[en] A series of rare-earth-doped sodium titanates with the chemical formula R_x H_y Na_4-(x+y)TiO₄·nH₂O (where R = Ce³⁺, Nd³⁺ and Sm³⁺) were grown employing solid-state fusion reaction technique. The physico-chemical investigations indicated that the new materials were self engineered into large particles enough to be used in sorption process and having crystalline structures containing localized Na⁺ ions. Equilibrium studies revealed that an enhancement in sorption efficiency of sodium titanate after rare-earth doping. The neodymium-rich sodium titanate exhibited a better exchange affinity for Cs⁺ compared to the other studied series. Data on the kinetics of cesium exchange fit well to pseudo-second order and intra-particle diffusion models. In a separate experiment, it was reported that the R-HNaTi series showed responsible sorption affinity toward Ce, Nd and Sm ions in their solution mixture with insignificant selectivity trend which reflects the high stability of titanate matrices. (author)

[en] Tin and zirconium silicates have been prepared with Sn/Si and Zr/Si molar ratios of I and 0.75, respectively. Kinetics and exchange studies of Zn²⁺ and Eu³⁺ ions on the prepared stannous and zirconium silicates have been carried out as a function of reaction temperature, particle diameters, solution concentration of the exchanging cations from water and alcohol-water mixture. The capacity of the exchangers for the studied cations from alcohol-water mixture were found higher than in pure aqueous solutions. The rate of exchange was dependent on particle diameters and independent on concentration of metal ions. The kinetic and thermodynamic parameters, vis. effective diffusion coefficients, activation energies and entropies of activation have been evaluated. Negative values of entropy, enthalpy and free energy of activation for Zn²⁺/H⁺ and Eu³⁺/H⁺ on both exchangers have been recorded at different conditions

[en] Sorption of Na(I), Cs(I) and Co(II) radionuclides from aqueous solutions by titanosilicate have been investigated. The time dependent studies for metal ions showed relatively rapid sorption kinetics between 5 and 30 min to reach equilibrium. A batch adsorption model based on assumption of the pseudo-second-order mechanism was applied to predict the sorption rate, while the equilibrium capacity was calculated at different temperatures. The adsorption of different radionuclides onto titanosilicate was found to be favored at high ions concentrations and low temperature for Na⁺ and Co²⁺ while at high temperature for Cs⁺. Activation energy of adsorption was computed to be 2.35, 24.11 and 5.74 kJ/mol for adsorption of Na(I), Cs(I) and Co(II), respectively. The results revealed that the adsorption of Cs⁺ is the highest relative to Na⁺ and Co²⁺ at different conditions which may be attributed to its low hydration energy. Further, the equilibrium isotherm for the interested ions was analyzed and it was found to obey Frundlich equation. (author)

[en] A new form of semicrystalline sodium titanate was synthesized at high temperature (1100-1150 deg C) by a reaction of TiO₂ with Na₂CO₃ in an equimolar ratio. The obtained product was characterized using IR, DTA-TG, X-ray diffraction and elemental analyses. According to X-ray patterns, H₂Ti₅O₁₁ x nH₂O with monoclinic structure has been formed on dehydration of semicrystalline sodium titanate. Kinetic studies of the order and activation energy of a new phase transformation have been determined from DTA-thermograms. The ion exchange behavior of semicrystalline sodium titanate was studied at different γ-doses as well as at different drying temperatures. The laboratory-scale ion exchange capacity, distribution studies and exchange performance for some radionuclides of a thermally prepared material were investigated. It was found that the exchange capacity was not changed after 100 kGy irradiation. (author)

[en] Modification of the physico-chemical properties of hydrous titanium dioxide (TiO₂) was conducted by using binding polyacrylonitrile (PAN) for the preparation of larger size particles having higher granular strength. The thermal behavior of the obtained composite has been studied by thermogravimetric and differential thermal analysis (TG/DTA). Sorption behavior of the TiO₂-PAN composite for removal of some hazardous radionuclides has been studied at different conditions such as, pH, contact time, ion concentrations and reaction temperature as well as the drying temperature. The effects of interfering ions as well as some complexing agents on the distribution ratio of the sorption process have been determined. As a result of the obtained data the optimum conditions for the removal of the studied radionuclides were recommended. (author)

[en] New advanced form of semicrystalline sodium titanate was synthesized at high temperature (1100-1150 degree) by a reaction of TiO₂ with Na₂CO₃ in an equimolar ratio. The obtained product was characterized using IR, DTA-TG,X-ray diffraction and elemental analyses. According to X-ray patterns, H₂Ti₅O₁₁.nH₂O with monoclinic structure may formed on dehydration of semicrystalline sodium titanate. Kinetic studies of the order (n) and activation energy (E_a) of a new phase transformation have been determined from DTA-thermo gram. The ion exchange behaviour of semicrystalline sodium titanate was studied at different gamma-doses as well as at different drying temperatures. The laboratory-scale ion exchange capacity, distribution studies and exchange performance for some radionuclides of a thermally prepared material were investigated. It was found that exchange capacity was not changed after an irradiation of up 100 KGy

[en] Hydrous titanium oxide (HTO) has been prepared in new different cobalt forms HTOC-I and HTOC-ll by direct precipitation in presence of 0.01 and 0.05 M CoCl₂ respectively. Powder XRD, DTA-TGA, ir, and elemental analysis characterized the new obtained products. The matrices were used for the removal of radioactive cesium, cobalt and cerium by studying the ¹³⁴Cs, ⁶⁰Co and ¹⁴⁴Ce distribution coefficients (K_D) by batch experiments at different ph ranges as well as at different reaction temperatures. The sorption affinity for ⁶⁰Co at low cobalt doped concentration of hydrous titanium dioxide (HTOC-I) is higher than for high cobalt one (HTOC-ll). The thermodynamic parameters of the exchange processes were studied by employing the van,t hoff equation

[en] Tin and zirconium silicates have been prepared with Sn/Si and Zr/Si molar ratios of 1 and 0.75, respectively. Kinetics and exchange studies of Zn²⁺ and Eu³⁺ ions on the prepared stannous and zirconium silicates have been carried out as a function of reaction temperature, particle diameters, solution concentration of the exchanging cations from water and alcohol-water mixture. The capacity of the exchangers for the studied cations from alcohol-water mixture was found higher than in pure aqueous solutions. The rate of exchange was dependent on particle diameters and independent on concentration of metal ions. The kinetic and thermodynamic parameters, vis. effective diffusion coefficients, activation energies and entropies of activation have been evaluated. Negative values of entropy, enthalpy and free energy of activation for Zn²⁺/M⁺ and Eu³⁺/H⁺ on both exchangers have been recorded at different conditions

[en] The kinetics of exchange reactions of Na⁺ and Co²⁺ ions on amorphous and crystalline sodium titanates have been studied at different reaction temperatures (25 degree, 40 degree and 60 -+1 degree) and different drying temperatures of the exchangers (50 degree 200 degree and 400-+1 degree). The conditions which are set to study the particle diffusion mechanism only and is confirmed from straight lines of B vs. 1/r² plots. The values of diffusion coefficients and other thermo-dynamic parameters are calculated at different operative conditions. Negative values of entropy change are recorded for all systems studied on both exchanger, which indicate that Na⁺ and Co²+ ions exchange with both forms of titanates in unhydrated state. The results revealed that, the ionic diffusion of Na⁺ ions is higher than Co²⁺ ions

[en] Iron(III) (FeTi) and chromium (III) titanates (CrTi) were prepared as cation exchange materials in a granular form. The rate of the isotopic exchange of Na⁺/*Na⁺ and Zn²⁺/*Zn²⁺ between aqueous solution and iron(III) and chromium(III) titanates in Na⁺ or Zn²⁺ form has been carried out radiometrically in the 25-60 deg C temperature range. The exchange rate is controlled by a particle diffusion mechanism and experimental and theoretical approaches have been used to obtain the rate of diffusion through the spherical particles of the exchangers. The values of self diffusion (D-bar) of Na⁺ and Zn²⁺ ions were measured at different operation conditions, particle size, reaction temperatures and drying temperatures of the matrix. The values of kinetic and thermodynamic parameters were calculated and their significance discussed. (author)