Leaching of heavy metals from post-neutralization sludge from zinc and lead metallurgy using complexing, alkaline and acidic agents

A solid-liquid extraction process has been studied on a laboratory scale for heavy metal extraction from a post-neutralization sludge sample from the zinc and lead industry. Three different types of leaching agents (HNO 3 , NTA, NaOH) were tested for potential metal recovery and with varying process parameters, i.e., leaching agent concentration, pH of the leaching agent (for NTA), solid/liquid ratio (S/L), temperature, and time. For selected metals the leaching efficiency, possibility of further concentrating the extracts by nanofiltration, and speciation analysis were evaluated. All the agents tested proved to be effective extractants for the metals tested, with optimal concentrations for the process being 1.5 mol/dm 3 , 0.08 mol/dm 3 , and 2 mol/dm 3 for HNO 3 , NTA, and NaOH, respectively. Use of nanofiltration process showed high efficiencies, especially for lead (up to 95 %) in the HNO 3 extracts with a feed solution at pH= 8. For zinc, retention coefficients were not less than 88 % for any of the solutions tested with the highest pH feed solution and cadmium (98 %) in the NTA at pH= 10 of the feed solution. The use of sequential extraction with the BCR method showed that Pb and Zn were removed from the most mobile (F1) fraction, which was not observed for Cd.