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  • Author or Editor: N. Sasidharan x
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Abstract  

A silica-titania (Si–Ti) mixed hydroxide gel with Ti to Si mole ratio of 11 was prepared. Studies on the sorption of radiostrontium from alkaline solutions having various concentrations of sodium were carried out with Si–Ti. The distribution coefficient (K d) of strontium decreased with increasing concentrations of sodium from 0.1 to 4.0 mol·dm–3. The plot of logK d versus log [Na+] gave a slope of –0.55 as against the theoretical value of –2.0. This suggests that some other paths in addition to the simple stoichiometric ion exchange is also existing for sorption. From pH titrations the pHpzc of Si–Ti was found to be 4.22 coinciding nearly with the pH sorption edge. An attempt was made to correlate the sorption results with the surface characteristics of the sorbent. It was found that sorption is favored when the surface of the sorbent transforms into an anionic form. Sharp increase in the sorption of strontium was observed when the equilibrium pH was between 7 and 10. This behavior could be attributed to the abrupt increase in net negative charge on the surface of the sorbent.

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Abstract  

The amphoteric nature of hydrous silica-titania gel and its sorption behaviour towards cesium were studied. In NaNO3 solution, the point of zero change (pHpzc) of the gel was found to be 4.22 by pH-titration. The fraction of protonated, deprotonated and neutral surface hydroxyl groups as a function of pH have been computed. Sorption of cesium increased with the increase of pH, reached maximum at a pH of 7 followed by a plateau. Significant uptake of cesium was observed even when the pH was less than pHpzc. Nearly 70% sorption was observed at pHpzc. The free energy of specific adsorption was found to be –18.7 kJ·mol–1.

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Abstract  

Laboratory experiments were performed on the sorption of cesium on gamma-irradiated silica-titania gel. The detrimental effects of absorbed dose on the affinity of the sorbent towards cesium was discussed. Data obtained from sorption studies were fit into heterogeneity based Freundlich isotherm. The empirical parameters, thus obtained were used to arrive at the site distribution function. The potential of site distribution function in foreseeing, the reusability and long-term residence of radionuclides in the sorbent has been highlighted.

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