REMOVAL OF MERCURY(II) FROM ACID MINE DRAINAGE BY MODIFIED OYSTER SHELL BIOSORBENT

Abstract

Mercury (Hg²⁺) contamination in acid mine drainage (AMD) remains a critical environmental concern that requires cost-effective and sustainable treatment solutions. In this study, phosphate-modified oyster shell (MOS) was synthesized and evaluated as a low-cost biosorbent for Hg²⁺removal. Characterization results confirmed the successful formation of calcium phosphate phases containing active PO₄³⁻and OH⁻groups, which served as the primary binding sites for mercury. Batch adsorption experiments showed rapid uptake, reaching equilibrium within 30 min, with removal efficiencies consistently above 90% across initial concentrations of 5–30 mg.L^-1. The optimal pH range was determined to be 5–7, where reduced proton competition enabled effective ion exchange and complexation with phosphate groups – conditions well aligned with partially neutralized AMD. Adsorption capacity increased with MOS dosage, with an optimal range of 1.0–1.5 g.L^-1. Regeneration experiments demonstrated that MOS retained significant performance after multiple adsorption–desorption cycles, indicating good structural stability despite the acidic environment. These results highlight MOS as a promising, practical, and sustainable biosorbent for mercury removal in AMD treatment applications.