Reduction and Oxidation of Fe³⁺ in Dioctahedral Smectites — 1: Reduction with Hydrazine and Dithionite

Abstract

Abstraet--Hydrazine and dithionite, both of which are strong reducing agents, react differently with various dioctahedral smectites. Both the nature of the reducing agent and the structure of the clay affect the course of the reaction. Hydrazine reduces octahedral Fe ~ § efficiently if the mineral has a low tetrahedral charge, The reducing action of dithionite does not depend upon the charge.The results obtained by different physical methods of investigation suggest that reduction of iron is associated with protonation of an adjacent OH group. The Fe 2+ formed is readily re-oxidised but the structural change~ occurring on reduction are reversible only when AI-OH-Fe, but not when Fe-OH-Fe associations are involved. Reaction mechanisms are proposed and changes in the distribution of iron in the octahedral sites are discussed. INTRODUCTIQN

Effects of Reduction and Reoxidation of Structural Iron on the Surface Charge and Dissolution of Dioctahedral Smectites

“…The replacement of Fe a § with Fe 2 § can create local instabilities in the crystal field energies of the Fe sites and thus provide the basis for structural rearrangements that include the dissolution of Fe and Si. These results clearly show that dissolution of Fe from the clay as a result of chemical reduction in CB buffer was very small, and far below the 20% value suggested by Rozenson and Heller-Kallai (1976) for unbuffered solutions.…”

Order-Disorder Phenomena Accompanying the Dehydroxylation of Dioctahedral Phyllosilicates

“…The distribution of iron ranges from complete preference for M(2) sites to none at alt. Thus, in phengite sample 77L27 (HellerKallai and Rozenson, 1980), iron occurs only in M(2) sites, whereas in nontronite it occupies the M(1) and M(2) sites in equal proportions (Goodman et al, 1976;Rozenson and Heller-Kallai, 1976). In other minerals intermediate states were observed.…”

Redox Treatment of an Fe/Al Pillared Montmorillonite. A Mössbauer Study

“…It is finally noted that the 292 K and 20 K spectra for sample SO reveal the presence of the following iron phases, quite common in montmorillonites (Rozenson and Heller-Kallai, 1976): one paramagnetic ferric phase (85%) and one paramagnetic ferrous phase (15%), both octahedrally co-ordinated in the silicate lattice. The chemical analysis (Table 1) shows that the iron, initially present in the clay, is about 7 times less than the iron uptaken by the clay after intercalation.…”