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Molybdenum binding to soil constituents in acid soils: An XAS and modelling study
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.ORCID iD: 0000-0001-8771-7941
2015 (English)In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 417, 279-288 p.Article in journal (Refereed) PublishedText
Abstract [en]

Despite its importance as a trace element, the binding mechanisms of molybdenum in soils are not well known. In this study, we studied the binding of molybdenum onto selected soil samples, and we used X-ray absorption spectroscopy (XAS) to characterize the coordination of molybdenum on three important environmental sorbents: ferrihydrite (Fh), amorphous aluminium hydroxide (Al(OH)(3)) and fulvic acid. The X-ray near-edge structure (XANES) data showed that the added molybdenum(VI) was not reduced, although for the organic samples the coordination shifted from tetrahedral to octahedral. The EXAFS (extended X-ray absorption fine structure) analysis showed that molybdenum(VI) on Fh and Al(OH)(3) was dominated by edge-sharing bidentate complexes with Mo center dot center dot center dot Fe and Mo center dot center dot center dot Al distances of 2.80 and 2.62 angstrom, respectively. For ferrihydrite, there was a minor contribution from a corner-sharing bidentate complex at 3.55 angstrom. Further, geochemical modelling suggested an additional role of an outer-sphere complex at high pH. A sample from a spodic Bs horizon had XANES and EXAFS features similar to those of Mo sorbed to Al(OH)(3), highlighting the importance of Al(OH)(3)-type sorbents in this soil. However, in the studied organic samples molybdenum(VI) was present in a distorted octahedral configuration as an organic complex. The results were used to improve molybdenum binding reaction equilibrium constants in the CD-MUSIC model for ferrihydrite and in the Stockholm Humic Model. Collectively the results show that acid soils may contain sorbents able to bind molybdenum efficiently, and thus prevent its leaching to waters.

Place, publisher, year, edition, pages
Elsevier, 2015. Vol. 417, 279-288 p.
Keyword [en]
Molybdate, Ferrihydrite, Aluminium hydroxide, Soils, Organic, Matter, Complexation
National Category
Geochemistry Environmental Sciences Soil Science
Research subject
Land and Water Resources Engineering
Identifiers
URN: urn:nbn:se:kth:diva-179158DOI: 10.1016/j.chemgeo.2015.10.016ISI: 000365098800023ScopusID: 2-s2.0-84944458765OAI: oai:DiVA.org:kth-179158DiVA: diva2:883257
Note

QC 20151216

Available from: 2015-12-16 Created: 2015-12-11 Last updated: 2016-02-12Bibliographically approved

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The full text will be freely available from 2017-10-24 08:51
Available from 2017-10-24 08:51

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Gustafsson, Jon Petter
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