Comparative Assessment of Lead (Pb) and Zinc (Zn) Leaching Behavior from Zinc Extraction Residues Using Monovalent and Divalent Chloride Salts

It is crucial for waste management to economically utilize the solid leach residues released in zinc production facilities, classified as hazardous waste because of the metals they contain, without harming the environment and human health. Although the disposal of these residues often requires special technologies, hazardous wastes are left in the environment or landfills because of the expense of these technologies and the inadequacy of legal sanctions in some cases. Therefore, it is important from both an economic and environmental perspective to evaluate these residues and return them to the industry. This work aims to extract Pb and Zn metals from zinc extraction residuals in the presence of various chloride salts such as magnesium chloride, calcium chloride and potassium chloride. For this purpose, the chemical analysis of ZER (zinc extraction residual) was conducted by the LiBO2 fusion-HNO3 solubilization method, and its Pb and Zn contents were found to be 15.88% and 10.02%, respectively. The leaching experiments were carried out in two ways. The first group of leaching experiments was carried out by boiling under reflux and stirring, and KCl salt was found to be the most suitable leaching agent. The second group of experiments was performed in Erlenmeyer flasks using a shaker incubator at different temperatures (25-55 degrees C) and at varied KCl concentrations (0.6-5 N). Based on the experimental findings, the extraction efficiency of lead (Pb) is substantially higher than that of zinc (Zn) in the presence of all investigated chloride salts. While Pb dissolution demonstrates a strong dependence on the chloride salt concentration, particularly beyond certain threshold levels, the Zn extraction yield exhibits minimal variation across the same concentration range. This indicates that chloride ions preferentially promote the solubilization of Pb species, likely due to the formation of more stable and soluble Pb-Cl complexes, whereas Zn appears to have a lower affinity for chloride complexation under the studied leaching conditions. On the other hand, the Pb extraction value increased with increasing KCl concentration, and it reached 80.9% in KCl concentration of 4 N. In addition, the amount of Zn dissolved at different KCl concentrations plateaued at 25%.