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Determination of the Redox Potentials of Solution and Solid Surface of Fe(II) Associated with Iron Oxyhydroxides
Li, Xiaomin1,4; Liu, Liang3,4; Wu, Yundang2; Liu, Tongxu2,4
2019
摘要While the redox properties of Fe(II) associated with iron minerals have been widely investigated given their significance in controlling the biogeochemical processes of elements and contaminants, a robust link between the experimental measurements and theoretical calculations of redox potentials (Eh) of Fe(II)-associated iron minerals is still lacking. In this study, the experimental and calculated Eh values of Fe(II) species in solution with ferrihydrite (Fhy) were investigated. Eh of the bulk system of Fe(II) and ferrihydrite [Fe(II)-Fhy] and Eh of Fe(II) associated with ferrihydrite [Fhy-associated Fe(II)] were examined by open circuit potential (OCP) and cyclic voltammetry (CV) measurements, respectively, both of which were also calculated on the basis of the modified Nernst equation. Both the experimental Eh values of bulk Fe(II)-Fhy obtained from the OCP measurements and the Eh values calculated for solution-phase Fe(II) decreased substantially with increasing Fe(II) concentrations, indicating that the redox potentials of bulk Fe(II)-associated with iron oxyhydroxides (Fe(II)-IOs) were determined by solution-phase Fe(II). The Eh values of bulk Fe(II)-IOs obtained from the OCP measurements for Fe(II)-Fhy were close to those of Fe(II)-Gth, and this finding was attributed to the Fe(II)-catalyzed transformation of ferrihydrite to goethite. The Eh values of surface-sorbed Fe(II) obtained from CV tests and the calculation for Fe(II)-Fhy were close to those of Fe(II)-Gth, implying that the redox potentials of surface-sorbed Fe(II) were determined by the redox couple of sorbed Fe(II) and freshly formed Fe(III) but not structural Fe(III); therefore, newly formed Fe(III) was more reactive than structural Fe(III). The anthraquinone-2,6-disulfonate (AQDS) reduction experiments revealed that, while 77.1-82.9% of AQDS could be reduced in the suspensions of Fe(II)-Fhy and Fe(II)-Gth, Fe2+ in solution without any iron oxides only reduced 9.1% of AQDS. By integration of electrochemical measurements and theoretical calculation, this study demonstrated that the redox couple of sorbed Fe(II) and freshly formed Fe(III) dominated the surface reactivity in the Fe(II)-associated iron minerals, which provides new insight into the redox properties of the Fe(II)-iron mineral system. © 2019 American Chemical Society.
DOI10.1021/acsearthspacechem.9b00001
发表期刊ACS Earth and Space Chemistry
卷号3期号:5页码:711-717
语种英语
EISSN24723452