Solid-state cadmium-113 nuclear magnetic resonance study of exchanged montmorillonites

Abstract

The solid-state 113Cd nuclear magnetic resonance of cadmium adsorbed on montmorillonite was investigated. An analysis of three montmorillonite samples and a brief comparison with other clays are included. The spectra contain cadmium oxoanion components of differing line widths with differential sensitivities to preparation conditions. Echo train experiments at various temperatures and delays indicate that the line widths are governed by dynamic processes rather than chemical shift dispersion.These same experiments show the heterogeneity of the cadmium sites. Included in the study are the effects of pH variation, exchanged clay form, pretreatment with alginic and humic acids, and airand freeze-drying. These results are described in terms of ions in different environments and ion motion. For montmorillonite some of these sites are considered to be near iron in the octahedral layer. The interlayer ion diffusion is related to metal ion transport in clay layers and the potential consequences of migration.(1) SUNY at Albany.

Nuclear Magnetic Resonance (NMR) Study of Cd2+ Sorption on Montmorillonite

“…Relatively strong negative chemical shifts characterize the dehydrated phase of Cd-rich vermiculite and are caused by the absence of H20 molecules shielding Cd from the influence of structural-oxygen ions (Laperche et al, 1990). Because only two-layer hydrated phases are present in our samples (Figure la), the --40-ppm component may depict Cd on the external surfaces of montmorillonite, consistent with the interpretation of Tinet et al (1991) and Bank et al (1989). Dynamics (slow relaxation and low cross-polarization rate) of the --40-ppm peak depicting Cd z+ suggest the Cd species is not surrounded by many H20 molecules.…”

“…The sample has a low Fe content (0.8 wt. % FezO3) which prevents line broadening or variations in chemical shift owing to ferromagnetic impurities, especially Fe 3 § (Bank et al, 1989).…”

“…The presence of more than one chemical environment for interlayer Cd-chloride species may cause chemical-shift dispersion in the MAS experiments, which would account for the observed broadening of the peak at -116 ppm (FWHH 8-11 kHz) in the 113Cd MAS spectra of samples treated with 1 M CdC12 (Figure 4). The influence of paramagnetic nuclei, also responsible for broadening of the ll~Cd NMR signal (Bank et al, 1989), is ruled out due to the low amount of octahedral iron present in the montmorillonite samples (0.8 wt. % of Fe203).…”

“…Nevertheless NMR was used to study ll3Cd sorbed on montmorillonite by Bank et al (1989). The MAS NMR spectra of ll3Cd in Cd-rich montmorillonite showed both a narrow signal (1 kHz) and a broad signal (6-9 kHz) which were interpreted as an edge site in interaction with the iron in the octahedral positions (narrow component) and an interlayer site with low chemical-shift anisotropy (broad component).…”

A Nuclear Magnetic Resonance (NMR) and Fourier-Transform Infrared (FTIR) Study of Glycine Speciation on a Cd-Rich Montmorillonite

“…The sample has a low Fe content (0.8 wt. % Fe203) and thus there is no NMR line broadening or variation in chemical shift owing to ferromagnetic impurities, especially relating to Fe 3+ (Bank et al, 1989).…”