Utilization of zinc ash for production of electrolytic zinc

Utilization of zinc ash, formed as a byproduct in the cathode sheet melting shops of electrowinning zinc plants, for production of electrolytic zinc, has been examined. Results of various methods investigated for removal of chlorine from the ash have been presented. Calcining is found to give the best results compared to washing or leaching the ash in alkaline solutions. Calcining is found to give the best results compared to washing or leaching the ash in alkaline solutions. Calcining at the temperature of 900°C for 45 min is found to remove 98% of the chlorine present with only 2-3% loss of zinc yielding a product containing 78% Zn and 0.03% Cl. Current efficiencies of the order of 97-99% were obtained on electrolysis of zinc sulphate solution prepared from the calcined ash. No build up of chlorine is noticed on continued use of calcined ash for preparation and subsequent regeneration of spent electrolyte. (Sarvashri G. Basu, P.K. Sinha and S.C. Aush, Senior Scientific Assistants and Dr. N. Dhananjayan, Scientist; National Metallurgical Laboratory)