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  • Author or Editor: K. Venkatesan 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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Abstract  

Mesoporous silica (MCM-41) with d (100) interplanar distance of 38 Å was prepared by a room temperature process through low surfactant templation technique. The surface of MCM-41 was functionalized with dithiocarbamate (dtc) ligand, named as MCM-41-dtc and this was characterized by X-ray diffraction, BET surface area, particle size analysis, 29Si MAS NMR spectra and sulphur analysis. The sorption of mercury from 0.1M HCl solution by MCM-41-dtc was studied as a function of pH, [Hg2+], time and temperature. The sorption data obtained at various initial concentrations of mercury were fitted into Langmuir adsorption model. Mercury speciation in solution and the sorption capacity measurements indicated possible formation of a 1 : 1 square planar complex in the solid phase. A very rapid sorption of mercury was observed in the initial stages of equilibration, which can be attributed to the large surface area, wide porosity and fine particle size of MCM-41-dtc, facilitating facile accessibility of mercury into the inner pores of the sorbent. The enthalpy change accompanied by the sorption of mercury was found to decrease from 83.7 to 6.2 kJ/mol, when the initial concentration of mercury was increased from 5.10-4M to 1.5.10-3M.

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Abstract  

The amphoteric acid-base behavior of hydrous zirconium oxide (HZO) was investigated by titrating HZO with 0.05M HNO3 and NaOH at constant ionic strength. The sorption of strontium from 0.05M NaNO3 solution was measured as a function of pH. Abrupt increase in sorption was observed at the equilibrium pH of 9. The experimental titration and strontium sorption data on HZO were evaluated using the constant capacitance model (CCM) and diffuse double layer model (DLM). Various model parameters of Surface Complexation Models (SCM) were estimated, numerically, by non-linear regression. Modeling the sorption and speciation of Sr2+ on HZO indicated that the hydrolysis of Sr2+ to lower charged SrOH+ is the pre-requisite for the abrupt sorption behavior at pH 9.

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Abstract  

The electrochemical behavior of ruthenium(III) and rhodium(III) in nitric acid medium has been studied at platinum and stainless steel electrodes by cyclic voltammetry. The cyclic voltammograms consisted of surge in cathodic current occurring at potentials of −0.13 V (Vs. Pd) and −0.15 V (Vs. Pd), which culminates into peaks at −0.47 V and −0.5 V due to the reductions of Ru(III) and Rh(III) to their metallic forms, respectively. Electrodeposition was carried out at stainless steel electrode and unlike palladium, the recovery of ruthenium and rhodium was limited to ~4% and ~14%, respectively. However, a different scenario was observed in case of electrodeposition from a ternary solution containing all these platinum metals. Ruthenium and rhodium deposited underpotentially in the presence of palladium and the recovery of ~20% and ~5% was observed for ruthenium and rhodium, respectively. Evolution of RuO4 at the anode and deposition of RuO2 in the anodic side was observed in all cases during electrolysis of ruthenium(III) containing solutions.

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Abstract  

Extraction of europium(III) from nitric acid medium by a solution of tri-n-butylphosphate (TBP) and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in the room temperature ionic liquid, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (amimNTf2 where a = butyl or hexyl or octyl), was studied. The distribution ratio of (152+154)Eu(III) in TBP-CMPO/bmimNTf2 was measured as a function of various parameters such as the concentrations of nitric acid, CMPO and NaNO3. Remarkably large distribution ratios were observed for the extraction of europium(III) when bmimNTf2 acted as diluent. The stoichiometry of metal-solvate in organic phase was determined by the slope analysis of extraction data.

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Abstract  

The commercially available crystalline silicotitanate inorganic ion exchanger, IONSIV IE-911, and its parent precursor, TAM-5, have been evaluated for the removal of 137Cs from nitric acid medium and simulated high-level liquid waste. The distribution coefficient (K d) of cesium decreased with increasing nitric acid concentration and at 3.0 M nitric acid, a distribution coefficient of 1150 mL/g and 2600 mL/g were obtained for IONSIV IE-911 and TAM-5, respectively. Rapid uptake of cesium followed by the establishment of equilibrium occurring within three hours. Loading of cesium in ion exchangers increased with the increase in the concentration of cesium in aqueous phase and from Langmuir adsorption model the apparent capacity of cesium was 69 mg/g and 82 mg/g for IONSIV IE-911 and TAM-5, respectively. The performance of the sorbent under dynamic conditions was assessed by following a breakthrough (BT) curve up to C/C o = 1, where C and C o are the concentrations of cesium in the effluent and feed, respectively.

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Abstract  

Three different room temperature ionic liquids (RTILs) namely protonated betaine bis(trifluromethylsulfonyl)imide ([Hbet][Tf2N]), N-butyl-N-methylpyrrolidinium bis(trifluromethylsulfonyl)imide (BMPyTf2N) and N-methyl-N-propylpiperidinium bis(trifluromethylsulfonyl)imide (MPPiTf2N) were synthesized and characterized by CHNS analysis, NMR and FTIR spectroscopy. Heat capacity measurements and thermogravimetric analysis of these RTILs were carried out and the results are reported in this paper.

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