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

The effect of Fe oxidation state on the specific surface area, S m , of nontronite was studied using the <2- µ m, Na + -saturated fraction of the SWa-1 and Garfield nontronite reference clays. The reduction of structural Fe 3+ in the octahedral sheet of the nontronite decreased S m 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 Fe 2+ content and was highly correlated with EGME adsorption (r = -.985). The relationship between S m and Fe 2+ was attributed to the collapse of partially or fully expanded layers to unexpanded layers.