Zinc and lead recovery from metallurgical sludges and dusts - by caustic soda leaching, solid-liq. sepn. and cementation

Abstract

Abstract Zinc- and lead-contg. sludges and dusts are treated by (a) caustic soda leahing with addn. of slaked lime to dissolve the zinc and lead, pref. at elevated temp.; (b) decantation to separate a sludge underflow from the soln. overflow; (c) conditioning the soln. by addn. of quicklime and a flocculant, followed by decantation to obtain a clear soln.; and (d) cementation by addn. of metallic zinc to separate zinc from the lead, the lead being held in prolonged contact with the cementation soln. to solubilise excess zinc powder. The process is used for Zn and Pb recovery from metal refinery residues contg. Zn, Pb, Fe, C, Si, Ca, Mg, etc. Zn and Pb are selectively extracted by the complexing action of hydroxyl ions to give 70-90% purity and 35-65% recovery of Pb of greater than 98% purity.

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