RU2598766C1 - Method of processing nitrate solutions containing rare-earth metals - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to hydrometallurgy of rare metals. Proposed method comprises extraction of rare-earth metals from nitrate solutions by means of an extractant with forming extracted complexes and washing the saturated extract containing complexes of rare-earth metals, using a cascade multistage system of the extraction process. Cascade multistage system, consisting of extraction, flushing and reaction parts, is used each part comprises five stages respectively. Mixture consisting of versatic, tributyl phosphate and diesel fuel, taken in ratio vol %: 40:10:50, is supplied as an extraction agent, and extraction is performed in the presence of ammonia. Saturated extract is washed from ions of NO₃ with ammonium chloride solution with concentration of 1N, after washing saturated extract of rare-earth metals is stage re-extracted by processing with hydrochloric acid solution with concentration of 1N to obtain a solution of rare-earth metals chlorides.

EFFECT: simplified process.

8 cl, 1 dwg, 1 ex

Description

The invention relates to hydrometallurgy of rare metals, in particular to the integrated processing of technological and productive solutions, and can be used in the extraction technology of the separation of chlorides of medium and heavy rare earth metals to obtain marketable products, including those suitable for subsequent use in the ion-exchange separation of rare earth metals.

Nitrate technological solutions are formed in the production of rare and non-ferrous metals in the process of hydrometallurgical processing of ore concentrates and in other chemical industries. It is well known that the processing of nitrate technological solutions is a difficult task. This is due to the fact that the nitrate ion does not form insoluble compounds with any metal cations and cannot be stored in the sludge collector after precipitation and separation from the solution, since all metal nitrates, including basic ones, are worse or better soluble in water. At the same time, nitrate ions are toxic to the environment and humans and solutions containing them cannot be thrown into the hydrographic network and the environment.

Methods of processing technological nitric acid solutions containing rare-earth metals (REM) are carried out according to the scheme for the conversion of the nitrate form of REM into a solution of REM chlorides developed in the industry to obtain solutions in the form of marketable products, including those suitable for subsequent use in the ion-exchange separation of REM. The resulting chloride solutions of rare-earth metals are subjected to zinc reduction of europium to a 2-valence state, followed by double sulfate precipitation. As a result, europium is selectively concentrated and removed from the system. The industrial method has the following disadvantages:

- multi-stage operations (dissolution, precipitation of double sulfates, etc.);

- high consumption of reagents;

- repeated repetition of the process and the complexity of operations;

- the difficulty of cleaning solutions and sediments from zinc;

- the presence of diverse technological equipment (reactors, filters, heated reactors, storage rings, etc.);

- low direct yield of the target product.

A known method of processing nitrate solutions containing REM into a solution of REM chlorides using ion-exchange processes [see V.V. Serebrennikov. Chemistry of rare earth elements. Tomsk: publishing house of Tomsk University, 1961]. REM nitrate solution is fed into an ion exchange column filled with cation exchange resin, for example, KU-2. Rare earth elements are sorbed and the nitric acid solution is washed out with a hydrochloric acid solution, ensuring the conversion of rare-earth nitrates to rare-earth chlorides.

With simplicity, the method has the following disadvantages:

- low productivity of the process with a transmission rate of solutions of 2 ml / min;

- low REM content in solution (up to 10 mg / l);

- in the case of extraction isolation and separation of rare-earth metals, the presence of special equipment in the form of ion-exchange columns with appropriate equipment;

- ion-exchange columns must be made of titanium, which leads to additional costs. Steel columns need to be gummed, since steel strongly corrodes in hydrochloric acid solutions and columns quickly fail. These disadvantages limit the use of ion exchange processes to solve the problem in practice.

A known method for the extraction of rare earth metals from acidic solutions in the form of solutions of nitrates or chlorides of rare-earth metals, suitable for subsequent industrial use or processing (see patent RU 2172719). The method includes introducing into the stock solution an organophosphorus reagent-collector in the form of dialkylphosphoric acid while purging the solution with gas to produce and separate a rare earth foam product from the solution. The isolated foam product is treated with nitric or hydrochloric acid with a concentration of at least 4 N at 70-100 ° C with the transfer of rare-earth metals into a solution that is separated from the regenerated collector reagent.

The disadvantages of the method are:

- the complexity of the technological process of the translation of rare-earth metals from the nitrate form of the solution into the chloride form;

- the need for special equipment in the form of flotation columns and the need to use expensive reagents.

A known method of multistage extraction processing of nitrate solutions containing a mixture of rare earth metal nitrates, carried out in a countercurrent extractor (see US patent US 6238566). During the extraction process, an initial aqueous solution containing rare-earth metal nitrates in the form of water-soluble salts is brought into contact with an organic extractant. The extraction process with an organic solvent containing, as extractant, a compound of phosphorus-containing organic acids, carboxylic acids and b-diketone, can be expressed by the equation:

Extraction, according to the known method, is carried out using a multi-stage countercurrent extractor containing a mixer and a sump. A characteristic feature of the known invention is the presence of ion-exchange dialysis, necessary to remove the free acid contained in the aqueous solution from the previous stage of the process. Ion exchange dialysis is included in each subsequent stage of the multi-stage extraction process. After the first stage of extraction treatment, at least part of the acid is removed from the aqueous solution using a diffusion dialyzer model TSD-2 with an integrated ion-exchange membrane. The known method is aimed at increasing the degree of extraction of rare earth metals up to about 94% from nitrate solutions containing a mixture of elements such as yttrium, lanthanum, neodymium, samarium, gadolinium. The method has the following disadvantages:

- does not allow to obtain a mixture of rare earth metals in the form of solutions REM chlorides without traces of NO ^- _3, i.e. in the form of marketable products suitable for subsequent industrial use or processing;

- the need for special equipment: the presence of a diffusion dialyzer with ion-exchange membranes, which are installed between the compartments of aqueous and organic solutions, which increases the cost of the process.

The closest in technical essence is the method used in industry for the extraction separation of rare earth metal concentrates of the yttrium group from nitrate solutions using tri-n-butyl phosphate (TBP) as an extractant, selected as a prototype (see SU 1786162).

The method is intended for continuous group separation and separation of the rare-earth metals of the yttrium group from nitrate solutions and is based on the formation of extractable complexes of medium rare-earth metals with diisooctylmethylphosphonate in the claimed concentration range of rare-earth metals, nitric acid and a salting out agent (ammonium nitrate) under the action of tri-n-butylphosphate ( as a sensitizing agent. Extraction is carried out using a cascade multi-stage separation system for a concentrate of medium rare-earth metals, consisting of an extraction part, including 20 steps (cells) necessary for group separation of rare-earth metals, and a washing part of the cascade, which includes 15 steps (cells).

The prototype method does not allow to obtain a mixture of rare earth metals in the form of marketable products: solutions of rare earth chlorides without traces of NO ^- ₃ , suitable for subsequent industrial use or processing.

First of all, for the successful isolation of samarium and gadolinium, it is necessary to bring the concentration of europium in the nitric acid solution to less than 0.1%. Today, for this, nitrate solutions of rare-earth metals are converted into chloride solutions, in which zinc reduction of europium to a 2-valence state is carried out, followed by double sulfate precipitation. As a result, europium is selectively concentrated and removed from the system.

The basis of the invention is a method of converting the nitrate form of a solution of rare-earth metals into the chloride one. The reverse procedure is mandatory: conversion of chloride solutions to nitric acid, from which, using oxalate precipitation, REM is transferred to a solid state, followed by calcination of oxalates to rare-earth oxides. From the foregoing, it follows that the present invention can be used in technologies for the isolation and separation of rare-earth metals from any feedstock.

The objective of the invention is the processing of nitrate solutions obtained from the production of rare, refractory metals and other industries, which would ensure the translation of rare-earth metals from the nitrate form of solutions into the chloride form of solutions in such a way as to achieve the technical result:

- simplification of the process of obtaining a mixture of rare-earth metals in the form of marketable products: solutions of rare-earth metals chloride without traces of NO ^- ₃ , suitable for subsequent industrial use or processing.

- the ability to use existing in the production of extraction equipment without additional equipment;

- the use of relatively cheap reagents (NH ₄ OH, NH ₄ Cl, HCl) and extractant.

The technical result is achieved by the fact that in the method of processing nitric acid solutions containing rare earth metals, including extraction of rare earth metals from nitric acid solutions with an extractant to form extractable complexes and washing a saturated extract containing complexes of rare earth metals using a cascade multi-stage extraction process system, according to the invention, a cascade is used multistage system consisting of extraction, washing and reaction part th, each part includes five steps, respectively, with a mixture consisting of versatic, TBP and diesel fuel taken in a ratio of vol.%: 40:10:50, and the extraction is carried out in the presence of ammonia, while washing of the saturated extract is carried out from NO ₃ ions by a solution of ammonium chloride with a concentration of 1N, and after washing, the stage of re-extraction of the saturated extract of rare-earth metals is carried out by treatment with a solution of hydrochloric acid with a concentration of 1N to obtain a solution of rare-earth meta chlorides llov.

The extractant can be fed to the cascade at a rate of 10 l / h in the presence of a solution of 7% ammonia.

The extractant and ammonia can be fed to the third stage of the extraction part of the cascade.

The initial nitrate solution of rare-earth metals can be fed into the extraction part of the cascade at a speed of 4 l / h.

The initial rare-earth metal nitrate solution can be fed to the fourth stage of the extraction part of the cascade, and the aqueous phase without rare-earth metals is allotted from the first stage.

The washing of the saturated extract of rare-earth metals from NO ₃ ions is carried out at a rate of 10 l / h at the tenth stage of the washing part of the cascade.

The processing of a saturated extract of rare-earth metals is carried out with a solution of hydrochloric acid at a rate of 2.7 l / h.

A solution of rare earth metal chlorides is withdrawn from the eleventh stage of the stripping part of the cascade without traces of NO ^- ₃ .

An organic solution containing 40 vol.% Is used as an extractant. % versatic (fatty acid) with a variable carbon content in the C ₇ -C ₁₀ alkyl chain; 10 about % tributyl phosphate (TBP); 50 about % diesel fuel. The ratio of the ingredients of the mixture versatic, TBP and diesel fuel, equal to: about. %: 40:10:50, determined empirically, based on the condition of sufficient viscosity of the organic phase with a viscosity of 8-10 centistokes and, as a result, the necessary mixing and separation of the nitric acid solution and the extractant while maintaining the degree of REM extraction in the chloride solution of more than 90% .

The components of the organic solution versatic, TBP and diesel fuel, taken in the ratio of about. %: 40:10:50, provide a complete separation of the nitric acid solution and the extractant.

Organic acid Versatic is known as the vinyl ester of fatty acids (in particular, as the acid Versatic ^® -9), under the name VeoVa9 ™ manufactured by Shell. Versatic organic acids are produced under the trademarks Versatic 9, Versatic 10, Versatic 11 (see the link on the website: utsrus.com> documents / seminary_doklady / sss2.pdf).

Tributyl phosphate - tributyl phosphate ester (C ₄ H ₉ O) ₃ PO.

The nitrate solution of rare-earth metals is treated with an extractant in the presence of a solution of 7% ammonia (NH ₄ OH), which allows you to adjust the acidity of the initial pH solution in the range of 4.3-4.5.

Supply to the fourth stage of the extraction part of the cascade of the technological nitric acid solution: 65 g / l of rare-earth metals, 2.6 g / l of the remaining impurities: Fe ₂ O ₃ , CaO, SiO ₂ , P, Na at pH = 4.5 and to the third stage - organic extractant solution in the presence of a solution of 7% ammonia (NH ₄ OH), provides the necessary distribution of components between the aqueous and organic phases at the fourth and fifth countercurrent stages of the cascade with a ratio of the aqueous and organic phases O: B = 1: 1, nitrate conversion rare earth elements into the organic phase with the formation of extractable s complexes of medium rare-earth metals. After phase separation, a saturated extract is formed. This operation is carried out in the mode of joint extraction of samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), yttrium (Y).

The saturated extract is washed at the tenth stage of the cascade with an aqueous solution of ammonium chloride (in contrast to the prototype method). Washing the obtained extract of rare-earth metals with a solution of ammonium chloride NH ₄ Cl with a concentration of 1N at a ratio of the aqueous and organic phases O: B = 1: 1 allows the extract to be purified from NO ₃ ions with a minimum ΣРЗМ content in the washing solution. The main part of the impurity elements remains in the chloride solution without ΣРЗМ, which is removed at the sixth stage of the cascade. Almost all NO3 ions are excreted with raffinate, and their content increases up to 50% against the content in the initial solution.

The washed extract is fed to the eleventh stage of the cascade for reextraction with a 1N hydrochloric acid solution and obtaining a solution of rare-earth metal chlorides. Reextract: ΣРЗМ chloride solution as the final rare-earth product is removed from the process with ΣРЗМ content of ~ 150 g / l.

The organic wash stream, carrying some REM in itself, combines with the extractant stream directed to the extraction operation of the initial process solution.

Thus, a new and unexpected opportunity was discovered to carry out continuous extraction and re-extraction processes with a sufficiently high productivity and to obtain a purified and concentrated final product in the form of rare-earth metal chlorides with a ΣРЗМ content of ~ 150 g / l.

For a clearer understanding of the invention, the accompanying drawing shows a schematic flow diagram of the processing of technological nitric acid solutions containing rare earth metals.

The method is carried out on a cascade installation containing extraction, washing and stripping parts, each of which contains five steps, respectively: 1, 2, 3, 4, 5; 6, 7, 8, 9, 10; 11, 12, 13, 14, 15. The method is carried out with the ratio of the organic and aqueous phases O: B = 1: 1. On the third stage 3 of the cascade serves extractant 17 containing 40 vol. % versatic (fatty acid) with a variable carbon content in the C ₇ -C ₁₀ alkyl chain; 10 about % tributyl phosphate (TBP); 50 about % diesel fuel. At the third stage 3 of the cascade, solution 16 (a solution of 7% ammonia) is supplied.

The initial technological nitric acid solution 18 containing 65 g / l of rare-earth metals, 2.6 g / l of the remaining impurities: Fe ₂ O ₃ , CaO, SiO ₂ , P, Na at pH = 4.3-4.5. At countercurrent stages 4 and 5, the necessary distribution of components between the aqueous and organic phases is achieved with the ratio of the aqueous and organic phases O: B = 1: 1, the conversion of rare earth nitrates to the organic phase with the formation of extractable complexes of secondary rare-earth metals: samarium (Sm), europium ( Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), yttrium (Y). The aqueous solution 23 is separated from the organic solution in the first stage of the cascade. An aqueous solution of ammonium chloride 19 is supplied to the tenth step 10 of the cascade, and a saturated extract of medium rare-earth metal complexes is fed to the sixth step 6 of the cascade. In the washing part of the cascade, the extract is washed from NO ₃ ions _.

An aqueous stream of 22 chlorides obtained from washing the extract, carrying NO ₃ ions in it, is withdrawn from stage 6 and connected to the feed stream.

The organic wash stream, carrying some REM in itself, combines with the extractant stream directed to the extraction operation of the initial process solution.

The washed extract is fed to the eleventh stage 11 of the cascade for re-extraction with a solution of 20 hydrochloric acid with a concentration of 1N and obtaining a re-extract: a solution of 21 rare-earth metal chlorides. Reextract 21 as the final rare earth product is removed from the process.

All operations are performed in countercurrent phase mode.

The essence of the claimed invention and its advantages are illustrated by the following example of a specific implementation.

An example of a specific implementation.

During the experiment, we took the initial technological aqueous nitric acid solution with a total concentration of rare-earth nitrates of 65 g / l, 2.6 g / l of the remaining impurities: Fe ₂ O ₃ , CaO, SiO ₂ , P, Na at pH = 4.5.

Technological aqueous nitrate solution contained REM, mass. %:

samarium - 22.8; europium - 5.7; gadolinium - 18.4; terbium - 2.1;

dysprosium - 8.3%; yttrium - 42.7%.

The extractant contained:

- 40 about. % versatic (fatty acid) with a variable carbon content in the C ₇ -C ₁₀ alkyl chain;

- 10 vol. % tributyl phosphate (TBP);

- 50 about. % diesel

The maximum saturation according to ΣРЗМ was ≈70 g / l. For the transfer scheme, saturation is taken ≈40 g / l (to exclude the supersaturation of the extractant in the cascade).

Submitted to the cascade:

in the 3rd step: extractant - 10 l / h (10 · 40 = g / h);

a solution of 7% ammonia NH ₄ OH - (1.8 ÷ 2) l / h;

in the 4th step, a solution of rare-earth metals

ΣРЗМ ≈100 g / l - (4 l / h) = 400 g / h;

From the 1st stage, the aqueous phase was diverted without ΣРЗМ.

Saturated by ΣRZM extract was fed to the 6th stage.

In the 10th step, a 1N NH ₄ Cl solution was supplied at a rate of 10 L / h (O: B = 1: 1), where the extract was washed from NO ₃ ions. The extract washed from NO ^- ₃ ions was fed to the 11th stage for reextraction.

A solution of 1N HCl was fed into the 15th stage at a rate that would ensure ~ 150 g / L after ΣREM in the reextract. The HCl solution was supplied at a rate of 2.7 L / h. ΣРЗМ chloride ~ 150 g / L without traces of NO ^- _{3 was} withdrawn from the 11th stage. This solution can be directed to the Zn reduction of europium.

Feeds:

3rd stage - Extractant - 10 l / h;

Ammonia solution (5 ÷ 7)% NH ₄ OH - (1.7 - 2) l / h;

4th stage - REM nitrate (~ 100 g / l) - 4 l / h;

10th step-NH ₄ Cl (1N) - 10 l / h (0: 6) = (O: B = 1: 1);

15th stage - HCl (1N) - 2.7 l / h.

Expiration from the steps:

1st, 6th steps - water phase without ΣРЗМ.

11th stage - re-extract (solution of REM chlorides) Σ150 g / l.

Finished product: the resulting chloride solution in terms of dry matter contained a mass fraction of the sum of REM oxides equal to 58%, including a mass fraction of the oxides of individual REMs per 100% of the sum of REM oxides:

mass fraction of samarium oxide (Sm ₂ O ₃ ) - 22.8%;

mass fraction of europium oxide (Eu ₂ O ₃ ) - 5.7%;

mass fraction of gadolinium oxide (Gd ₂ O ₃ ) - 18.4%;

mass fraction of terbium oxide (Tb ₂ O ₃ ) - 2.1%;

mass fraction of dysprosium oxide (Dy ₂ O ₃ ) - 8.3%;

mass fraction of yttrium oxide (Y ₂ O ₃ ) - 42.7%.

The proposed method allows to obtain valuable finished products that can be returned to circulation in the metallurgical industry and widely used in other areas of chemical production, in addition, the method allows you to convert chloride solutions of rare-earth metals into nitric acid solutions of rare-earth metals, from which the conversion of rare-earth metals into solid condition with subsequent calcination of oxalates to REM oxides.

The method provides a reduction in the consumption of chemical materials, reagents, such as acids, etc. about 10 percent while increasing the efficiency of equipment by 20 percent compared with the prototype.

Claims (8)

1. A method of processing nitric acid solutions containing rare earth metals, comprising extracting rare earth metals from nitric acid solutions with an extractant to form extractable complexes and washing a saturated extract containing complexes of rare earth metals using a cascade multistage extraction process system, characterized in that a cascade multistage system is used consisting of extraction, washing and reaction parts, with each part comprising five steps respectively, moreover, a mixture consisting of versatic, TBP and diesel fuel, taken in a ratio of vol.%: 40:10:50, is fed as an extractant, and extraction is carried out in the presence of ammonia, while washing of the saturated extract is carried out from NO ₃ ions with a solution ammonium chloride with a concentration of 1N, and after washing, carry out the stage of re-extraction of the saturated extract of rare earth metals by treatment with a solution of hydrochloric acid with a concentration of 1N to obtain a solution of rare earth chlorides. 2. The method according to p. 1, characterized in that the extractant is fed to the cascade at a speed of 10 l / h in the presence of a solution of 7% ammonia. 3. The method according to p. 1, characterized in that the extractant and ammonia are fed to the third stage of the extraction part of the cascade. 4. The method according to p. 1, characterized in that the nitric acid solution of rare-earth metals is fed into the extraction part of the cascade at a speed of 4 l / h 5. The method according to p. 1, characterized in that the nitric acid solution of rare-earth metals is fed to the fourth stage of the extraction part of the cascade, and the aqueous phase without rare-earth metals is removed from the first stage. 6. The method according to p. 1, characterized in that the washing of the saturated extract from NO ₃ ions is carried out at a rate of 10 l / h at the tenth stage of the washing part of the cascade. 7. The method according to p. 1, characterized in that the processing of the saturated extract of rare-earth metals with a solution of hydrochloric acid is carried out at a speed of 2.7 l / h 8. The method according to p. 1, characterized in that the solution of rare-earth metal chlorides is withdrawn from the eleventh stage of the stripping part of the cascade without traces of NO ^- ₃ .

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