%0 Journal Article
%T Abiotic Reduction of Chlorate by Fe(II) Minerals: Implications for Occurrence and Transformation of Oxy-Chlorine Species on Earth and Mars
%J -
%D 2019
%R https://doi.org/10.1021/acsearthspacechem.8b00206
%X Recent investigations have reported a widespread occurrence of chlorate (ClO3每) and perchlorate (ClO4每) throughout the solar system, including terrestrial arid environments. ClO3每 and ClO4每 are deposited/accumulated at an approximate equal molar ratio, with some exceptions, such as the Antarctica Dry Valley soils (MDV) and perhaps Martian surface material, where ClO4每 is the dominate ClOx每 species. All known ClO4每 production mechanisms produce molar ratios of ClO3每/ClO4每 equal to or much greater than 1, suggesting that reduced ratios may be due to post-depositional mechanism(s). The objective of this study was to investigate potential iron-mediated abiotic reduction of ClO3每, similar to transformation mechanisms reported for nitrate (NO3每) by Fe(II) minerals. Three types of Fe(II)-containing minerals, w邦stite (FeO), siderite (FeCO3), and sulfate green rust (GRSO42每), were investigated in completely mixed batch reactors as potential ClO3每 reductants at a range of pH (4每9) and iron mineral concentrations (1每10 g/L). ClO3每 was stoichiometrically reduced to chloride (Cl每) by w邦stite, siderite, and green rust, but no transformation occurred by dissolved Fe(II). W邦stite and green rust reduced NO3每 but not by siderite. When both NO3每 and ClO3每 are reduced simultaneously, ClO3每 is reduced preferentially to NO3每, although the effect is somewhat concentration-dependent. An increased background salt concentration (NaCl) increased ClO3每 reduction but decreased NO3每. The stability of ClO3每 and subsequent impacts on the ratio of ClO3每/ClO4每 in the environment have implications for understanding the cycling of oxyanions and stability of iron minerals, and related to this, the ratio of ClO4每 and ClO3每 may be an indicator of the past availability of free water. On Mars, these reactions may help to explain the unusually high concentrations of ClO4每 compared to ClO3每 and NO3每
%U https://pubs.acs.org/doi/10.1021/acsearthspacechem.8b00206