Sorption of some radionuclides from liquid waste solutions using anionic clay hydrotalcite sorbent.

129I and 79Se are potentially important anionic radionuclides in safety assessments due to their high mobility, radiotoxicity, and long half life's (1.7 × 107 and 3.27 × 105 years, respectively). This study is interested in the sorption of 131I and 75Se radionuclides onto magnesium iron hydrotalcite (Mg/Fe HTlc). Mg/Fe HTlc was prepared by co-precipitation technique and characterized using different analytical tools such as FT-IR, XRD, XRF, TGA & DTA, SEM, and BET. Results obtained from this study showed that the adsorption process was a very fast equilibrium time (20 min). The distribution coefficient values as a function of pH have high separation factors for 131I at all different pHs. Reaction kinetic obeys the pseudo-second-order model. Maximum sorption capacity for 131I and 75Se has the values 21.45, and 9.25 mg/g respectively. Sorption isotherms are more relevant to a Langmuir isotherm. The % removal of 131I is decreased by increasing the concentration of competing species. The investigation evidenced that the prepared sorbent is suitable for the removal of 131I and 75Se from radioactive waste and could be considered potential material for purification of effluent polluted with these radionuclides.

Removal of strontium radionuclides from liquid scintillation waste and environmental water samples.

Strontium-90 (t1/2 = 29 y) is one of the most concerned isotopes in both nuclear accidents and reprocessing of nuclear fuel. In this study, the removal of strontium using low cost and valuable Dowex-HCR-S/S (DHS) resin was achieved. The kinetic and equilibrium sorption studies have been investigated using batch technique. The results of kinetic studies showed that the pseudo-second-order kinetic model was found to correlate well with the experimental data. Equilibrium data were also analyzed by sorption isotherm models indicating that the monolayer capacity of Sr(II) at equilibrium is 400.0 mg/g. It was concluded that resin has an efficient sorption capacity compared to many sorbents. The thermodynamic parameters of the removal (ΔHo, ΔSo, and ΔGo) were also determined. The removal process was endothermic and spontaneous. The resin has been successfully applied for the removal of 85Sr from organic liquid scintillator waste and some environmental waters such as tap water, river water, sea water and ground water samples. The present work concludes that the low-cost and commercial DHS resin used under these conditions has a major possibility as an efficacious material for the removal of 90Sr from environmental and real radioactive wastewaters. It can therefore have a site in the treatment of radioactive liquid waste because it is of an affordable and commercially available retention material.

Sorption of some radionuclides from nuclear waste effluents by polyaniline/SiO2 composite: Characterization, thermal stability, and gamma irradiation studies.

Polyaniline/SiO2 composite was successfully prepared via in situ polymerization using polyvinyl alcohol as a surfactant. The prepared PAn/SiO2 composite was used for the removal of Zr(IV), U(VI), and Mo(VI) ions from their liquid solutions. PAn/SiO2 composite was characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The synthesized composite was irradiated with γ-radiation from a Co-60 radioactive source with absorbed dose 50, 100, and 150 kGy and the corresponding changes in structural properties of the composites were studied. The thermal and radiation stabilities of PAn/SiO2 composite in terms of saturation capacities were studied. PAn/SiO2 composite has a good thermal stability as it retained about 78.83% of its saturation capacity upon heating at 400±1 °C, while the saturation capacity of PAn/SiO2 composite was increased from 191.28 to 319.16 mg/g for Zr(IV) with varying the irradiated doses from 0 to 150 kGy. The sorption studies for several metal ions revealed marked selectivity of PAn/SiO2 composite towards Zr(IV), U(VI), and Mo(VI) ions with selectivity order; Zr(IV) > U(VI) > Mo(VI). The results indicated that PAn/SiO2 composite removed 95.33, 75.97, and 52.87% from Zr(IV), U(VI), and Mo(VI) ions, respectively at pH 3.26. Hence, analytical utility of PAn/SiO2 composite was accomplished by performing some quantitative separation such as separation of U(VI) ions from monazite leachate and separation of Zr(IV), U(VI), and Mo(VI) ions from simulated liquid waste. Thermodynamic parameter studies concluded that the adsorption of Zr(IV), U(VI), and Mo(VI) ions was spontaneous and endothermic in nature.

Assessment of nano-sized stannic silicomolybdate for the removal of 137Cs, 90Sr, and 141Ce radionuclides from radioactive waste solutions.

Synthesized nano-sized stannic silicomolybdate was tested for the adsorption of 137Cs, 90Sr, and 141Ce radionuclides from radioactive waste solutions using batch experimentations in single metal solution. The sorption examinations were performed under the effect of some key parameters such as (pH, contact time, initial metal concentration, adsorbent weight, and temperature). Isothermal records were found to be well fitted with Langmuir adsorption model. The evaluated mean adsorption energy from the D-R isotherm model has been achieved as 18.25, 34.92, and 37.47 kJ mol-1 for 137Cs, 90Sr, and 141Ce radionuclides respectively, further conferring to the chemical process of the adsorption. The adsorption interaction of 137Cs, 90Sr, and 141Ce radionuclides onto SnSiMo obeyed pseudo-second-order rate equation. The adsorption process was controlled by particle diffusion mechanism, while intraparticle diffusion was not only the rate-limiting step. The positive values obtained for the entropy of activation suggest that there is an important change occurring in the internal structure of SnSiMo throughout the adsorption procedure.

Synthesis and physico-chemical characterization of cellulose/HO7Sb3 nanocomposite as adsorbent for the removal of some radionuclides from aqueous solutions.

Novel organic-inorganic nanocomposite cellulose/HO7Sb3 was prepared chemically by sol-gel mixing of organic poly cellulose into inorganic Sb(OH)5. The prepared nanocomposite was used as an adsorbent for the adsorption of La (III), Co (II) and Cs (I) from aqueous solutions. The adsorbent was characterized by XRD, FTIR, TEM, SEM and TGA. TEM analysis of cellulose/HO7Sb3 shows some dispersed HO7Sb3 particles in the cellulose matrix; having spherical shapes with different sizes with average particle size less than 21 nm. Furthermore, XRD and FTIR analysis confirm the formation of HO7Sb3 structure on poly-crystalline cellulose. The synthesized cellulose/HO7Sb3 demonstrated bifunctional ion-exchange groups (C-OH and Sb-OH) appearing in the FTIR absorption bands at about 1061 and 560 cm-1, respectively. The impacts of various adsorption parameters such as contact time, pH, initial metal concentrations, the amount of cellulose/HO7Sb3 nanoparticles, competing ions and complexing agent and reaction temperature were investigated using batch adsorption experiments. In terms of saturation capacity, this hybrid material retained about 80.05% of the initial saturation capacity when it irradiated by γ-radiation with dose = 50 kGy, at 150 kGy, sharp capacity loss (~ 96%) was observed. Cellulose/HO7Sb3 exhibits selectivity for La (III), Co (II) and Cs (I) in the order of La3+ > Co2+ > Cs+. The changes in the values of free energy (ΔG°) and enthalpy (ΔH°) indicate the spontaneous, feasible and endothermic nature of the sorption process. Radiometric data shows high removal and decontamination efficiency of the prepared nanocomposite especially for La-140 and Co-60. While, Cs-137 removal is less than the other radionuclides.