RU2830550C1 - Method of separating terbium and dysprosium - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the technology of rare-earth elements, specifically to separation of terbium and dysprosium from a concentrate containing terbium, dysprosium, impurities of lighter rare-earth elements and impurities of heavier rare-earth elements. Method involves extraction with an organophosphorus cation-exchange compound, washing and re-extraction. Process is carried out in the mode of complete internal irrigation, completely extracting terbium and accumulating it in the extraction part of the cascade in the connected vessel. Dysprosium is re-extracted from the extract in two steps, completely returning the first re-extract containing dysprosium into the cascade as a washing solution and accumulating it in a connected vessel in the washing part of the cascade.

EFFECT: method increases purity of terbium and dysprosium.

5 cl, 3 dwg, 3 tbl

Description

The proposed invention relates to the field of rare earth element (REE) technology. Of all the rare earth elements, terbium and dysprosium can be noted as the most popular elements, not only due to the fact that they are used in highly efficient devices, but also due to the low content of these elements in rare earth concentrates. Dysprosium is an important additive in the production of neodymium magnets; without terbium, it is impossible to produce effective phosphors. In the work [. Abreu, RD and Morais, CA, Study on separation of heavy rare earth elements by solvent extraction with organophosphorus acids and amine reagents, Miner. Eng. 2014, Vol. 61. P. 82-87. [https://doi.org/10.1016/j.mineng.2014.03.0] the separation of heavy REE by seven extractants was studied: three organophosphorus acids (DEHPA, IONQUEST 801 and CYANEX ^® 272), DEHPA/TOPO mixture (neutral ester) and three amines (ALAMINE 336, ALIQUAT 336 and PRIMENE JM-T). It was found that Ionquest 801 is the most convenient for the separation of heavy REE, since it has a lower affinity for REE compared to D2EHPA, which facilitates back-extraction from Ionquest 801 than from D2EHPA. Moreover, the number of steps required to remove REE from Ionquest 801 is much less than that observed when using D2EHPA. In the report [Kim, JS, Kumar, BN, Radhika, S., Kantam, ML, and Reddy, BR, Studies on selection of solvent extractant system for the separation of t rival Sm, Gd, Dy and Y from chloride solutions, Int. J. Miner. Process. 2012. V. 112-113, R. 37-42. https://doi.org/10.1016/j.minpro.2012.07.00] a suitable system for the separation of a mixture of rare earth elements was selected using organophosphorus acid (TOPS 99), phosphonic acid (РС 88А), phosphinic acid (CYANEX 272), monothiophosphinic acid (CYANEX 302), phosphine oxide (CYANEX 923, CYANEX 921) and amines based on (ALAMIN 336, ALIKVAT 336). It was found thatРС 88А is the best extractant with a high separation factor for the Dy-Y pair with the Sm-Gd pair. It was found that Cyanex 572 solutions exhibit the highest selectivity in the separation of STH by the Eu/Sm lines ( = 1.5), Tb/Gd ( - 4.2), Dy/Tb ( = 2.1), Y/No ( = Y/No and Er/Y ( = 2.2), and the Cyanex 572 - TBP mixture - along the Eu/Sm lines ( = 1.5). It is shown that the addition of up to 0.37 M TBP to 1 M Cyanex 572 increases the saturation of the extractant to 28 g/l by REE and reduces the consumption of nitric acid for REE re-extraction. The disadvantage of this solution, like the others, is that a sequence of separation operations is proposed first along one line and then along the other, i.e. at least two separation cascades are required. The closest in technical solution and achieved result is the method described in the source [S.L. Mishra, H. Singh, S.K. Gupta. Simultaneous purification of dysprosium and terbium from dysprosium concentrate using 2-ethyl hexyl phosphonic acid mono-2-ethyl hexyl ester as an extractant. Hydrometallurgy. Volume 56, Issue 1, May 2000, Pages 33-40. https://doi.org/10.1016/S0304-386X(00)00064-5].

Solvent extraction of rare earth chlorides obtained from monazite produces a heavy rare earth fraction containing 60% _Y2O3 , which is further purified to 93% _Y2O3 to yield a concentrate containing >50% _Dy2O3 , 14% _Tb4O7 , ₁₀ % _{Gd2O3 ,} 2.4% _{Ho2O3 and} 21% _Y2O3 . The concentrate was processed to obtain dysprosium _by extraction of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl _ester (PC 88A) in paraffin _kerosene . The separation factors Dy/Gd, Dy _/ Tb, Y/Dy, Ho/Dy and Er/Dy were determined experimentally. Counter-current extraction and washing tests were conducted under optimal conditions using mixer-sedimenters with a mixer capacity of 50 ml. The separation process yielded 85% yttrium, 83% terbium and 97% dysprosium concentrate. The disadvantage of the technology is the need for additional cascades to obtain commercial grade terbium and dysprosium, i.e. with a purity of at least 99.9%. To increase the purity of terbium and dysprosium, the author proposes the following technical solution.

Neutral extractants, in particular TBP, are not effective for separating samarium-europium-gadolinium. Alkylphosphoric acids, such as di-2-ethyl hexylphosphoric acid (D2EHPA), or phosphonic or phosphinic acids are most effective for separating these elements. Table 1 shows the results of the distribution of REE nitrates in the D2EHPA-Ln(NO ₃ ) ₃ -HNO ₃ system.

The separation factors decrease with increasing equilibrium concentration of REE in the aqueous phase. The optimum concentration is 90-120 g/l (for REE oxides). For separation of terbium and dysprosium, it is proposed to use a non-stationary separation process with accumulation of separation products, in this case, terbium and dysprosium, in the cascade stages.

The counter-current process was simulated on funnels in the 1 funnel 2 stage mode with full internal irrigation. The initial aqueous solution contained 120 g/ ^dm3 of REE (calculated as oxides) and 0.7 mol/dm3 of ^nitric acid. The content of individual REE in the concentrate, % by weight: terbium 9.9%, dysprosium 90.1%. The extractant was a 30% solution of di-2-ethylhexyl phosphoric acid (D2EHPA) in kerosene. The phase ratio was O : B = 3 : 1. The extractant was introduced into the 1st funnel. The aqueous phase was collected from the 2nd funnel, combined with the raffinate from the first chamber, evaporated to 120 g/ ^dm3 , neutralized with ammonium hydroxide and introduced into the 2nd funnel. The outgoing organic phase was re-extracted with a nitric acid solution of 3 mol/ ^dm3 concentration, the re-extracts were combined, evaporated to 100-120 g/ ^dm3 and introduced into the 5th funnel. A total of 10 withdrawals of the organic and aqueous phases were made. Since the saturating solution was introduced into the second funnel (4th stage), six stages were involved in the separation. It is evident that terbium is concentrated in the first stage, and dysprosium is almost purified from terbium and is concentrated in the last 6-10 stages (Fig. 1).

Terbium and dysprosium zones are already formed at this small number of stages. When the number of stages increases to 40-50, the zones move apart and accumulation zones are formed for impurity elements lighter than terbium and heavier than dysprosium. The dysprosium concentrate contains terbium and dysprosium in a ratio of 1:10, as well as impurities of lighter rare earth elements, in particular, 0.5% by weight of lighter elements and 0.2% by weight of impurities of heavier elements: 0.1% holmium and 0.1% erbium. An extraction cascade containing 75-80 stages is required to separate terbium and dysprosium. Containers for accumulation of terbium and dysprosium, respectively, are connected to certain stages in the extraction part of the cascade and in the washing part of the cascade. It is desirable to use 30-35% vol. as an extractant. alkylphosphonic acid solution (mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid or diisooctylphosphinic acid solution (Suanex-272). The advantage of these acids is that a mineral acid solution of a minimum concentration of 0.5-1.0 mol/ ^dm3 is required for re-extraction of REE. In the absence of phosphonic acid, the separation process can be carried out using a 30% solution of D2EHP in an inert diluent.

The disadvantages of using D2EHP, as indicated earlier, include the need to use fairly concentrated nitric acid solutions for re-extraction of REE from the organic phase. The basic scheme for isolating terbium and dysprosium from concentrate is shown in Fig. 2. The extractant is introduced into the first stage, and a tank for accumulating terbium is connected to stages 15–17. The initial solution is introduced into stage 35, the wash solution is introduced into stage 65, and a tank for accumulating dysprosium is connected to stages 50–52. The first recording solution is introduced into stage 70, the second into stage 75. A 1–2 mol/dm3 ^nitric acid solution is used as a reacting solution in the case of using phosphonic acid as an extractant, and 3–4 mol/dm3 ^nitric acid when using D2EHP. The initial solution contains 100-120 g/ ^{dm3 of} REE calculated as oxides and 0.05-0.3 mol/ ^dm3 of nitric acid when using phosphonic acid and 0.7-1.5 mol/dm3 ^{of nitric} acid when using D2EGFK. Initially, all the cells of the cascade and the containers are filled with the initial solution. A neutralizer is added to the first chambers of the extraction part of the cascade, which can be ammonium hydroxide or sodium hydroxide to neutralize the released hydrogen ions. The process parameters are selected such as to completely extract terbium from the aqueous phase, leaving gadolinium in the aqueous solution. At a REE concentration in the aqueous phase of 100 g/ ^dm3 and 25 g/ ^dm3 in the organic phase (for 30-35% of the extractant) and a separation factor of dysprosium and terbium ( = 1.8, the phase ratio in the extraction cascade will be Vorg.:Vinit.:Vprom.= 12-10:1:1.85. At the re-extraction stage, the phase ratio is Vorg.:Vaqueous= 1:0.3-0.6. The effect of the separation coefficient of dysprosium and terbium can be seen from Table 2 and the purity of terbium for the required number of stages and the ratio of phase flows.

Table 2

Effect of the partition coefficient of dysprosium and terbium and the purity of terbium for the required number of stages and the ratio of phase flows (x ₀ and x _n are the initial and final content of terbium, q is the enrichment factor, q and G are the enrichment factor and the selection of pure terbium)

It is evident that in order to obtain terbium containing less than 0.001% dysprosium, it is necessary to almost double the number of stages and increase the flows of the organic and aqueous phases. The extract leaving stage 65 is treated with a stripping solution, completely removing dysprosium into the aqueous phase. The resulting solution is evaporated to a concentration of 100-120 g/l, adjusted for nitric acid content and sent to stage 65 as a washing solution. The remaining impurities of holmium and erbium in the organic phase are removed in the second stripping into the aqueous phase and removed from the process. The process of feeding the initial solution is carried out until terbium and dysprosium accumulate in the corresponding containers to a content of 97-98% of the main substance. After this, the feed of the initial solution is stopped, the feed of the washing solution is increased by the proportion of the reduced initial solution. In this mode, the process will be brought to the complete removal of impurities of lighter elements, in particular, samarium, europium, gadolinium from the middle of the cascade and from the tank in which terbium and holmium, erbium and heavier elements are accumulated from the washing part. In this mode, impurities of lighter and heavier elements are removed from the washing part of the cascade and from the tank intended for the accumulation of dysprosium. After the accumulation of dysprosium and terbium in the said tanks with a content of the main substance of more than 99.9-99.99%, the process is stopped. The distribution of terbium, dysprosium and impurities by the stages of the cascade is shown in Fig. 3.

Terbium and dysprosium are drained from the containers, impurities of heavier elements are removed from the second reextract, and impurities of lighter elements are removed from the first chambers of the cascade. The results of the separation are given in Table 3.

The positive result is not only the separation of terbium and dysprosium, but also the additional purification of terbium from lighter REEs, and dysprosium from heavier elements.

Claims (5)

1. A method for separating terbium and dysprosium from a concentrate containing terbium, dysprosium, impurities of lighter rare earth elements (REE) and impurities of heavier REE, comprising a stage of extraction with an organophosphorus cation exchange compound, washing and re-extraction, characterized in that the process is carried out in a full internal irrigation mode, completely extracting terbium and accumulating it in the extraction part of the cascade in a connected container, re-extracting dysprosium from the extract in two stages, completely returning the first re-extract containing dysprosium to the cascade as a wash solution and accumulating it in a connected container in the wash part of the cascade. 2. The method according to paragraph 1, characterized in that during the complete extraction of terbium, impurities of lighter rare earth elements remain in the aqueous phase, which are removed from the process. 3. The method according to paragraph 1, characterized in that the re-extract from the second stage contains impurities of heavier rare earth elements, which are removed from the process. 4. The method according to item 1, characterized in that when terbium and dysprosium accumulate in the connected containers to a content of 97-98%, the supply of the initial solution is stopped, and the flow of the washing solution is increased by the volume of the initial solution. 5. The method according to item 4, characterized in that after cleaning the solutions of the middle of the cascade, the connected containers and the reextract from impurities of lighter and heavier elements and achieving the required purity of terbium and dysprosium in the connected containers of 99.9-99.95%, the process is stopped, the solutions of terbium and dysprosium nitrates are drained from the connected containers and removed as finished products, and the process is repeated again.

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