The mobility of chromium (Cr) is controlled by minerals, especially iron (oxyhydr)oxides. The influence of organic carbon (OC) on the mobility and fate of Cr(VI) during Fe(II)-induced transformation of iron (oxyhydr)oxide, however, is still unclear. We investigate how low-weight carboxyl-rich OC influences the transformation of ferrihydrite (Fh) and controls the mobility of Cr(VI/III) in reducing environments and how Cr influences the formation of secondary Fe minerals and the stabilization of OC. With respect to the transformation of Fe minerals, the presence of low-weight carboxyl-rich OC retards the growth of goethite crystals and stabilizes lepidocrocite for a longer time. With respect to the mobility of Cr, low-weight carboxyl-rich OC suppresses the Cr(III)non-extractable associated with Fe minerals, and this suppression is enhanced with increasing carboxyl-richness of OC and decreasing pH. The presence of Cr(III) mitigates the decrease in total C associated with Fe minerals and increases the Cnon-extractable especially for Fh organominerals made with carboxyl-rich OC. Our study sheds new light on the mobility and fate of Cr in reducing environments and suggests that there is a potential synergy between Cr(VI) remediation and OC stabilization.
Keywords: Fe minerals; Fe(II); chromium; ferrihydrite; mobility; organic carbon.