Sorption of curium by silica colloids: effect of humic acid

Sorption of curium by silica colloids has been studied as a function of pH and ionic strength using (244)Cm as a tracer. The sorption was found to increase with increasing pH and reach a saturation value of ∼95% at pH beyond 5.3. The effect of humic acid on the sorption of (244)Cm onto silica was studied by changing the order of addition of the metal ion and humic acid. In general, in the presence of humic acid (2 mg/L), the sorption increased at lower pH (<5) while it decreased in the pH range 6.5-8 and above pH 8, the sorption was found to increase again. As curium forms strong complex with humic acid, its presence results in the enhancement of curium sorption at lower pH. At higher pH the humic acid present in the solution competes with the surface sites for curium thus decreasing the sorption. The decrease in the Cm sorption in presence of humic acid was found to be less when humic acid was added after the addition of curium. Linear additive model qualitatively reproduced the profile of the Cm(III) sorption by silica in presence of humic acid at least in the lower pH region, however it failed to yield quantitative agreement with the experimental results. The results of the present study evidenced the incorporation of Cm into the silica matrix.

Thermodynamic study of Th(IV) complexes with dicarboxylates by potentiometry and calorimetry

The thermodynamic quantities (ΔG c, ΔH c and ΔS c) for formation of Th(IV) complexes with dicarboxylic ligands, namely, malonate, succinate, glutarate and adipate were determined using potentiometry and calorimetry. The protonation constants of the dicarboxylate ligands were determined by potentiometric titration of the ligand solution, while the corresponding enthalpy values were taken from the literature. In the case of Th(IV)-malonate, multiple species (ML j , j=1–3) were revealed from the potentiometric data, while in the case of higher homologues, the data for only 1:1 complex could be obtained owing to precipitation at higher ligand concentration. The effect of chain length on the thermodynamic parameters of Th(IV)-dicarboxylate complexation was studied. All the complexation reactions were found to be highly entropy driven, which is the characteristic of the hard acid (metal ion) and hard base (ligand) interactions. The TΔS c values for 1:1 complexes were found to be nearly constant while the ΔH c values increased from malonate to glutarate and then leveled off in adipate. The thermodynamic data of Th(IV) have been compared with corresponding data for U(VI) and rare earths.

Selective separation of radio-cesium from acidic solutions using supported liquid membrane containing chlorinated cobalt dicarbollide (CCD) in phenyltrifluoromethyl sulphone (PTMS)

A supported liquid membrane method was developed using chlorinated cobalt dicarbollide (CCD) in phenyltrifluoromethyl sulphone (PTMS) as the carrier, impregnated in PTFE flat sheet membranes for the selective separation of Cs(I) from nitric acid feed solution. Solvent extraction studies were carried out for optimizing the feed as well as strip conditions. >95% Facilitated transport of Cs(I) was observed in about 3h when 1M HNO(3) and 8M HNO(3) were used as the feed and strip solutions, respectively while 0.025M CCD in PTMS was used as the carrier extractant. Selectivity studies, carried out using a mixture of radiotracers viz. (51)Cr, (59)Fe, (99)Mo, (99m)Tc, (106)Ru, (137)Cs, (152)Eu and (241)Am, indicated selective transport of Cs(I) with DF values >100. Though reproducibility of the transport data was excellent when carried out in two successive transport experiments with freshly loaded carrier solvent, the stability of the membrane was poor which restricts its long term use.

Selective caesium transport using hollow fibre-supported liquid membrane containing calix[4]arene-bis-naphthocrown-6 as the carrier extractant

Polypropylene hollow fibre-based supported liquid membrane (HFSLM) containing calix[4]-bis-2,3-naphtho-crown-6 in 20% (v/v) n-dodecane+80% (v/v) 2-nitrophenyl octyl ether (NPOE) as the carrier solvent was employed for the first time to investigate the transport behaviour of radio-caesium. The carrier solution was 1 mM calix[4]-bis-2,3-naphtho-crown-6 in 20% (v/v) dodecane+80% (v/v) NPOE+0.4% alamine 336 and the feed was 3 M HNO3 while distilled water was used as the receiver phase. In spite of high viscosity of the carrier solvent, quantitative (>99%) transport was possible in about 6 h. Significant amount of acid transport was also noticed which was ascribed to a co-transport mechanism involving encapsulated hydronium ion. Selectivity studies were carried out by taking a mixture of radiotracers, viz. 51Cr, 59Fe, 85,89Sr, 137Cs, 152,154Eu and 241Am, which represent some of the elements present in the high level waste, in the feed solution. The decontamination factors for various metal ions were found to be in the range 540–890. High decontamination factors as well as possibility of working over several days without deterioration of the liquid membrane suggested possible application of the system for the recovery of radio-caesium from high level waste. Studies on the membrane stability indicated reproducible transport data over 40 h.

Sorption of 137Cs, 133Ba and 154Eu by synthesized sodium aluminosilicate (Na-AS)

Sodium aluminosilicate has been synthesized by solution route for use as a sorbent for various radionuclides. It was characterized by XRD, zeta potential, BET surface area, FTIR spectroscopy and site density measurement. Sorption studies of (137)Cs, (133)Ba and (154)Eu on synthesized sodium aluminosilicate have been carried out at varying pH (3-10). Sorption of all the metal ions was found to increase with pH of suspension with the saturation value increasing with the oxidation state of metal ion. Effect of Aldrich humic acid (2mg/l) on sorption was also investigated. In case of (137)Cs, the sorption was not affected by the presence of humic acid, while in case of (133)Ba and (154)Eu, sorption was enhanced at lower pH and decreased at higher pH in presence of HA. A series of experiments were carried out for (154)Eu sorption on sodium aluminosilicate at various conditions. Sorption of europium was analyzed by different sorption isotherms, viz., Freundlich and D-R isotherm. Thermodynamic data reveal sorption phenomena as endothermic and spontaneous. Studies were further extended to find out effect of diverse ions (Ca(2+) and CO(3)(2-)) on sorption of europium.

Selective recovery of uranium from THOREX feed by hollow fibre supported liquid membrane technique containing di(2-ethylhexyl) isobutyramide (D2EHIBA) as the carrier

Hollow fibre supported liquid membrane (HFSLM) studies were carried out for the selective recovery of uranium from THOREX feed solution (0.2 g/L U+200 g/L Th+0.03 M HF+0.1 M Al(NO3)3 at 4 M HNO3) using di(2-ethylhexyl) isobutyramide (D2EHIBA) as the carrier and distilled water as the strippant. About 85% of uranium was selectively transported into the receiver phase in 30 min with <1% contamination from thorium. On the other hand, under identical conditions of feed and strip solutions, about 90% of uranium was recovered in the same time when 5% TBP (tri-n-butyl phosphate) was used as the carrier, but a relatively large amount of thorium (>10%) was also co-transported to the product side. Strip phase acidity analysis revealed significant amount of acid co-transport with both the carriers. Acid transport was found to increase with the total salt content of the feed solution. The transport of metal ions was explained with the help of a theoretical model. Stability of the liquid membrane was also studied over about 5 d for long term reusability.