Cation Migration in Smectite Minerals: Electron Spin Resonance of Exchanged Fe³⁺ Probes

Abstract

Abstract--The migration of interlayer Fe 3+ cations into the structure of heated montmorillonite and Laponite has been studied by electron spin resonance (ESR), MiSssbauer spectroscopy, and magnetic susceptibility measurements. The intensity of the ESR signal corresponding to interlayer Fe 3 § in air-dried montmorillonite and Laponite increased linearly as the amount of interlayer Fe 3 § increased. Changes in the spectra after thermal treatment indicate that Fe 3+ cations migrated into the pseudohexagonal cavities of dehydrated montmorillonite and Laponite. The electrostatic interaction between the Fe 3+ and the oxygen atoms defining the entrance to these cavities and the proton of the structural OH groups at the bottom of the cavities differ for the two smectites. Ferric cations were apparently bound more strongly within the pseudohexagonal cavities of the dehydrated montmorillonite than within the cavities of Laponite, because the montmorillonite did not rehydrate after heating. The differences in the binding of Fe 3 § cations within the pseudohexagonal cavities of montmorillonite and Laponite were probably due to variations in the ability of the protons of the structural OH groups to reorient. An additional electronic interaction occurred in the heated Laponite, in which small cations were able to promote the formation of structural defects, which gave rise to a sharp ESR signal at g = 2.00. No evidence for the penetration of Fe 3+ cations into the vacant octahedral sites of montmorillonite was found.

Synthesis and Characterization of Magnetically Modified Clay Composites

“…Figure shows the XRD patterns of the samples Z-Na (a), Z-Fe (b), Z-FeAc (c), and Z-Femag1 (d). As can be seen, replacement of the sodium ions by the iron ions changes the d 001 parameter of the parent montmorillonite from 12.5 to 14.6 Å . After exposure of the Z-Fe sample to acetic acid vapors, there is an expansion of the interlayer region from 14.6 Å for the iron-saturated clay to 18 Å.…”

Effect of Sequestering Intrinsic Iron on the Electron Paramagnetic Resonance Signals in Powdered Soy Proteins

“…Another prominent feature in Figure (B) is a broad peak approximately g = 2.2 found in one of the commercial ISP samples. A review of the literature indicates that this may be a form of hydrated surface iron (Coyne ; Luca and Cardile ). This peak at approximately g = 2.2 was greatly reduced after this same material was dehydrated with molecular sieves for 10 d (Figure C).…”

Dehydration, Diffusion and Entrapment of Zinc in Bentonite

“…Ben Hadj-Amara et al (1987) examined cation migration in Ni-exchanged beidellite using X-ray modeling techniques; their results suggested that Ni migrated into the vacant octa- hedral sites. Luca and Cardile (1989) studied the Fe(III) migration in smectites using electron spin resonance, M6ssbauer spectroscopy, and magnetic susceptibility measurements; no evidence for the penetration of Fe(III) into the vacant octahedral sites of montmorillonite was found. However, the penetration of Zn into the vacant octahedral sites of smectites is unlikely under field conditions where the temperatures and degree of desiccation are relatively low when compared with the conditions referred to above.…”