RU2437838C1 - Method of producing iridium (iii) chloride salts - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing iridium (III) chloride salts involves obtaining an iridium compound and thermal treatment thereof, characterised by that the iridium compound is obtained in form of its solution via treatment with a reducing agent in form of hydrazine chloride or oxalic acid, iridium (IV) chloride solution until achieving redox potential value (relative a silver chloride comparison electrode) equal to 450-600 mV, and the solution is then stripped to dryness; in order to obtain iridium (III) chloride hydrate, the residue from stripping the solution undergoes thermal treatment at temperature 115-130°C until a powdered product is obtained; in order to obtain anhydrous iridium (III) chloride, the residue undergoes thermal treatment at temperature 350-400°C until obtaining constant mass.

EFFECT: method of obtaining iridium chloride salts enables to obtain soluble iridium chloride salts containing crystallisation water as well as anhydrous compounds.

2 tbl

Description

The method of producing chloride salts of iridium (III) relates to the chemical and metallurgical production of platinum group metals (PGM) and their compounds.

A known method of producing iridium (III) chloride, including the deposition of a solution of iridium hydroxide from a chloride solution and its subsequent calcination in an atmosphere of chlorine containing traces of CO at temperatures up to 600 ° C in bright light with direct sunlight or a burning magnesium ribbon [1; 2]. The method adopted for the prototype.

The disadvantage of this method is the complexity of the hardware design and high safety requirements for the synthesis of compounds. This method allows to obtain only anhydrous iridium (III) chloride. In addition, it does not allow to obtain a compound of high purity, since iridium hydroxide almost always contains impurities of one or another alkali metal, depending on the composition of the alkali used.

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 iridium (III) chloride, which includes obtaining the iridium compound and its subsequent heat treatment, the iridium compound is obtained in the form of its solution by treatment with a reducing agent, which uses hydrazine chloride or oxalic acid, iridium hydrochloric acid solution (IV) to the value of the redox potential (ORP) of 450-600 mV (relative to the silver-silver reference electrode), then the solution is evaporated to dryness: for I iridium (III) chloride hydrate heat treating the precipitate from the solution is carried out at evaporation temperatures 115-130ºS to obtain a powdery product; to obtain anhydrous iridium (III) chloride, heat treatment of the precipitate is carried out at a temperature of 350-400ºС to constant weight.

The essence of the method is as follows. In the initial hydrochloric acid solution, iridium is in the oxidation state (IV). When the iridium solution is treated with a reducing agent, hydrazine chloride or oxalic acid, to an ORP value of 450-600 mV (relative to the silver-silver reference electrode), Ir (IV) is reduced to Ir (III) in accordance with chemical equations (1) and ( 2). If the ORP value is less than 450 mV (relative to the silver – silver reference electrode) in the solution, partial reduction of iridium to lower oxidation states is possible, and, accordingly, the Cl: Ir molar ratio in the obtained compound will change.

In addition, this leads to unproductive consumption of reducing agent. If the ORP value is more than 600 mV (relative to the silver-silver reference electrode), the complete reduction of Ir (IV) to Ir (III) does not occur.

Upon evaporation to dryness of a hydrochloric acid solution of iridium after a reduction treatment, a spongy precipitate of chloride salts of iridium of variable composition is formed, containing both crystallized and unbound water. During its subsequent heat treatment at a temperature of 115-130 ° C, the precipitate gradually turns into a powder of iridium (III) chloride hydrate. This is a water-soluble compound of olive-brown or olive-green color with a mass fraction of iridium of 50-56%. It is with such a mass fraction of iridium that the soluble salt of iridium (III) chloride hydrate is in demand among consumers and is widely used in various fields of engineering and technology. For each molecule of iridium (III) chloride, there are from 3 to 5 molecules of crystallization water. When the evaporation process is carried out at lower temperatures, a very hygroscopic, spreading out in air compound is obtained, the mass fraction of iridium in which is less than 50%. If the temperature during evaporation exceeds 130 ° C, the resulting iridium (III) chloride hydrate begins to lose crystallization water, due to which the salt becomes limitedly soluble in water and the mass fraction of iridium in it exceeds 56%.

In anhydrous iridium (III) chloride, the mass fraction of iridium should be at least 64%. When the chloride salt of iridium (III) is heated at a temperature below 350 ° C, crystallization water is not completely removed, and the mass fraction of iridium in the resulting salt will be less than 64%. In the case of heating at temperatures above 400 ° C, not only complete removal of moisture occurs, but also partial decomposition of the salt, associated with the loss of chloride ions, and the molar ratio Cl: Ir becomes less than 3.

Examples

Experience 1. 100 ml of a hydrochloric acid solution of iridium (IV) with a metal concentration of 100 g / l was treated with oxalic acid at a temperature of (80-90) ºС until the specified value of the redox potential was reached. Then the solution was evaporated to dryness. The resulting spongy precipitate of chloride salts of iridium was charged into the reaction flask of a rotary evaporator and heated at a given temperature to obtain a powdery product of iridium (III) chloride hydrate. In the obtained salt samples, the mass fraction of iridium and chloride ions was determined by chemical methods, and then the molar ratio Cl: Ir was calculated. The results are shown in table 1.

Experiment 2. 100 ml of a hydrochloric acid solution of iridium (IV) with a metal concentration of 100 g / l was treated with oxalic acid at a temperature of (80-90) ºС until the specified value of the redox potential was reached. Then the solution was evaporated to dryness. The resulting spongy precipitate of chloride salts of iridium was loaded into a quartz glass and heated in an oven at a given temperature to a constant weight. In the obtained samples of the anhydrous salt of iridium (III) chloride, the mass fraction of iridium and chloride ions was determined by chemical methods, and then the molar ratio Cl: Ir was calculated. The results are shown in table 1.

Experiment 3. 100 ml of a hydrochloric acid solution of iridium (IV) with a metal concentration of 100 g / l was treated with hydrazine chloride at a temperature of (80-90) ºС until the specified value of the redox potential was reached. Then the solution was evaporated to dryness. The resulting spongy precipitate of chloride salts of iridium was charged into the reaction flask of a rotary evaporator and heated at a given temperature to obtain a powdery product of iridium (III) chloride hydrate. The obtained samples were determined by chemical methods, the mass fraction of iridium and chloride ions was determined, and then the molar ratio Cl: Ir was calculated. The results are shown in table 2.

Experience 4. 100 ml of a hydrochloric acid solution of iridium (IV) with a metal concentration of 100 g / l was treated with hydrazine chloride at a temperature of (80-90) ºС to achieve a given value of the redox potential. Then the solution was evaporated to dryness. The resulting spongy precipitate of chloride salts of iridium was loaded into a quartz glass and heated in an oven at a given temperature to a constant weight. In the obtained samples of the anhydrous salt of iridium (III) chloride, the mass fraction of iridium and chloride ions was determined by chemical methods, and then the molar ratio Cl: Ir was calculated. The results are shown in table 2.

Table 1 Experience number Reducer consumption, g / 1 g Ir Heat treatment temperature, ºС AFP after recovery, mV iridium (III) chloride hydrate Mass fraction of Ir in salt,% The molar ratio of Cl: Ir in salt one 0.32 120 550 52.6 3.15 2 0.57 120 410 47.7 2.9 3 0.23 120 700 49.1 3.54 four 0.32 105 550 49.4 3.06 5 0.32 150 550 58.2 3.1 6 0.35 370 550 64.5 3.16 7 0.57 370 410 65.1 2.81 8 0.23 370 700 62.3 3.35 9 0.32 250 550 61.7 3.08 10 0.33 500 540 66.8 2.41

table 2 Experience number Reducer consumption, g / 1 g Ir Heat treatment temperature, ºС AFP after recovery, mV iridium (III) chloride hydrate Mass fraction of Ir in salt,% The molar ratio of Cl: Ir in salt one 0.12 120 530 53.1 3.2 2 0.19 120 400 49.3 2.87 3 0.07 120 700 49.6 3.64 four 0.14 105 510 49.8 3.12 5 0.14 150 520 58.6 3.21 6 0.13 370 520 64.8 3.14 7 0.20 370 400 65.0 2.9 8 0.08 370 700 62.9 3.4 9 0.14 250 520 62.2 3.1 10 0.13 500 540 67.4 2.32

As can be seen from the above examples, the use of the proposed method allows to obtain iridium (III) chloride hydrate with a mass fraction of iridium of 50-56% and iridium (III) chloride with a mass fraction of iridium of at least 64%.

Literature

1. G. Brower. Inorganic Synthesis Guide. V.5, M .: Mir, 1985, p. 1836.

2. Synthesis of complex compounds of platinum group metals. Directory. M .: Nauka, 1964, p. 206.

Claims (1)

A method of producing chloride salts of iridium (III), including the preparation of an iridium compound and its subsequent heat treatment, characterized in that the iridium compound is obtained in the form of its solution by treatment with a reducing agent, which uses hydrazine chloride or oxalic acid, iridium (IV) hydrochloric acid solution to values of the redox potential relative to the silver-silver reference electrode, equal to 450-600 mV, then the solution is evaporated to dryness: to obtain iridium (III) chloride hydrate, heat treatment of precipitates and by evaporating the solution is carried out at a temperature of 115-130 ° C to obtain a powdery product; to obtain anhydrous iridium (III) chloride, heat treatment of the precipitate is carried out at a temperature of 350-400 ° C to constant weight.