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Metal sorption to Spodosol Bs horizons: Organic matter complexes predominate

DOI: 10.1016/j.chemosphere.2018.01.004 DOI Help

Authors: Charlotta Tiberg (Swedish University of Agricultural Sciences; Swedish Geotechnical Institute) , Carin Sjostedt (Swedish University of Agricultural Sciences) , Jon Petter Gustafsson (Swedish University of Agricultural Sciences; KTH Royal Institute of Technology)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemosphere

State: Published (Approved)
Published: January 2018
Diamond Proposal Number(s): 8188

Open Access Open Access

Abstract: While metal sorption mechanisms have been studied extensively for soil surface horizons, little information exists for subsoils, for example Spodosol Bs horizons. Here the sorption of cadmium(II), copper(II) and lead(II) to seven Bs horizons from five sites was studied. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that cadmium(II) and lead(II) were bound as inner-sphere complexes to organic matter. Addition of o-phosphate (to 1 μmol l−1) did not result in any significant enhancement of metal sorption, nor did it influence EXAFS speciation. An assemblage model using the SHM and CD-MUSIC models overestimated metal sorption for six out of seven soil samples. To agree with experimental results, substantial decreases (up to 8-fold) had to be made for the fraction ‘active organic matter’, fHS, while the point-of-zero charge (PZC) of ferrihydrite had to be increased. The largest decreases of fHS were found for the soils with the lowest ratio of pyrophosphate-to oxalate-extractable Al (Alpyp/Alox), suggesting that in these soils, humic and fulvic acids were to a large extent inaccessible for metal sorption. The low reactivity of ferrihydrite towards lead(II) can be explained by potential spillover effects from co-existing allophane, but other factors such as ferrihydrite crystallisation could not be ruled out. In conclusion, organic matter was the predominant sorbent for cadmium(II), copper(II) and lead(II). However, for lead(II) the optimised model suggests additional, but minor, contributions from Fe (hydr)oxide surface complexes. These results will be important to correctly model metal sorption in spodic materials.

Journal Keywords: Cadmium; Copper; Lead; Soil; EXAFS; Assemblage model

Subject Areas: Chemistry, Environment

Instruments: B18-Core EXAFS

Added On: 09/01/2018 16:01


Discipline Tags:

Desertification & Pollution Earth Sciences & Environment Chemistry

Technical Tags:

Spectroscopy X-ray Absorption Spectroscopy (XAS) Extended X-ray Absorption Fine Structure (EXAFS)