DD274142A3 - PROCESS FOR THE PREPARATION OF HEXACHLORIRIDIUM (IV) ACID - Google Patents

Abstract

In accordance with the method, a precipitated Diammoniumhexachloriridat (IV), which was obtained from an iridium-containing solution loaded with accompanying elements, suspended in a preferably hydrochloric solution and dissolved by adding a reducing agent under special conditions. The solution is given to an acidic cation exchanger, followed by the addition of an oxidizing agent, the iridium content to H2IrCl6 reacted, and volatile components are removed from the solution. The process ensures, according to the objective, the production of a pure H2IrCl6 solution with readily available means and high reproducibility.

Description

Field of application of the invention

The invention relates to a process for the preparation of pure, salt-free Hexachloriridium (IV) acid (H ₂ IrCl ₆ ). This is particularly used for the preparation of catalysts containing elemental iridium as the active ingredient.

Characteristic of the well-known technical solutions

For the preparation of H ₂ IrCl ₆ several methods have become known:

The digestion of elemental iridium with chlorine in the presence of anhydrous barium chloride. The resulting BaIrCl ₆ is reacted with the stoichiometric amount of sulfuric acid to H ₂ IrCl ₆ , the precipitated barium sulfate is separated by filtration.

A variant of this method is to convert elementary iridium by melting with barium peroxide in iridium (IV) oxide, to convert this with hydrochloric acid to H ₂ IrCl ₆ and again precipitate barium using sulfuric acid as barium sulfate.

From solutions containing iridium in the form of its compounds, insoluble iridium oxide hydrate is precipitated by alkalis, this is washed out several times and then reacted with hydrochloric acid to H ₂ IrCl ₆ .

(Gmelin: Handbuch der anorganischen Chemie, System No. 67, Ir, Verlag Chemie 1939, pp. 64-65; I.I.Öernjaev: Synthesis of Complex Compounds of Platinum Metals, Verlag Nauka, Moscow 1964.)

- In solution of iridium compounds in the presence of nitric acid by means of ammonia in a multi-stage process, an unspecified complex lridiurn (IV) hydroxide precipitated, this is washed and reacted with hydrochloric acid to H ₂ IrCl ₆ . The final product then contains about 0.05% sodium chloride (DE-OS 1,964,554).

The sparingly soluble (NH ₄ I ₂ IrCl _{6 is} precipitated from dissolved iridium compounds by means of ammonium chloride

* Ammonium ions are then destroyed by oxidation, either by boiling for several hours with a mixture of hydrochloric acid or nitric acid, or by reacting with chlorine gas at temperatures <4 ° C. (Brauer: Handbook of Preparative Inorganic Chemistry, Stuttgart 1981, Vol. 3, p. 1375.)

The disadvantages of these methods are that

- The digestion with barium peroxide or chloride requires expensive chemicals and the complete separation of finely divided BaSO ₄ precipitate is known to be expensive. Furthermore, there is no separation of accompanying elements;

in the case of oxide hydrate precipitation, it is virtually impossible to remove the entrained salts by washing out, so that H ₂ IrCl ₈ can contain up to 10% sodium chloride, and all accompanying elements which form poorly soluble oxide hydrates;

- The precipitation of a complex lr (IV) hydroxide despite cumbersome operation does not lead to a salt-free, pure product;

- The oxidative destruction of the ammonium from the intermediate (NH ₄ J ₂ IrCl _{6 is} cumbersome and dangerous because under certain conditions explosive Chlorstickstoifvorbindungen can form.

Object of the invention

The object of the invention is to develop a process for the preparation of salt-free, pure Hexachloriridium (IV) acid while avoiding listed deficiencies.

Explanation of the essence of the invention

The invention has for its object to develop a process for the preparation of H ₃ IrCl ₆ high purity using ion exchangers.

According to the invention, the object is achieved by initially precipitating in a known manner from an iridium-containing solution by means of ammonium chloride (NH ₄ I ₂ IrCl _{6 ),} thereby achieving concentration of the iridium and a preliminary separation of interfering components, for example alkali metal salts. By removing the mother liquor by washing in a known manner, the wet precipitate is suspended and dissolved by the action of a reducing agent to convert (NH ₄ I ₂ IrCl ₆ to slightly soluble Ir (III) compounds.) This reducing agent must be so obtained that it converts Ir (IV) rapidly and completely into Ir (III), but does not interfere with the further stages of the process, by forming iridium complexes with the reagents introduced or by introducing unwanted components and readily available reducing agents under suitable reaction conditions with respect to Aci di, t and temperature of the solution used. Preferably suitable are SO ₂ at C _{l) C} | · = 0.05-0.1 M, room temperature; Oxalic acid or ammonium oxalate at C _HC i = 0.05-0.1 M; 80-9O ⁰ C; Hydroxalaminhydruchlorid at C _Ha = 0.1-0.5M, 6O ⁰ C. Under these conditions, Ir (IV) is converted quickly (S 30 min) in Ir (III), without causing an interfering reaction of the iridium with the reducing agent. The iridium (III) is present in solution as a mixture of different chloro / aquo complexes. Subsequently, the resulting solution is passed through a column which is filled with a strongly acidic cation exchanger, preferably based on a crosslinked polystyrene having sulfonic acid groups, in the H ⁺ -form. As a result, the NH ₄ ⁺ ions and other cations present, such. As alkali ions, quantitatively separated. It has also been found that impurity components, such as iron and other heavy metal ions, are also completely retained. Iridium remains almost completely in the passing solution and is a complex acid of general composition H _n [M ¹¹¹ Ol _x (H ₂ OIy (OH) ₇ ] VOr. It has been found that checking for the desired final form certainly achieves H ₂ IrClg If the solution is highly saline, ie contains at least 4M HCI, preferably 6M HCl, and an oxidizing agent is used which does not introduce any undesirable components Preferably hydrogen peroxide or chlorine was used. Heating with an excess of oxidizing agent all III) is converted into Ir (IV) and excess reducing agent is destroyed without residue, then the excess hydrochloric acid and the oxidizing agent are removed by evaporation, conveniently in vacuo, and a solution of H ₂ IrCl ₆ in the desired concentration is obtained.

embodiment

The invention will be explained with reference to eir.es embodiment. From a solution of the composition (in g / l) 50 Ir; 22 NaCl; 0.8 Fe; 0.4 Cu; 0.4Zn, which originates from other process stages, for example from the extractive workup of the Pt metals, is precipitated with NH ₄ Cl in a known manner, the black compound (NH ₄ I ₂ IrCl ₆ ("Iridiumsalmiak"), filtered off and washed with dilute NH ₄ CI solution washed several times. the wet precipitate is transferred to a suitable vessel and conc there with about 151 water, the 80-100ml. hydrochloric acid was added, slurried. For this purpose, 300 g of oxalic acid dissolved in water was added (about 1.3 times The mixture is heated with stirring to 80-90 ° C. After a short time, the entire precipitate is dissolved, allowed to cool, filtered and this iridium-containing reading is passed through an acid filled with about 18% of the strongly acidic cation exchanger Wofatit KPS and which is present by conventional treatment with hydrochloric acid in the H ⁺ form, run at a moderate flow rate.Then, the column is for displacement of the in the chenvolumen the column iridium-containing solution with water washed until colorless. The combined iridium-containing solution is salt-free, is largely evaporated and with the same volume of conc. Hydrochloric acid added. In the thus obtained about 6M hydrochloric acid solution, either chlorine is passed or it adds about öOml 30% H ₂ O ₂ per 11 solution. This mixture is heated for 1.5 h and added again after cooling with oxidizing agent. Subsequently, the excess of hydrochloric acid and of the oxidizing agent is distributed under vacuum by evaporation and the concentration of pure iridium chloroauric acid is adjusted by concentration.

The method is simple to perform and provides reproducible results with high reliability. Using cheap and readily available chemicals, a high yield of pure HjlrCle-containing final solution is obtained, which, based on the iridium content, contains impurities of more than 0.01% NaCl, Fe, Cn, Zn. This will provide a product that guarantees the production of high quality catalysts.

Another advantage is that dals can be used with any excess of reducing or oxidizing agents, whereby high expenses for content determination and dosage are not required.

Claims (10)

1. A process for the preparation of Hexachloriridium (IV) acid from an iridium-containing solution by precipitation of DiammoniumhexachloriridatllV), separation and washing of the precipitate and conversion to H ₂ IrCl ₆ , characterized in that the largely free from the residual Diammoniumhexachloriridat (IV) - Precipitate is suspended and dissolved by addition of a reducing agent in the form of an iridium (ill) compound and the solution is fed to a strongly acidic cation exchanger, that the iridium-containing continuous solution is adjusted to at least 4M HCl and receives an addition of an oxidizing agent and that from the final solution volatile components are removed. 2. The method according to claim 1, characterized in that sulfur dioxide, oxalic acid, ammonium oxalate or hydroxylamine hydrochloride are used in stoichiometric excess as the reducing agent. 3. The method according to claim 1 and 2, characterized in that the Diammoniumhexachloriridat (IV) precipitate is suspended in a 0.05 to 0.1 molar hydrochloric acid and reductively dissolved by introducing SO ₂ at room temperature. 4. The method according to claim 1 and ?, Characterized in that the Diammoniumhexachloriridat (IV) precipitate in a 0.05 to 0.1 molar hydrochloric acid and dissolved by addition of Oxalsäuru or ammonium oxalate at 80 to 90 ⁰ C reductively. 5. The method according to claim 1 and 2, characterized in that the Diammoniumhexachloriridat (IV) precipitate in an O, 01-bisO, 5molaren hydrochloric acid and dissolved by addition of hydroxylamine hydrochloride at 50 to 80 ⁰ C reductively. 6. The method according to claim 1, characterized in that a cation exchanger based on a crosslinked polystyrene having sulfonic acid groups is used. 7. A method claim 1, characterized in that in the iridium-containing solution after passing through the cation exchanger, a content of 6M HCl is set. 8. The method according to claim 1, characterized in that hydrogen peroxide or chlorine gas are used in stoichiometric excess as the oxidizing agent. 9. The method according to claim 1 and 8, characterized in that the oxidant-containing solution is kept at boiling heat for at least 1 hour. 10. The method according to claim 1, characterized in that removed by evaporation under vacuum from the final solution of volatile components and the content of H ₂ IrCl ₆ are adjusted to the desired concentration.