Electrolytic recovery of lead in used lime leachate from municipal waste incinerator

The purification of municipal incinerator gases generates huge quantities of both fly ashes and used lime, containing high amount of heavy metals (Pb, Cd, Zn and Hg). The used lime is mainly contaminated by Pb and often considered as hazardous waste. This paper is related to a laboratory study on the performance of electrochemical techniques used to recover Pb from leachate produced during used lime decontamination. Two types of electrolytic units (monopolar and bipolar electrode cells) using different electrode materials were studied. Effectiveness was measured in terms of energy consumed, weight of residue sludge produced and reduction in Pb concentration. Results showed that the best performances for Pb removal (in terms of effectiveness and cost) were obtained by initially adjusting the pH of UL leachate to pH 7.5-8.5 with sulphuric acid followed by electrochemical treatment using bipolar electrode (mild steel) system operated at current intensity of 1.5 A through only 5 min. The yield of Pb removal was 98.8 ± 1.3% and an amount of 4.9 ± 1.3 kg trt−1 of metallic sludge was produced. The optimal conditions determined for Pb recovery involved a total cost of CAN$ 1.66 t−1 of dry residue treated, including acid consumption, energy consumption and metallic sludge disposal.