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Abstract  

Ion-exchanged montmorillonite-rich materials (ca. 96% purity) like NaMt, Fe(II)Mt, Co(II)Mt, Ni(II)Mt and Cu(II)Mt showed catalytic activity in the ozonation of oxalic acid in water at room temperature, in the pH range 3.4–6.0. The conversion of oxalic acid exceeds 95% after 180 min of ozone bubbling in the presence of Fe(II)Mt. The oxalic acid removal efficiency was found to increase swiftly with the acid character of the clay surface up to a certain level, but decreases gently with excessive surface acidity. The pH exerts a strong influence on the catalyst efficiency, because it induces changes in the composition of both the liquid media and catalyst. The synergic action of ozone and clay catalysts at acidic pH seems to involve ozone adsorption and interaction between cation and adsorbed oxalate. The negative effect of increasing pH between 3.44 and 6.0 is discussed in terms of a decrease in the amount and mobility of the cation in the vicinity of the clay surface, and of a decay in the clay surface area available to ozonation.

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Journal of Thermal Analysis and Calorimetry
Authors: A. V. Ursu, G. Jinescu, F. Gros, I. D. Nistor, N. D. Miron, G. Lisa, M. Silion, G. Djelveh, and A. Azzouz

Abstract

Ca–bentonite originating from a Romanian deposit was leached in 0.5–8.0 M HCl solution at 90 °C for 4 h. This material was fully characterized through BET, thermogravimetry, X-rays diffraction, and elemental analysis. The acid treatment at high temperature altered the crystallinity, but produced an increase in the surface area and thermal stability. The resulting acid-treated bentonite turned out to be an efficient adsorbent in both liquid and gaseous media. The changes of the clay mineral properties were discussed in terms of structural modification of the bulk material and increase in the number of edge terminal aluminol and silanol sites. The kinetic parameters of first dehydration step, reaction order (n), apparent activation energy (Ea) and pre-exponential factor (ln A) were calculated by the Freeman–Carroll method.

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