Effects of environmental factors on the removal of heavy metals by sulfide-modified nanoscale zerovalent iron.

Sulfide-modified nanoscale zerovalent iron (S-nZVI) has excellent reducing performance for heavy metals in water. The influence of environmental factors on the reactivity can be used to explore the practical feasibility of S-nZVI and analyze the reaction mechanism in depth. This study compared the removal effect and mechanism of Cu and Ni by nanoscale zerovalent iron (nZVI), S-nZVI, and carboxymethyl cellulose-modified nanoscale zerovalent iron (CMC-nZVI). The results show that the pseudo-first-order kinetic constant of Cu removal by nZVI, S-nZVI, and CMC-nZVI was 1.384, 1.919, and 2.890 min, respectively, and the rate of Ni removal was 0.304, 0.931, and 0.360 min, respectively. The removal mechanism of S-nZVI was similar to that of nZVI and CMC-nZVI. Specifically, Cu was predominantly removed by reduction, while Ni removal included adsorption and reduction. Environmental factors had a specific inhibitory effect on the removal of Cu but had a negligible impact on Ni. The condition of low pH, the presence of Cl and humic acid (HA) promoted the corrosion consumption of Fe, in which H directly corroded Fe at low pH. At the same time, Cl and HA inhibited the adsorption or binding of heavy metal ions on the particle surface, thereby reducing the electron transfer and utilization efficiency. The passivation of NO reduced the anaerobic corrosion of the material in water but suppressed the release of electrons, thereby reducing the reduction efficiency of the three types of materials. The anaerobic corrosion of S-nZVI was less affected by environmental factors, and it can still maintain more than 80% of the electronic utilization efficiency under different environmental factors, which illustrates that S-nZVI has broad prospects for practical applications in heavy metal polluted water.