RU2404129C2 - Method of obtaining yellow rhodium sulphate powder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: rhodium sulphate solution is obtained from its chloride solution, from which rhodium hydroxides are precipitated by adding an ammonia solution. The obtained rhodium hydroxides are washed and then dissolved in sulphuric acid. The rhodium hydroxides are dissolved in molar ratio Rh : H₂SO₄ = (1 : 6) - (1 : 16) and at reaction temperature of 5-20 °C. The obtained reaction mixture is held at room temperature for not less than 20 hours and the rhodium salt formed is separated from the mother solution and dried.

EFFECT: invention enables to obtain yellow rhodium sulphate powder having high rhodium output (up to 39,8 wt %).

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Description

The method for producing rhodium sulfate powder relates to the chemical and metallurgical production of platinum group metals (PGM) and their compounds.

A known method of producing a powder of rhodium sulfate, including precipitation of barium water from a solution of rhodium trichloride - rhodium oxide (III) hydrate, dissolving rhodium oxide (III) hydrate in dilute sulfuric acid, filtering off the insoluble precipitate, evaporating the aqueous solution first in a water bath and then to dryness in vacuum over sulfuric acid to form a red powder of rhodium sulfate [1].

The disadvantages of the method include: the duration of the process of obtaining salt by this method, the heterogeneity of the compounds in chemical composition and size.

A known method of producing rhodium sulfate powder, including obtaining the initial cake by heat treatment of a mixture of rhodium powder with barium peroxide, leaching the cake in dilute sulfuric acid, treating the pulp with a solution of hydrogen peroxide, separating the precipitate of barium sulfate, adjusting the pH to 1.0-3.0, separating the precipitate and evaporating solution in a rotary evaporator at a temperature of (120-160) ° C to obtain dry salt [2].

The disadvantages of the method: the long duration of the process of obtaining the target product, the formation of the "red" form of the sulfate salt of rhodium, the basis of which are polymer forms unsuitable for the preparation of electrolytes.

A known method of producing rhodium sulfate, including obtaining a sulfate solution of rhodium from chloride, precipitation of rhodium hydroxides by adding an ammonia solution, washing rhodium hydroxides and their subsequent dissolution in sulfuric acid [3]. This method is the closest in technical essence to the claimed method and adopted as a prototype.

The disadvantages of the method include the fact that it does not allow to obtain a powder of rhodium sulfate. In addition, as shown by the results of physicochemical research methods, in the resulting sulfate solution, rhodium is not only in the form of [Rh (H ₂ O) ₆ ] ₂ (SO ₄ ) ₃ · nH ₂ O (yellow rhodium sulfate), but also in the form of dimers, trimers, and other polymeric compounds.

The technical result, which the invention is directed to, is to obtain a yellow rhodium sulfate powder.

The desired technical result is achieved by the fact that in the claimed method for producing a powder of yellow rhodium sulfate, including obtaining a sulfate solution of rhodium from its chloride solution, precipitation of rhodium hydroxides by adding an ammonia solution, washing rhodium hydroxides and their subsequent dissolution in sulfuric acid, dissolving rhodium hydroxides is carried out at molar the ratio of Rh: H ₂ SO ₄ = 1: 6-1: 16 and a temperature of 5-20 ° C, while the resulting reaction mixture was kept at room temperature for at least 20 hours, and the resulting The ol rhodium is separated from the mother liquor and dried.

The essence of the method is as follows. Upon dissolution of rhodium hydroxides in sulfuric acid, solutions are formed containing sulfate complexes of various compositions, and depending on the dissolution conditions, both the composition of the complexes and their ratio change. Rhodium sulfate is widely used for the preparation of rhodium electrolytes. It is known that galvanic coatings of higher quality are obtained if the so-called yellow rhodium sulfate [Rh (H ₂ O) ₆ ] ₂ (SO ₄ ) ₃ · nH ₂ O is used for the preparation of the electrolyte. The presence of other sulfate forms in the solution usually has a negative effect.

It was experimentally found that if the dissolution of rhodium hydroxides in sulfuric acid is carried out under cooling, without allowing the reaction mixture to be heated above 20 ° C, and the molar ratio Rh: H ₂ SO ₄ = 1: 6-1: 16, then from the resulting solution some time the yellow salt begins to precipitate. If the dissolution process is carried out at a temperature above 20 ° C, then the salt yield decreases or it does not form at all. Cooling the reaction mixture below 5 ° C is impractical, since it requires the use of special expensive equipment. Compliance with a molar ratio of Rh: H ₂ SO ₄ ensures optimal product yield. At a molar ratio of Rh: H ₂ SO ₄ less than 1: 6, the yield of yellow rhodium sulfate powder is also significantly reduced. The increase in the molar ratio of Rh: H ₂ SO ₄ more than 1:16 leads to unproductive consumption of acid and does not have a positive effect on increasing the yield of the desired product. A similar situation is with the duration of exposure of the reaction mixture. After dissolving the rhodium hydroxides in sulfuric acid, in order to achieve the maximum possible yield of the target product, it is necessary to withstand the reaction mixture for a certain time at a given temperature. Studies have shown that the reaction mixture must be maintained for at least 20 hours. A shorter reaction time leads to a decrease in salt yield, and a longer one practically does not increase this indicator.

Special studies were carried out of the obtained rhodium compound after its separation from the mother liquor, as well as the mother liquors. The chemical forms of rhodium were studied by NMR ¹⁰³ Rh and ¹⁷ O. For research, the salt was transferred into solution. It was found that rhodium in the salt solution exists in the form of the ion pair {[Rh (H ₂ O) ₆ ] ³⁺ · SO ₄ ^2- } ⁺ . In the solid phase, the salt is [Rh (H ₂ O) ₆ ] ₂ (SO ₄ ) ₃ · nH ₂ O (n = 3-5). It was found that the polymer forms of rhodium in this compound are about 1%. In the mother liquor, on the contrary, a whole set of different polymer forms of rhodium was found.

The same method was used to study the chemical forms of rhodium in a sulfate solution obtained by the prototype method. It turned out that in it only (20-40)% of rhodium is in the form {[Rh (H ₂ O) ₆ ] ³⁺ · SO ₄ ^2- } ⁺ , the rest in the form of various polymeric sulfate compounds.

Thus, the proposed method allows to separate the monomeric form of the sulfate complex of rhodium from the polymer to obtain a powder of yellow rhodium sulfate.

Examples

To obtain a powder of rhodium sulfate, we took several samples of sulfate solutions weighing 100 g with a rhodium content of 7.47% each. The solutions were treated with ammonia to a pH of 6-8, the obtained hydroxides were separated from the mother liquor by filtration, washed with water and dissolved in a predetermined volume of concentrated sulfuric acid while cooling to 15.40 and 60 ° C. The resulting reaction mixture was aged 10-40 hours and then filtered. The salt was washed with ethyl alcohol and weighed. The yield of rhodium sulfate powder was determined. The results are presented in table 1.

Table 1. The dissolution conditions GO rhodium The output of Rh in the powder of rhodium sulfate,% The molar ratio of Rh: H ₂ SO ₄ The duration of exposure of the pulp, hour Temperature ° C 1: 4.5 24 fifteen 16.7 1: 6 38.6 1: 9 37.9 1:16 39.8 1:18 38.1 1:16 10 19.2 40 38.9 1: 9 thirty 40 16.5 60 Salt does not form

Information sources

1. I.A. Fedorov. Rhodium. M .: Nauka, 1966, p. 53.

2. Patent No. 2296713 (Russia). A method of producing a powder of rhodium sulfate / Ilyashevich V.D., Pavlova E.I.

3. V.I. Liner. Modern electroplating. M .: Metallurgy, 1967, p. 349.

Claims (1)

A method of obtaining a powder of yellow rhodium sulfate, including obtaining a sulfate solution of rhodium from its chloride solution, precipitation of rhodium hydroxides by adding an ammonia solution, washing rhodium hydroxides and their subsequent dissolution in sulfuric acid, characterized in that the dissolution of rhodium hydroxides is carried out at a molar ratio of Rh: H ₂ SO ₄ = (1: 6) - (1:16) and the temperature of the reaction mixture 5-20 ° C, the resulting reaction mixture was kept at room temperature for at least 20 hours, and the resulting rhodium salt was separated from the mother liquor ora and dried.