Metallic lead recovery from lead-acid battery paste by urea acetate dissolution and cementation on iron

A suitable hydrometallurgical and environmentally friendly process was studied to replace the currently used practices for recycling lead-acid batteries via smelting. Metallic lead was recovered by cementation from industrial lead sludge solutions of urea acetate (200 to 500 g/L) using different types of metallic iron substrates (nails, shaving or powder) as reducing agents. Under specific operating conditions, up to 99.7% of lead acid battery paste, mainly composed of PbSO4, PbO2 and PbO·PbSO4 species, was converted to metallic lead.. The conversion of the metallic lead and rate of the cementation reaction were strictly dependent on the type of iron substrate used as the reductant and the best operating conditions were found with iron powder. The rate constant of the lead recovery reaction under these conditions was 3 · 10- 3 1/s and the rate determining process was the diffusion controlled cathodic reaction (Ea = 1.9 kJ/mol). The reaction residues and the recovered lead were characterized by XRD analysis. Metallic lead morphology and purity were studied by SEM and EDS respectively. Addition of proper amounts of concentrated sulphuric acid to the exhausted cementation solution led to the quantitative recovery of iron(II) by crystallization of (NH4)2SO4FeSO4.6H 2O.