Document Detail

Sulfate availability drives divergent evolution of arsenic speciation during microbially-mediated reductive transformation of schwertmannite.
MedLine Citation:
PMID:  23373718     Owner:  NLM     Status:  Publisher    
The effect of SO42- availability on the microbially-mediated reductive transformation of As(V)-coprecipitated schwertmannite (Fe8O8(OH)3.2(SO4)2.4(AsO4)0.004) was examined in long-term (up to 400 days) incubation experiments. Iron EXAFS spectroscopy showed siderite (FeCO3) and mackinawite (FeS) were the dominant secondary Fe(II) minerals produced via reductive schwertmannite transformation. In addition, ~25% to ~65% of the initial schwertmannite was also transformed relatively rapidly to goethite (αFeOOH), with the extent of this transformation being dependent on SO42- concentrations. More specifically, the presence of high SO42- concentrations acted to stabilize schwertmannite, retarding its transformation to goethite and allowing its partial persistence over the 400 day experiment duration. Elevated SO42- also decreased the extent of dissimilatory reduction of Fe(III) and As(V), instead favoring dissimilatory SO42- reduction. In contrast, where SO42- was less available, there was near-complete reduction of schwertmannite- and goethite-derived Fe(III) as well as solid-phase As(V). As a result, under low SO42- conditions, almost no Fe(III) or As(V) remained towards the end of the experiment and arsenic solid-phase partitioning was controlled mainly by sorptive interactions between As(III) and mackinawite. These As(III)-mackinawite interactions lead to the formation of an orpiment (As2S3)-like species. Interestingly, this orpiment-like arsenic species did not form under SO42--rich conditions, despite the prevalence of dissimilatory SO42- reduction. The absence of an arsenic sulfide species under SO42--rich conditions appears to have been a consequence of schwertmannite persistence, combined with the preferential retention of arsenic oxyanions by schwertmannite. The results highlight the critical role that SO42- availability can play in controlling solid-phase arsenic speciation, particularly arsenic-sulfur interactions, under reducing conditions in soils, sediments and shallow groundwater systems.
Edward D Burton; Scott G Johnston; Peter Kraal; Richard Bush; Salirian R Claff
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2013-2-4
Journal Detail:
Title:  Environmental science & technology     Volume:  -     ISSN:  1520-5851     ISO Abbreviation:  Environ. Sci. Technol.     Publication Date:  2013 Feb 
Date Detail:
Created Date:  2013-2-4     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0213155     Medline TA:  Environ Sci Technol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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