RU2254391C1 - Method of production of metallic thallium - Google Patents

Abstract

FIELD: separation and cleaning of metallic thallium, isotope-enriched thallium inclusive.

SUBSTANCE: contaminated metallic thallium is dissolved in diluted nitric acid for obtaining concentrated solution of thallium sulfate; then, solution is cleaned from admixtures and thallium halogenide is settled for subsequent dissolving in sulfuric acid and electroevolution of thallium from cleaned solution Tl₂SO₄ is performed. Solution obtained during dissolving of metal in diluted nitric acid is neutralized with ammonia to pH 11 and thallium iodide is settled from it. Concentrated solution of thallium sulfate is obtained through dissolving settled thallium iodide in sulfuric acid at heating. Solution thus obtained is cleaned from admixtures by settling of lead in form of its sulfide and iron and chromium in form of hydroxides. Thallium halogenide is settled in form of iodide from solution neutralized by ammonia to pH 10-11. Thallium iodide is settled from solutions at concentration of thallium of 1-4 g/l, lead is separated from solution at concentration of thallium of 60-80 g/l, iron and chromium are separated from solution at concentration of 20-40 g/l and electroevolution is performed from solution at concentration of 75-85 g/l.

EFFECT: possibility of obtaining degree of thallium purity of 99,9995% at minimum losses at all stages of chemical treatment.

2 cl, 5 ex

Description

The invention relates to the field of isolation and purification of thallium, including isotope-enriched obtained by electromagnetic separation.

A known method of extracting thallium from complex production solutions (RF patent No. 161491), comprising adding chlorine and an oxidizing agent to the initial solutions of the addend, followed by precipitation of thallium with a 1-1.5% aqueous solution of methyl violet.

The disadvantage of this method is the use of inaccessible reagent, as well as the complexity of further processing of the obtained precipitate.

There is also known a method of extracting thallium from sulfuric acid solutions with an extractant synthesized from isooctyl alcohol and metallic iodine (RF patent No. 169794).

The disadvantage of this method is the impossibility of obtaining a pure product and the complexity of further processing of the concentrate.

Closest to the claimed technical solution is a method for purifying thallium metal, which includes dissolving contaminated metal in dilute nitric acid, obtaining a concentrated solution of thallium sulfate by treating a solution of thallium salt with sulfuric acid when heated, purifying the solution from impurities by separating lead in the form of sulfate, followed by recovery of small amounts of the resulting thallium (III) salts of sulfur dioxide, repeated deposition of thallium in the form of the TlCl halide and electrolytic separation the removal of thallium from a purified solution of Tl ₂ SO ₄ (Manual on Preparative Inorganic Chemistry, edited by G. Bauer, Publishing House of Foreign Literature, M., 1956, p. 409).

The main disadvantage of this method when using it to obtain expensive isotope-enriched thallium is that it does not provide the allocation of thallium without significant losses. It was experimentally established that with a single deposition of TlCl, thallium losses are 10-15%.

In addition, when using this method requires additional operations to restore the oxidized Tl (III) to Tl (I).

The disadvantage of this method should also include the fact that it does not provide the necessary degree of purification of thallium from certain impurities, in particular copper and silver.

An object of the invention is to obtain pure metal thallium, including isotope-enriched, with minimal losses at all stages of chemical processing.

This object is achieved by the fact that the contaminated metal-metal thallium is dissolved in diluted nitric acid, a concentrated solution of thallium sulfate is obtained, the solution is purified from impurities, thallium halide is precipitated, followed by its dissolution in sulfuric acid, and thallium is electrolytically separated from the purified solution of Tl ₂ SO ₄ . The solution obtained by dissolving the metal in dilute nitric acid is neutralized with ammonia to pH 11 and thallium iodide is precipitated from it. Obtaining a concentrated solution of thallium sulfate is carried out by dissolving the precipitated thallium iodide in sulfuric acid when heated. Purification of the resulting solution from impurities is carried out by deposition of lead in the form of its sulfide, and iron and chromium in the form of hydroxides. Thallium halide is precipitated as iodide from a solution neutralized with ammonia to pH 10-11. In this case, thallium iodide is precipitated from solutions with a thallium concentration of 1-4 g / l, lead is separated from a solution with a thallium concentration of 60-80 g / l, iron and chromium from a solution with a thallium concentration of 20-40 g / l, and electrolytic the selection is carried out from a solution with a concentration of thallium 75-85 g / l.

In the claimed technical solution, the proposed method for the preliminary precipitation of thallium iodide allows practically without loss to concentrate thallium contained in the nitric acid solution, while reducing oxidized Tl (III) to Tl (I) and at the same time ensure the separation of the main amount of impurities soluble in ammonia medium. The proposed method for purification of a solution of thallium sulfate by sequential separation of impurities in the form of sulfides and hydroxides, as well as the precipitation of thallium iodide, provides a high degree of purification of the solution of Tl ₂ SO ₄ with minimal losses at all stages of chemical processing.

The analysis of publicly available sources of information on the prior art did not allow to identify a technical solution identical to the declared one, on the basis of which a conclusion is made about the unknownness of the latter, i.e. compliance presented in this application of the invention with the criterion of "novelty."

A comparative analysis of the claimed solution with known technical solutions revealed that the presented set of distinctive features is not known to a person skilled in the art and does not follow explicitly from the prior art, on the basis of which it is concluded that the invention presented in this application meets the criterion of "inventive step" .

The proposed method for producing pure metallic thallium was implemented as follows.

Example 1

10 g of metallic thallium containing about 10% impurities, including copper, iron, chromium, lead, silver, calcium, nickel, sodium, etc., were dissolved in nitric acid (1: 3) with heating. The resulting solution was diluted with distilled water to a thallium concentration of 1 g / L and neutralized with ammonia to pH 11. In this case, the copper impurity formed a soluble copper-ammonia complex. The solution was heated to 50 ° C and potassium iodide was added at the rate of 0.81 g KI per 1 g Tl and an excess of 10 g / L. The solution with the precipitate was heated at 70 ° C and stood for 10-14 hours. The TlI precipitate was filtered off and washed with wash liquid. The filtrates were analyzed for thallium content. It was 1.5 mg / L. The TlI precipitate was dried at 110-120 ° C and dissolved in H ₂ SO ₄ (1: 1) by heating until the iodine vapor was completely distilled off. The resulting solution was cooled, diluted with distilled water to a thallium concentration of 60 g / L, heated to 80 ° C and precipitated sulfides of impurities Pb, Cu, Ag. The precipitate was filtered off, washed, dried at 100-120 ° C and analyzed for thallium content. It amounted to 0.45%. The filtered solution of TL ₂ SO _{4 was} diluted to a thallium concentration of 20 g / L, boiled to remove H ₂ S vapor and cooled to 40-45 ° C. The solution was neutralized with ammonia to pH 9-10 and hydroxides of iron and chromium impurities precipitated. After 8-10 hours of aging, the hydroxide precipitate was filtered off, washed, dried at 110-120 ° C and analyzed for thallium content. It amounted to 0.62%. The filtered solution of thallium sulfate was diluted with water to a thallium concentration of 1 g / L, neutralized with ammonia to a pH of 10-11, and thallium iodide was precipitated as described above. The TlI precipitate was filtered off, washed and dried at 110-120 ° C. The filtrate was analyzed for thallium content. It was 1.3 mg / L.

The TlI precipitate was dissolved in H ₂ SO ₄ (1: 1) by heating until the iodine vapor was completely removed. A solution of Tl ₂ SO _{4 was} diluted with distilled water to a thallium concentration of 75 g / l and an electrolytic isolation of thallium metal was performed at a current density of 3-5 A / cm ² .

The resulting metal was washed with deionized water, dried with filter paper at room temperature and analyzed for impurities by a mass spectral method. The total content of impurities of 71 elements amounted to 0.0001%. Loss of thallium during purification was 1.3%.

Example 2

Metallic thallium was isolated as in Example 1, but thallium iodide was precipitated from a solution with a concentration of 4 g / l, sulfides were precipitated from a solution with a thallium concentration of 80 g / l, precipitation of iron and chromium hydroxides from a solution with a thallium concentration of 40 g / l, and the electrolytic separation of metallic thallium - from a solution with a concentration of thallium 85 g / l.

The thallium content in iodide filtrates was <0.1 mg / L, the thallium content in sulfide sludge was 0.82%, and the thallium content in hydroxide sludge was 1.10%. The total impurity content in metallic thallium was 0,0009%. Loss of thallium during cleaning amounted to 0.5%.

Example 3

Metallic thallium was isolated as in Example 1, but thallium iodide was precipitated from a solution with a concentration of 0.5 g / l, impurity sulfides were precipitated from a solution with a thallium concentration of 55 g / l, and iron and chromium hydroxides were precipitated from a solution with a thallium concentration 15 g / l, and the electrolytic separation of thallium metal from a solution with a thallium concentration of 70 g / l. The thallium content in iodide filtrates was 6.3 mg / L, the thallium content in sulfide sludge was 0.24%, and the thallium content in hydroxide sludge was 0.32%. The impurity content in metallic thallium was 0.018%, including 0.004% Pb, 0.012% Cu and 0.005% Ag. Loss of thallium during purification was 1.7%.

Example 4

Metallic thallium was isolated as in Example 1, but thallium iodide was precipitated from a solution with a thallium concentration of 5 g / l, impurity sulfides from a solution with a thallium concentration of 85 g / l, iron and chromium hydroxides from a solution with a thallium concentration of 45 g / l and the electrolytic separation of thallium metal from a solution with a thallium concentration of 80 g / l.

The thallium content in iodide filtrates was <0.1 mg / L, the thallium content in sulfide sludge was 0.77%, and the thallium content in hydroxide sludge was 1.35%. The content of impurities in metallic thallium was 0.002%. The loss of thallium during purification was 3.5%.

Example 5

The production of thallium metal was carried out but the "Guide to Preparative Inorganic Chemistry" edited by G. Brower, Publishing House of Foreign Literature, M., 1956, selected as the closest technical solution.

10 g of thallium, containing about 10% of impurities, was dissolved in nitric acid (1: 3) with heating. To the resulting solution was added 4 ml of H ₂ SO ₄ (the excess of sulfuric acid was ~ 15%) and heated until the complete removal of the nitric acid vapor and the beginning of the release of sulfuric acid vapor. The solution was cooled, diluted with water to a thallium concentration of 50 g / L and the precipitate of lead sulfate was filtered. The precipitate was washed with water. SO ₂ gas was passed into the filtered thallium sulfate solution for an hour to reduce oxidized Tl (III) to Tl (I).

The Tl ₂ SO ₄ solution was diluted with distilled water to a thallium concentration of 20 g / L, heated to boiling, and 0.025 ml of HCl was added with constant stirring until the TlCl precipitation was complete. The solution with the precipitate was cooled to room temperature, the TlCl precipitate was filtered off, washed with distilled water and dried at 110 - 120 ° C. The TlCl precipitate was dissolved in H ₂ SO ₄ (1: 1) with heating, and TlCl was re-precipitated as described above. The hydrochloric acid filtrates were combined and analyzed for thallium content. It amounted to 2.23 g / l.

Dried thallium chloride was treated with H ₂ SO ₄ (1: 1) while heating to completely remove the HCl vapors. Electrolytic isolation of thallium metal was carried out from a solution with a thallium concentration of 20 g / l, at a current density of 3-5 A / cm ² . The resulting metal was washed with deionized water, dried with filter paper and analyzed for impurities. It amounted to 0.031%, including 0.008% Pb, 0.011% Ag and 0.009% Cu. Loss of thallium during cleaning amounted to 12.8%.

The results showed that when using the known technical solution, compared with the proposed one, the thallium losses during the cleaning of the thallium sulfate solution significantly increased and the chemical purity of the obtained metal decreased, which is especially unacceptable in the production of isotopically enriched metal thallium.

The proposed method for producing pure metallic thallium has been tested in the production of stable isotopes. It allowed to isolate isotopically enriched thallium-203 in the form of a metal with a purity of 99.9995%. Losses during cleaning amounted to 0.4%.

The developed method allows the use of standard equipment and available reagents, does not require large energy consumption. The method is also suitable from an environmental point of view, since the resulting alkaline filtrates are neutralized by an acid solution, and iodine vapors are trapped by a trap.

Claims (2)

1. A method of producing thallium metal, including dissolving a contaminated metal in dilute nitric acid, obtaining a concentrated solution of thallium sulfate, purifying the solution from impurities, precipitating thallium halide with its subsequent dissolution in sulfuric acid and electrolytic isolation of thallium from a purified solution of Tl ₂ SO ₄ , characterized the fact that the solution obtained by dissolving in dilute nitric acid is neutralized with ammonia to a pH of 11 and thallium iodide is precipitated from it, obtaining a concentrated solution with thallium ulphate is carried out by dissolving the precipitated thallium iodide in sulfuric acid when heated, the resulting solution is purified from impurities by precipitation of lead in the form of its sulfide, and iron and chromium in the form of hydroxides, thallium halide is precipitated in the form of iodide from neutralized with ammonia to pH 10-11 solution . 2. The method according to claim 1, characterized in that thallium iodide is precipitated from solutions with a thallium concentration of 1-4 g / l, lead deposition is carried out from a solution with a thallium concentration of 60-80 g / l, iron and chromium from a solution with a concentration thallium 20-40 g / l, and electrolytic separation is carried out from a solution with a concentration of thallium 75-85 g / l.