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Title: REDUCTION OF FE(III) IN GRIFFITHITE

Author
item KOMADEL, PETER - SLOVAK ACAD. OF SCIENCES
item MADEJOVA, JANA - SLOVAK ACAD. OF SCIENCES
item Laird, David
item XIA, Y - UNIVERSITY OF ILLINOIS
item STUCKI, JOSEPH - UNIVERSITY OF ILLINOIS

Submitted to: Clay Minerals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Chemical reactions occurring on the surfaces of clay minerals in soils help to break down pesticides and other organic contaminants in soils. One of the important chemical reactions involves the movement of electrons into and out of iron atoms that are part of the clay structure. We studied this reaction and found that the structure of clay minerals has a big effect on the ability of electrons to move in and out of the clay. This new fundamental knowledge will help scientists to better understand how contaminants break down in soils.

Technical Abstract: Griffithite is a trioctahedral smectite with dioctahedral domains, found in the less than 2 micron fraction of weathered basic rock from Griffith Park, California. Crystalline admixtures are concentrated in the 0.2-2 micron fraction, while the less than 0.06 micron fraction is primarily an iron-rich saponite with negative charge located on the tetrahedral sheets. The octahedral occupancy is about 91%, and about 26% of the octahedra contain trivalent atoms imparting a net positive charge to the octahedral sheet. Medium levels of Fe(III) reduction in griffithite, up to 60% of total Fe, can be achieved by adding solid sodium dithionite to clay dispersions in a citrate-bicarbonate buffer. By contrast, greater than 90% reduction of Fe(III) is achieved in nontronites using the same method. The lower reducibility of Fe(III) in griffithite relative to nontronites may be due to structural differences between griffithite and nontronites, such as a more negative tetrahedral charge and positive octahedral charge.