RU2573905C1 - Method of processing rare-earth concentrate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be applied for processing and deactivation of rare-earth concentrate (REC), extracted from apatite concentrate and products of its processing - phosphogypsum and extraction phosphoric acid. Rare-earth concentrate, extracted from raw material, which contains products of uranium-thorium series decay, are dissolved in nitric acid with heating and agitation of pulp, which is then diluted with water and cooled. After this, hydrogen peroxide with consumption which ensures 98.0-99.5% reduction of cerium (+4) to cerium (+3) is added. Then nitric acid solution of rare-earth elements (REE) is separated by means of filtration, from which thorium is separated in co-precipitation with barium sulphate by addition of sulphates and soluble barium compounds. Then neutralisation to pH 2.5-3.9 is carried out by mixing at temperature 35-45°C for 1.0-1.5 hours. Barium-thorium cake is separated by filtration.

EFFECT: invention makes it possible to simplify obtaining of deactivated REE oxides from products of apatite concentrate processing with reduction of expenditures.

2 cl, 3 tbl

Description

The invention relates to methods for processing and deactivating rare-earth concentrate (REM), isolated from raw materials containing decay products of the uranium-thorium series, and can be used for processing REM isolated from apatite concentrate and its processed products - phosphogypsum and extraction phosphoric acid, and another type of raw material containing decay products of the uranium-thorium series.

Kola apatite concentrate contains about 1% of rare earth oxides (REE). When it is processed into phosphate fertilizers, dissolving REE in sulfuric or nitric acids passes into a nitrate-phosphate solution or phosphogypsum. Due to the proximity of the chemical properties of REE and thorium (as well as its decomposition products), when REE is isolated from nitrate-phosphate solution or phosphogypsum, the latter are concentrated in the final product - REE concentrate. Their content depends on the processing technology of apatite concentrate and ranges from 0.1 to 0.3% for thorium. In accordance with applicable standards and sanitary rules for ensuring radiation safety (see. Basic sanitary rules for ensuring radiation safety [OSPORB - 99/2010]. - Sanitary rules and regulations. - SP 2.6.1.2612-10) it requires its use in the national economy deactivation.

A known method of extraction purification of nitrate REE solutions from thorium and impurities (RU 2517651, 05.27.2014). The method includes multistage countercurrent extraction of impurities from an aqueous nitric acid solution with tributyl phosphate (TBP). For cleaning, a solution with a REE concentration of 100-150 g / l is used. To clean REE from impurities and thorium, this method uses 5 stages of extraction, 3-5 stages of washing and 5 stages of stripping. Get a solution with a ballast impurity content of less than 4% of the total REE and a radionuclide content less than the maximum permissible levels.

The disadvantages of the method are its multi-stage, as well as the undesirable introduction of TBP in a solution intended for the production of fertilizers, since when evaporating nitrate solutions, the presence of organophosphorus compounds prone to hydrolysis can cause spontaneous decomposition of ammonium nitrate, which is part of the fertilizer, accompanied by fire and explosion.

There is also known a method of processing phosphate rare-earth metals isolated from apatite (RU 2484018, 06/10/2013), including its dissolution with nitric acid, processing the resulting solution with oxalic acid with the precipitation of rare-earth oxalates in two stages. The precipitate of thorium oxalates and REE obtained in the first stage of deposition, washed with a filtrate separated from the precipitate of oxalates of REE in the second stage of deposition. Flushing from a filter with a specific activity of 170-500 Bq / kg is returned to fertilizer production. In the second stage of precipitation, REE oxalates are obtained that do not contain thorium; after their calcination, REE oxides with a specific activity of 130-200 Bq / kg are obtained.

The disadvantage of this method is the low degree of REE extraction in the finished product, since part of the REE is discharged with thorium sludge into fertilizers. In addition, for the subsequent processing of the rare-earth metals, it is necessary to convert it from the oxalate form to the oxide form, which is performed by calcining at a temperature of at least 850 ° C, which is an energy-consuming operation.

Closest to the claimed method is a method of processing loparite concentrate (RU 2145980, 02.27.2014), including grinding it with classification, opening with nitric acid with a concentration of 650-700 g / l at 115-118 ° C. The oxide cake obtained by opening the concentrate is washed with water to obtain a pure hydrated cake, used for subsequent processing, and a combined REE nitrate solution containing ballast impurities and impurities of the uranium-thorium series. The REE solution is neutralized with soda to a pH of 4.5–5.0 and subjected to decontamination with sedimentation using ammonium sulfate and barium nitrate of all impurities, including thorium and mesotorium, by agitation of the pulp at 70-80 ° C for 6-8 hours. Iron-thorium cake with all impurities is separated by filtration and sent for disposal, a pure nitrate REE solution is used for subsequent processing.

The disadvantage of this method is the high energy and material costs for its implementation - agitation of the pulp for 6-7 hours at 70-80 ° C and pH-4.5-5.0.

The objective of the invention is to simplify the process of processing and decontamination of rare-earth metals extracted from raw materials containing decay products of the uranium-thorium series, and reducing the cost of its processing. A method of obtaining RZK from phosphogypsum is known from patent RU 2487834, 07.20.2013.

The problem is solved by changing the composition of the precipitator used to isolate the associated impurity elements and thorium (as well as its decay products) during the processing and decontamination of rare-earth metals, and process parameters.

The technical result of this invention is the production of deactivated REE oxides from the processing products of apatite concentrate, for example phosphogypsum, and increasing the technical and economic efficiency of the method of processing and deactivation of REEs while simplifying it.

The technical result is achieved by the fact that the rare earth concentrate is dissolved in nitric acid during heating and agitation of the pulp, which is then diluted with water and cooled. After that, hydrogen peroxide is added at a flow rate that ensures the restoration of cerium (+4) to cerium (+3) by 98.0-99.5%. Then, nitric acid solution of rare-earth elements (REE) is separated by filtration, from which thorium (mesotorium) is separated by coprecipitation with barium sulfate by adding sulfates and soluble barium compounds, and then neutralized to pH 2.5-3.9 by stirring at a temperature of 35- 45 ° C for 1.0-1.5 hours, followed by separation of barium-thorium cake by filtration.

The presence of cerium (+4) in the REE solution allows the processing and deactivation of rare-earth metals with a mixed co-precipitator - cerium hydroxide (+4) and barium sulfate at a low precipitation pH (2.5-3.9) in a short time (1.0-1 , 5 hours) with moderate heating of the solution (35-45 ° C), ensuring the purification of REE oxides from impurities (calcium, silicon, phosphorus, thorium and its decomposition products) to a content of at least 99.0% of the main substance in the final product and decontamination to the sanitary norm. The advantage of the proposed method is obviously simplified the process and reduced energy and material costs for its implementation.

The following are examples of the processing of rare-earth metals extracted from dump phosphogypsum of OJSC "Voskresensk Mineral Fertilizers" (patent RU 2487834), and the claimed method.

I. The composition of the REE (wt.%), Isolated from the dump phosphogypsum of OJSC "Resurrection Mineral Fertilizers", are shown in table 1.

II. The inventive method: a sample of RZK in 300 g was dissolved in 0.4 l of 67% nitric acid when heated to 80-95 ° C and agitation of the pulp for 2.0-2.5 hours, after which the pulp was diluted with water to a density of 1,550 g / cm ³ and cooled to 40 ° C. Next, the pulp was divided into 2 parts, a hydrogen peroxide solution was added to each with stirring, based on the achievement in the filtrate of the degree of reduction of cerium (+4) to cerium (+3) by 98.0-99.5%. Then the insoluble precipitate was separated by filtration, and the filtrate (nitric acid solution of rare-earth elements (REE)) was analyzed.

Next, experiments were conducted on the decontamination and purification of the filtrate from impurities by coprecipitation of thorium (and its decay products) with barium sulfate and cerium hydroxide (+4) at various precipitant rates and precipitation pH. For experiments, 100 ml of the filtrate was taken. A weighed portion of dry barium hydroxide and the calculated amount of ammonium sulfate in the form of a 20% solution were added to the filtrate, after which the solution was neutralized with an ammonia solution to pH 2.5-3.9 and agitated at a temperature of 35-45 ° C for 1.0-1 ,5 o'clock. The precipitate formed (barium-thorium cake) was separated on the filter, washed with water, dried to constant weight, the yield was determined and analyzed for the content of REE and thorium oxides. Oxalates were precipitated from the filtrate combined with the promoter at pH 1, washed with water, dried to constant weight and calcined at 850 ° C for 1.5 hours. The resulting product was analyzed for the content of REO, impurities and thorium. The results of the experiments are shown in table 3.

The results of the study show that the processing and deactivation of RZK according to the claimed method using a mixture of cerium hydroxide (+4) and barium sulfate can intensify the process, as a result of which it takes place at a lower deposition pH in a shorter time - 1.0-1.5 hours and in mild mode (heating no more than 45 ° C). In addition, the consumption of soluble barium compounds and sulfates is reduced.

New processing and decontamination parameters - pH range, precipitant consumption and agitation time are not obvious.

The claimed processing and decontamination parameters are (the content of oxidized cerium (+4) in the initial solution is not less than 0.5-2.0% of its total amount, the precipitation pH of barium-thorium cake 2.5-3.9, the consumption of barium compounds and sulfate to REE oxides = 0.024: 0.06: 1.0 in moles, agitation time 1.0-1.5 hours) provide a fairly complete and selective release of impurities and the amount of radionuclides (thorium and its decay products) into the solid phase. The resulting REE oxide contains at least 99.0% of the basic substance and meets sanitary standards for the sum of the uranium-thorium series radionuclides (Basic sanitary rules for ensuring radiation safety [OSPORB - 99/2010]. Sanitary rules and regulations. - SP 2.6.1.2612-10 ) Loss of REE with barium-thorium cake is not more than 2.4%. An increase in the pH and consumption of barium compounds (cerium (+4)) and sulfate do not affect the degree of purification and deactivation of rare-earth metals, however, they increase the consumption of reagents and losses of rare-earth metals with barium-thorium cake.

.

The deactivation of rare earth concentrate is carried out at a molar ratio $$B{a}^{+2}:S{O}_{\mathrm{four}}^{-2}:R3\mathrm{ABOUT}=(\mathrm{0,023}-\mathrm{0,025}):(\mathrm{0,057}-\mathrm{0,063}):\mathrm{1,0}$$

.

Claims (2)

1. A method of processing a rare-earth concentrate isolated from raw materials containing decay products of the uranium-thorium series, characterized in that the rare-earth concentrate is dissolved in nitric acid by heating and agitating the pulp, which is diluted with water and cooled, after which hydrogen peroxide is added at a flow rate that ensures reduction of cerium (+4) to cerium (+3) by 98.0-99.5%; nitrate solution of rare-earth elements (REE) is separated by filtration, from which thorium is separated by coprecipitation with barium sulfate by Adding soluble sulfates and barium compounds, and then neutralized to pH 2,5-3,9, while stirring at 35-45 ° C for 1.0-1.5 hours followed by separation of thorium-barium cake filtration. 2. The method according to p. 1, characterized in that the deactivation of the rare earth concentrate is carried out at a molar ratio of Ba ⁺² : SO ₄ ^-2 : REO = (0.023-0.025) :( 0.057-0.063): 1.0.