The role of liquid membranes in the selective separation and recovery of zinc for the regeneration of Cr(III) passivation baths

This work aims at the separation of the metallic impurities, namely Zn2+ and Fe3+, from trivalent chromium spent passivation baths used in the galvanic industry by means of selective liquid membranes as an efficient and necessary step in the regeneration of the baths for their useful life extension. A Liqui-Cel hollow fiber membrane contactor separated the spent bath from an emulsion phase constituted of an organic liquid membrane consisting of Cyanex®272, kerosene and 1-decanol and an acidic receiving solution. Real spent passivation baths were used as feed solutions, with complex composition, being the main metallic content: Cr3+ (4500–9350 mg L−1), and Zn2+ (2500–11,780 mg L−1) and Fe3+ (20–93 mg L−1) as tramp ions. The influence of different operational variables on the kinetics of the separation of zinc and chromium as well as on the enrichment of zinc over iron and chromium in the stripping phase was investigated. The variables under study were the pH of the feed mixture, the initial zinc concentration, the carrier concentration in the liquid membrane, and the type and concentration of acid, hydrochloric acid and sulphuric acid used as stripping agent.