Interactions between iron mineral-humic complexes and hexavalent chromium and the corresponding bio-effects.

The interfacial behaviors of chromium are fundamental for understanding the environmental effects of chromium in contaminated environments. However, complex surfaces can cause chromium to exhibit a variety of behaviors, especially when humic substances are considered. This work illustrated the role of humics (humic acid and fulvic acid) during the adsorption of Cr(VI) onto iron minerals (magnetite and hematite). The interfacial behaviors were investigated through their adsorption kinetics, adsorption isotherms, and thermodynamics. Then, the microbial diversity was monitored to reflect the bio-effects of Cr(VI) adsorbed onto four iron oxide-humic complexes. The differences in the adsorption capacities and mechanisms of Cr(VI) on the surfaces of the iron mineral-humic complexes were observed. Humics obviously decreased the adsorption capacities of Cr(VI) on the hematite complexes and relieved the decline in the microbial diversity; meanwhile, humics imposed relatively insignificant changes to the Cr(VI) adsorption capacity onto the magnetite complexes. Thus, the corresponding microbial diversity might be mainly affected by released micelles formed by Cr(VI) and humics. These results illustrate the complexities of the interfacial behaviors of Cr(VI) on the surfaces of iron mineral-humic complexes and broaden the current understanding of chromium migration and transportation.