RU2525877C2 - Method of processing phosphogypsum - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the technology of processing phosphogypsum - wastes of enterprises, producing phosphoric fertilisers. The method includes opening phosphogypsum with sulphuric acid, further extraction of rare-earth elements (REE) and processing purified phosphogypsum with calcium oxide. In the course of opening with one solution of sulphuric acid successively processed are 1-3 lots of phosphogypsum with heating, the water phase is separated by filtration, the sediment is washed with water, apatite is added to the filtrate in a ratio of S:L=1:10-20, with the second heating at a temperature of 50-70°C and mixing for 1-2 hours with neutralisation with sulphuric acid to a concentration not lower than 0.1 mol/l. After that the sediment of the secondary phosphogypsum is separated by filtration and supplied to the beginning of the process. Calcium oxide or hydroxide and then ammonium hydroxide or carbonate are successively introduced into the filtrate until pH=2-3.5, the REE sediment is separated by filtration, and calcium hydroxide or oxide is introduced into the filtrate until pH=7-8, the sediment of feed tricalcium phosphate is separated by filtration, washed with water and discharged from the process.

EFFECT: technical result consists in the reduction of expenditures due to the creation of economically efficient technology.

4 cl, 2 tbl, 2 ex

Description

The present invention relates to a technology for the processing of phosphogypsum - waste phosphate processing by sulfuric acid technology. Almost all phosphorites contain impurities whose presence is undesirable in fertilizers. Thus, Kingisep phosphorite contains 2.6% (mass.) Of fluorine, in Kovdorsky - 1.4, in the Karatau deposit - 2.3, in the Kola Apatites - 3.2. At the same time, such an impurity as rare earth elements having a high cost is desirable to extract from phosphorites. Part of the impurities passes into calcium sulfate, which is formed in large quantities upon opening with sulfuric acid. In the hemihydrate process, up to 90% of the REE contained in apatite goes into phosphogypsum, and in the two-hydrate process, only 60-70%. Considering the scale of apatite processing (8-10 million tons per year) and the REE content in apatite (0.8-1%), the organization of the process of separation of REE from phosphogypsum will fully ensure the RF industry with such scarce elements. Despite the numerous studies carried out on this problem, not a single phosphogypsum processing plant is operating in the Russian Federation. From the methods known in the literature for the extraction of REE from phosphogypsum, methods based on the treatment of phosphogypsum with sulfuric acid followed by precipitation of REE by precipitation with magnesium oxide [1], collector reagent — di-2-ethylhexylphosphoric acid [2], and crystallization of REE double sulfates [3] can be noted. ] or sorption [4]. The closest in technical solution and the achieved result is the method described in the patent [5]. According to the patent, several portions of phosphogypsum are treated sequentially with a solution of sulfuric acid, increasing the concentration of sulfuric acid at each stage, depending on the content of phosphorus pentoxide in the aqueous solution. The concentration of sulfuric acid reaches 24% of the mass. The disadvantage of the proposed technology is that it is practically impossible to subsequently rationally dispose of such an amount of acid. 3-4 g of REE in the leach solution account for 250-300 g / l of sulfuric acid, i.e. 80-100 kg of sulfuric acid is required per 1 kg of recovered REE, which makes the proposed method economically less attractive. The purpose of the invention is to reduce the consumption of sulfuric acid and a more rational use of all components of phosphogypsum.

We believed that the main task of the phosphogypsum processing process should be to obtain a harmless product that does not contain toxic fluorine impurities, with acceptable costs from an economic point of view.

The main problem is that the purification of phosphogypsum from impurities (mainly fluorine) requires the use of sulfuric acid solutions, as described in many patents. But in this case, the processing of phosphogypsum becomes unprofitable. To achieve this goal - to reduce costs and create a cost-effective technology of phosphogypsum, the authors propose the following technical solution.

This goal is achieved in that the processing of 1-3 batches (optimally 2 batches) of phosphogypsum is carried out with the same sulfuric acid solution when heated to a temperature of 70-100 ° C for 1-2 hours at a ratio of T: W = 1: 1- 3. Then the pulp is separated by filtration, the precipitate is washed with water, apatite is added to the filtrate in the ratio T: L = 1: 10-20, neutralizing sulfuric acid to a content of at least 0.1 mol / l, it is heated again at a temperature of 50-70 ° C and stirring within 1-2 hours, the precipitate of secondary phosphogypsum is separated by filtration and sent to the head of the process. Calcium oxide or hydroxide is successively introduced into the filtrate, then ammonium hydroxide or carbonate until pH = 2.0-3.5 is reached, and a REE precipitate is separated by filtration. After separation of the REE precipitate, hydroxide or calcium oxide is introduced into the filtrate to pH = 7-8, the precipitate of tricalcium phosphate is separated by filtration, washed with water and removed from the process.

To remove fluorine ion at the stage of phosphogypsum treatment with acid and with the introduction of apatite, the process is carried out with stirring and supply (bubbling) of air to the pulp. For opening use a solution containing 0.3-0.6 mol / l of sulfuric acid. At the end of the process, purified phosphogypsum is treated with a pulp of calcium oxide to a pH of 6.5-7.5. Filtrates and washings are used to wash sediments in previous operations.

Adding apatite to the leach solution allows using sulfuric acid introduced into the process in the most economical way for processing apatite raw materials to obtain additional products (as well as in the main operation of the plant processing apatite using sulfuric acid technology). The second important point is that the separation of impurities (iron, aluminum and REE) is carried out at the highest possible pH value (without coprecipitating calcium phosphate salts) in order to isolate all impurities as much as possible. Subsequent addition of calcium oxide or hydroxide provides a clear precipitate of tricalcium phosphate, which can be used to prepare feed phosphates. When developing the technology, we were afraid that when apatite was added to the REE sulfate solution (from leaching of primary phosphogypsum) REE sulfates would co-precipitate with the formation of REE sulfate. Phosphoric acid released during the administration of apatite could also contribute to coprecipitation. When apatite is added, secondary phosphogypsum is formed by the reaction:

5 H ₂ SO ₄ + Ca ₅ F (PO ₄ ) ₃ + = 5CaSO ₄ + 3Н ₃ РО ₄ + HF

As our experiments showed, when calcium oxide is added to a REE sulfate solution containing from 1 to 6 g / L REE oxides and 0.5-1.5 mol / L sulfuric acid, a calcium sulfate bulk precipitate forms, but REE remain in solution on 90-95%. When apatite is added to similar solutions with the formation of calcium sulfate, slightly more REE precipitates - up to 10-15%. The difference in theoretical, calculated amount of REE remaining in the solution does not exceed 10-15%. The difference of 10-15% may be due to REE losses during analysis (double reprecipitation with ammonia and dissolution). The released phosphoric acid in small amounts (15-20 g / l) in the presence of sulfuric acid does not significantly affect the precipitation of REE. In general, coprecipitation is not so scary, because the resulting secondary phosphogypsum is sent to the head of the process, however, direct extraction of REE may decrease. When processing phosphogypsum obtained from phosphorites that do not contain or contain a small amount of REE, precipitation is carried out to isolate impurities (iron, aluminum, titanium, etc.) before obtaining tricalcium phosphate.

Example 1

To carry out the technological process, phosphogypsum was used, containing: P ₂ O ₅ - 0.8%, fluorine - 0.4%, CaO - 39.5%, REE oxides - 0.6%. To 50 g of phosphogypsum was added 100 ml of a solution of sulfuric acid with a concentration of 0.4 mol / L. The pulp was heated for 2 hours at a temperature of 95-100 ° C with stirring and bubbling with air. After 2 hours, the pulp was filtered and the precipitate was washed with 70 ml of water, which was sent to prepare a new portion of the leach solution. The washed precipitate was mixed with 0.1 g of calcium hydroxide to pH = 7.4 and removed as a finished product - purified phosphogypsum. The mass of purified phosphogypsum (dried) 51.7 g, the content of impurities (wt%): PrO5 <0.1, F <0.1, V <0.02, Cr <0.02, MnO <0.02, Hg <0.02, As <0.02, Th <0.02, U <0.02, Cd <0.02, Sb <0.02, Co <0.02, Ni <0.02, Zn <0 02, Pb <0.02. To the filtrate (100 ml) containing 1.2 g / L REE and 0.43 mol / L sulfuric acid, 2.6 g Apatite was added and heated for one hour at a temperature of 50 ° C. The precipitate of secondary phosphogypsum was separated by filtration, washed with 5 ml of water, the solution from washing was added to the filtrate, and the precipitate of secondary phosphogypsum was sent to the head of the process. From the filtrate containing 0.1 mol / L sulfuric acid, 1.25 g / L REE and 14 g / L phosphorus (calculated as P ₂ O ₅ ), 0.8 g / L fluorine, rare earths were first precipitated with calcium oxide to pH = 1.5-1.7, then ammonium hydroxide to pH = 3.1. After filtration, the precipitate containing REE and impurities was washed with 10 ml of water and the washing solution was added to the filtrate. REE sediment was removed from the system as a finished product. The mass of the precipitate REE 0.84 g, the content of REE in the sediment 14.9%. Lime milk was gradually added to the filtrate until a pH of 7.1 was reached. The precipitated tricalcium phosphate precipitate was separated by filtration and washed with water. The mass of the dried precipitate of tricalcium phosphate is 3.14 g. The precipitate of tricalcium phosphate was removed as a finished product. In the current production, the filtrate and the washing solution are sent to the preparation of solutions of the main apatite processing technology.

Example 2

To 50 g of phosphogypsum was added 100 ml of a solution of sulfuric acid with a concentration of 0.6 mol / L. The pulp was heated for 2 hours at a temperature of 95-100 ° C with stirring and bubbling with air. After 2 hours, the pulp was filtered and the precipitate was washed with 70 ml of water, which was sent to prepare a new portion of the leach solution. The washed precipitate was mixed with 0.1 g of hydroxide and removed as a finished product - purified phosphogypsum. The mass of dried phosphogypsum is 52.6 g, the content of impurities (mass%): P ₂ O ₅ <0.1, F <0.1, V <0.02, Cr <0.02, MnO <0.02, Hg <0.02, As <0.02, Th <0.02, U <0.02, Cd <0.02, Sb <0.02, Co <0.02, Ni <0.02, Zn <0 02, Pb <0.02. To the filtrate (100 ml) containing 1.52 g / L REE and 0.54 mol / L sulfuric acid, 4 g Apatite was added and heated for one hour at a temperature of 50 ° C. The precipitate of secondary phosphogypsum was separated by filtration, washed with 5 ml of water, the solution from washing was added to the filtrate, and the precipitate of secondary phosphogypsum was sent to the head of the process. From the filtrate containing 1.5 g / l REE and 20.3 g / l phosphorus (calculated as P ₂ O ₅ ), rare-earth elements were first precipitated with calcium hydroxide to pH = 2, then ammonium hydroxide to pH = 2.8. The precipitate containing REE and impurities was washed with 10 ml of water and the washing solution was added to the filtrate. REE sediment was removed from the system as a finished product. The mass of the precipitate REE 0.75 g, the content of REE-20.2%. Lime milk was gradually added to the filtrate until a pH of 7.0-7.5 was reached. The precipitated tricalcium phosphate precipitate was separated by filtration and washed with water. The weight of the dried precipitate of tricalcium phosphate is 4.1 g. The precipitate of tricalcium phosphate was removed as a finished product. In the current production, the filtrate and the washing solution are sent to the preparation of solutions of the main apatite processing technology.

An increase in the G: T ratio in favor of the aqueous phase of more than 3.0 when treating phosphogypsum with sulfuric acid is undesirable due to the difficulty of the subsequent disposal of large volumes of aqueous solutions. The decrease in the ratio of T: W to 1 or less leads to a viscous pulp, especially when processing dried phosphogypsum. The influence of the parameters on the results of phosphogypsum treatment is given in Table 1.

Table 1 The influence of the processing conditions of phosphogypsum on the extraction of fluoride and phosphate ions (content in the initial phosphogypsum: F - 0.4%, P ₂ O ₅ - 0.6%) No. Content, mol / L H ₂ S0 ₄ , The ratio of T: W Continued. heating hours Processing Temperature, ° C Contents F% Contents R, % one 0.4 1: 2 1,5 90 <0.1 <0.1 2 0.4 1: 2 1,5 fifty 0.2 <0.1 3 0.2 1: 2 2 90 0.3 0.2 four 0.4 1: 2 0.5 90 0.2 <0.1 5 0.4 1: 0.5 1,5 90 <0.1 0.2

The ratio of T: G at the stage of adding apatite depends on the selected concentration of sulfuric acid, which is sent to open phosphogypsum. It is necessary to add such an amount of apatite, which is necessary to neutralize sulfuric acid to a residual content of 0.1-0.15 mol / l (in accordance with the above equation). The pH of the deposition of REE from the leach solution depends on the concentration of phosphate and fluoride ions in the solution (the content of these ions is determined by the amount of fluorine and phosphorus in the initial phosphogypsum and the amount of apatite introduced). The higher the concentration of phosphate ions, the lower the pH value, REE hydrate phosphates begin to precipitate and vice versa. The effect of pH on the degree of REE deposition from the leach solution is given in Table 2.

Table 2. The effect of pH on the degree of REE deposition from phosphogypsum leaching solution (sulfuric acid content in the solution is 0.1 mol / L, REE - 1.7 g / L, P ₂ O ₅ - 22 g / L). No. pH The content of REE in the filtrate, g / l The extraction of REE in the sediment,% one 1.06 1.7 0 2 1,52 1.7 0 3 2.73 0.3 82.3 four 3.10 <0.1 > 94 5 3.52 <0.1 > 94

The addition of apatite should be carried out until a residual acidity of at least 0.1 mol / l is reached in order to prevent the precipitation of REE hydroxophosphates and impurities.

A feature of the proposed technical solution is that the cost of heating the pulp of phosphogypsum with sulfuric acid is offset by the subsequent use of heated mother liquors to accelerate the decomposition of the injected apatite and the precipitation of tricalcium phosphate (we noticed that the precipitation of tricalcium phosphate with calcium oxide proceeds at a higher rate when the pulp is heated to 40- 50 ° C). In addition, the mother liquors after isolation of tricalcium phosphate contain virtually no impurities (all impurities are removed with a REE precipitate) with the exception of small amounts of ammonium sulfate (equilibrium in sulfate ion with calcium sulfate) with a temperature of 30-40 ° C and can be reused for processing new portions of phosphogypsum after adjustment for sulfuric acid. The heat treatment of phosphogypsum with sulfuric acid promotes the recrystallization of phosphogypsum with the formation of calcium sulfate crystals suitable for the production of building materials, for subsequent use in the production of building materials. The resulting phosphogypsum does not contain harmful impurities and can be used in road construction, as additives in the production of cement, for the production of various building materials, etc. The economic efficiency of the proposed technical solution is ensured by the optimal use of all resources:

1. Sulfuric acid remaining after opening of phosphogypsum is spent on the processing of apatite to obtain marketable products.

2. The energy costs of heating the pulp during the initial processing of phosphogypsum are reused for the decomposition of apatite.

3. When REE is isolated, the process is carried out at the maximum possible pH value for a more complete precipitation of impurities of iron, fluorine, titanium, etc., in order to obtain a more pure tricalcium phosphate, suitable for the production of feed phosphate.

The positive effect of the proposed technical solution is to reduce the consumption of sulfuric acid, reducing costs for cleaning phosphogypsum with the simultaneous receipt of additional valuable products.

Literature

1. Lebedev V.N., Lokshin E.P. "A method for extracting rare earth elements from phosphogypsum." RF patent №2158317 from 02.16.1999, according to class. C22B 59/00.

2. Vershkov A.V., Vershkova Yu.A., Lokshin E.P., Masloboev V.A. "A method for extracting rare earth elements from acidic solutions." RF patent No. 2172712 according to class C22B 59/00.

3. Lokshin EP, Kalinnikov VT, et al. “Method for the extraction of rare-earth elements from phosphogypsum”. RF patent No. 2293781 dated 04/04/2005, according to class. C22B 59/00.

4. Lokshin EP, Tareeva OA, Kalinnikov V.T. "A method of processing phosphogypsum for the production of rare earth concentrate (REE) and gypsum." RF patent No. 2458999 dated 04/28/11, according to class. C22B 59/00.

5. Lokshin EP, Vershkov AV, Vershkova Yu.A., Masloboev V.A. "A method of extracting lanthanides from phosphogypsum." RF patent No. 2167105 by class C22B 59/00.

Claims (4)

1. The method of processing phosphogypsum by opening with sulfuric acid, including the subsequent extraction of rare earth elements and processing the purified phosphogypsum with calcium oxide, characterized in that one solution of sulfuric acid is treated sequentially with 1-3 batches of phosphogypsum when heated to a temperature of 70-100 ° C for 1-2 hours at a ratio of T: L = 1: 1-3, the aqueous phase is separated by filtration, the precipitate is washed with water, apatite is added to the filtrate in a ratio of T: L = 1: 10-20, and secondly heated at a temperature of 50-70 ° C and stirring within 1-2 hours from n by neutralization of sulfuric acid to a concentration of at least 0.1 mol / L, the precipitate of secondary phosphogypsum is separated by filtration and sent to the beginning of the process, and calcium oxide or hydroxide is subsequently introduced into the filtrate, then ammonium hydroxide or carbonate until pH = 2-3.5 , the REE precipitate is separated by filtration, and calcium hydroxide or calcium oxide is introduced into the filtrate to pH = 7-8, the feed tricalcium phosphate precipitate is separated by filtration, washed with water and removed from the process. 2. The method according to claim 1, characterized in that to remove the fluorine ion at the stage of phosphogypsum treatment with acid, the process is carried out with stirring and air supply to the pulp. 3. The method according to claim 1, characterized in that for opening use a solution containing 0.3-0.6 mol / l of sulfuric acid. 4. The method according to claim 1, characterized in that the purified phosphogypsum is treated with a pulp of calcium oxide to a pH of 6.5-7.5.