didamony et al. in the studies of reduction in the concentration of radionuclides in phosphogypsum by using suitable organic extractants. This process was accompanied by

of the process. The composition of the rare earth concentrate is presented in **Table 3**.

and production of anhydrite cement was also a subject of work

O3

O3 0.2

O7 0.1

O3 <0.1

O3 <0.1

O3 <0.1

O3 <0.1

O3 <0.1

) from the leach solution, and (iii)

Perspective of Obtaining Rare Earth Elements in Poland http://dx.doi.org/10.5772/intechopen.80743 17

additional waste threatening the environment is generated.

of the rare earth concentrate (containing up to 25% Ln2

reduction in the concentration of REE up to 80.1% [47–49].

O3 24.8 Dy2

O3 15.9 Ho2

O3 1.9 Er2

O3 0.9 Tm2

O3 0.44 Yb2

O3 0.3 Lu2

**Table 3.** The composition of the concentrate of REO [14]

ThO2 0.2

CeO2 50.5 Tb4

**Component % Component %**

O5

taneous recovery of P2

La2

Nd2

Sm2

Gd2

Eu2

Y2

Very interesting, the novel method used for processing Polish uranium ores was a leaching in the membrane contactor with helical flow equipped with tubular metallic membrane. In this process, lanthanum was co-extracted with uranium from dictyonema shales with 78% of efficiency [39]. The process was carried out at ambient temperature, and the yield of leaching was higher than obtained in the stationary reactor with heating and mixing. The additional advantage of using the membrane contactor is a possibility of conducting two processes: leaching and solid-liquid separation in one apparatus.

The post-leaching solution obtained from the separation of solid residue from liquid is a mixture of various metal ions. The further purification and separation of metals can be achieved by solvent extraction followed by stripping to aqueous phase or by ion exchange. By using solvent extraction, we cannot avoid some of the problems associated with this process. A third phase between aqueous and organic phases is often formed in solvent extraction process. It is related to the solubility of the metal-extractant complex in the organic solution. The formation of the third phase may cause many difficulties; first of all, it leads to organic solvent loss. The minimization of the formation of the third phase can be achieved by addition of a modifier to the organic phase [40] or by application of membrane contactors, a multistage mixer-settler arrangement with concurrent flow of two phases—aqueous and organic [41].

Ion exchange proved also itself as an effective separation method of metals from water solutions. Danko et al. proposed to use Dowex 1X10 and Dowex 50WX4 for valuable metals extraction from pregnant leach liquors from extraction of Polish ore. The recovery of lanthanides was 99% [42].
