Effect of amendments on the leaching behavior of alkaline anions and metal ions in bauxite residue.

A column leaching experiment was used to investigate the efficacy of amendments on their ability to remove alkaline anions and metal ions from bauxite residue leachates. Treatments included, simulated acid rain (AR), phosphogypsum + vermicompost (PVC), phosphogypsum + vermicompost + simulated acid rain (PVA), and biosolids + microorganisms (BSM) together with controls (CK). Results indicated that amendment could effectively reduce the leachate pH and EC values, neutralize OH-, CO32-, HCO3-, and water soluble alkali, and suppress arsenic (As) content. Correlation analysis revealed significant linear correlations with pH and concentrations of OH-, CO32-, HCO3-, water-soluble alkali, and metal ions. BSM treatment showed optimum results with neutralizing anions (OH-, CO32-, and HCO3-), water soluble alkali, and removal of metal ions (Al, As, B, Mo, V, and Na), which was attributed to neutralization from the generation of small molecular organic acids and organic matter during microbial metabolism. BSM treatment reduced alkaline anions and metal ions based on neutralization reactions in bauxite residue leachate, which reduced the potential pollution effects from leachates on the soil surrounding bauxite residue disposal areas.