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MedLine Citation:
PMID:  23050862     Owner:  NLM     Status:  Publisher    
Layered, poorly-crystalline Mn(IV)O2 phases are abundant in the environment. These mineral phases may rapidly oxidize Cr(III) to more mobile and toxic Cr(VI) in soils. There is still, however, little knowledge of how Cr(III) oxidation by Mn(IV)O2 proceeds at the microscopic and molecular levels. Therefore, the sorption mechanisms of Cr(III) and Cr(VI) on Random Stacked Birnessite (RSB), δ-MnO2, and Acid Birnessite (AB) were determined by Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). These three synthetic Mn(IV)O2, which are poorly-crystalline phases and have layered structures, were reacted with 50 mM Cr(III) at pH 2.5, 3 and 3.5 before being analyzed by EXAFS. The results indicated that Cr(VI) was loosely sorbed as an outer-sphere complex on Mn(IV)O2, while Cr(III) was tightly sorbed as an inner-sphere complex. Further research is needed to understand why Cr(III) stopped being significantly oxidized by Mn(IV)O2 after 30 minutes. This study, however, demonstrated that the formation of a Cr surface precipitate is not necessarily responsible for the cessation in Cr(III) oxidation. Indeed, no Cr surface precipitate was detected at the microscopic and molecular levels on Mn(IV)O2 surfaces reacted with Cr(III) for 1 hour, although the Cr(III) oxidation ceased before 1 hour of reaction at most employed experimental conditions.
Gautier Landrot; Matthew Allen Ginder-Vogel; Kenneth John Livi; Jeffrey P Fitts; Donald L Sparks
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-10-11
Journal Detail:
Title:  Environmental science & technology     Volume:  -     ISSN:  1520-5851     ISO Abbreviation:  Environ. Sci. Technol.     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-11     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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