8. Platinoid separation processes

Direct leaching methods (hydrometallurgy) or after heat treatment (pyrometallurgy + hydrometallurgy) are not very or not at all selective. The result is always an aqueous solution containing platinoids, which must be separated and purified.

• Extraction of silver and gold: as in many cases, silver and gold are found together with PGMs in the aqueous solution, these two precious metals are extracted by selective precipitation before the PGMs are separated from each other. When hydrochloric attack is carried out in concentrated HCl, insoluble silver chloride is formed and collected by filtration. Unfortunately, the H[AgCl ₂ ] complex remains in solution. It is therefore preferable to lower the acid concentration in order to reduce the solubility of the silver chloride. Remaining traces of silver can...