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Title: Retention mechanisms of citric acid in ternary kaolinite-Fe(III)-citrate acid systems using Fe K-edge EXAFS and L3,2-edge XANES spectroscopy

Organic carbon (OC) stability in tropical soils is strongly interlinked with multivalent cation interaction and mineral association. Low molecular weight organic acids (LMWOAs) represent the readily biodegradable OC. Therefore, investigating retention mechanisms of LMWOAs in mineral-cation-LMWOAs systems is critical to understanding soil C cycling. Given the general acidic conditions and dominance of kaolinite in tropical soils, we investigated the retention mechanisms of citric acid (CA) in kaolinite-Fe(III)-CA systems with various Fe/CA molar ratios at pH ~3.5 using Fe K-edge EXAFS and L-3,2-edge XANES techniques. With Fe/CA molar ratios >2, the formed ferrihydrite mainly contributed to CA retention through adsorption and/or coprecipitation. With Fe/CA molar ratios from 2 to 0.5, ternary complexation of CA to kaolinite via a five-coordinated Fe(III) bridge retained higher CA than ferrihydrite-induced adsorption and/or coprecipitation. With Fe/CA molar ratios ≤ 0.5, kaolinite-Fe(III)-citrate complexation preferentially occurred, but less CA was retained than via outer-sphere kaolinite-CA complexation. This study highlighted the significant impact of varied Fe/CA molar ratios on CA retention mechanisms in kaolinite-Fe(III)-CA systems under acidic conditions, and clearly showed the important contribution of Fe-bridged ternary complexation on CA retention. In conclusion, these findings will enhance our understanding of the dynamics of CA and other LMWOAs in tropicalmore » soils.« less
Authors:
 [1] ;  [2] ;  [3] ;  [2] ;  [2] ;  [4] ;  [5] ;  [3]
  1. Univ. of Delaware, Newark, DE (United States). Dept. of Plant and Soil Sciences
  2. Univ. of Saskatchewan, Saskatoon (Canada). Canadian Light Source Inc.
  3. Univ. of Delaware, Newark (United States). Delaware Environmental Inst., Dept. of Plant and Soil Sciences
  4. Inst. of Ecology and Environment Paris, Thiverval-Grignon (France). CNRS, IEES, UMR (CNRS-INRA-UPMC-UPEC-IRD)
  5. Univ. of Newcastle, (Australia). Global Centre for Environmental Remediation (GCER); Univ. of South Australia, Mawson Lakes (Australia). Centre for Environmental Risk Assessment and Remediation (CERAR)
Publication Date:
OSTI Identifier:
1282972
Grant/Contract Number:
AC02-98CH10886
Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 6; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Research Org:
Univ. of Delaware, Newark (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY x-ray-absorption; tetrahedrally coordinated fe(iii); differential orbital covalency; soil solution concentrations; dissolved organic-matter; forest soils; surface complexes; carboxylic-acids; iron; sorption