RU2329314C2 - Method of obtaining hydrated rhodium oxide (iii) - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of obtaining hydrated rhodium oxide (III) pertains to chemical and metallurgical production of platinum group metals and their compounds. The method involves treatment of a chloride solution of rhodium with an alkali until its concentration in the pulp becomes 1.0-2.0 mol/l. The pulp is subsequently heated to 85±15°C and the precipitate is separated from the master solution. Separation of the precipitate is done by repeated re-pulping of the precipitate in diluted inorganic acid and subsequent filtration.

EFFECT: obtaining a Rh₂O₃·nH₂O precipitate with low content of impurities of chloride ions from a rhodium chloride salt solution.

2 tbl, 2 ex

Description

The method of producing hydrated rhodium (III) oxide (Rh ₂ O ₃ · nH ₂ O) relates to the chemical and metallurgical production of platinum group metals (PGM) and their compounds.

A known method of producing hydrated rhodium (III) oxide [1] (rhodium (III) oxide hydrate), comprising adding a small amount of alkali to a solution of RhCl ₃ . The pink-red precipitate that first forms gradually turns into yellow Rh ₂ O ₃ · 5H ₂ O.

The disadvantage of this method is that its description does not indicate the costs of the reagents, methods of separating the precipitate formed from the mother liquor. In addition, the method provides for the preparation of hydrated rhodium (III) oxide only from a solution of simple rhodium chloride.

A known method of producing hydrated rhodium (III) oxide [2]. It includes: treatment with an alkali of an aqueous solution of Na ₃ [RhCl ₆ ] or K ₃ [RhCl ₆ ] without an excess of alkali, sedimentation of the precipitate for 12 hours and its subsequent repeated washing by decantation. This method is adopted as a prototype.

The disadvantage of this method is the lack of description of the parameter of the process for producing rhodium compounds, the long duration of the washing process by decantation. As the studies showed, when precipitating hydrated rhodium oxide without excess alkali, complete destruction of the rhodium chloride complexes cannot be achieved. In the precipitate obtained after alkaline treatment, the mass fraction of chloride ions with respect to the mass fraction of rhodium reaches several percent even after thorough washing with water.

The technical result, the achievement of which the invention is directed, is the elimination of these disadvantages.

The desired technical result is achieved by the fact that in the known method for producing hydrated rhodium (III) oxide, including treatment with an alkali of a solution of rhodium chloride, separation of the precipitate and repeated washing of the precipitate, treatment with alkali is carried out until its concentration in the pulp reaches 1.0-2.0 mol / L and is heated pulp at a temperature of 70-100 ° C, and repeated washing of the precipitate is carried out by repeated pulping of the precipitate in dilute mineral acid, followed by filtration.

The essence of the method is as follows. The alkali treatment of the rhodium chloride salt solution is carried out with a certain excess of it (1.0-2.0) mol / L. Excess alkali is introduced in order to achieve complete destruction of the rhodium chloride complexes. With an excess of alkali of less than 1.0 mol / L, the complete destruction of the rhodium chloride complexes is not achieved. The introduction of more than 2 mol / L of excess alkali leads to unproductive consumption of reagents and partial dissolution of the rhodium compound. The heating of the pulp after treatment with alkali is carried out at a temperature of (85 ± 15) ° C. At temperatures below 70 ° C, the destruction efficiency of rhodium chloride complexes is reduced. The use of temperatures above 100 ° C is complicated by the need to increase the pressure in the reaction apparatus. Repeated washing of the precipitate is carried out by repeated decomposition of the precipitate in dilute mineral acid and subsequent filtration. The mother liquor contains sodium hydroxide, which is adsorbed on a precipitate of Rh ₂ O ₃ · nH ₂ O and when pulled in water, it cannot be separated. If, for this purpose, dilute mineral acid is used (for example, H ₂ SO ₄ or HNO ₃ ), then NaOH is converted into soluble salts of such acids and removed with a washing solution during filtration.

EXAMPLES

Example 1

To obtain hydrated rhodium (III) oxide, 3 samples of a solution of Na ₃ [RhCl ₆ ], each 200 ml in volume, were taken. The rhodium concentration in the solutions was 0.3 mol / L. The samples were treated with a solution of sodium hydroxide to a specified excess alkali, the pulp was heated at a temperature of 90 ° C for one hour, and the hydrated rhodium oxide was filtered. Then, 20 g of the precipitate from each sample was pulped into 100 ml of a 0.1 m sulfuric acid solution, the pulp was heated at a temperature of 90 ° С for 60 minutes and filtered. The operation was repeated 4 times with the replacement of the wash solution. In all washing solutions, after the fourth washing, a qualitative reaction to Cl ^- (by the addition of a solution of silver nitrate) gave a negative result. The washed Rh ₂ O ₃ · nH ₂ O was dissolved in sulfuric acid and the mass fraction of sodium and chlorine ions relative to rhodium was determined in the resulting solution (see Table 1).

Table 1 Experience number The concentration of NaOH in the pulp, mol / l Mass fraction of impurities in Rh ₂ O ₃ · nH ₂ O with respect to Rh,% Na ⁺ Cl ^- one 0.1 0.03 3.40 2 1.5 0.04 0.22 3 3.0 0.06 0.18

In experiments No. 2 and No. 3, the mass fraction of chloride ions is significantly less than in experiment No. 1. This quality of hydrated rhodium (III) oxide, as a rule, suits consumers.

Example 2

To obtain hydrated rhodium (III) oxide, 2 samples of a solution of Na ₃ [RhCl ₆ ], each 200 ml in volume, were taken. The rhodium concentration in the solutions was 0.3 mol / L. The samples were treated with sodium hydroxide solution until the alkali concentration in the pulp was equal to 1.5 mol / L, the pulp was kept for a certain time at a given temperature and the hydrated rhodium oxide was filtered. Then, 20 g of the precipitate from each sample was pulped in 100 ml of a 0.1 m nitric acid solution, the pulp was heated at 90 ° C for 60 minutes and filtered. The operation was repeated 4 times with the replacement of the wash solution. In all washing solutions, after the fourth washing, a qualitative reaction to Cl ^- (by the addition of a solution of silver nitrate) gave a negative result. The washed Rh ₂ O ₃ · nH ₂ O was dissolved in nitric acid and the mass fraction of sodium and chlorine ions relative to rhodium was determined in the resulting solution (see Table 2).

table 2 Experience number T, ° С Mass the proportion of impurities in Rh ₂ O ₃ · nH ₂ O with respect to Rh,% Na ⁺ Cl ^- one 80 0.04 0.25 2 thirty 0.07 3.3

Literature

1. I.A. Fedorov. Rhodium. M .: Nauka, 1966, p. 49.

2. G. Brauer, F. Weigel and others. Guide to inorganic synthesis. T.5. Per. from German / ed. G. Brauer. - M .: Mir, 1985.S. 1841-1842.

Claims (1)

A method of obtaining hydrated rhodium (III) oxide, including treatment with an alkali of a solution of rhodium chloride salt, separation of the precipitate and repeated washing of the precipitate, characterized in that the treatment with alkali is carried out until its concentration in the pulp reaches 1.0-2.0 mol / l and the pulp is heated at a temperature of 70-100 ° C, and repeated washing of the precipitate is carried out by repeated decomposition of the precipitate in dilute mineral acid, followed by filtration.