9. Purification processes for separated metals

Conventional dissolution-precipitation methods are well suited to the treatment of small quantities of material, and have the advantage of being reversible in the event of failure. However, they are often supplemented by the use of selective solvents and resins.

• Platinum: it is possible to purify (NH ₄ ) ₂ [PtCl ₆ ] by numerous successive crystallizations, but large quantities of water are required for solution. The low solubility of the precipitate can be improved by operating above 100 ˚C and under a pressure of at least 2 bar. But the most effective method is to carry out oxidative hydrolysis of the accompanying platinoids at 90 ˚C and in a slightly acidic or neutral medium. The hydroxocomplexes and oxyhydrates...