Deferration Effect on Structural Ferrous-Ferric Iron Ratio and CEC of Vermiculites and Soils

C. B. Roth*, M. L. Jackson and J. K. Syers
Department of Soil Science, University of Wisconsin, Madison, Wisc. 53706
* Present address: Department of Agronomy, Purdue University, Lafayette, Indiana 47907.

Abstract: Deferration by reduction of free Fe2O3 with Na2S2O4 in the presence of Na citrate and NaHCO3 caused a change in valence state of 10 to 35 per cent of the total structural iron in micaceous vermiculites, soils, nontronite, and muscovite. An increase in Fe2+ on deferration was accompanied by an equivalent decrease in Fe3+. Subsequent treatment with H2O2 reoxidized the structural Fe2+ previously formed.

Sesquioxide coatings on micaceous vermiculites were examined electron microscopically. These coatings were composed predominantly of Fe2O3 with approximately 10 per cent by weight of Al2O3 and small amounts of SiO2, as determined by chemical analysis of the deferration extracts.

The cation exchange capacity (CEC) increased 10–60 per cent as a result of deferration of micaceous vermiculites and soils. Treatment of the deferrated sample with H2O2 restored the Fe3+ content to approximately the original value but the CEC was not affected. Consequently, the increase in CEC on deferration was attributed to the removal of the positively charged sesquioxide coating. The reversible change in valence of structural iron without an equivalent change in CEC was attributed to deprotonation-protonation of the structure (OH ⇄ O2−) simultaneous with the oxidation-reduction of iron (Fe2+ ⇄ Fe3+) in the phyllosilicate layer.

Clays and Clay Minerals; December 1969 v. 17; no. 5; p. 253-264; DOI: 10.1346/CCMN.1969.0170502
© 1969, The Clay Minerals Society
Clay Minerals Society (www.clays.org)