Infrared study of the effects of thermal treatment on montmorillonite-benzidine complexes - IV. Mn-, Co-, Ni-, Zn-, Cd- and Hg-montmorillonite

Transition metal montmorillonites were saturated with benzidine (BEN) and heated gradually to 200°C, in a vacuum cell supported by KBr windows. IR spectra were recorded before and after the thermal treatment and at various temperatures during this treatment. X-ray diffractions were recorded before and after the thermal treatment. Hg clay shows properties similar to those of Mg and Ca clays. In the interlayer BEN is bound to Hg through a water molecule bridge, either by proton accepting (type A) or by proton donation (type B). Some BEN is also protonated (type D). Initially type A predominates, but after the thermal treatment, when the film is rehydrated, the amounts of types B and D increase. With Mn-, Co-, Ni-, Zn- and Cd-montmorillonite a direct coordination of the benzidine by the dehydrated metallic cation is obtained (type C), in addition to small amounts of types A, B and D. During the thermal treatment water is evolved and associations A and B are completely transformed to C. At elevated temperatures the following associations were identified in trace amounts, ammonium-amine, BEN bound to non-structured water, hydrophobic adsorbed BEN and BEN bound to the oxygen plane (types E, F, H and J, respectively). During the thermal treatment of Co and Cd clays some of the benzidine was oxidized, probably to semiquinone and quinoidal cation.