Redox reactions between manganese oxides and chromium(III)-containing iron oxides can affect the mobility of soluble Cr(VI) contaminants in natural and engineered systems. Building on previous knowledge of birnessite as an oxidant for Cr-containing solids, we systematically evaluated the rates and products of the oxidation of Cr(III) in iron oxides by birnessite. We found that pH and the Fe/Cr ratio greatly influenced the Cr(VI) production rates. A multi-chamber reactor was used to assess the role of solid-solid contact in CrxFe1-x(OH)3-MnO2 interactions. A dialysis membrane divided the reactor into two chambers, eliminating the possibility of direct contact of the solids in each chamber but allowed dissolved species to diffuse across the membrane. The Cr(VI) production rate was much lower in multi-chamber experiments (CrxFe1-x(OH)3||MnO2) than in completely mixed batch experiments under the same condition, indicating that the redox interaction is greatly accelerated by physical contact or close proximity of the two solids. During the redox reaction, new manganese oxides appeared and X-ray photoelectron spectroscopy (XPS) indicates that after reaction the surfaces of the manganese oxides are predominantly Mn(III) and Mn(II).

Rates and products of MnO2 oxidation of Cr(III)-containing iron oxides

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.