MoS42- intercalated magnetic layered double hydroxides for effective removal and expedient recovery of heavy metals from soil

Abstract

Mg-Al layered double hydroxides with MoS42- intercalated and magnetic modification by Fe3O4 (M−MoS4−LDH) was synthesized by one-pot method for capturing and separating heavy metals (Cu2+/Pb2+/Zn2+/Ni2+) from soil. The intercalation of MoS42- considerably improved the removal efficiency of heavy metals, and magnetic materials facilitated the separation of heavy metals from the soil to overcome the potential risk of the absorbed heavy metals. Removal kinetics of heavy metals were found to better follow the intraparticle diffusion model and pseudo-second-order kinetic model. The adsorption results of Cu2+ and Pb2+ were better described by the Freundlich isotherm, and Langmuir isotherm model well fitted the Zn2+ and Ni2+ adsorption data. Additionally, adsorption mechanism of M−MoS4−LDH for Cu2+/Pb2+/Zn2+/Ni2+ with different concentrations was also be explored. As the concentration of Cu2+/Pb2+/Zn2+/Ni2+ in soil was small, MoS42- preferentially combined with heavy metals, and heavy metals were immobilized in the interlayer of LDHs layer. With the increase of heavy metals, the precipitation for Cu2+/Pb2+ and the isomorphic substitution for Zn2+/Ni2+ were investigated and proposed. The co-existing ions experiments demonstrated that M−MoS4−LDH has high selective adsorption efficiency for heavy metals, column leaching experiments indicated that the heavy metals eventually immobilized by M−MoS4−LDH and prevented further migration in soil. Regeneration and recovery experiments suggested that M−MoS4−LDH could be reused for several time with high-efficiency and avoiding secondary contamination. This work provided an excellent removal and convenient recovery strategy for the treatment of heavy metal contaminated soil.