Effective adsorption of heavy metals on layered double hydroxides modify through dithiocarbamate prepared by CS2 and different molecular weight of polyethyleneimine

Abstract

Dithiocarbamate (DTC) with different molecular weight were prepared to modify Mg-Al layered double hydroxides (LDH-DTC) for adsorbing Cu(II), Pb(Ⅱ), Zn(Ⅱ), Cd(Ⅱ) from contaminated soil. The structural and morphology characterization indicated that DTC was wrapped outsides LDHs layer, and the coating layer became thicker with the increase of DTC molecular weight. The adsorption performance of LDH-DTC for heavy metal was investigated and adsorption kinetics was well followed pseudo-second-order and intraparticle diffusion model. The data of adsorption isotherm showed that the adsorption of Cu/Pb fitted Freundlich model, while the adsorption process of Zn/Cd fitted Langmuir model. Additionally, adsorption mechanism of LDH-DTC for Cu(II)/Pb(Ⅱ)/Zn(Ⅱ)/Cd(Ⅱ) with different concentration was explored. As the concentration of heavy metals was low, heavy metals first react with DTC encapsulated outside LDHs. With the increase of concentration, adsorption site of DTC was completely occupied, Cu(Ⅱ)/Pb(Ⅱ) began to react with the exposed LDHs layer to form precipitation, and Zn(Ⅱ)/Cd(Ⅱ) were immobilized on the LDHs layer by isomorphous replacement. The effects of pH, coexistence ions, heavy metal leaching, reuse, column leaching, and metal morphology classification experiments were also conducted, and these results revealed a high stability and favorable interception. The excellent adsorption performance suggested LDHs modified by DTC offered a promising method to immobilize heavy metals from soil and into practical application.