Purification of zinc sulfate solutions from chloride using extraction with mixtures of a trialkyl phosphine oxide and organophosphorus acids

Chloride stripping from the zinc extract is carried out with alkaline solutions (NaOH). The separation of chloride and zinc occurs at a final pH value of the strip liquors of 6-7 under which conditions chloride almost completely pass into the aqueous phase, while zinc remains in the organic phase forming zinc dialkylphosphinate. Thus the mixtures of TRPO with CYANEX 272 advantageously differ from the extraction systems containing TRPO alone wherefrom acceptable chloride stripping is not possible. Zinc stripping from the organic phase is carried out with a sulfuric acid solution.