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Iron Redox Chemistry of Clays and Oxides: Environmental Applications

James E. Amonette
James E. Amonette
Pacific Northwest National Laboratory, P.O. Pox 999 K8-96, 902 Battelle Boulevard, Richland, WA 99352
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January 01, 2002


Iron (Fe) is the most abundant element in the earth, and fourth most abundant in the earth’s crust where it comprises about 5.1 wt% (1.9 atom%). This abundance, together with an aqueous standard reduction potential for the ferric/ferrous couple (+0.77 V) that is roughly midway between the limits for aqueous chemistry (−1.1 to +1.8V), gives Fe a central role in buffering (poising) the redox chemistry in natural systems. Nearly all the Fe occurs in the structures of minerals, but the greatest fraction of this Fe that is accessible to aqueous solution is associated with the clay-sized oxides, oxyhydroxides, and layer silicates, which are chemically dominant in soils and sediments because of their large specific surfaces. From an environmental perspective, therefore, the clay-sized Fe-bearing minerals represent an inorganic source or sink for electrons that can be manipulated to achieve environmental goals.

This chapter briefly discusses the mineral forms of Fe and its use as a reductant. The fundamental chemistry of Fe, including the structural, thermodynamic and kinetic factors affecting its reactivity are then discussed. The chapter concludes with a survey of the environmental applications of mineral forms of Fe, with a major emphasis on contaminant remediation technologies involving dithionite-generated Fe(II).

A little more than one-fifth of the volume of the earth’s crust is made of Fe-bearing primary minerals (Table 1), chiefly silicates such as olivine, pyroxene, amphibole, and biotite, but also oxides such as magnetite and ilmenite. The Fe content of the silicate minerals is commonly in the 10–20 wt% range

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Clay Minerals Society Workshop Lectures

Electrochemical Properties of Clays

Alanah Fitch
Alanah Fitch
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Clay Minerals Society
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January 01, 2002




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