Method of extracting rare-earth elements from phosphogypsum

FIELD: chemistry.

SUBSTANCE: invention relates to the technology of producing compounds of rare-earth elements during complex processing of apatites, particularly extraction of rare-earth elements from phosphogypsum. The method involves preparation of pulp from phosphogypsum and sorption of rare-earth elements on a sorbent. The pulp is prepared from ground phosphogypsum and sulphuric acid solution with pH=0.5-2.5 until achieving liquid:solid ratio of 4-7. Sorption is carried out directly from the phosphogypsum pulp on a sorbent with sulphuric acid functional groups for 5-7 hours with solid:sorbent ratio of 4-7.

EFFECT: high efficiency of the method owing to higher extraction of rare-earth elements without a filtration step.

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The invention relates to a process of producing compounds of rare earth elements (REE) by integrated processing of Apatite, in particular the production of REE concentrate from phosphogypsum.

In world practice, the decomposition of Apatite carried out mainly by sulfuric acid scheme with getting wet-process phosphoric acid. The main departure is phosphogypsum (calcium sulphate contaminated by impurities of P₂About₅, F, Fe, Al, Sr, REE), which goes up to 75% REE containing Apatite.

Annually in the country are going in the dumps millions of tons of phosphogypsum with a content of about 0.5% of the REE in the form of oxides. However, the known methods of extracting rare earth elements from phosphogypsum, providing for the processing of the various reagents, solutions of ammonium carbonate, followed by dissolving the formed calcium carbonate in nitric acid, solution phosphoric and nitric acids, solutions of ammonium sulfate in the presence of sulfuric acid, not found application in industry because of the high cost of the Regents, as well as high energy and labor costs in obtaining concentrates REE. Therefore, development of a method for extracting rare earth elements from phosphogypsum ensuring the profitability of the recycling tonnage of waste to produce commodity products, is an extremely important task.

The most effective to handle ostypes the use of solutions of sulphuric acid, enables not only to fully extract REE, but to get washed away impurities calcium sulfate, suitable for the production of binders.

The method for extracting rare earth elements from phosphogypsum sulfuric acid solution with a concentration of 22-30 wt.% if F:T=1.8-to 2.2 extraction of REE and sodium in the solution, separating the insoluble residue, increasing the degree of supersaturation of the solution of REE by ensuring that the content of sodium in a solution of 0.4-1.2 g/l with the further crystallization of REE concentrate and its separation from the mother liquor. However, the proposed allocation method REE from sulfate solutions is difficult because of the high costs of Regents (sodium sulfate), as well as high energy and labor costs in obtaining concentrates related to filtration and washing of sediments [Lokshin EP, Kalinnikov V.T., Ivlev KG, Levin B.V., Pogrebnyak O.S Patent (19) RU (11) 2293781 (13) C1 a Method for extracting rare earth elements from phosphogypsum. 2005].

The closest in technical essence and the achieved result is a method (prototype) extracting rare earth elements from phosphogypsum, including the processing of phosphogypsum with a solution of sulfuric acid, filtering the slurry of phosphogypsum and the allocation of the resulting solution amount REE [Pushkin GY, P.P. Melnikov, Malikov, VA and other Application exchanger KMDF to highlight REE of phosphate and sulfate solutions // problems of atomic the eoir of technology. Series: Chemical problems of nuclear power. - 1992. Vol.5. P.77-80.].

The prototype, phosphogypsum is treated with a solution of sulfuric acid with a concentration of 2N H₂SO₄when the ratio W:T=3:1 for 1 hour. Then, the phosphogypsum slurry filtered. In the three-stage processing gain solution with a concentration of 1.75 g/l REE, from which REE are sorption on the sorbent KMDF, with respect to the volume of solution:the mass of the ion exchanger = 10 ml/g for 4 h, the Degree of REE extraction from the solution does not exceed 71%.

The main disadvantage of this method is its lack of profitability due to the low degree of REE extraction from the solution after processing of phosphogypsum with sulfuric acid, the high cost of the sorbent, the presence of stage filtration of phosphogypsum slurry. This stage is time-consuming and energy-intensive process that does not economically viable extraction of REE in this way. In addition, at this stage there is a loss of REE by cocrystallization with gypsum and deposition of double sulphates REE.

The present invention is to increase the degree of extraction of REE in the final product while reducing the cost of implementation of the method.

This object is achieved according to the method which consists in sorption extraction of rare earth elements from phosphogypsum using sorbent with sulfoxylate functionalintegral. To do this, first preparing a slurry of phosphogypsum grinding it and dissolving in sulfuric acid solution of pH=0.5÷2 to the ratio of W:T (liquid:solid)=4÷7, and sorption was carried out directly from the pulp of phosphogypsum, bypassing the stage filtration for 5÷7 hours, with respect to solid:sorbent=4÷6.

The use of sorption of slurries (sorption leaching) allows to increase the degree of extraction of rare-earth elements from phosphogypsum. It is known [Chemistry and technology of rare and scattered elements. part 2 / edited by Bolshakova K.A. M.: Higher school, 1976, 360 S.]that sulfate environment contributes to the re-deposition of dissolved REE in the form of sparingly soluble double sulphates, which reduces the degree of extraction of rare-earth elements from phosphogypsum sulfuric acid. The constant presence of the sorbent in such a system enables the output of the dissolved REE ions from the solution phase sorbent, thereby shifting the equilibrium towards the formation of both oxides and double sulphates REE. When this is achieved the minimum use of sulfuric acid by acidification of the pulp phosphogypsum hydrogen ions and functional groups of the sorbent.

In addition, the low cost, prevalence, good performance for pulp processes and a large exchange capacity on REE sorbent with sulfoxylate functional groups, significantly increase the cost effective the awn process.

The decrease and increase in the pH of the pulp phosphogypsum beyond these impractical. In the first case is sharply reduced sobiraemosti REE, and, consequently, the degree of extraction. At pH more than 2.5 decreases the solubility of REE oxides in the solid part of the phosphogypsum. When the ratio W:T less than 4 solid bad pomeshivaem pulp phosphogypsum, which complicates the process of sorption of REE. When the ratio W:T 7 more sharply increase the volume of the solution, which leads to an increase in the number of equipment. At the same time, positive effects on the recovery of REE is not observed. The maximum sobiraemosti REE achieved during sorption 5÷7 hours. When the contact time less than 5 hours the degree of REE extraction insignificant, when contact time is over 7 hours increase the degree of extraction does not occur. With respect to solid:the sorbent is less than 5 degree of REE extraction is practically unchanged. When the increase in this ratio in excess of 6 degree of REE extraction decreases.

Example 1. A portion of the sorbent with sulfoxylate functional groups in the amount of 4 grams (in terms of dry weight) were placed in the reactor and poured it in the phosphogypsum slurry containing 20 grams of phosphogypsum (in terms of absolutely dry) when the ratio W (sulfuric acid solution):T (phosphogypsum)=5 and kept under stirring to use the e 5 hours at various pH at room temperature. The research results are summarized in table 1.

Example 2. A portion of the sorbent with sulfoxylate functional groups in the amount of 4 grams (in terms of dry weight) were placed in the reactor and poured her a slurry containing 20 grams of phosphogypsum (in terms of absolutely dry) at a ratio of W:T=5 and kept at premesis the Institute for 5 hours, with the pH of the pulp phosphogypsum = 1,5. Also conducted the experiment with the same conditions, but without addition of sulfonic cation exchanger. The research results are given in table 2

Example 3. A portion of the sorbent with sulfoxylate functional groups in the amount of 4 grams (in terms of dry weight) were placed in the reactor and poured her a slurry containing 20 grams of phosphogypsum (in terms of absolutely dry) with a pH of 1.5, and kept under stirring for 5 hours at different ratios W:T at room temperature, with constant maintenance of the pH of the pulp. The research results are summarized in table 3

Example 4. A portion of the sorbent with sulfoxylate functional groups in the amount of 3 grams (in terms of dry weight) were placed in the reactor and poured her a slurry containing 20 grams of phosphogypsum (in terms of absolutely dry) at a ratio of W:T=5 and pH=1,5 kept under stirring for 3, 5, 6, 7, and 9 hours at room temperature. The research results are summarized in table 4.

Example 5. A portion of the sorbent with sulfoxylate functional groups in the number of 2,86; 3,33; 4,0; 5,0; 6,67 (the ratio of solid:sorbent is appropriately 7, 6, 5, 4, 3) grams (in terms of dry weight) were placed in the reactor and poured her a slurry containing 20 grams of phosphogypsum (in terms of absolutely dry) at a ratio of W:T=5 and pH=1,5 kept under stirring for 5 hours at room temperature. The research results are summarized in table 5.

Example 6. Sample sorbents in the amount of 4 grams (in terms of dry weight) were placed in the reactor and filled in their slurry containing 20 grams of phosphogypsum (in terms of absolutely dry) at a ratio of W:T=5 and pH of 1.5 was kept under stirring for 5 hours at room temperature. The research results are summarized in table 6.

Thus, the technical result of the proposed method for extracting rare earth elements from phosphogypsum is determined by the high efficiency of this method due to the increase of REE extraction by sorption leaching, reduce the use of sulfuric acid, high capacity sorbent with sulfoxylate functional groups of REE, the process of sorption directly from the pulp of phosphogypsum, bypassing the stage of the filter.

The method for extracting rare earth elements from phosphogypsum, comprising preparing a slurry of phosphogypsum, the sorption of rare earth elements on the sorbent, wherein the preparation of the pulp lead from the crushed phosphogypsum and sulfuric acid solution with a pH of 0.5÷2.5 to ratio W:T (liquid:solid)=4÷7, and sorption was carried out directly from the pulp fo fogies sorbent sulfoxylate functional groups within 5÷7 h with respect to solid:sorbent=4÷6.