Heterogeneous redox reactions on mineral surfaces control the oxidation state, and therefore the mobility of nutrients and contaminants in soils. Structural iron Fe(II)/Fe(III) couple in the octahedral sheet of clay minerals can directly participate in electron transfer reactions. We studied the redox behavior of two substrates: natural nontronite clay NAu-1, and freshly synthesized iron-rich phyllosilicate in batch laboratory experiments with redox active elements - arsenic (As), chromium (Cr), and selenium (Se). The reactivity of natural clay depends on the Fe(II)/Fe(III) ratio in clay structure and the identity and speciation of the �probe� element (e.g. cation CrOH2+ vs. neutral H3AsO30 vs. anion SeO32-). Fully oxidized NAu-1 readily oxidizes Cr(III); however it does not oxidize As(III). Partially reduced NAu-1 with an Fe(II)/Fetotal ratio of ~0.2 and dithionite-treated synthetic phyllosilicate promotes extensive oxidation of As(III), but not Se(IV), under both oxic and anoxic conditions. Apparent surface reactivity decreases with time.This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.  Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Reactivity of structural Fe(II)/Fe(III) redox couple in natural and synthetic smectite clay

247th National Meeting (2014)

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