RECOVERY OF ZINC FROM ASHES OF AUTOMOBILE TIRE WASTES BY PH CONTROLLED SOLUTIONS OF AMMONIUM CHLORIDE

This paper concerns the recovery of zinc from fly ashes generated by incineration plant of automobile tire wastes. The recovery is obtained by two extraction steps with a pH-controlled ammonia chloride solution. The ashes contain about 51% wt of zinc, 1% wt of iron and aluminium and small quantities (less than 0.1% wt) of cobalt, copper and lead. Various factors affect the performance and efficiency of leaching: temperature, concentration, pH and time were studied using a factorial experimental design. After two steps with ammonium chloride 3mol/L, L/S=6 ml/g, pH 5.4 and T=72°C the leaching liquor has been purified in a sample step by cementation with metallic zinc powder without activation. Traces of Pb,As,Sb,Se,Mo,Ni have been cleared by cementation with zinc. The fly ash and residue composition was determined by X-ray and its elemental composition by ICP-OES and IC. The obtained results show that recovery efficiency amounts to 98% wt for zinc; the concentration of zinc in the leach liquors reaches more than 45g/L while most of the iron is not leached. The purified solution containing zinc allows the direct recovery of high grade zinc by electro-deposition.