Recovery of Valuable Metals from Lead Smelting Slag by Methanesulfonic Acid Leaching: Kinetic Insights and Recycling Potential

The depletion of natural resources remains a major global challenge, emphasizing the need to develop sustainable processes that enable both metal recovery and waste recycling. This study investigates the leaching of valuable metals from lead smelting slag using methanesulfonic acid (MSA), a biodegradable and environmentally benign reagent. Batch experiments were performed under different MSA concentrations (0.35–1.4 M) and temperatures (22–80 °C). Metal dissolution increased nearly linearly with acid concentration up to 1 M, with maximum recoveries after 60 min of 85% Zn, 64% Pb, 75% Cu, and 68% Fe. Copper dissolution was governed by the oxidation of Cu2S, while Fe leaching was affected by pH variations that promoted re-precipitation. Kinetic modeling indicated mixed chemical–diffusion control mechanisms, with activation energies of 22.6 kJ mol−1 for Zn and 31–33 kJ mol−1 for Pb, Cu, and Fe. Beyond efficient metal extraction, the process generated a leach residue with reduced concentrations of base metals and a mineralogical composition dominated by stable calcium-silicate phases, improving its potential suitability for reuse in construction or mining backfill applications. Overall, methanesulfonic acid proved to be an effective and sustainable lixiviant, combining high metal recovery with the generation of recyclable slag, thereby contributing to circular metallurgical practices.