Kinetics of Reductive Dissolution of Hematite by Bioreduced Anthraquinone-2,6-disulfonate

Authors

Chongxuan Liu, Pacific Northwest National LaboratoryFollow
John M. Zachara, Pacific Northwest National LaboratoryFollow
Nancy Foster, Pacific Northwest National LaboratoryFollow
Janae Strickland, Pacific Northwest National Laboratory

Date of this Version

2007

Citation

Environ. Sci. Technol. 2007, 41, 7730-7735

Abstract

The reductive dissolution of hematite (α-Fe₂O₃) was investigated in a flow-through system using AH2DS, a reduced form of anthraquinone-2,6-disulfonate (AQDS), which is often used as a model electron shuttling compound in studies of dissimilatory microbial reduction of iron oxides. Influent flow rate, pH, and Fe(II) and phosphate concentrations were varied to investigate the redox kinetics in a flow-through reactor. The hematite reduction rates decreased with increasing pH from 4.5 to 7.6 and decreased with decreasing flow rate. The rates also decreased with increasing influent concentration of Fe(II) or phosphate that formed surface complexes at the experimental pH. Mineral surface properties, Fe(II) complexation reactions, and AQDS sorption on hematite surfaces were independently investigated for interpreting hematite reduction kinetics. AH₂DS sorption to hematite was inferred from the parallel measurements of AQDS and AH₂DS sorption to α-AI₂O₃, a redox stable analog of α-Fe₂O₃. Decreasing Fe(II) and increasing AH₂DS sorption by controlling flow rate, influent pH, and Fe(II) and phosphate concentrations increased the rates of reductive dissolution. The rates were also affected by the redox reaction free energy when reductive dissolution approached equilibrium. This study demonstrated the importance of the geochemical variables for the reductive dissolution kinetics of iron oxides.