Characteristics and mechanism of effectively capturing arsenate by sulfate intercalated and self-doping layered double hydroxide derived from field acid mine drainage

A novel approach was investigated for the synthesis of sulfate intercalated iron based layered double hydroxides (LDHs) from field acid mine drainage (AMD) by co-precipitating Fe3+, Mg2+ and SO42- ions. By strategically controlling the Mg2+/Fe3+ molar ratios in AMD, the structural and interfacial properties of LDHs were effectively regulated. Compared to LDHs synthesized from chemical reagents, which had charge density of 3.99 e/nm2 and basal spacing of 0.816 nm, the AMD-synthesized LDHs exhibited higher charge density of 5.34 e/nm2 and larger interlayer d-spacing (0.872 nm) due to the incorporation of co-existing Al3+ and Ca2+ in AMD. The LDHs synthesized from AMD displayed a higher adsorption capacity of 80.16 mg/g and demonstrated strong antiinterference ability, with the removal efficiency of As(V) being maintained at approximately 96% across a pH range of 2.0 to 9.0. The effective capture of arsenate was attributed to the anion exchange of arsenate ions with interlayer sulfate, as well as the strong metalloid binding affinities between the -OH active sites and arsenate. This study revealed that the self-doping LDHs derived from AMD were superior for As(V) removal and the adverse impacts of AMD were alleviated.