TY - JOUR
T1 - Iron(III) fate after complexation with soil organic matter in fine silt and clay fractions
T2 - An EXAFS spectroscopic approach
AU - Giannetta, Beatrice
AU - Siebecker, Matthew G.
AU - Zaccone, Claudio
AU - Plaza, César
AU - Rovira, Pere
AU - Vischetti, Costantino
AU - Sparks, Donald L.
N1 - Funding Information:
This research was supported in part by the National Science Foundation Experimental Program to Stimulate Competitive Research grant number EPS-0814251. Use of the Stanford Synchrotron Radiation Lightsource is supported by the U.S. Department of Energy under contract No. DE-AC02-76SF00515. C.P. acknowledges support from the Spanish State Plan for Scientific and Technical Research and Innovation (2013-2016), award ref. AGL201675762-R (AEI/FEDER, UE). The authors thank Miguel Juanco, Materials Characterization Service (ICA-CSIC), for XRD analysis.
Funding Information:
This research was supported in part by the National Science Foundation Experimental Program to Stimulate Competitive Research grant number EPS-0814251 . Use of the Stanford Synchrotron Radiation Lightsource is supported by the U.S. Department of Energy under contract No. DE-AC02-76SF00515 . C.P. acknowledges support from the Spanish State Plan for Scientific and Technical Research and Innovation (2013-2016), award ref. AGL201675762-R (AEI/FEDER, UE). The authors thank Miguel Juanco, Materials Characterization Service (ICA-CSIC), for XRD analysis.
Publisher Copyright:
© 2020 Elsevier B.V.
PY - 2020/6
Y1 - 2020/6
N2 - Iron (Fe) speciation in soils is highly dependent on environmental conditions, mineralogy, and chemical interactions with soil organic matter (SOM). The fine silt and clay (FSi + Cl) particle size fraction of soils constitutes a primary organo-mineral fraction and contains SOM with long turnover time. In this study, the FSi + Cl particle size fractions isolated from a coniferous forest, a grassland, a technosol, and an agricultural soil were reacted with Fe(III) at pH 7. Unreacted and reacted samples were then investigated by means of extended X-ray absorption fine structure (EXAFS) spectroscopy. Statistical methods were used to determine goodness-of-fit parameters for linear combination fitting (LCF) and wavelet transformation (WT) of the Fe K-edge EXAFS data. WT separated spectral contributions from different backscattering atoms in higher coordination shells located at similar interatomic distances from the central absorbing Fe atom. LCF results paired with WT showed that the FSi + Cl particle size fractions consisted of a mixture of Fe phyllosilicates, Fe (hydr)oxides, and organically complexed Fe in different proportions. Our research revealed that after sorption experiments, in which Fe(III) was added to the system, increasing amounts of Fe(III)-SOM complexes were found in the solid phase of grassland and agricultural soils, whereas the precipitation of Fe(III) led to the preferential formation of ferrihydrite in the coniferous forest soil and in the technosol. Although the quantitative Fe-mediated organic carbon stabilization effect after Fe(III) addition is shown in this work, Fe speciation is not clearly related to SOM amount or quality (i.e., carbon-to-nitrogen ratio). The variation of Fe chemical speciation among the soil fractions likely translates into differences in their environmental fate.
AB - Iron (Fe) speciation in soils is highly dependent on environmental conditions, mineralogy, and chemical interactions with soil organic matter (SOM). The fine silt and clay (FSi + Cl) particle size fraction of soils constitutes a primary organo-mineral fraction and contains SOM with long turnover time. In this study, the FSi + Cl particle size fractions isolated from a coniferous forest, a grassland, a technosol, and an agricultural soil were reacted with Fe(III) at pH 7. Unreacted and reacted samples were then investigated by means of extended X-ray absorption fine structure (EXAFS) spectroscopy. Statistical methods were used to determine goodness-of-fit parameters for linear combination fitting (LCF) and wavelet transformation (WT) of the Fe K-edge EXAFS data. WT separated spectral contributions from different backscattering atoms in higher coordination shells located at similar interatomic distances from the central absorbing Fe atom. LCF results paired with WT showed that the FSi + Cl particle size fractions consisted of a mixture of Fe phyllosilicates, Fe (hydr)oxides, and organically complexed Fe in different proportions. Our research revealed that after sorption experiments, in which Fe(III) was added to the system, increasing amounts of Fe(III)-SOM complexes were found in the solid phase of grassland and agricultural soils, whereas the precipitation of Fe(III) led to the preferential formation of ferrihydrite in the coniferous forest soil and in the technosol. Although the quantitative Fe-mediated organic carbon stabilization effect after Fe(III) addition is shown in this work, Fe speciation is not clearly related to SOM amount or quality (i.e., carbon-to-nitrogen ratio). The variation of Fe chemical speciation among the soil fractions likely translates into differences in their environmental fate.
KW - Fe speciation
KW - Linear combination fitting
KW - Physical fractionation
UR - http://www.scopus.com/inward/record.url?scp=85080050283&partnerID=8YFLogxK
U2 - 10.1016/j.still.2020.104617
DO - 10.1016/j.still.2020.104617
M3 - Article
AN - SCOPUS:85080050283
SN - 0167-1987
VL - 200
JO - Soil and Tillage Research
JF - Soil and Tillage Research
M1 - 104617
ER -