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

• A novel and magnetic adsorbent by intercalating MoS 4 2- into LDHs. • Higher removal efficiency of heavy metals by M-MoS 4 -LDH from soil. • Removal mechanism of interlayer fixation, isomorphic substitution and precipitation. • MoS 4 2- between layers reacted with heavy metals to improve removal efficiency. • Favorable interception and stable recoverability of adsorbent in soil. Mg-Al layered double hydroxides with MoS 4 2- intercalated and magnetic modification by Fe 3 O 4 (M-MoS 4 -LDH) was synthesized by one-pot method for capturing and separating heavy metals (Cu 2+ /Pb 2+ /Zn 2+ /Ni 2+ ) from soil. The intercalation of MoS 4 2- 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 Cu 2+ and Pb 2+ were better described by the Freundlich isotherm, and Langmuir isotherm model well fitted the Zn 2+ and Ni 2+ adsorption data. Additionally, adsorption mechanism of M-MoS 4 -LDH for Cu 2+ /Pb 2+ /Zn 2+ /Ni 2+ with different concentrations was also be explored. As the concentration of Cu 2+ /Pb 2+ /Zn 2+ /Ni 2+ in soil was small, MoS 4 2- 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 Cu 2+ /Pb 2+ and the isomorphic substitution for Zn 2+ /Ni 2+ were investigated and proposed. The co-existing ions experiments demonstrated that M-MoS 4 -LDH has high selective adsorption efficiency for heavy metals, column leaching experiments indicated that the heavy metals eventually immobilized by M-MoS 4 -LDH and prevented further migration in soil. Regeneration and recovery experiments suggested that M-MoS 4 -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.