In-situ immobilization of arsenic and antimony containing acid mine drainage through chemically forming layered double hydroxides

Acid mine drainage (AMD) rich in arsenic (As) and antimony (Sb) is considered as a significant environmental challenge internationally. However, simultaneous removal of As and Sb from AMD is still inadequately studied. In this study, a highly effective and simple approach was proposed for mitigating As and Sb-rich AMD, which involves in-situ formation of layered double hydroxides (LDHs). Following the treatment, the residual concen-trations of iron (Fe), magnesium (Mg), sulfate, As and Sb in field AMD were decreased from their initial con-centrations of 1690, 1524, 2055, 7.8 and 10.6 mg L-1, respectively, to 1.3, 12.4, 623, 0.006 and 0.004 mg L-1, respectively. Chemical formula of the resulting As and Sb-loaded LDHs can be identified as [Mg4.226Fe2.024(OH)2](SO4)(AsSb)0.006 & BULL;mH2O. The dissolution rates of metal(loid)s in As and Sb-loaded LDH were lower than 1% under strongly acidic and alkaline environments. In presence of the mixed adsorbates, the As immobilization capacity by LDHs was significantly decreased, with an apparent intervention from Sb. However, As did not have a significant effect on the immobilization of Sb by LDH. As was immobilized by LDHs through anion exchange and complexation with -OH groups, while Sb was captured by anion exchange and complexation with Mg(H2O)2+6 . Density functional theory (DFT) calculations further proved the above conclusions. This novel approach is effective and can be applied for in-situ AMD treatment from abandoned mines.