CHROMIUM OXIDATION-REDUCTION CHEMISTRY CONTROLLED BY IRON AND MANGANESE (HYDR)OXIDE SURFACES AND SOILS: COLUMN LEACHING AND SPECTROSCOPIC STUDIES

Abstract

Soil interfaces, including those defined by horizons and iron (Fe(III)) and manganese (Mn(III,IV)) (hydr)oxide mineral surfaces, are a largely unstudied area in soils research, especially in terms of their oxidation-reduction properties. This study attempted to address two questions related to this research deficiency. The first: how chromium (Cr) redox changes throughout mineralogically different soil horizons, and the second: how Cr redox structurally alters Fe(III) and Mn(III,IV) (hydr)oxides in synthetic, soil, and microbial systems. Both parts of the study used column leaching experiments along with Cr speciation techniques to study simulated soil horizon interfaces and Fe/Cr and Mn/Cr redox systems. X-ray absorption spectroscopic techniques were also utilized to analyze the mineral structure of Fe(III) and Mn(III,IV) (hydr)oxides. The results of the study indicate that there are significant interfacial properties affecting Cr(VI) reduction and that Cr(III) oxidation does change the mineral structures of synthetic, soil, and fungal Mn(III,IV)(hydr)oxides to varying degrees.