Abstract: Infrared and Mössbauer spectroscopy show that the extent of the reduction of nontronite is dependent on the chemical composition of the nontronite and on the nature of the reducing agent. Hydrazine reversibly reduces about 10% of the iron in all of the nontronites studied irrespective of composition and it is suggested that the resulting ferrous iron occurs only in distorted octahedral sites. Similar conclusions are reached for the dithionite reduction of the nontronites containing little tetrahedral iron, but for those with more than one in eight silicons replaced by iron, changes brought about by dithionite treatment are irreversible due to dissolution of appreciable quantities of iron. Results from both spectroscopic techniques suggest that iron in tetrahedral sites is preferentially dissolved and that up to 80% of the structural iron can be reduced.
Evidence is presented for the formation in these extensively reduced nontronites of a small amount of a mica-like phase resembling celadonite or glauconite, and, as dithionite is used for the pretreatment of soils, the implication of this observation is briefly discussed.
The use of deuterated hydrazine as a reducing agent has enabled the nontronite absorption band near 850 cm-1 to be assigned to a Si-O (apical) stretching vibration, which is inactive in the infrared for perfect hexagonal symmetry, but which is activated by distortions in the tetrahedral layer.