RU2708718C1 - Method of processing phosphogypsum wastes to obtain a concentrate of ree and gypsum plaster - Google Patents

Abstract

FIELD: waste processing and disposal.

SUBSTANCE: invention relates to recycling production wastes and environmental protection and can be used in chemical industry and other industries associated with use of rare-earth elements, as well as the binder binding agent of construction gypsum released during production can be used in construction. Extraction of REM from phosphogypsum involves treatment of phosphogypsum with sulfuric acid solution in at least one step, filtration, extraction of insoluble REE precipitate from obtained solution by introduction of acetic acid or its soluble salts at consumption for deposition 35÷95 mol% on REE from a stoichiometrically required amount in a circulating solution in a deficiency while maintaining a pH of the mother solution of less than 3.0. Precipitation of the REE acetates is separated from the mother solution, washed, dried and optionally calcined to obtain a REE concentrate in a salt or oxide form. Separated mother solution containing sulfuric acid and REE in sulphate form is directed as a recycle stream into a unit for neutralization of phosphogypsum, where a balance amount of sulfuric acid is supplied to compensate its losses with salts of REE and gypsum pulp. Filtered phosphogypsum undergoes additional washing from residual amounts of sulphate REE with mother solution, from which precipitate of insoluble REE compounds is separated by way of acetic acid introduction and sediment separation by filtration. Washed phosphogypsum is neutralized with the main calcium compound CaO in order to neutralize trace amounts of sulfuric acid, dried and realized as gypsum.

EFFECT: invention increases degree of recovery of obtained concentrate REE up to 98÷99 % at improvement of its quality, reduction or complete exclusion of waste water discharges by changing types of used reagents and modes of their application.

1 cl, 1 dwg

Description

A method of processing phosphogypsum waste to obtain REE concentrate and building gypsum

The invention relates to technologies for the integrated processing of phosphogypsum to obtain a concentrate of rare earth metals (REE) and gypsum.

Phosphogypsum is a large-tonnage waste of the production of mineral fertilizers. Currently, about 200 million tons of phosphogypsum has been accumulated in the dumps of industrial enterprises in Russia, production in such cities as Voskresensk, Balakovo, Cherepovets, Meleuz, Volkhov, Uvarovo are examples of large deposits of phosphogypsum, and these figures increase by 10-15 million annually. tons of waste. Dumps of phosphogypsum form huge white mountains, occupying significant land areas, they dust in the wind, fall into the soil, pollute aquifers with harmful soluble compounds of fluorine, phosphorus and other impurities.

Phosphogypsum contains from 80 to 98% gypsum and can be classified as gypsum raw material. The modern construction industry testifies to the great demand for gypsum and products based on it; therefore, the use of phosphogypsum in the production of gypsum binders with a shortage of natural raw materials for natural gypsum is one of the most promising directions for the processing of phosphogypsum. In addition to gypsum, the dumps of phosphogypsum of the largest Russian enterprises contain about 100,000 tons of rare earth metals (REE). Their isolation can significantly change the situation with rare-earth elements not only in Russia, but also in the world economy.

The processing of phosphogypsum waste, in addition to solving the problem of rare-earth elements and building materials, solves the problems of rational use of raw materials and the environment, since the storage of phosphogypsum inevitably causes environmental damage due to pollution of water resources with harmful substances, primarily soluble fluorine compounds, dusting in the atmosphere and inefficient use of land occupied by dumps.

A known method of extracting rare earth elements (REE) from phosphogypsum by treating the latter with nitric acid and subsequent extraction of REE by extraction with phosphinooxide (I. N. Martynova et al. Study of the distribution of REE upon extraction from acidic nitrate-phosphate solutions. Sat. Processing and physical chemistry -wa. of the joint rare El-Comrade Apatity, 1984, pp. 6-8.).

The disadvantage of this method is the need to use costly trialkylphosphine oxide and the impossibility of complete liquid phase extraction of REE from the organic phase. In addition, due to the high losses of phosphine oxide with the aqueous phase, this method is uneconomical and requires additional facilities for the disposal of phosphine oxide and wastewater.

A well-known nitric acid technology for the separation of rare-earth elements from apatite, giving up to 85% of their separation in a solution containing phosphorus and fluorine (see article V.D. Kosynkin et al. “State and prospects of development of the rare-earth industry of Russia”, railway station “Metals ”, No. 1, 2001).

The disadvantages of this method include the impossibility of using working solutions in a closed cycle and the subsequent low degree of REE extraction in the technological process in a closed cycle mode, as well as the formation of a significant amount of wastewater.

A known method of extracting REE from phosphogypsum (RU 2293781 C1, Lokshin and others, 02.20.2007). The method includes treating phosphogypsum with a solution of sulfuric acid to extract rare earth elements and sodium into the solution, separating the insoluble residue, increasing the degree of supersaturation of the solution with rare earth elements to crystallize REE concentrate, separating the concentrate from the mother liquor and processing the concentrate. Phosphogypsum is treated with a solution of sulfuric acid with a concentration of 22 ÷ 30% of the mass, at W: T = 1.8 ÷ 2.2 and a duration of 20 ÷ 30 minutes to exclude spontaneous crystallization of the rare-earth element concentrate from the solution to separate the insoluble residue, increasing the degree of supersaturation of the solution achieved by ensuring the sodium content in the solution of 0.4 ÷ 1.2 g / l. The sodium content in the solution is regulated by introducing into it a sodium salt (mainly sulfate).

The disadvantage of this method is the formation of finely dispersed, gel-like sediments, the selection of which is associated with technological difficulties and additional losses, as well as the need to dispose of a significant amount of wastewater generated during processing. The extraction of REE is 60 ÷ 70%.

A known method of extracting rare earth elements from phosphogypsum (RU 2412265 C1, Abramov and others, 02.20.2011). The method includes acid extraction of REE compounds from phosphogypsum, separation of an insoluble precipitate of crystalline gypsum from the extraction solution and extraction of REE compounds from the extraction solution, in which acid extraction is carried out with a solution of a mixture of sulfuric and nitric acids in a ratio of 3.2 to 1.2, with a concentration of 1 to 3% wt., With a ratio of W: T from 4 to 5, for 8 to 12 minutes. with simultaneous hydroacoustic action using a rotary-pulsating apparatus on a stirred extraction suspension. The extraction of REE compounds from the extraction solution is carried out by cation-exchange sorption by passing the extraction solution through a cation-exchange filter. After extraction of the REE from the extraction solution, it is regenerated and returned to the stage of acid extraction.

The disadvantage of this method is the need to neutralize acids, large volumes of circulating solutions, the formation of a large amount of wastewater, as well as the complexity of the technology of sorption extraction and processing of desorbate.

A known method of processing phosphogypsum for the production of REE concentrate and gypsum (RU 2458999 C1, Lokshin et al., IHTREMS KSC RAS, 08.20.2012). Leaching is carried out with a solution of sulfuric acid with a concentration of 1 ÷ 5 wt%, REE extraction from the leaching solution is carried out by sorption using sulfocationite in hydrogen or ammonium form, followed by desorption of REE with ammonium sulfate and introducing ammonia or ammonium carbonate into the resulting desorbate, with the precipitation and separation of hydroxide or REE carbonate concentrate. Leaching is carried out by passing a solution of sulfuric acid through a layer of phosphogypsum at a rate of 0.5 ÷ 25 m ³ per 1 m ² per day or by agitation leaching. The neutralization of the gypsum precipitate is carried out by the main calcium compound.

The disadvantage of this method is the complex hardware implementation associated with the cycle operation of the sorption / desorption of REE from solution and the formation of significant quantities of washing and wastewater requiring disposal.

A known method of treating phosphogypsum with water, a weak solution of sulfuric acid or a solution of mineral salt when processing the pulp with ultrasound for 5 ÷ 20 minutes (RU 2104938 C1, Mitsar LLP, 02.20.1998). The aqueous phase of REE is separated from the precipitate of calcium sulfate. The resulting solution is treated with a gaseous mixture of ammonia and air taken in the ratio of ammonia: air = 1: 2-4) at a temperature of 25 ÷ 60 ° C until a pH of 3.5 ÷ 6.6 is reached, the optimum pH value is 5.5 ÷ 6 ,4. REE precipitate in the form of well-filtered, fairly dense precipitation of hydratophosphates, which are well separated from the solution. When the temperature rises above 60 ° C, sediment sludge increases insignificantly, but this requires significant energy costs. An increase in pH to values of 7–8 causes the coprecipitation of calcium with REE and leads to the suspension freezing, i.e. the impossibility of its separation from the aqueous solution. At a lower pH, the completeness of REE release is not achieved. Precipitation with a mixture of ammonia and air is necessary because when using pure ammonia with rare earths, calcium precipitates.

The disadvantage of this method is the use of gaseous ammonia-air precipitator, as well as the sensitivity of the REE output to changes in temperature and pH, which are difficult to keep at predetermined limits during industrial, large-scale implementation of the process.

Closest to the proposed technical solution is a method of extracting REE from phosphogypsum with a solution of sulfuric acid, filtering, introducing a precipitator into the resulting solution, holding the pulp for 0.5 ÷ 1.5 hours, followed by precipitation by filtration and differs from the prototype in that REE is isolated from a solution from the treatment of phosphogypsum with the introduction of oxalic acid or its soluble salts in an amount of 250 ÷ 300% mol, from stoichiometry on REE in solution when neutralizing a solution of sulfuric acid to pH = 1.0 ÷ 2.5, after which the precipitate is oxalato separated from the mother liquor by filtration, washed, dried and calcined.

The main disadvantage of this method is the generation of a large amount of acidic wastewater.

The objective of the invention is to improve the quality, increase the degree of extraction of the resulting REE concentrate to 98 ÷ 99%, increase its quality, reduce the cost of its production, reduce or completely eliminate waste water discharges by changing the types of reagents used and the modes of their use.

The problem is solved by changing the type of reagent used and the mode of its use for the extraction and concentration of REE from solution after processing of phosphogypsum.

The technical result of the method is to increase the efficiency of phosphogypsum processing technology, to ensure high quality of REE concentrate and a high degree of REE extraction from phosphogypsum, to reduce or completely eliminate wastewater discharges by changing the types of reagents used and their application modes.

The problem is solved and the technical result is achieved by the method of treating phosphogypsum with solutions of sulfuric acid with a concentration in the range of 5 ÷ 50% by weight, in one or more successive stages, and at each stage, solutions of different concentrations can be applied, with a general ratio of W: T (liquid and solid phase) 1.0 ÷ 5.0: 1, followed by filtration of the resulting dispersion, REE extraction by introducing the precipitator - acetic acid into the resulting acidic solution at a deposition rate of 35 ÷ 95 mol%. on REE from the stoichiometrically required amount in the circulating solution (in deficiency) while maintaining the pH of the solution less than 3.0 units, subsequent separation of the insoluble precipitate of REE acetates from the mother liquor by filtration, washing with process water, drying, while the resulting REE concentrate can be shipped to the consumer both in salt form and in oxide form after preliminary calcination of REE concentrate.

After separation of the insoluble precipitate of REE acetates, the mother liquor containing sulfuric acid with a concentration of 5–20 wt% and REE in sulfate form with a concentration of 0.2–2.0 wt% is sent as a recycle stream to the phosphogypsum neutralization unit, which also the balance amount of sulfuric acid is supplied to make up for its losses with REE salts and gypsum pulp.

After separation of the solid and liquid phases with a residual moisture content of 10-15% by weight, the filtrate is washed from the residual REE sulfates in order to extract them by feeding a recycle mother liquor, after which the solution containing REE sulfates is fed to an additional extraction unit, which also contains acetic solution acid with a concentration of 10 ÷ 70% of the mass, for precipitation of REE in the form of insoluble salts at a flow rate of deposition of 35 ÷ 95 mol%. on REE from the stoichiometrically necessary amount (in deficiency) while maintaining the pH of the solution less than 3.0 units, after which the charge of REE acetates is separated from the mother liquor on the filtration unit, washed with additional process water and sent to the drying and calcining unit, and the filtrate is reused as a recirculating mother liquor, which is sent to the gypsum washing unit, and the washed gypsum is then sent to the neutralization unit, where the main calcium compound, for example, quicklime (CaO), is also supplied with in excess of no more than 10% molar to neutralize the balance amount of sulfuric acid, and then the resulting mixture goes to the drying unit, where they receive dried construction gypsum.

The invention is illustrated by the schematic diagram of the installation for implementing the method of processing technology of phosphogypsum.

The installation comprises a neutralization unit 1 connected by a piping system, a liquid and solid phase separation unit 2, an extraction unit 3, a filtration unit 4, a drying and calcining unit 5, a gypsum washing unit 6, an extraction unit 7, a filtration unit 8, a gypsum neutralization unit 9, a unit dehydration and drying of gypsum 10.

The method is as follows.

The initial phosphogypsum is fed to neutralization unit 1, where sulfuric acid solution with a concentration in the range of 5–50 wt% is fed through line 11 into one or several successive stages, and solutions of different concentrations can be used at each stage, with a general ratio of W: T (liquid and solid phase) 1.0 ÷ 5.0: 1, which is introduced in the form of solutions of the required concentration, or is obtained by mixing concentrated sulfuric acid supplied through line 12 with recycled water supplied through line 13, and the resulting cm all of this is directed to a solid-liquid phase separation unit 2, where it is separated into streams of an acid solution of REE 14 and washed phosphogypsum 15.

The flow of an acidic solution of REE through a pipe 14 is fed to the extraction unit 3, where a solution of acetic acid with a concentration of 10 ÷ 70 wt% is also fed through a pipe 16 to precipitate a REE in the form of insoluble salts at a deposition rate of 35 ÷ 95 mol%. on REE from the stoichiometrically required amount in the circulating solution (in deficiency) while maintaining the pH of the solution less than 3.0 units, after which the mother liquor is sent through pipeline 17 to filtration unit 4, where the precipitate of REE acetates is separated from the mother liquor, and additionally washed with technological water and sent to the drying and calcining unit 5, where the decomposition of REE salts occurs with the formation of the oxide form of REE 18 and decomposition gases discharged through the pipe 19, while the resulting REE concentrate can be shipped to the consumer as oxide form, and in salt form without performing the preliminary calcination stage, and the mother liquor discharged from filtration unit 4 through line 13 containing sulfuric acid with a concentration of 5–20 wt% and REE in sulfate form with a concentration of 0.2–2 , 0% of the mass, is directed as a recycle stream to the neutralization unit of phosphogypsum 1, where the balance amount of sulfuric acid is also supplied through pipeline 12 to make up for its losses with REE salts and gypsum pulp.

The filtrate after separation of the solid and liquid phases in block 2, with a residual moisture content of 10 ÷ 15% of the mass, is fed through pipeline 15 to the washing unit 6, where gypsum is washed from the residual REE sulfates in order to be extracted by feeding the recycle mother liquor through pipeline 20, after which a solution containing REE sulfates through a pipe 21 is fed to the extraction unit 7, where a solution of acetic acid with a concentration of 10 ÷ 70 wt% is also fed through a pipe 22 to precipitate REE in the form of insoluble salts at a deposition rate of 35 ÷ 95 mol%. on REE from the stoichiometrically required amount in the circulating solution (in shortage) while maintaining the pH of the solution less than 3.0 units, after which the mother liquor is sent via pipeline 23 to the filtration unit 8, where the precipitate of REE acetates is separated from the mother liquor, additionally washed with technological water and sent to the drying and calcining unit 5, where they are mixed with the raw materials coming from the filtration unit 4, and the liquid is reused as a recycle solution, which is sent via pipeline 20 to the washing unit 6, washed In this case, the IPS is sent via pipeline 24 to the neutralization unit 9, where the main calcium compound, for example, quicklime (CaO), with an excess of no more than 10% molar to neutralize the balance amount of sulfuric acid, is also fed through pipeline 25 and then the resulting mixture goes to the block dehydration 10, from where drained building gypsum is discharged along the conveyor belt 26.

Thus, the proposed invention allows to increase the degree of extraction of the obtained REE concentrate up to 98 ÷ 99%, increase its quality, reduce the cost of its production, reduce or completely eliminate wastewater discharges by changing the types of reagents used and the modes of their use.

Claims (1)

A method of extracting rare earth metals from phosphogypsum, including treating phosphogypsum with a sulfuric acid solution in at least one stage, filtering, extracting insoluble REE compounds from the precipitate by introducing acetic acid, separating the precipitate by filtration, characterized in that the rare earth metals are extracted from the solution with acetic acid or its soluble salts at a flow rate of deposition of 35 ÷ 95 mol%. on REE from the stoichiometrically necessary amount in the circulating solution is deficient while maintaining the pH of the mother liquor less than 3.0, subsequent separation of the precipitate of REE acetates from the mother liquor, washing, drying and, if necessary, calcining to obtain REE concentrate in salt or oxide form, moreover the separated mother liquor containing sulfuric acid and REE in sulfate form is sent as a recycle stream to the phosphogypsum neutralization unit, in which a balance amount of sulfuric acid is supplied In order to make up for its losses with REE salts and gypsum pulp, the filtered phosphogypsum is subjected to additional washing from residual REE sulfates with a mother liquor, from which a precipitate of insoluble REE compounds is isolated by introducing acetic acid and separating the precipitate by filtration, and the washed phosphogypsum is neutralized with the main compound calcium CaO to neutralize trace amounts of sulfuric acid, after which it is dried and sold as building gypsum.

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