RU2633859C1 - Method for processing monazite - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves opening crushed monazite with a 7-10 M solution of nitric acid at a temperature of 150-250°C and a pressure of 1.5-2.5 MPa for 100-200 minutes at a ratio of T:F=1:10. After this, the nitrate solution formed from the ballast impurities is extracted, and the extraction separation of the purified nitrate solution is performed with 100% TBF. As a result, solutions of heavy REE+ yttrium, medium-heavy and light REE with total specific α-activity less than 1⋅10^-8 Ku/(kg of REE). Radioactive thorium and uranium are derived from monazite in the form of wastes of group II, which can be sent to the dump without special burial.

EFFECT: reducing the number of technological redistributions at the dissection of monazite ore.

2 cl, 2 dwg

Description

The invention relates to a technology for the integrated processing of ore materials with the aim of obtaining rare earth elements (REE).

The monazite ore mineral consists of REE and thorium phosphates and is one of the main sources of REE. The presence of thorium suggests considering monazite as a potential source of thorium - a raw material for nuclear energy. The main task in the technology of monazite is the destruction of a sufficiently strong crystal lattice of REE and thorium phosphates. Existing methods suggest two solutions: sintering with carbonate-alkaline compounds of the metals of the first group or treatment of monazite with aqueous solutions of mineral acids or alkalis.

There are various options for opening monazite with alkaline reagents: calcination with sodium carbonate [1], fusion with sodium hydroxide [2], treatment with potassium hydroxide solution when heated [3]. There is a description of the method [4], which includes processing a 45% sodium hydroxide solution at 140 ° C for 3 hours of ground monazite, filtering the separation of trisodium phosphate, selective dissolution of REE hydroxides in hydrochloric acid, and thorium and uranium are extracted from the remaining cake by dissolving in nitric acid. The disadvantage of this method is that the extraction of thorium does not exceed 97-98%, and the remaining 2-3% of primary thorium creates a radioactive background in the waste, and therefore, in accordance with sanitary standards, such waste must be sent for special disposal. The use of special waste storage facilities with a large amount of waste rock in monazite (10-15%) significantly increases the cost of processing monazite.

A known method of processing monazite [3], including grinding, processing when heated with a solution of alkali metal hydroxide, the allocation of salts of phosphoric acid, dissolving cake in mineral acid, followed by the allocation of rare earth elements (REE), thorium and uranium, and the treatment is carried out with a solution of potassium hydroxide in the ratio (wt.): monazite: potassium hydroxide = 1: 1.0-1.5 to obtain a solution of tripotassium phosphate, potassium hydroxide and a precipitate containing hydroxides of thorium, uranium, REE, unopened monazite and gangue, which is processed they are charged with nitric acid, removing REE nitrates into the solution, precipitated REE carbonates from the solution with potassium carbonate, the remaining cake is treated with potassium carbonate solution with the conversion of uranium into solution and subsequent precipitation in the form of dioxouran dihydroxide and the cake is finally treated with nitric acid solution with extraction of thorium into solution, precipitation thorium with a solution of potassium carbonate, and the mother liquors from the deposition of REE, thorium, uranium and tripotassium phosphate are sent to receive fertilizers.

The disadvantage of this method is the need for the conversion of REE hydroxides into a nitric acid solution for further purification.

Sulfuric acid methods are known for the enrichment of monazite ores containing REE [5, 6], when thorium and rare-earth elements and phosphoric acid are formed during treatment with concentrated sulfuric acid and heating. Due to the complexity of the separation of thorium sulfates and REE by a significant amount of radioactive waste water, this method has been replaced at a number of enterprises with an alkaline method for opening monazite.

The aim of the invention is to create a method for processing monazite, which allows to reduce the number of process steps during the opening of monazite ores, by extraction methods to separate solutions of total REE from thorium and uranium to sanitary standards, to separate the total solution of REE into light, medium and heavy REE and to remove radioactive thorium from monazite and uranium in the form of waste of group II, which can be sent to the dump without special disposal.

The problem is solved in that the method of processing monazite, including heating the crushed monazite with a solution of nitric acid under pressure, while the concentration of the solution of nitric acid is (7-10) M, the heating temperature is (150-250) ° C, the ratio T: W = 1:10, pressure (1.5-2.5) MPa, heating time (100-200) min; extraction purification of nitrate solution from ballast impurities; extraction separation of the nitrate solution with 100% TBP into the total REE solution and thorium-containing nitrate solution; extraction separation of 100% TBP of the light REE group from the total REE solution evaporated to 400 g / l, extraction separation of the reextract evaporated to 200 g / l in the system of 100% TBP-quaternary ammonium bases (PAO) into heavy REE and yttrium ( TRZE + Y) and moderate heavy REE (STRZE); isolation and concentration of thorium and uranium from nitrate solutions and their preparation in the form of hydroxocarbonates.

The basis for the development of the proposed method is to reduce the number of process steps during the opening of the monazite with nitric acid in comparison with the use of sulfuric acid (Fig. 1).

In the experiments, we used the monazite concentrate OGU URALMONATSIT (Krasnoufimsk), which has an average composition: REE oxides - 54.0% wt., ThO ₂ - 5.4% wt., U ₃ O ₈ - up to 0.2% wt., P ₂ O ₅ -22.5% wt.

The use of nitric acid is complicated by its low boiling point; therefore, the regimen for opening monazite was experimentally selected in order to obtain a nitrate solution of REE and thorium-containing products. For this, monazite, crushed to a particle size of less than 0.1 mm, interacted with a (7-10) M nitric acid solution under a pressure of (1.5-2.5) MPa at a temperature of (150-250) ° С for (100-200) min, the ratio of T: W = 1: 10. The analysis of the resulting solution by the mass spectral method showed that rare earth elements went into the nitrate solution by 55-60%, while thorium and uranium went almost completely.

In FIG. Figure 2 shows the proposed flow chart of the processing of monazite with the separation of REE into groups.

After opening the ore concentrate with nitric acid, the nitrate solution containing rare earth elements, thorium, uranium and impurities is subjected to purification from ballast impurities by the extraction method with 100% TBP. After purification, the raffinate solution containing impurities is disposed of, the extract, a nitrate solution with REE, thorium and uranium, is fed to extraction purification and separation. REE and thorium with uranium are re-extracted from the organic phase 0.2 N HNO ₃ , the resulting solution is hydrolytically cleaned with alkali or aqueous ammonia, bringing the pH of the solution with rare-earth metals to a pH of 3 to 5, and some of the radioactive impurities are also deposited. Then carry out the extraction purification of the solution of rare-earth metals from thorium and uranium 30% TBP. An extract containing thorium and uranium is used to produce thorium hydroxocarbonate with further burial.

In laboratory conditions, according to the proposed extraction scheme, a total REE nitrate solution was obtained with a total specific α-activity of less than 1⋅10 ^-8 Ku / (kg REE). Reextract - the total solution of REE - evaporated to a concentration of 400 g / l and carry out extraction with 100% TBP. A raffinate is obtained containing a light REE group and an extract with heavy REE (TRZE) + yttrium and a group of moderate REE (STRZE) (Sm, Eu, Dy, Gd, Tb). REE separation of the yttrium subgroup is carried out in the TBP-Quaternary ammonium base (PAO) system after evaporation of the solution to 200 g / L. At the same time, moderate heavy REE (Sm, Eu, Dy, Gd, Tb) pass into the extract, and yttrium and heavy rare earth metals remain in the raffinate.

The proposed method for processing monazite can reduce the number of technological redistributions during the opening of monazite ores. The method provides an extraction method for separating a solution of total REE and thorium. The resulting raffinate contains REE with a specific α-activity of less than 1⋅10 ^-8 Ku / (kg REE), the extract contains thorium and uranium. As the safest option is proposed with the separation, concentration and subsequent burial of thorium in the form of a precipitate of hydroxocarbonates with a specific α-activity of less than 1⋅10 ^-3 Ku / kg, as waste of the middle (second) activity group, the transportation of which is carried out in sealed plastic bags, placed in metal negotiable containers. If necessary, ThO ₂ can be obtained from thorium hydroxocarbonate by calcination.

The resulting total REE solution by extraction methods is divided into light, medium and heavy REE.

Literature

1. RU 2242528. Method for opening monazite concentrate. С22В 60/02, С22В 59/00. Otub. 12/20/2004.

2. Kaplan G.E., Uspenskaya T.A., Orlov V.K. et al. Metallurgy of thorium. Papers of the Soviet delegation at the International Conference on the Peaceful Use of Atomic Energy, Geneva, 1955 / Research in the field of geology, chemistry and metallurgy. - M.: Publishing House of the Academy of Sciences of the USSR, 1955.S. 105.

3. RU 2323989. A method of processing monazite. C22B 59/00, C22B 60/02, C01F 17/00, C01F 15/00, C01G 43/00. Otub. 05/10/2008.

4. Bearse A.E., Calkins G. D., Clegg J.W., Filbert R. B. Thorium and rare earth from monazite. Chem. eng. progr., 1954, v. 50, P. 235-239.

5. The patent of Germany No. 4297456. The method of beneficiation of ores containing rare earth metals. Kl. C22B 3/08, 3/44. Claim 08/29/90. Otub. 01/09/92.

6. French patent No. 2643911. A method of processing ores containing rare earth metals. Kl. C22B 59/00. Claim 03.03.89. Otub. 09/07/90.

Claims (2)

1. A method of processing monazite, including acid opening by heating the crushed monazite under pressure to obtain a nitrate solution, characterized in that the opening is carried out with a solution of nitric acid with a concentration of 7-10 M, at a heating temperature of 150-250 ° C, the ratio of T: W = 1:10, a pressure of 1.5-2.5 MPa, a heating time of 100-200 min, followed by extraction purification of the nitrate solution from ballast impurities, and after extraction purification, the extraction separation of the nitrate solution with 100% tributyl phosphate (TBP) is carried out on su mmar solution of rare-earth elements (REE) and thorium-containing nitrate solution, extraction separation of 100% TBP of the light REE group from the total solution of REE evaporated to 400 g / l, extraction separation of the reextract evaporated to 200 g / l in the 100% TBP-quaternary ammonium system bases (PAO) for heavy REE + yttrium and moderate heavy REE. 2. The method according to p. 1, characterized in that thorium and uranium are extracted from nitrate solutions in the form of hydroxocarbonates.

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