Selective extraction of zinc and iron from passivating baths

In this work, the viability study of the removal of zinc and iron from chromium (III) passivating baths is presented. The Emulsion Pertraction Technology (EPT), a liquid-liquid extraction process performed in membrane contactors has been applied. Real passivating baths with the following metal concentrations have been tested: Zn, 7000 mg/L; Fe, 30 mg/L and Cr, 5500 mg/L respectively. After the EPT treatment and at the applied experimental conditions, these concentrations were decreased to 2450 mg/L of Zn and 4 mg/L of Fe, while the chromium concentration was maintained approximately at the initial value. The EPT process allowed the simultaneous recovery of Zn in a concentrated stripping phase. The influence of the pH of the feed phase strongly affected the kinetics of metals removal. A value of pH = 2.5 allowed to attain the required high selectivity values of α_Zn/Cr.