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Chapter 8 Properties and Behaviour of Iron in Clay Minerals
Handbook of Clay Science Edited by F. Bergaya, B.K.G. Theng and G. Lagaly Developments in Clay Science, Vol. 1 r 2006 Elsevier Ltd. All rights reserved.
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Chapter 8
PROPERTIES AND BEHAVIOUR OF IRON IN CLAY MINERALS J.W. STUCKI Department of Natural Resources and Environmental Sciences, University of Illinois, W-321 Turner Hall, 1102 S. Goodwin Ave, Urbana, IL 61801-4798, USA
Because iron (Fe) is the fourth most abundant element in the Earth’s crust (6% of mass), next to oxygen, silicon, and aluminium, its ubiquitous presence in clays and clay minerals should be no surprise. It is, in fact, an intimate part of many processes occurring in natural ecosystems. Murad and Fischer (1988) have reviewed many pools of iron that exist in nature and discussed the geobiochemical cycle of iron (summarised briefly in Fig. 8.1), illustrating how it is transformed from one pool to another. They have also pointed out the many connections within and between the mineral or inorganic phases of iron and its organic or biological phases in the environment. The number and complexity of these interactions are great, so a complete discussion of the significance of terrestrial iron would fill many volumes. In this chapter, emphasis is placed on a description of the phases in which iron occurs in clay minerals and the properties and behaviours it imparts to them by virtue of its susceptibility to oxidation and reduction (redox) reactions. As is evident from Fig. 8.1, redox is a pathway that is common to several of the inter-pool transformations and thus exerts much influence on terrestrial ecosystems. An expanded treatise on iron in soils and clay minerals was published by Stucki et al. (1988), who reviewed the chemistry, detection, and characterisation of iron in oxides, carbonates, sulphides and sulphates, phyllosilicates, agricultural soils, hydromorphic and lateritic soils, and pedogenic processes. The treatise also touched on the role of microorganisms in determining the fate of iron in soils and sediments. Since that work was published, much progress has been made in understanding and characterising structural iron in smectites, especially in relation to redox processes. Advances have also been made in the study of iron in other phyllosilicate minerals such as kaolinite and mica. The effects of structural iron on clay mineral properties have been reviewed by Stucki (1988) and Stucki and Lear (1989). Since then little new information has come to light regarding the overall effect of structural iron on clay mineral properties, although much has been learned about the effects brought about by changes in the DOI: 10.1016/S1572-4352(05)01013-5
423
Chapter 8
PROPERTIES AND BEHAVIOUR OF IRON IN CLAY MINERALS J.W. STUCKI Department of Natural Resources and Environmental Sciences, University of Illinois, W-321 Turner Hall, 1102 S. Goodwin Ave, Urbana, IL 61801-4798, USA
Because iron (Fe) is the fourth most abundant element in the Earth’s crust (6% of mass), next to oxygen, silicon, and aluminium, its ubiquitous presence in clays and clay minerals should be no surprise. It is, in fact, an intimate part of many processes occurring in natural ecosystems. Murad and Fischer (1988) have reviewed many pools of iron that exist in nature and discussed the geobiochemical cycle of iron (summarised briefly in Fig. 8.1), illustrating how it is transformed from one pool to another. They have also pointed out the many connections within and between the mineral or inorganic phases of iron and its organic or biological phases in the environment. The number and complexity of these interactions are great, so a complete discussion of the significance of terrestrial iron would fill many volumes. In this chapter, emphasis is placed on a description of the phases in which iron occurs in clay minerals and the properties and behaviours it imparts to them by virtue of its susceptibility to oxidation and reduction (redox) reactions. As is evident from Fig. 8.1, redox is a pathway that is common to several of the inter-pool transformations and thus exerts much influence on terrestrial ecosystems. An expanded treatise on iron in soils and clay minerals was published by Stucki et al. (1988), who reviewed the chemistry, detection, and characterisation of iron in oxides, carbonates, sulphides and sulphates, phyllosilicates, agricultural soils, hydromorphic and lateritic soils, and pedogenic processes. The treatise also touched on the role of microorganisms in determining the fate of iron in soils and sediments. Since that work was published, much progress has been made in understanding and characterising structural iron in smectites, especially in relation to redox processes. Advances have also been made in the study of iron in other phyllosilicate minerals such as kaolinite and mica. The effects of structural iron on clay mineral properties have been reviewed by Stucki (1988) and Stucki and Lear (1989). Since then little new information has come to light regarding the overall effect of structural iron on clay mineral properties, although much has been learned about the effects brought about by changes in the DOI: 10.1016/S1572-4352(05)01013-5