Zn²⁺ adsorption in ferric-silicates microstructures in sulfidic tailings mediated through mineral weathering by Acidithiobacillus species

Heavy metals released from metallic sulfidic tailings pose significant environmental threats by contaminating surface and groundwater in mining areas. Sustainable rehabilitation methods are essential to remove or stabilize these metals, improving the quality of acid mine drainage and minimizing pollution. This study examines the adsorption capacity of zinc ions (Zn²⁺) by different iron-silicate mineral groups under natural weathering and bacteria-regulated weathered conditions. Batch experiments revealed that all tested mineral groups exhibit limited adsorption Zn²⁺ on iron-silicate surfaces, with adsorption behavior aligning with Langmuir and Freundlich isotherm models. Among the mineral groups, pristine iron-muscovite (2.58 mg/g) and iron-chlorite (4.52 mg/g) demonstrated the highest Zn²⁺adsorption capacity, primarily due to favorable ion exchange properties and surface characteristics. Acidic conditions induced by pyrite oxidation and the experimental growth medium slightly reduced Zn²⁺ adsorption in samples without microbial inoculation. In contrast, the addition of Acidithiobacillus species modestly enhanced Zn²⁺ adsorption, likely through microbial alteration of silicate surface properties and the formation of secondary iron-silicate aggregates with high adsorption potential. The dominant adsorption mechanisms included electrostatic attractions, surface complexation and coprecipitation. It is recommended to elevate pH levels and thus enhance metal ion adsorption through the incorporation of alkaline additives such as zeolites or bauxite residue to optimize Zn²⁺ immobilization in sulfidic tailings. This study highlights the importance of both microbial and clay mineral selection in designing effective strategies for stabilizing Zn²⁺ in metallic sulfidic tailings.