Platinum as a Metallic Material
Precipitation of the Metallic Precursor Material
The purification of the precursor materials containing precious metals and the separation of the platinum from the other precious metals are achieved, for example, by repeated precipitation and ion exchange treatment of hydrochloric acid solutions. The result of these processes is the high purity [PtCl6]2- complex either as ammonium hexachloroplatinate, (NH4)2[PtCl6], or hexachloroplatinic acid, H2[PtCl6].
The metallic platinum is won either by precipitation from solutions of these compounds or by the thermal dissociation of the ammonium hexachloroplatinate. Precipitation from the ammonium compound is usually achieved by adding hydrazine as a reducing agent:
Hexachloroplatinic acid can be reduced directly to metallic platinum by the electrolysis of its solution in hydrochloric acid.
When heated to temperatures above about 500 , ammonium hexachloroplatinate dissociates to yield pure platinum. This process is known as calcination.
Whereas the calcination of the ammonium compound offers economic advantages on a production scale, the electrolytic reduction of hexachloroplatinic acid is preferred to an increasing extent because it does not involve the use of environmentally hazardous nitrogen compounds.