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Effect of iron oxides on positive and negative charges in clays and soils

Published online by Cambridge University Press:  14 March 2018

M. E. Sumner
M. E. Sumner*
Affiliation:
Soil Science Laboratory, University of Oxford
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Abstract

The contribution of free iron oxides to positive and negative charge distribution has been studied on soils and synthetic kaolinite-iron oxide complexes over a wide range of pH values. The charge on the iron oxides is pH-dependent, being positive at low and negative at high pH values, respectively, and accounts for a considerable proportion of the pH-dependent negative charge in soils. Iron oxides increase the buffer capacities of all soils and kaolinite-iron oxide complexes. A considerable proportion of the surface of the clay fraction is covered by iron oxides, resulting in a decreased negative charge on the clay. The isoelectric points of iron oxides in soils are considerably higher than those reported for pure iron oxides. A number of the soils studied were isoelectric at their field pH values, so that under field conditions they would be expected to be extremely infertile. Evidence is presented to show that kaolinite has a permanent negative charge, confirming the view that isomorphous substitutions occur.

Type
Research Article
Information
Clay Minerals Bulletin , Volume 5 , Issue 29 , July 1963 , pp. 218 - 226
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1963

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