Vermiculite

About: Vermiculite is a research topic. Over the lifetime, 2320 publications have been published within this topic receiving 37142 citations.

Reference Chlorite Characterization for Chlorite Identification in Soil Clays

Abstract: Literature pertaining to differential thermal and X-ray diffraction of chlorite minerals is reviewed. Optical, DTA, and X-ray data for eleven chlorite samples of clinochlore, prochlorite, thuringite, corundophilite, and leuchtenbergite are given. The effect of particle size (105 to −1 μ) on DTA, X-ray diffraction, glycol retention, and cation exchange capacity are given for two thuringites, one clinochlore, and one prochlorite. Identification of chlorite by DTA in a soil clay containing a mixture of minerals is improbable at the present time except under very favorable circumstances. However, for relatively pure chlorite samples, variations in chemical composition are reflected in the differential thermal curves. The largest change in the thermogram is produced by ferric iron which lowers the peak temperature from 720° C to 610° C. Differences in thermal behavior between low and high ferric iron chlorite species are maintained for any given particle size. Chlorite thermograms obtained by different investigators show much greater variation than the differences in thermograms for other clay minerals determined on different equipment. X-ray diffraction can be used to positively identify chlorite in a soil clay, (a) by careful analysis of reflections at least as great as 14 A, and (b) by the influence heat treatment (550° C for 30 minutes) has on the X-ray pattern. Heat treatment produces marked changes in the X-ray pattern of the finer particle size samples and the magnitude of the change effected is greater for high iron chlorites (thuringite) than for low iron chlorites (clinochlore and prochlorite). Olivine is not the recrystallization product for thuringite. The smallest size fractions show no tendency toward vermiculite or montmorillonoid. Cation exchange capacity for silt size chlorites varies from 4 to 32 m.e./100gm., and for −2 μ chlorite particles from 30 to 47 m.e./100gm. Cation exchange capacities for −2 μ and −1 μ chlorites are essentially the same. Ethylene glycol retention increases with decreasing particle size. Glycol retention for −2 μ chlorite samples varies from 25 to 40 mg, glycol/gm, clay. For −1 μ chlorite material, glycol retention is 2 to 4 times greater than for −2 μ material.

Effect of the Si/Al ordering on structural parameters and the energetic stabilization of vermiculites – a theoretical study

Abstract: The effect of the Si/Al distribution in the tetrahedral sheets of the vermiculite mineral has been investigated employing density functional theory. The structures of six models for vermiculite with the structural formula (Mg4)(Mg12)(Si8Al8)O40(OH)8·24(H2O) per unit cell were fully optimized. The models differ by the T···Mg2+···T′ coordination of the interlayer Mg2+ cations by two central cations from the adjacent tetrahedral sheets of the 2:1 vermiculite layers (T,T′=Si,Al). We observed the formation of very strong hydrogen bonds between water molecules solvating the interlayer Mg2+ cations and the surface basal oxygen atoms of the 2:1 layers. The directionality of hydrogen bonds is the major factor determining the layer stacking in the vermiculite structure. Results showed that the most stable model is that where only silicon atoms in the tetrahedral sheets coordinate all interlayer Mg2+ cations.

X‐ray findings, lung function, and respiratory symptoms in black South African vermiculite workers

Abstract: Health effects have been documented among American vermiculite workers who mined and processed vermiculite contaminated with amphibole asbestos, viz., tremolite-actinolite. Workers mining and processing South Africa vermiculite (N = 172), which contains very little asbestos, underwent x-ray examination and lung function testing and completed a respiratory symptom questionnaire. The vermiculite workers were compared with other workers involved in the mining or refining of copper. Only two of the vermiculite workers showed evidence of small opacities of 1/0 or more (according to the ILO 1980 classification); lung function was comparable with the other groups of workers, and there was no excess of respiratory symptoms among the vermiculite workers. It is concluded that workers exposed to vermiculite that is minimally contaminated with asbestos are probably not at risk for pneumoconiosis, lung function impairment, or respiratory symptoms. It is likely that the health effects observed in other studies of vermiculite workers are the result of concomitant asbestos exposure. A risk of mesothelioma caused by the fiber content of the vermiculite cannot be excluded by this study.

A DFT study on the adsorption of benzodiazepines to vermiculite surfaces

Abstract: Widespread use of pharmaceuticals such as benzodiazepines has been resulting over the last decades in the dissemination of residues of these compounds in the environment, and such fact has been raising increasing concern. The generally low efficiencies of conventional wastewater treatment processes for the removal of this type of pollutants demands for the development of alternative or complementary water and wastewater treatment technologies, among which adsorption processes have been gaining popularity, provided that cheap efficient adsorbents are found. Clay materials have been one of the popular choices in this regard. In the present study, quantum chemical calculations have been performed by periodic DFT using the projector augmented-wave (PAW) method to characterize the interactions of two benzodiazepine molecules, alprazolam and diazepam, with a surface of clay mineral, vermiculite. It was observed that both molecules interact strongly with the vermiculite surface, both through a water-bridge binding and by cation-bridge provided by the exchangeable Mg2+ cations of the vermiculite surface. The results point to an interesting potential of vermiculite to be used efficiently as filter medium to remove these pollutants from water and wastewater.