RU2607862C1 - Method of extracting rare-earth metals and producing gypsum plaster from anhydrite - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to a method of processing apatite with extraction and obtaining a concentrate of rare-earth metals and gypsum plaster from phosphogypsum – wastes from sulphuric acid technology of producing phosphoric acid from apatite. Method includes preliminary mechanical activation of calcium sulphate anhydrite with subsequent leaching of rare-earth metals in a solution with recrystallisation of phosphogypsum from calcium sulphate anhydrite to dihydrate. Leaching is carried out with 5 % solution of HNO₃ with addition of 15 % Ca(NO₃)₂ at normal conditions for 6 hours. Degree of extraction of rare-earth metals into solution is higher than 95 %, degree of conversion of anhydrite into gypsum is higher than 97 %. Obtained effect achieved through properly selected conditions for preliminary mechanical activation of anhydrite. Maximum degree of extraction of rare-earth metals into solution is achieved at values of total amount of energy stored in form of surface areas of coherent dissipation and microdeformations, more than 5.8 kJ/mol.

EFFECT: disclosed is a method of processing of apatite.

9 cl, 1 tbl, 1 ex

Description

The invention relates to a method for the complex processing of apatite with the extraction and production of a concentrate of rare earth metals (REM) and gypsum from phosphogypsum - a waste of sulfuric acid technology for producing phosphoric acid from apatite.

A known method of extracting rare-earth metals from phosphogypsum (RF Patent No. 2225892), including sequential leaching of them from several portions of phosphogypsum with a circulating solution of 20-25% sulfuric acid at W: T = 2-3 for 60 minutes, separating the insoluble residue from the productive solution crystallization of REM concentrate in the form of sulfates by adjusting the productive solution to a state of REM supersaturated by increasing the acid concentration in it to more than 30% at a temperature of 20-80 ° C. The crystallization of rare-earth sulfates is preferably carried out in the presence of seed from them at L: T not more than 100 for 0.4-3 hours. The extraction of rare-earth metals into a concentrate is in the range of 50-60%, then it is subjected to conversion to obtain concentrated solutions of nitrates or chlorides of rare-earth metals .

The disadvantages of the method are a significant number of technological operations.

A known method of extraction of rare-earth metals from phosphogypsum (RF Patent No. 2167105), including their portioned leaching, separation of the mother liquor from the solid phase and its repeated use for leaching new portions of phosphogypsum, water washing of the insoluble residue using a leaching solution during leaching. In this case, the leaching of rare-earth metals from the first portion of phosphogypsum is carried out with a 2-6% solution of sulfuric acid at W: T = 2-3, and for each subsequent portion of phosphogypsum, the acid concentration is increased according to the above condition. The leach solution is used at least three times, and the maximum concentration of sulfuric acid in the leach solution is 24%.

The disadvantages of the method are the multi-stage process of leaching of rare-earth metals, the need for a sufficiently clear control and regulation (maintenance) of the required condition, as well as the relatively low extraction of rare-earth metals from phosphogypsum into the solution.

There is also a method of extracting rare-earth metals from phosphogypsum (RF Patent No. 2293781), according to which phosphogypsum is treated with a solution of sulfuric acid with a concentration of 22-30 wt. % at W: T = 1.8-2.2 for 20-30 minutes with the extraction of rare earth elements and sodium into the solution, preventing spontaneous crystallization of the rare earth element concentrate from the leach solution with such a duration of the process until it is separated from the insoluble residue. After separation of the insoluble residue in the solution, the degree of supersaturation with REM is increased by providing a sodium concentration in it in the range of 0.4-1.2 g / l using mainly sodium sulfate or carbonate.

The disadvantages of this method are the significant loss of rare-earth metals contained in the wet insoluble residue and in preparation for disposal, as well as the accumulation of impurities in the products of the process.

Known nitric acid technology for the separation of rare earth elements from apatite, giving up to 85% of their allocation in a solution containing phosphorus and fluorine (Kosynkin VD and others. Status and development prospects of the rare earth industry of Russia / Metals, No. 1, 2001).

The disadvantages of this method include the inability to use working solutions in a closed cycle and the subsequent low degree of extraction of rare-earth metals in the technological process in closed-loop mode.

Previously, the authors of the present invention have described a method for extracting rare earth metals and producing building gypsum from phosphogypsum hemihydrate (RF patent No. 2528576). The method includes successive stages of recrystallization of phosphogypsum and dissolution of rare-earth metals. In this case, the recrystallization of hemihydrate or anhydrite of calcium sulfate into dihydrate is carried out in the presence of a soluble calcium salt at a concentration of 0.075-3.75 M in terms of Ca ²⁺ in a slightly acidic medium at pH> 1. Dissolution is carried out with a strong acid with pK _a <0 at a concentration of 0.2-8 M in terms of H ⁺ . The degree of extraction of rare-earth metals in solution is up to 95%, the residual content of impurities of phosphorus, fluorine and alkali metals in calcium sulfate dihydrate does not exceed 0.3 wt.%, 0.1 wt.%, 0.05 wt.%, Respectively. The technical result is to increase the efficiency of extraction of rare-earth metals with the simultaneous purification of calcium sulfate from phosphorus and fluorine. The specified RF patent No. 2528576 is fully incorporated into the present description by reference.

This method according to a combination of similar features: the use of anhydrite, its treatment with HNO ₃ solutions with the addition of Ca (NO ₃ ) ₂ under normal conditions, we have adopted as a prototype.

The disadvantage of this method is the high duration of the transition anhydrite-dihydrate due to the high stability of the anhydrite, since under normal conditions the detected conversion occurs in several weeks.

The present invention solves the problem of efficiently extracting rare earth metals (REM) and producing gypsum from anhydrite. In the framework of the present invention, the term REM is used to mean lanthanides and yttrium. Also, the symbol Ln is used to indicate the above elements.

The solution to this problem is achieved through targeted preliminary mechanical activation of stable forms of anhydrite before recrystallization, which reduces the duration of recrystallization to acceptable for production and increases the efficiency of extraction of rare earth metals and obtaining building gypsum from anhydrite.

The problem is solved in a method for the extraction of rare earth metals (REM) and the production of gypsum from anhydrite, including the treatment of anhydrite with strong acid (pK _a <0) in a concentration of 0.2-8 M (in terms of H ⁺ ) in the presence of a soluble calcium salt in concentration of 0.075-3.75 M (in terms of Ca ²⁺ ) under normal conditions, characterized in that the anhydrite undergoes preliminary mechanical activation to the total amount of stored energy corresponding to a change in the surface of the coherent scattering regions and the microde formations, more than 5.8 kJ / mol. Subsequent recrystallization is carried out for about 6 hours.

As a strong acid, it is preferable to use nitric acid, hydrochloric acid, or a mixture thereof. It is preferable to use nitric acid and / or hydrochloric acid in concentrations of 5-250 g / l and 5-300 g / l, respectively (0.2-8 M in terms of H ⁺ ).

As a soluble calcium salt, it is preferable to use chloride or calcium nitrate in concentrations of 10-300 g / l and 10-500 g / l, respectively (0.075-3.75 M in terms of Ca ²⁺ ).

Under normal conditions are meant close to standard conditions for pressure and temperature, namely a pressure of 1 atm. (10 ⁵ Pa) and a temperature in the range of 10-45 ° C, preferably in the range of 20-30 ° C.

The term "mechanical activation" means a process of mechanical action on solids, during which a deformation of the crystal lattice of a solid occurs with the formation of linear and point defects, for example, a shift of layers, a change in the volume of unit cells, etc. Moreover, part of the mechanical energy supplied to the solid during activation is absorbed by the solid with an increase in the supply of free (internal and surface) energy.

The term "stored energy" characterizes the excess energy that the material acquires after mechanical activation.

As devices used for mechanical activation, disintegrators, planetary centrifugal and vibration mills of an industrial type known to a person skilled in the art can be used.

The amount of stored energy corresponding to a change in the surface of the regions of coherent scattering and microstrains can be estimated during mechanical activation on periodically selected samples of the activated material, or can be predicted in advance by conducting trial mechanical activation under various conditions.

Evaluation of the amount of stored energy allows not only to evaluate, but also to control the reactivity of the activated material not by the degree or speed of its reaction and the degree of extraction of rare-earth metals in solution, that is, at the final stage of recrystallization, but by the degree of its structural changes immediately after extraction from the mechanical activator.

The degree of mechanical impact on the anhydrite crystal lattice was estimated by the amount of stored energy using the method described in the work of E.V. Bogatyreva, A.G. Ermilova "Assessment of the proportion of energy stored during the mechanical activation of mineral raw materials." Inorganic Materials, 2008, Volume 44, p. 242-247:

ΔE _Σ = ΔE _d + ΔE _S + ΔE _ε ,

where ΔE _d is the amount of energy stored in the form of a change in the interplanar spacings of the crystal lattice of the compound:

ΔE _d = KE _latt .

K is the coefficient of the relative change in the volume of the unit cell of the compound (modulo);

E _latt is the energy of the crystal lattice of the compound.

ΔE _S is the amount of energy stored in the form of the surface of areas of coherent dispersion (CSR):

E _surf - surface energy of the compound before activation;

V _mol is the molar volume of the compound;

D _i , D ₀ are the sizes of the coherent dispersion regions of the compound after mechanical activation and before it, respectively.

ΔE _ε is the amount of energy stored in the form of microdeformations:

Ε _Y is the Young's modulus of the compound;

ε _i , ε _o - the root mean square microdeformation of the compound after mechanical activation and before it, respectively.

The authors of the present invention found that the amount of energy stored in the form of anhydrite in the form of coherent scattering regions and microstrains correlates with the degree of REM extraction and the degree of conversion of anhydrite to gypsum. At the same time, it turned out that the amount of energy stored by anhydrite in the form of a change in the interplanar spacings of the anhydrite crystal lattice varies nonlinearly depending on the duration of mechanical activation and does not correlate with the degree of REM extraction and the degree of conversion of anhydrite to gypsum.

The greatest activation effect is manifested when the amount of energy stored by anhydrite in the form of energy corresponding to a change in the surface of the regions of coherent scattering and microstrains is more than 5.8 kJ / mol. The degree of conversion of anhydrite to gypsum for 6 hours of recrystallization in this case is more than 97%, and the extraction of rare earth metals (REM) is more than 95%. A decrease in the duration of recrystallization from 6 to 3 hours is accompanied by a decrease in the extraction of rare-earth metals in solution to 62-77%. In unactivated anhydrite under the same conditions for 6 hours, the degree of conversion of anhydrite to gypsum is 13.5%, and the recovery of rare-earth metals is 10.2%.

A decrease in the total amount of energy stored in the form of coherent scattering and microdeformation regions to 5.2 kJ / mol of anhydrite upon recrystallization for 6 hours is accompanied by a decrease in the extraction of rare-earth metals into solution to 69%, and the degree of conversion of anhydrite to gypsum is more than 97%.

A decrease in the total amount of energy stored in the form of coherent scattering and microdeformation regions to 3.3 kJ / mol of anhydrite upon recrystallization for 6 hours is accompanied by a decrease in the extraction of rare-earth metals into solution to 23%, and the degree of conversion of anhydrite to gypsum is more than 97%.

Provided that the total amount of stored energy is more than 5.8 kJ / mol anhydrite, the degree of REM extraction into the solution is more than 95% after 6 hours of leaching under normal conditions.

The present invention is explained in more detail below with reference to examples of its implementation, serving solely for illustrative purposes and in no way limiting the scope of the present invention defined by the attached claims.

Example.

Anhydrite containing more than 99% fraction with a particle size of less than 67.5 microns of the following chemical composition was subjected to mechanical activation, in mass%: 37.2 CaO; 55.73 SO ₃ ; 0.569 Ln ₂ O ₃ ; 0.0364 MgO; 0.009 Al ₂ O ₃ ; 0.0117 Fe ₂ O ₃ ; 0.0049 TiO ₂ ; 2.13 SrO; 0.0016 MnO; 0.226 Na ₂ O; 0.0096 K ₂ O; 0.1264 P ₂ O ₅ ; 0.0132 SiO ₂ .

Activation was carried out in a LAIR-0.015 centrifugal planetary mill with a developed acceleration of 25 g, with a ratio of the mass of grinding media and the mass of the loaded anhydrite 800: 10, the degree of filling of the mill drum with balls of 60%.

Specific examples of implementation are presented in the Table.

Designations in the Table: τ _а - duration of machining (activation), τ _high - duration of leaching, Т: Ж - ratio of solid and liquid components in the pulp during conversion.

E _latt = 9607.1 kJ / mol (determined by the Fersman method. Fersman AE Selected works. Volume IV. - M .: Publishing House of the USSR Academy of Sciences, 1958. - 588 p.)); V _mol = 59.15 cm ³ / mol, E _surf = 0.724 J / m ² and E _Y = 74.29 GPa (determined by the method described in the work of Zuev V.V., Aksenova G.A., Mochalov N. A. et al. Investigation of the specific energies of the crystal lattices of minerals and inorganic crystals to evaluate their properties // Ore dressing. 1999. No. 1-2. P. 48-53).

The data presented show that the amount of energy stored by anhydrite in the form of regions of coherent scattering and microstrains correlates with the degree of extraction of rare earth metals and the degree of conversion of anhydrite to gypsum. Under the conditions of mechanical activation, up to the total amount of stored energy corresponding to a change in the surface of the regions of coherent scattering and microstrains, more than 5.8 kJ / mol, the degree of REM extraction into the solution is more than 95% after 6 hours of leaching.

Although the present invention has been described in detail above, it will be apparent to those skilled in the art that changes can be made and equivalent replacements made, and such changes and replacements are not outside the scope of the present invention as defined by the appended claims.

Claims (13)

1. A method of extracting rare earth metals (REM) from anhydrite to produce gypsum, comprising treating anhydrite with a strong acid with pK _a <0 in the presence of a soluble calcium salt with recrystallization of anhydrite into gypsum, the anhydrite being subjected to mechanical activation before the total amount of stored energy corresponding to a change in the surface of the regions of coherent scattering and microstrains, more than 5.8 kJ / mol. 2. The method according to p. 1, in which the concentration of the indicated strong acid is 0.2-8 M (in terms of H ⁺ ), and the concentration of the indicated soluble calcium salt is 0.075-3.75 M (in terms of Ca ²⁺ ) . 3. The method according to claim 1, in which calcium nitrate or calcium chloride or a mixture thereof is used as a calcium salt, and nitric or hydrochloric acid or a mixture thereof is used as an acid. 4. The method of claim 1, wherein a 5% (1.04 M) nitric acid solution is used as the strong acid. 5. The method of claim 1, wherein a 15% (1, 2 M) calcium nitrate solution is used as the soluble calcium salt. 6. The method according to p. 1, in which the mechanical activation is carried out using disintegrators, planetary centrifugal and vibration mills of industrial type. 7. The method according to p. 1, in which the stored amount of energy corresponding to a change in the surface of the areas of coherent scattering and microstrains is determined by analyzing the degree of structural changes in the samples taken of the activated material, or they are predicted by carrying out trial mechanical activation under various conditions. 8. The method according to p. 1, in which the amount of energy stored in the form of a surface of areas of coherent dispersion (CSR) is determined by the formula:

where E _surf is the surface energy of the compound before activation, V _mol is the molar volume of the compound, D _i , D ₀ are the sizes of the coherent dispersion regions of the compound after and before mechanical activation, respectively, and the amount of energy stored in the form of microstrains is estimated by the formula:

where Ε _Y is the Young's modulus of the compound, ε _i , ε _o is the mean square microdeformation of the compound after mechanical activation and before it, respectively. 9. The method according to p. 1, in which the treatment with strong acid during recrystallization in gypsum subjected to mechanical activation of anhydrite is carried out for about 6 hours.