Effects of Iron Oxidation State on the Specific Surface Area of Nontronite

Paul R. Lear1 and Joseph W. Stucki
Department of Agronomy, University of Illinois, Urbana, Illinois 61801
1 Current address: EPL Bio-Analytical Services, Inc., Decatur, Illinois 62525.

Abstract: The effect of Fe oxidation state on the specific surface area, Sm, of nontronite was studied using the <2-µm, Na+-saturated fraction of the SWa-1 and Garfield nontronite reference clays. The reduction of structural Fe3+ in the octahedral sheet of the nontronite decreased Sm as measured by the adsorption of 2-ethoxyethanol (ethylene glycol-monoethyl ether, EGME). The swellability in water of the nontronite also decreased during reduction. The amount of nonexchangeable Na+, on the other hand, increased with increasing Fe2+ content and was highly correlated with EGME adsorption (r = -.985). The relationship between Sm and Fe2+ was attributed to the collapse of partially or fully expanded layers to unexpanded layers.

Key Words: Ethylene glycol-monoethyl ether • Iron • Nontronite • Oxidation • Specific surface area

Clays and Clay Minerals; December 1989 v. 37; no. 6; p. 547-552; DOI: 10.1346/CCMN.1989.0370607
© 1989, The Clay Minerals Society
Clay Minerals Society (www.clays.org)