Rhodium is concentrated in mother solutions after platinum \xD0\xB8 palladium separation from hydrochloric solutions appeared after platinum processing or Cu and nickel electrochemical refining. Contaminating metals are extracted by nitration, after which rhodium chloride complexes pass into Na3[Rh(NO2)6], and precipitated by NH4Cl as (NH4)2Na[Rh(NO2)6]. It is dissolved by heating with hydrochloric acid and reduced by formic acid; heating in hydrogen at 1000°C yields rhodium sponge.
Rhodium affinage (refining) is processed by chlorine treatment of rhodium sponge which results into [Rh(NH3)5Cl]Cl2, [Rh(NH3)3Cl3], (NH4)3[Rh(SO3)3], (NH4)3[RhCl6] complexes with further roasting until rhodium sponge appears. Various extraction and ion exchange methods are used in this process. Pure rhodium sponge is smelting in induction furnaces with inert atmosphere. |