Selective Removal of Arsenic and Antimony by Alkaline Leaching with Sodium Sulfide: Remediation of Metalloids-Contaminated Concentrates from Zimapán, Hidalgo, Mexico

Selective alkaline leaching was evaluated to remove arsenic (As) and antimony (Sb) from a polymetallic copper concentrate from Zimapán, Mexico, where these metalloids cause environmental risk and smelter penalties. Batch tests used sodium sulfide (Na2S) in alkaline media, varying reagent concentrations and temperature; kinetic modeling identified the rate-controlling step, and X-ray diffraction (XRD) plus scanning electron microscopy/energy-dispersive spectroscopy (SEM–EDS) assessed phase changes. The kinetic analysis indicated chemical control with a higher reaction order for Na2S than for NaOH. A quadratic regression described the process and identified Na2S concentration and temperature as the dominant factors. Maximum extractions reached 91.9% for As and 72.1% for Sb while limiting dissolution of value-bearing sulfides, as supported by XRD and SEM–EDS. Environmental indices (Igeo, EF) classified As and Sb as highly contaminating and geochemically enriched in the feed, underscoring the need for selective removal. Overall, alkaline leaching with Na2S provides a technically feasible and environmentally favorable route to remediate metalloids and upgrade polymetallic concentrates.