Leaching Behavior and Mineralogical Control of Heavy Metal Elements in Bauxite Under High Sulphate Acid Mine Drainage Conditions

Shanxi Province in China is one of the world’s major bauxite producers. The co-existence of coal and bauxite mining makes this province particularly prone to acid mine drainage (AMD) and, thus, a significant area for investigating heavy metal mobility in an aluminum-rich geological environment. In this study, heavy metal leaching from bauxite under simulated AMD conditions and the geochemical mechanisms controlling their mobility were examined in this study. XRF analysis demonstrated that the bauxite is predominantly composed of Al2O3, Fe2O3 and SiO2, while XRD, FTIR, and SEM-EDS revealed that diaspore and kaolinite dominate bauxite, together with accessory Fe- and Ti-bearing phases, providing reactive surfaces for adsorption and precipitation. After batch leaching with synthetic acidic sulphate solutions (pH = 3), Ca(OH)2 neutralization was regulated. The data reveal that pH is the key factor controlling heavy metal mobility. Acidic conditions enhanced metal release while alkaline conditions favored hydroxide precipitation, surface complexation and co-precipitation. The removal efficiency was 91%–99% for Cd and Zn, 100% for Cd and Zn, 69%–90% for Cr, 35%–100% for Cu, 92%–100% for Ni and up to 100% for Pb. The chemical and mineralogical composition played an indirect role by providing adsorption sites but did not prevent the release of metals under acidic conditions. These results reveal that pH adjustment is the major mechanism controlling heavy metal immobilization in AMD-impacted bauxite systems and contributes to the knowledge of geochemical processes controlling metal mobility in acidic mine drainage.