High performance self-assembled sulfidized nanoscale zero-valent iron for the immobilization of cadmium in contaminated sediments: Optimization, microbial response, and mechanisms.

ABSTRACT

Sulfidized nanoscale zero-valent iron (S-nZVI) showed excellent removal capacity for cadmium (Cd) in aqueous phase. However, the remediation effects of S-nZVI on Cd-contaminated sediment and its interactions with microorganisms in relation to Cd fate remain unclear. The complexity of the external environment posed a challenge for Cd remediation. This study synthesized S-nZVI with different S and Fe precursors to investigate the effect of precursors and applied the optimal material to immobilize Cd in sediments. Characterization analysis revealed that the precursor affected the morphology, Fe0 crystallinity, and the degree of oxidation of the material. Incubation experiments demonstrated that the immobilization efficiency of Cd using S-nZVIFe3++S2- (S/Fe = 0.14) reached the peak value of 99.54%. 1% and 5% dosages of S-nZVI significantly reduced Cd concentration in the overlying water, DTPA-extractable Cd content, and exchangeable (EX) Cd speciation (P < 0.05). Cd leaching in sediment and total iron in the overlying water remained at low levels during 90 d of incubation. Notably, each treatment maintained a high Cd immobilization efficiency under different pH, water/sediment ratio, organic acid, and coexisting ion conditions. Sediment physicochemical properties, functional bacteria, and a range of adsorption, complexation and precipitation of CdS effects dominated Cd immobilization.