Premium
Characterization of Chromium Bioremediation Products in Flow‐Through Column Sediments Using Micro–X‐ray Fluorescence and X‐ray Absorption Spectroscopy
Author(s) -
Varadharajan Charuleka,
Han Ruyang,
Beller Harry R.,
Yang Li,
Marcus Matthew A.,
Michel Marc,
Nico Peter S.
Publication year - 2015
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2014.08.0329
Subject(s) - ferrihydrite , xanes , chromium , chemistry , extended x ray absorption fine structure , goethite , bioremediation , dissolution , biogeochemical cycle , sorption , x ray absorption spectroscopy , absorption (acoustics) , x ray photoelectron spectroscopy , environmental chemistry , spectroscopy , absorption spectroscopy , chemical engineering , materials science , adsorption , contamination , ecology , physics , organic chemistry , quantum mechanics , composite material , biology , engineering
Microbially mediated reductive immobilization of chromium is a possible remediation technique for sites contaminated with Cr(VI). This study is part of a broader effort investigating the biogeochemical mechanisms for Cr(VI) reduction in Hanford 100H aquifer sediments using flow‐through laboratory columns. It had previously been shown that reduced chromium in the solid phase was in the form of freshly precipitated mixed‐phase Cr(III)‐Fe(III) (hydr)oxides, irrespective of the biogeochemical conditions in the columns. In this study, the reduced Cr phases in the columns were investigated further using spectroscopy to understand the structure and mechanisms involved in the formation of the end products. Several samples representing potential processes that could be occurring in the columns were synthesized in the laboratory and characterized using X‐ray absorption near edge structure (XANES) and X‐ray scattering. The XANES of Cr(III) particles in the columns most closely resembled those from synthetic samples produced by the abiotic reaction of Cr(VI) with microbially reduced Fe(II). Microbially mediated Cr‐Fe reduction products were distinct from abiotic Cr‐Fe (hydr)oxides [Cr x Fe 1‐x (OH) 3 ] and organically complexed Cr(III) sorbed onto the surface of a mixed ferrihydrite‐goethite mineral phase. Furthermore, analyses of the abiotically synthesized samples revealed that even the end products of purely abiotic, iron‐mediated reduction of Cr(VI) are affected by factors such as the presence of excess aqueous Fe(II) and cellular matter. These results suggest that Cr x Fe 1‐x (OH) 3 phases made under realistic subsurface conditions or in biotic cultures are structurally different from pure Cr(OH) 3 or laboratory‐synthesized Cr x Fe 1‐x (OH) 3 . The observed structural differences imply that the reactivity and stability of biogenic Cr x Fe 1‐x (OH) 3 could potentially be different from that of abiotic Cr x Fe 1‐x (OH) 3 .