RU2549412C1 - Method of processing monazite concentrate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to rare and radioactive element technologies and can be used to obtain concentrates of rare and rare-earth elements from monazite. The method of processing monazite concentrate includes treating the feed stock with a mixture of sulphuric acid and ammonium fluoride at 200-230°C for 30-40 min, purifying the obtained product from phosphate and fluoride products by sublimation, water leaching sulphates of rare-earth elements, neutralising the solution with barium chloride, selectively separating the thorium, uranium, iron and rare-earth product, wherein separation of the rare-earth product is carried out through a step of precipitating double salts of rare-earth elements with ammonium sulphate, followed by conversion into nitrates of rare-earth elements through a calcination step, dissolving in nitric acid and solvent refining from thorium impurities.

EFFECT: invention provides high degree of extraction and purity of the rare-earth product.

3 cl, 2 dwg, 3 ex

Description

The invention relates to the technology of rare and radioactive elements and can be used to obtain concentrates of rare and rare earth elements from monazite.

A known method of opening monazite concentrate [Zelikman A.N., Korshunov B.G. Metallurgy of rare metals. - M.: Metallurgy, 1991., p. 353-354], based on the decomposition of ore by concentrated sodium hydroxide solution at a temperature of 110-140 ° C for 3 hours, at a flow rate of 300% of the stoichiometric amount, by pulping, filtering the precipitated hydroxides from a phosphate solution, followed by dissolution in hydrochloric acid and selective precipitation REE hydroxides. The disadvantage of this method is the high consumption of the opening agent and the energy intensity of the evaporation and crystallization processes used for the separation of phosphates and the regeneration of sodium hydroxide.

A known method of processing monazite concentrate (prototype) [Zelikman A.N., Korshunov B.G. Metallurgy of rare metals. - M.: Metallurgy, 1991, p. 352-353], including the decomposition of the concentrate with 96% sulfuric acid at 180-200 ° C, at a flow rate of 250-300% of the stoichiometrically required amount for 2-4 hours, the extraction of REE sulfates from the reaction mass by aqueous leaching and neutralization of the solution with barium chloride subsequent stepwise neutralization and selective precipitation of REE phosphates at a pH of 2.3. The disadvantage of this method is the low degree of REE extraction and contamination of the rare-earth product with inseparable hydrophosphates of thorium, iron, aluminum, titanium and silicon.

The objective of the present invention is to develop a process for the integrated processing of monazite concentrate with a high degree of extraction and purity of the final rare earth product.

The task is achieved in that the opening of the concentrate is carried out with a mixture of sulfuric acid and ammonium fluoride, taken in a ratio of 1: 1.3, respectively, with a stoichiometric ratio of monocyte: sulfuric acid 1: 1.2. The opening mechanism can be represented as a sequential process of hydrofluorination of components of a monazite concentrate with ammonium fluoride followed by the conversion of fluorination products to sulfates by reaction with sulfuric acid present in the system. The process is carried out in a rotary kiln at a temperature of 200-230 ° C for 30-40 minutes

After carrying out sulfuric acid hydrofluorination, the obtained cake is heated to 300-350 ° C to transfer to a gaseous state and remove volatile reaction products from the system. When the temperature rises, the gas phase passes: an excess of the opening agent (ammonium fluoride and sulfuric acid), hexafluorosilicate and ammonium hexafluorotitanate, phosphorus fluorides, ammonium phosphates. The gas phase is sent to selective desublimation, followed by regeneration of the opening agent and capture of phosphorus compounds to produce phosphate fertilizers.

Metal sulfates remain in the solid phase, while the initial charge has a high specific surface area suitable for leaching. The leaching process is carried out with a 20% aqueous solution of sulfuric acid to exclude the likelihood of sulfate hydrolysis.

The solution is neutralized and deactivated by introducing barium chloride into the solution, which increases the degree of coprecipitation of radioactive barium, radium, calcium, and lead. Radioactive insoluble sulfates localized in the solid residue are separated by filtration for further cementation and burial. A mother liquor containing sulfates of uranium, thorium, iron and REE is heated to 70-80 ° C and crystalline ammonium sulfate is added to it in excess of 200% of the stoichiometrically necessary amount for the formation of REE double sulfate salts. The solution was incubated for an hour, the resulting double salts were separated from the mother liquor by filtration. REE double sulfates are sent for conversion to REE nitrates and purification of thorium impurities.

The mother liquor after precipitation of the REE double salt is directed to the allocation of glandular, thorium and uranium cake. The process is carried out by treating the mother liquor with ammonia water with the associated regeneration of ammonium sulfate. The precipitate of hydrated thorium, uranium and iron is separated by filtration from the solution for further extraction of uranium and thorium or cementation and burial.

The separated ammonium sulfate solution is evaporated and crystallized, the obtained crystals are returned to the cycle to the stage of obtaining REE double sulfate salts.

At the stage of separation of thorium and uranium, regenerated ammonia water is used, which is formed as a result of the interaction of monazite concentrate with ammonium fluoride.

The conversion section is necessary for the conversion of sulfates of double salts into REE nitrates and the separation of thorium impurities. A convenient compound for conversion to nitrates is REE oxides, which can be obtained by calcining double salts in a rotary kiln at a temperature of 1350-1400 ° C. REE and Th oxides are sent for dissolution with nitric acid followed by the separation of thorium from the nitric acid solution by extraction methods.

The purified REE nitrate solution is the final commercial product and can be used to separate the REE mixture into individual components.

Example 1

A portion of monazite concentrate composition: REE ₂ O ₃ 27%, P ₂ O ₅ 11.1%, ThO ₂ 2.7%, UO ₂ 0.1%, Fe ₂ O ₃ 1.8%, Al ₂ O ₃ 1, 4%, SiO ₂ 2%, TiO ₂ 1.1%, CaO 0.7%, MgO 0.6%, ZrO ₂ 1.5%, weight 50 g, according to the stoichiometric ratio of monazite: sulfuric acid 1: 1.2 , mixed with a mixture of 45.4 g of sulfuric acid and 59 g of ammonium hydrofluoride (ratio of opening agents 1: 1.3) and incubated at 220 ° C for 40 minutes. The resulting product is heated to 340 ° C and maintained at this temperature until the evolution of gaseous reaction products ceases. 66.7 g cake was washed with 200 ml of a 20% aqueous solution of sulfuric acid and treated with 20 ml of a 20% solution of barium chloride, precipitating radioactive Ra, Ba, Pb. The precipitate is sedimented and filtered, the mass of the utilized radioactive residue is 8 g, with a content of unreacted REE oxides of 8.7% (0.7 g). The purified sulfate solution is heated to 80 ° C and ammonium sulfate weighing 87.7 g is added. The solution is kept for 1 hour, the formed crystals of double salts are separated from the mother liquor by filtration. A mother liquor containing thorium and iron sulfates is mixed with 40 g of 25% ammonia water. The solid reaction products (hydrated thorium and iron) are filtered off and disposed of. Double REE sulfates in an amount of 92.11 g are heated at 1400 ° C until the evolution of gaseous reaction products ceases. The resulting oxides weighing 27.15 g are dissolved in 100 ml of 35% nitric acid, the resulting solution is subjected to the standard operation of purifying REE nitrates from thorium impurities by extraction methods. The content of REE nitrates in the purified solution is 264.9 g / l, the degree of REE extraction from the initial monazite concentrate is 98.1%.

Example 2

A portion of a monazite concentrate 50 g of the composition according to example 1 is mixed with a mixture of 75 g of sulfuric acid and 112.5 g of ammonium hydrofluoride (ratio of opening agents monazite; ratio of opening agents 1: 1.5) and kept at 200 ° C within 2 hours. The resulting product is heated to 340 ° C and maintained at this temperature until the evolution of gaseous reaction products ceases. A cake is formed in an amount of 65.9 g. In Example 1, cake is washed with a solution of sulfuric acid and deactivated with a solution of barium chloride, the mass of the utilized radioactive residue is 8 g, with a REE content of 6.25% (0.5 g). In Example 1, a solution of REE nitrates with a concentration of 266.8 g / L is extracted from the purified sulfate solution, the degree of REE extraction from the initial monazite concentrate is 98.8%.

Example 3

A portion of a monazite concentrate of 50 g of the composition of Example 1 is mixed according to a stoichiometric ratio of monazite: sulfuric acid 1: 1 with a mixture of 37.8 g of sulfuric acid and 49 g of ammonium hydrofluoride (ratio of opening agents 1: 1) and kept at 260 ° C for 20 minutes. The resulting product is heated to 340 ° C and maintained at this temperature until the evolution of gaseous reaction products ceases. A cake is formed in an amount of 72.7 g. According to Example 1, cake is washed with a solution of sulfuric acid and deactivated with a solution of barium chloride, the mass of the utilized radioactive residue is 11 g, the content of unreacted REE oxides in the residue is 3.75 g (34%). From the purified solution of Example 1, the following is carried out: precipitation of REE double sulfate salts, filtration and thermal decomposition of crystals, dissolution of REE oxides in nitric acid, purification of REE nitrates from thorium by extraction methods. The content of REE nitrates in the purified solution is 247.8 g / l, the degree of REE extraction from the initial monazite concentrate is 91.7%.

Thus, from the above examples it follows that the proposed method allows to increase the degree of REE extraction to 98%, to reduce the consumption of sulfuric acid and wastewater while ensuring a high degree of purification from thorium, iron, aluminum, titanium and silicon.

Claims (3)

1. A method of processing a monazite concentrate, including processing the feedstock with sulfuric acid, water leaching of REE sulfates and neutralizing the solution with barium chloride, followed by selective isolation of the thorium, uranium, ferrous and rare earth product, characterized in that the processing of the initial monazite concentrate is carried out in a mixture of sulfuric acid and ammonium fluoride at a temperature of 200-230 ° C for 30-40 minutes, the resulting product is purified from phosphate and fluoride products by sublimation distillation, rare earth product is introduced through the stage of precipitation of REE double salts with ammonium sulfate, followed by conversion to REE nitrates through the stages of calcination, dissolution in nitric acid, and extraction purification from thorium impurities. 2. The method according to p. 1, characterized in that the leaching process is carried out with a solution of sulfuric acid. 3. The method according to p. 1, characterized in that the production of glandular, thorium and uranium product is carried out from the mother liquor after precipitation of REE double salts.

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