Effective removal of heavy metal ions by attapulgite supported sulfidized nanoscale zerovalent iron from aqueous solution

Sulfidation of nanoscale zero valent iron (nZVI) has attracted increasing interest for improving the reactivity and selectivity of nZVI towards heavy metal ions. In this study, attapulgite-loaded sulfide modified nZVI (APT/SnZVI) was synthesized, and used for removal Cr(VI), Cu(II) and Zn(II) alone or coexisting. The morphology and structure characterizations indicated that sulfide-modified nZVI particles were well distributed and immobilized on the attapulgite surface. Batch experiments of Cr(VI), Cu(II) and Zn(II) removal were conducted at varying mass ratios, S/Fe ratios, pH and initial concentrations. Moreover, kinetic and thermodynamic analyses were used to study the removal process, and possible mechanisms of removal for Cr(VI), Cu(II) and Zn(II) were discussed. The results of removal performance tests demonstrated that APT/S-nZVI displayed high removal capacity and fast removal rate for three heavy metal ions compared to the nZVI, which derived from the synergistic effects of the strongly reducing characteristics of nZVI combined with high electronic conductivity of FeS and high surface area of APT. Dynamic studies revealed that the removal process was highly consistent with the pseudo-second order model for three metal ions adsorption and reaction process. Additionally, combined the value of activation energy, it has been proved that the removal Cr(VI) and Cu(II) were controlled by chemical surface-limiting step, and removal Zn(II) was controlled by chemically diffusion step. The modification of S changes the removal mechanism between APT/S-nZVI and metal ions, which is closely related to the redox potential of metal ion and the solubility product constant (Ksp) of metal sulfides. Overall, the work suggests that APT/S-nZVI has a good potential for the elimination of micropollutants in the aquatic environment.