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Cesium radioisotopes are among the majors that are presented in liquid radioactive waste causing long-term environmental threats. The mandatory treatment of these streams is regenerative goal in wh...

Individual metakaolin-based alkali activated binder (AAB) was utilized to optimize binary and ternary ones having f e l d s p a r / m e t a k a o l i n and s l a g / f e l d s p a r + m e t a k a o l i n ratios of 0.3 and 0.4, respectively. These three AABs had the ability to directly solidify 10.0 (FMK0-10R), 8.0 (FMK3-8R) and 12.0% (S4FMK3-12R) of the nuclear grade KY-2 beads, respectively, recording compressive strength values greater than twice the waste acceptance criteria. Leaching of 134Cs, 60Co and 152+154Eu, whether singularly or multiply loaded, was assessed. The multi-radionuclidic systems recorded greater leached fractions in the order of: 152+154Eu>134Cs>60Co. Among the studied systems, S4FMK3-12R formulations recorded the lowest diffusion coefficient values (D). Gamma-irradiation made a desired influence on all studied leaching systems with inverse relationships with the applied irradiation doses. Irradiating the optimized ternary AAB with 3.0 KGy (S4FMK3-12R-ɣ3) yielded the lowest D value (6.65 × 10−13 cm2/s), when single component-60Co was diffused. The leachability indexes of all irradiated AABs were not only greatly exceeded the value of 6 but also sometimes be twice such value. XRD, FT-IR and SEM examinations of S4FMK3, S4FMK3-12R and S4FMK3-12R-ɣ3 reflected their multi-layered semicrystalline natures and to what extent these AABs and the solidified beads had good and poor radiation stabilities, respectively, with a proposed three-step mechanism of such instability.

Radio-cesium constitutes major environmental threats. Sorption of hazardous species onto geopolymeric sorbents is relatively recent and may give information about the retention mechanisms when geopolymers are applied to immobilize radwastes. Here, Na-MK, K-MK, Na-MKBFS, and K-MKBFS geopolymeric sorbents were synthesized from metakaolin (MK) and blast furnace slag (BFS) and were characterized using XRD, XRF, FT-IR, DTA/TGA and SEM. FT-IR/XRF results clarified the impact of mono-valent alkali cation (M+) in dividing the sorbents into Al-rich (sodium-based) and Si-rich (potassium-based). All sorbents were amorphous to semi-crystalline containing mica-phyllosilicates (greater in Si-rich), tobermorites (greater in MKBFS-based), gehlenite, calcite, quartz, hematite and hydrotalcite. Isotherms of 134Cs radionuclide sorption were constructed, being regular with a positive temperature effect. Al-rich sorbents gave higher sorption capacities than Si-rich ones. Na-MK sorbent recorded the more distinctive sorption capacity (74.95 mg/g; at 333 K). Langmuir, Freundlich and D-R models were used to disclose the capacities and mechanisms governing the sorption processes. Sorption of Cs+ onto the examined sorbents was favorable. All systems were controlled by ion exchange mechanism, except 134Cs/K-MK system which was controlled by physi- sorption mechanism. 134Cs/Na-MK GP system was the only spontaneous among all. The endothermic natures were the common denominator between the tested systems.

The present study introduces a new approach based on an irradiated tin target's impurity to produce a125Sb/125mTe radioisotope generator. A prepared generator gel matrix of zirconium-silico-tungstate was loaded with 6660 MBq (180 mCi) activity of the separated antimony. The loading and elution method has been studied as a function of the concentration of H2SO4 acid solution. The effect of mild oxidant (ascorbic acid) in the loading and complexing agent (acetic acid) in elution was investigated to improve the generator's elution profile. A mixture of (0.5 M) ascorbic acid and (0.5 M) H2SO4 acid solution as a loading solution resulted in a maximum distribution of 125Sb. In comparison, using (0.4 M) acetic acid as an eluent solution 125mTe yield reached 88.7% and minimised percentage of 125Sb breakthrough was obtained (

Sorption of fission products onto polycondensed aluminosilicates (PC-AS(s)) is a relatively recent and gets out the mechanisms by which the formers are trapped. Here, PC feldspar (PC-FD), perlite (PC-PR) and their blend (PC-FDPR) were synthesized by the alkaline activation using Na-/K-silicates at Si-modulus of 1.35. XRD patterns revealed the semi-crystalline natures of sorbents. Na- and K-feldspars were detected in PC-FD while Na-based carbonate crystals were detected in others. Components of the poly(sialate-disiloxo) structure were detected in FT-IR spectra. Thermographs were deconvoluted and the amounts of the sticking and zeolitic water were estimated. Kinetic batches for sorption of 134Cs and 152+154Eu onto the elaborated yields were constructed. Ranking of sorbed amounts (qe) was varied from 134Cs (PC-FDPR>PC-FD>PC-PR) to 152+154Eu (PC-PR>PC-FD>PC-FDPR). Maximum qe was recorded at elevated temperature (323 K) to be 4.28 and 1.45 mg/g for 134Cs/PC-FDPR and 152+154Eu/PC-PR, respectively. Along all batches, chemi-sorption mechanism is common denominator. The effective diffusion coefficients (Di) were in the order of 10−14 m2/s. Both PC-FD and PC-FDPR recorded greater Di values of 134Cs than 152+154Eu. The low values of Ea (kJ/mol) reflected the weak adsorbats-adsorbents interactions. While, the high negative values of ∆S‡ suggested that the studied radionuclides were sorbed in associative reaction mechanism

The present work was established to determine the applicability of local Egyptian kaolinite and blast furnace slag (BFS) as raw materials toward the synthesis of geopolymers and subsequent immobilization of cobalt-60, which is one of the most abundant radionuclides generated in radioactive waste streams in Egypt. XRF, XRD, FT-IR, and SEM techniques were used to characterize the local raw materials and their corresponding alkali activated products. Metakaolin (MK) was obtained by thermal treatment of Egyptian Sinai kaolin 750 °C/4 h. MK and five different BFS content (5, 10, 30, 50 and 80%) were used to synthesize geopolymeric matrices using an alkaline activator of Si-modulus = 1.35 at solid/liquid ratios of 0.8. Compressive strength tests were performed indicating that 50% BFS addition gave the highest values of compressive strength. The IAEA standard leaching tests of cobalt-60 from the solidified waste matrices were carried out. The effective diffusion coefficients of cobalt-60 radionuclides from the solidified waste matrices were calculated to be in the order of 10 −14 cm 2 /s. Leaching of radionuclides was examined to be controlled by the wash-off mechanism with very acceptable values. These results gave encouragement that the tested Egyptian raw materials can be conveniently applied for the synthesis of geopolymers that can be used as a low-cost and high-efficiency materials for the immobilization of radioactive waste.

The direct incorporation of α-Keggin structure, [PMo12O40]3−, derived from ammonium molybdophosphate into the mesopores of MCM-41 silica to synthesis MP/MCM-41 composite was carried out using soft-templating approach which based on surfactant self-assembly. The aimed composite material was characterized by XRD, FT-IR, SEM and BET techniques. Sorption properties of the synthesized composite powder were evaluated through sorption of lead, copper and cadmium ions from their multicomponent aqueous solutions. Preliminary studies of cation hydrolysis using MINTEQA2 software program was accomplished indicating that at pH of 5 the highest percent of free Pb2+, Cu2+ and Cd2+ was attained. Batch sorption tests were carried out at different initial heavy metal ion concentrations revealing that the synthesized composite has great selectivity to lead ions over copper and cadmium ions. The experimentally obtained sorption results were analyzed using pseudo-1st and -2nd order kinetic models to stand on the possible sorption mechanisms indicating the sorption behavior of the studied ions onto MP/MCM-41 composite belonged to the pseudo 2nd order kinetic model and the sorption process was a chemical process. Isotherm plots were constructed and analyzed using Langmuir and Freundlich isotherm models. Results indicated that the best fitting to the experimentally obtained data was obtained when Langmuir isotherm model was applied.

Pure zeolites can be synthesized from silica extracts obtained from fly ash by alkaline leaching. The extraction potential of industrial by-product fly ash was investigated under repeated fusion process conditions. The amount of extracted silica was 131.43 g/kg ash while the amount extracted alumina was limited to 41.72 g/kg ash. The results of zeolite synthesis from the Si-bearing extracts demonstrated that pure zeolites with high cation exchange capacity (4.624 meq/g) can be produced. The sorption potential of synthesized A-X zeolite blend for the removal of cesium ions has been investigated. The influences of pH, contact time and temperature have been reported. Thermodynamic parameters such as changes in Gibbs free energy (DeltaG degrees), enthalpy (DeltaH degrees) and entropy (DeltaS degrees) were calculated. A comparison of kinetic models applied to the sorption data was evaluated for pseudo first-order, pseudo second-order and homogeneous particle diffusion models. The results showed that both the pseudo second-order and the homogeneous particle diffusion models were found to best correlate the experimental rate data.

Zeolites are preferred ion exchange materials for the removal of radioisotopes from aqueous nuclear wastes because of their selectivity, radiation and temperature stability, and good compatibility with the cement matrix. Loaded materials, which are not regenerated, are preferably embedded in a solid matrix prior to ultimate storage in a repository. The aim of the present study is to investigate the possibility of solidifying exhausted synthetic zeolite A, loaded with 137Cs and/or 90Sr radionuclides, in Ordinary Portland Cement (OPC). Several factors affecting the characteristics of the final solidified waste product towards safe disposal such as mechanical strength and leaching behavior of the radionuclides have been studied. A simplified mathematical model based on diffusion mechanism for cylindrical geometry waste matrix has been simulated to predict the release rates of the investigated radionuclides from cement matrix. The predicted values are discussed in relation to experimentally observed leach rates to confirm the proposed mechanism in the model. The obtained results showed that the presence of zeolite A in the final cemented wastes improve the mechanical characteristics of the solidified cement matrix (mechanical strength and setting times) towards the safety requirements and reduce considerably the radionuclides leach rates.