Sulfidation of Cd-Sch During the Microbial Sulfate Reduction: Nanoscale Redistribution of Cd

Abstract

Schwertmannite exists in the environments rich in iron and sulfate. Microbes that use iron or sulfate can cause the phase transition of Sch, further resulting in the redistribution of coexist-pollutants. However, how S/Fe molar ratio affects the microbial-mediated Sch transformation and the fate of Cd have not yet been clarified. Here, this study investigated the effect of S/Fe on minerals transformation and the fate of Cd during the microbial reduction of Cd-loaded Sch by Desulfovibrio vulgaris. The presence of Cd retarded the process of sulfate reduction, whereas the increase of S/Fe helped SRB resist the toxicity of Cd and accelerated the S(-II) generation, promoting the formation of newly secondary minerals. With S/Fe increased, mackinawite as the main minerals replaced vivianite. The morphology of minerals gradually became regular, and the surface morphology altered from prismatic clusters to rosette-like structure. The distribution of Cd varied from uniformly distributed on minerals to locally enriched in the mixed minerals of vivianite and FeS. The enrichment of Cd was not only directly related to the content of FeS, but also had a strong correlation with phosphorus. The mixed minerals of vivianite and FeS were more conducive to the fixation of Cd. Cd mainly existed in the oxidizable phase. These findings have important implications for understanding the biogeochemistry of iron (oxyhydr)oxide and Cd behavior in anaerobic environment.

Keywords: cadmium, Schwertmannite, Mineral transformation, Desulfovibrio vulgaris, Sulfidation, S/Fe.