RU2484018C2 - Method of treating rare-earth phosphate concentrate separated from apatite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of separating deactivated rare-earth elements during nitric acid treatment of apatite concentrate from nitrate-phosphate solutions. The method of treating a rare-earth phosphate concentrate isolated from apatite involves decomposition of the rare-earth phosphate concentrate with nitric acid, treating the obtained solution with oxalic acid with precipitation of rare-earth oxalates in two steps, at the first step of precipitation of oxalates of thorium and rare-earth elements, 5-10% oxalic acid in stoichiometric amount is added to rare-earth elements present in the solution, and at the second step of precipitation of rare-earth oxalates, 110-115% oxalic acid in stoichiometric amount is added to rare-earth elements present in the initial solution, and the rare-earth oxalates are then calcined to rare-earth oxides.

EFFECT: invention provides high economic efficiency of the process, which is achieved by avoiding the need to process and bury the precipitate containing thorium.

3 cl, 2 ex

Description

The invention relates to methods for the isolation of deactivated rare earth elements (REE) during the nitric acid processing of apatite concentrate from nitric phosphate solutions obtained by dissolving the REE phosphate concentrate.

Khibiny apatite concentrate contains ≈1% REE oxides. The thorium content in it is 0.001-0.003%, which determines the specific activity of 0.004-0.12B c / g, below the norm acceptable for non-radioactive materials, in accordance with the Sanitary Rules (SP 2.6.1.798-99) ≤0.74 Bq / g . Due to the proximity of chemical properties to the properties of REEs, upon separation of REEs from apatite concentrate, thorium is concentrated in the final product — REE oxides — to a content of 0.1-0.3%. The specific activity of the rare-earth product is 4.2-12.5 Bq / g, which, according to the Sanitary Rules, does not allow attributing it to non-radioactive materials.

A known method of processing a phosphate rare-earth concentrate isolated from apatite, including the decomposition of the REE concentrate with concentrated (10-12N) nitric or hydrochloric acid when heated, processing the resulting solution with oxalic acid with its 200% excess in excess of a stoichiometric amount to REE with the precipitation of rare earth oxalates separation of the oxalate precipitate, washing and calcining it to obtain the sum of REE oxides containing 93-95% of the main substance, 5-7% of impurities - mainly calcium, iron, cre Niya, phosphorus. ("Complex nitric acid processing of phosphate raw materials. / Ed. By Goldinova A.L. and Kopyleva B.A. - L: Chemistry, 1982, p.157-159)

A known method of processing a phosphate rare earth concentrate isolated from apatite. / Patent RU No. 2148019, MKI CO1F 17/00, C22B 3/06 /. The decomposition of rare-earth phosphate rare-earth concentrate was carried out by simultaneous dissolution in nitric or hydrochloric acid in the presence of oxalic acid. The precipitate of oxalates is washed with water and calcined to REE oxides. This method is adopted as a prototype.

The disadvantages of these methods is to obtain REE oxides with a thorium content exceeding sanitary standards (SP 2.6.1.798-99). The operation of separating thorium by these methods of processing phosphate rare-earth concentrates to REE oxides is not provided.

There is also known a method of decontamination of REE in the processing of loparite concentrate by separation from the nitric acid solution of REE iron thorium cake, which is subjected to subsequent processing and disposal. (Patent No. 2145980 “Method for processing loparite concentrate”, MKI C22B 59/00, 34/12).

The disadvantage of this method is the need for additional processing of thorium iron cake and the organization of its burial.

There is also a method of extraction separation of thorium from REE during their extraction with tributyl phosphate. (Zelikman. N.A. et al. “Metallurgy of rare-earth metals of thorium and uranium.” Because of ferrous and non-ferrous metallurgy. M., 1960).

The disadvantages of the method include its multistage nature, the introduction of organophosphorus compounds, which is undesirable in the production of fertilizers, since the ingress of impurities of organophosphorus compounds prone to hydrolysis can cause spontaneous decomposition of ammonium nitrate, which is part of the fertilizer. In addition, the separation of thorium concentrates from organic solutions will require additional processing operations and the organization of burial or storage of the resulting thorium products.

The technical result of this invention is the production of deactivated total rare earth concentrates during the nitric acid processing of apatite with the exception of discharges, increasing the economic efficiency of the method due to its simplification.

The technical result is achieved by the fact that fractional (two-stage) precipitation of REE oxalates is carried out from nitric phosphate solutions obtained by decomposition of a rare-earth phosphate concentrate with nitric acid. At the first stage of precipitation, oxalic acid is introduced in an amount of 5-10% of the stoichiometry on REEs present in the solution. The consumption of oxalic acid in the second stage of deposition of oxalates is 110-115% of the stoichiometry on REE contained in the initial nitric-phosphoric acid solution. Thorium oxalate is precipitated together with part of REE oxalates. The precipitate of thorium oxalates and REE is separated from the solution by filtration. The precipitate is washed off the filter with the filtrate stream obtained in the second deposition stage — deactivated REE oxalates, and then returned to the fertilizer production.

The resulting suspension due to dilution of the precipitate by the filtrate is non-radioactive and can be sent to the production of fertilizers. Thus, thorium, which was in apatite concentrate and passed into the main product - fertilizers, is again returned to their production.

After the second stage of deposition, REE oxalates are obtained with a specific activity of 0.13-0.2 Bq / g, satisfying the sanitary standards SP 2.6.1.798-99. For materials with which work without restrictions is allowed, the specific activity should be <0.74 Bq / g. The mother liquor of the second stage of REE deposition is also non-radioactive.

The advantage of the proposed method lies in the fact that after calcination of the REE oxalates obtained in the second stage of deposition, the REE oxides are non-radioactive and correspond to class 1 according to the sanitary rules, allowing you to work with them without restrictions. In addition, the disposal of sludge containing thorium does not require additional costs for its processing and disposal, which makes the process of separation of REEs cost-effective.

Example 1. The experiments were carried out using nitrate-phosphate solutions obtained in the production of fertilizers at JSC AKRON after the operations of separation of calcium nitrate. Sodium cremofluoride was isolated from this solution. The resulting nitrate-phosphate solution had a composition, ppm%:

REO - 0.47; Th 0.00047; P ₂ O ₅ - 22.5; Ca - 3.82; F is 0.2.

From this solution, phosphate rare-earth concentrate (MFC) was precipitated with gaseous ammonia at pH 1.4. The sediment of the FRPK was separated from the solution and dissolved in 12N nitric acid. The resulting nitric phosphate solution (AFR) composition, ppm%:

REO - 6.67; Th is 0.0067; P ₂ O ₅ - 6.31; Ca - 1.06; HNO ₃ - UN; F is 0.001;

heated to 90 ° C and then oxalic acid was added to the solution. The consumption of oxalic acid is 5% of the REE content in the PRA. The extraction of REE under conditions of acidity of 1.3 N and a low consumption of oxalic acid is 2% of the content in AFR. The resulting suspension was kept at 20-25 ° C for 20 hours. Then the precipitate was separated from the solution by filtration. After separation of the precipitate, the nitric phosphate solution was treated with oxalic acid at a temperature of 70-80 ° C for 1 hour. The consumption of oxalic acid is 115% of the REE content in the initial PRA. The resulting suspension was kept at 20-25 ° C for 2 hours. After this, the precipitate of REE oxalates was separated by filtration. The filtrate was sent to wash off the first precipitate of thorium oxalates and REE. The resulting suspension of the composition, ppm%:

REO - 0.1; Th is 0.004; P ₂ O ₅ - 4.4; Ca - 0.7; C ₂ O ^- 4 - 0.18; specific activity - 0.17 Bq / g; enters the production of fertilizers at the stage of neutralization. REE oxalates obtained in the second deposition stage were dried and calcined at a temperature of 800 ° C for 6 hours. The composition of the REE oxides, ppm%:

REO - 99; Th is 0.005; P ₂ O ₅ - 0.4; Ca - 0.3; specific activity - 0.2 Bq / g. Extract REE 98% of the content in the original PRA.

Example 2. Experiments were carried out according to the proposed method described in example 1 with the exception that the nitrate-phosphate solution contained a large amount of thorium. The composition of the solution, ppm%:

REO - 0.5; Th is 0.0015; P ₂ O ₅ - 23; Ca - 3.9; F is 0.18.

After deposition of the FRAZ and its dissolution in nitric acid, a nitric phosphate solution of the composition was obtained, ppm%:

REO - 4.86; Th - 0.015; Ca - 0.73; F is 0.001; HNO ₃ - 1.9N.

The consumption of oxalic acid in the first stage of the deposition of thorium oxalates and REE was 10% of the REE content in the AFR. The consumption of oxalic acid in the second stage of precipitation of pure REE oxalates is 110% of the REE content in the initial PRA. The extraction of REE in the first precipitate 5% of the content in the original PRA. The extraction of REE in the second precipitate of oxalates is 95%. The suspension after washing off the first precipitate of thorium oxalates and REE from the filter had a composition, ppm%:

; удельная активность - 0,5 Бк/г.REO - 0.24; Th - 0.012; Ca - 0.52; $$C_2{O}_{\mathrm{four}}^{-}-0.32$$

; specific activity - 0.5 Bq / g.

The composition of the REE oxides obtained after calcination of deactivated oxalates, ppm%:

REO - 99; Th is 0.003; P ₂ O ₅ - 0.3; Ca - 0.2; specific activity - 0.13 Bq / g.

The positive effect of REE deactivation by the proposed method is provided by carrying out a two-stage process of deposition of oxalates, where at the first stage, thorium is separated from the main amount of REE contained in apatite processing products in order to isolate them. Moreover, the economic efficiency of the process is achieved by the absence of the need for processing and disposal of products containing thorium.

Claims (3)

1. A method of processing a phosphate rare earth concentrate isolated from apatite, comprising decomposing a phosphate rare earth concentrate with nitric acid, treating the resulting solution with oxalic acid with precipitation of rare earth oxalates and calcining them to rare earth oxides, characterized in that the treatment with oxalic acid is carried out in two stages, moreover, the first stage of precipitation of thorium oxalates and REE serves 5-10% of oxalic acid from stoichiometry on REE present in the solution, to the second stage of precipitation of oxalates of REE - 110-115% oxalic acids from stoichiometry on REE present in the initial solution. 2. The method according to claim 1, characterized in that the precipitate of thorium oxalates and REE obtained in the first stage of deposition is washed off with a filtrate separated from the precipitate of oxalates of REE in the second precipitation stage, rinsing from the filter with a specific activity of 0.17-0 5 Bq / g is returned to fertilizer production. 3. The method according to claim 1, characterized in that in the second stage of precipitation receive REE oxalates that do not contain thorium, after calcination, REE oxides with a specific activity of 0.13-0.2 Bq / g are obtained.