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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040 |a ViAlAGI  |c ViAlAGI 
072 7 |a 02C  |2 georeft 
100 1 |a Curtis, C. D.  |e analytic author  |u University of Manchester, Department of Earth Sciences, Manchester 
245 1 4 |a The aqueous geochemistry of metals in the weathering environment; strengths and weaknesses in our understanding of speciation and process 
300 |a p. 235-246 
500 |a In English. 26 refs. 
500 |a Abstract number: 03M/2622 
500 |a Category Section: Environmental studies 
500 |a Affiliation: University of Manchester, Department of Earth Sciences; Manchester; GBR; United Kingdom 
500 |a Affiliation: Natural History Museum; ; GBR; United Kingdom 
500 |a Affiliation: Birbeck College; ; GBR; United Kingdom 
500 |a Key title: Mineralogical Magazine 
500 |a Source note: 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 
500 |a Publication type: conference paper or compendium article 
504 |b 26 refs. 
510 3 |a GeoRef, Copyright 2019 American Geosciences Institute. 
520 |a 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). 
650 7 |a Aqueous solutions  |2 georeft 
650 7 |a Clastic sediments  |2 georeft 
650 7 |a Clay  |2 georeft 
650 7 |a Complexing  |2 georeft 
650 7 |a Hydration  |2 georeft 
650 7 |a Hydrolysis  |2 georeft 
650 7 |a Ligands  |2 georeft 
650 7 |a Metals  |2 georeft 
650 7 |a Mobility  |2 georeft 
650 7 |a Organic compounds  |2 georeft 
650 7 |a Phosphates  |2 georeft 
650 7 |a Sediments  |2 georeft 
650 7 |a Soils  |2 georeft 
650 7 |a Solute transport  |2 georeft 
650 7 |a Sorption  |2 georeft 
650 7 |a Thermodynamic properties  |2 georeft 
650 7 |a Weathering  |2 georeft 
700 1 |a Williamson, B.,  |e monographic author  |u Natural History Museum 
700 1 |a Hudson-Edwards, K. A.,  |e monographic author  |u Birbeck College 
711 2 |a Mineralogical Society spring meeting  |d (2001 :  |c Surrey, United Kingdom)  
773 0 |a Entwistle, J. A.  |t Mineral particles and the environment  |d London : Mineralogical Society, Apr. 2003  |k Mineralogical Magazine  |x 0026-461X  |n 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 type: conference paper or compendium article  |g Vol. 67, no. 2  |h illus., incl. 5 tables 
856 |u urn:doi: 10.1180/0026461036720097