The aqueous geochemistry of metals in the weathering environment; strengths and weaknesses in our understanding of speciation and process

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doi: 10.1180/0026461036720097
Authors:Curtis, C. D.
Author Affiliations:Primary:
University of Manchester, Department of Earth Sciences, Manchester, United Kingdom
Other:
Natural History Museum, United Kingdom
Birbeck College, United Kingdom
Volume Title:Mineral particles and the environment
Volume Authors:Entwistle, J. A.; Williamson, B.; Hudson-Edwards, K. A.
Source:Mineralogical Magazine, 67(2), p.235-246; Mineralogical Society spring meeting, Surrey, United Kingdom, April 2001, J. A. Entwistle, B. Williamson and K. A. Hudson-Edwards. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0026-461X
Publication Date:2003
Note:In English. 26 refs.; illus., incl. 5 tables
Summary:Soil profiles developed in different climates and physical settings are highly variable in structure, in mineralogy, in the local biosphere and in the compositions of the soil gas and water phases. Discussion of metals in "the weathering environment" needs to acknowledge and address this diversity. The thermochemical methods developed by Pourbaix (1949) and Garrels and Christ (1965) remain useful predictors of metal speciation and solubility but the approach is valid only for processes involving carbonates, sulphides, hydroxides and similar minerals in soils and sediments. Almost no primary silicates are thermodynamically stable: they spontaneously decompose to non-equilibrium solid products with metal release determined by kinetics. Hydrolysis constants for aquo-complexes are useful indicators of metal speciation, mobility and availability. Recent work on soluble soil organic matter confirms that the active ligands are overwhelmingly oxygen based: phenols, carboxylic acids, alcohols. Many of these molecules compete very effectively with aquo-complexes to form strong metal chelates and appear to be responsible for substantial Al and Fe mobilization within and translocation down soil profiles. It is important to note also that strong clay mineral/organic matter associations (clay-organic complex) will fix metals as a consequence of the same chelation reactions (in this case removing them from solution-retardation).
Sections:Environmental studies
Subjects:Aqueous solutions; Clastic sediments; Clay; Complexing; Hydration; Hydrolysis; Ligands; Metals; Mobility; Organic compounds; Phosphates; Sediments; Soils; Solute transport; Sorption; Thermodynamic properties; Weathering
Abstract Numbers:03M/2622
Record ID:2003051799
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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