Assessment of Heavy Metal Mobilization in Zinc Hydrometallurgy Residues and Their Environmental Impact

 

This study analyzes the natural and induced mobilization of lead (Pb), cadmium (Cd), and arsenic (As) present in residues generated during zinc hydrometallurgy, aiming to evaluate their environmental impact and associated risks under uncontrolled conditions. Differential X-ray diffraction was employed to characterize mineralogical and amorphous phases under simulated environmental scenarios. Results indicate that all samples exhibit high susceptibility to releasing potentially toxic elements (PTEs) depending on environmental conditions.

Chemical characterization of residues and runoff waters from affected areas was performed, determining pH, electrical conductivity, salt content, and total and soluble concentrations of Zn, Pb, Cd, and As. Subsequently, toxicity bioassays (Microtox®, Ostracods, Gammarus, and Phytotest) were applied to leachates and contaminated waters. Mineralogical analysis identified previous industrial processes that influence physicochemical properties and PTE mobility.

The most critical scenarios correspond to: (i) natural mobilization of Cd and Zn due to rainfall, and (ii) changes in redox conditions in anoxic environments (flooding or incorporation of organic matter), that promote the reduction of  As (V) to As (III) . High concentrations of soluble salts increase hazard potential, generating ecotoxicological risks and potential carcinogenic effects through oral ingestion

Results confirm elevated levels of heavy metals and significant toxic effects in residues and associated waters, highlighting the need to implement preventive measures and management strategies to minimize environmental and health impacts.