Volume 93, Issue 8

The prediction of the migration for radionuclides in geologic media requires a quantitative knowledge of retardation phenomena. For this purpose, the sorption of Am(III) onto a model mineral — α-alumina — is studied here, including the effects of groundwater chemistry: pH and concentrations of small organic ligands (acetate, oxalate and carbonate anions). This work presents some experimental evidences for the synergic sorption mechanism of americium–ligand cationic complexes onto the alumina. As its anionic complexes were not sorbed, Am(III) cations were desorbed as a result of the formation of anionic complexes in the aqueous phase. By using the ion-exchange theory, and a corresponding restricted set of parameters — exchange capacities and thermodynamic equilibrium constants — the whole set of sorption experiments of Am(III) cationic species onto the α-alumina was modelled in various chemical conditions.

Studies were conducted on the dissolution of Th-doped borosilicate glass, a complex assemblage of 24 different elements in various proportions, in a wide range of pH values (0.5 to 12) and carbonate (as high as 6.2 m) and bicarbonate (as high as 1.0 m) concentrations, and as a function of time to determine whether the observed thorium concentrations exhibit an equilibrium phenomenon and to ascertain whether existing thermodynamic data can be used to interpret these results. Measurable Th concentrations were observed in either the very acidic (pH 0.5 to 4) solutions or alkaline solutions containing relatively high carbonate/bicarbonate concentrations. Steady state Th concentrations were reached over time from both the oversaturation and undersaturation directions, indicating that Th concentrations are controlled by an equilibrium solubility phenomenon. The XRD, EXAFS, and thermodynamic analyses of solubility data failed to definitively identify the nature of the solubility-controlling solid in this complex system; however, the data suggests that the solubility-controlling solid most likely involves the Th-silicate phase and that the observed Th concentrations are up to many orders of magnitude lower than in equilibrium with ThO 2 (am). The solubility study also showed that existing thermodynamic data for carbonato complexes of Th can be used to reliably predict Th concentrations in relatively dilute to concentrated carbonate/bicarbonate solutions.

Batch ion exchange tests have been employed to evaluate the ability of SuperLig® 644 resin to remove 137 Cs from highly alkaline nuclear waste solution. The batch sorption data indicated the SuperLig® 644 resin has a relatively high sorption affinity for cesium with a predicted number of bed volumes required to reach 50% breakthrough in a column operation (generally known as λ value) of ∼400 based on an initial total cesium concentration of 12.1 μg/mL. The sorption data also obey the Freundlich and Dubinin–Radushkevich isotherms.

Column ion exchange tests have been used to demonstrate the ability of SuperLig® 644 resin to remove 137 Cs from highly alkaline radioactive waste. The column test resulted in 137 Cs removal and overall decontamination factor of 99.6% (lead column) and 517000 (lag column) respectively. The concentration of 137 Cs in the lag column effluent (0.000423 μCi 137 Cs/mL) was two orders of magnitude below the low-activity waste vitrification limit of 0.087 μCi 137 Cs/mL. The bed volume (BV=175) at the onset of breakthrough exceeded the requirement of 100 BV at 50% breakthrough. Cesium elution with 0.5 M HNO 3 was adequate with a peak BV of 3.5. C / C 0 =0.01 occurred at 10 BV of eluant, which is less than the target of 15 BV. Further, 99.99% of sorbed cesium was eluted from the resin. The residual 137 Cs on the regenerated resin after the column operation was 23 μCi/g dry Na + form resin.

Removal of the radioactive tracer 60 Co from solution using pottery and its raw material (potter's clay) was studied at different conditions. The results confirmed that pottery (as a natural cheap material) has a high ability to sorb the radiotracer. The rate of sorption was found to increase with increasing surface area of the sorbent, shaking time, amount of sorbent and pH of the aqueous solution. The sorption by the potter's clay material was found to be slightly higher than the pottery, because of the presence of humic, and other organic, materials. The capacity of the sorbents for the sorption of Co 2+ was found 10.35, 9.68, mmole metal/g sorbent for raw and pottery, respectively. The sorption behavior is described by a Freundlich type isotherm, within the experimental Co 2+ concentrations used. The sorption mechanism was suggested to occur via adsorption and ion exchange. By using a pottery container (pot) as a filtering device, low level radioactive waste solution containing 60 Co + (152,154) Eu or 60 Co + (152,154) Eu + 65 Zn were completely decontaminated.

The current study was devoted to the determination of various thermodynamic and kinetic parameters resulting from the fixation of Sr 2+ by natural samples of kaolinite and clinoptilolite minerals. The sorption process followed pseudo second order kinetics, with faster sorption on kaolinite compared to clinoptilolite, where the uptake is affected by intraparticle diffusion. Freundlich and Dubinin–Radushkevich isotherm models described the data more adequately than Langmuir model, and clinoptilolite showed a higher strontium sorption capacity than kaolinite. Thermodynamically, the activation energy of Sr 2+ sorption by kaolinite and clinoptilolite were respectively, −8.5 and −18.4 kJ/mol. The sorption process on both minerals was spontaneous and endothermic at all the studied concentrations, with Δ H ° being 11.3 and 9.8 kJ/mol, for sorption on kaolinite and clinoptilolite, respectively. The findings of this study were compared with those of an earlier study on the uptake of Cs + by the same minerals.

Instrumental Neutron Activation Analysis technique (INAA) and Atomic Absorption Spectrometry (AAS) have been employed for the characterization of 40 trace elements in suspended particulate matter (SPM) and soil samples from Pakistan's industrially important cities of Gujranwala and Faisalabad. The air particulates, which were collected from five different locations of each city, indicate moderate to unhealthy air quality with SPM levels above the World Health Organization (WHO) guidelines. Enrichment factors (EF) for all the elements have been calculated with respect to their concentrations in the soils. Some of the areas of Gujranwala show high EF values for Pb, Cr, Cu, Cd and Ca, which may indicate contributions due to heavy traffic with automotive exhaust, tanneries and many other acute anthropogenic activities in this area. The presence of high concentration of Cr is due to chrome plating units and leather industry in the adjoining areas. Similarly few sites from Faisalabad have high Pb, Cd and Sb contents from vehicular aerosols with the contributions from coal combustion, battery manufacturing industries, lead smelters and numerous other industries. IAEA Reference Materials were analyzed for the validation of INAA and AAS procedures employed and to ensure the accuracy and precision of the characterized data.