Effect of phosphate on lead removal during a copper recycling process from wastes using ammoniacal chloride solution

Abstract

Techniques for the removal of lead have been studied in order to develop a hydrometallurgical copper recycling process consisting of copper leaching from wastes using an ammoniacal chloride solution and subsequent copper electrowinning. The solubility of Pb(II) in the ammoniacal chloride solution increased with ammonia concentration; this was attributable to the formation of a lead ammine complex. The lead dissolution was depressed from the order of 10−3 M to the order or 10−5 M by the addition of phosphate into the leaching solution because of the precipitation of chloropyromorphite (Pb5(PO4)3Cl), while no significant effect was observed by the addition of carbonate. Linear sweep voltammetry and potentiostatic electrolysis in the solution containing Pb(II) revealed that lead was deposited during the copper electrowinning, even in the potential region more positive than the equilibrium redox potential for the Pb/Pb(II) couple on the lead electrode, because of the alloy formation with copper. In a galvanostatic electrolysis, however, the lead content at the electrodeposited copper cathode was found to be lower than 5 ppm at the current density range of 125–400 A/m2, when the Pb(II) concentration in the electrolyte was 5×10−5 M. Since this Pb(II) concentration was achieved by the phosphate addition, these results indicated the effectiveness of phosphate for lead removal in the copper recycling process using the ammoniacal chloride solution.