Zinc Chloride and Hydrochloric Acid Coextraction from Galvanizing Pickling Waste in the Presence of Iron(II). Results with Hollow Fiber Membrane Contactors

Abstract

Spent pickling acid from the industrial galvanizing process currently requires specialist disposal, yet there is the potential to recover the zinc as a valuable metal. In this work, we compare the extraction of zinc using tributyl phosphate from real galvanizing effluent and laboratory prepared solutions. Both commercial and handmade hollow fiber membrane contactors are used for this purpose. While the zinc is effectively extracted, care must be taken to prefilter the solution upstream of the membrane contactor to minimize crud formation and interfacial effects. The extraction of both zinc and HCl from the effluent is satisfactorily described using mathematical models for both the multicomponent equilibria and mass transfer balances. In development of the multicomponent equilibrium model, the thermodynamic equilibrium constants obtained from the ZnCl2–NaCl–HCl aqueous system were found to be applicable to the ZnCl2–FeCl2–HCl system.