Microstructure of gamma-ray developed polymeric nanocomposite respecting cesium and cobalt removal from aqueous solutions.

The nanoparticles of fly ash (FA) were obtained by high energy ball milling of their parent Class C kind for subsequent synthesis of poly(acrylamide-acrylic acid)/fly ash (poly(AM-AA)/FA) nanocomposite. The gamma-radiation induced polymerization was applied to achieve this concern. Different techniques were utilized to characterize such nanocomposite. The sorption abilities of the synthesized nanocomposite toward 60Co2+ and 134Cs + radionuclides were evaluated using batch and fixed-bed column approaches. Batches were designed at constants of solution pH (6.5-7.0 ± 0.02), nanocomposite particle size and dosage (106-250 µm and 0.1 L/g, respectively). The microstructure of such nanocomposite (<100 nm) was mainly amorphous with porous rough surfaces containing homogenous distribution of the incorporated nano-FA. About 56.46 and 47.9 mg/g of Co2+ and Cs+ were sorbed at equilibrium with an ion exchange reaction mechanism. Langmuir, Freundlich and Dubinin-Radushkevich D-R isotherm model parameters were calculated indicating the favorability of all sorption processes. The spontaneous and endothermic natures of sorption were observed by the calculated ΔG° and ΔH° thermodynamic parameters, respectively. Thomas, Yoon-Nelson and Adams Bohart models were fitted to the fixed-bed column data at varied conditions. The predicted sorption capacities of Thomas were very close to those obtained experimentally. Modeling of the fixed-bed column data dominates that the external mass transfer kinetics was predominant in the initial parts of the fixed-beds. Values required for retaining 50% of the initial sorbate concentration were extended from 89.05 to 68.55 to 177.2 and 149.3 min for 60Co2+ and 134Cs + radionuclides, respectively, by increasing bed depth from 1.5 to 3.0 cm. Modification of FA to its nano-scale form with the subsequent synthesis of a nanocomposite material having sorption capabilities made a duplicate beneficial environmental concern.

Two-step method for preparation of NaA-X zeolite blend from fly ash for removal of cesium ions.

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.

Immobilization of cesium and strontium radionuclides in zeolite-cement blends.

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 (137)Cs and/or (90)Sr 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.

Diagnosis of early pre-patent schistosomiasis by cystatin capture enzyme-linked immunosorbent assay.

To test the efficacy of detecting anti-Schistosoma mansoni cysteine proteinase antibodies (CP Abs) by cystatin capture (CC) ELISA in the diagnosis of prepatent schistosomiasis (before egg passing); 253 schistosome negative individuals were selected and divided into two groups. The first comprised 118 children whose first water contact occurred in March and April 1999 (primarily infected), and the second 135 individuals were previously treated for schistosomasis (re-infected). All the individuals were followed up triweekly by stool for detecting schistosome eggs and by serological tests for detecting antibodies against CP and anti-soluble egg antigens (SEA) by ELISA technique. CP seropositivity was detected in 92 from all examined individuals, out of them 38 were primarily infected (PI) children (20 of them were pre-patently treated), the rest; 54 were re-infected patients (28 out of them were pre-patently treated). The untreated (44) individuals from both groups were followed up till they passed eggs within 4 weeks and then were treated (post-patent). CP Abs were reassessed for the 92 patients after treatment, only 11 (12%) were still seropositive with marked decrease in optical density (O.D.) level than before treatment. Anti-SEA IgM Abs were sought in the 92 CP seropositive sera, and the seropositivity rate was lower in 38 PI children (5.3%) than in the 54 re-infected individuals (92.6%). The anti-SEA seropositivity rate in the PI children was 5% in the pre-patent and was 94.4% in the post-patent. None of the 161 CP seronegative individuals passed eggs up to 12 weeks.

Ion exchange behaviour of hydrous tin oxide: Kinetics of anion exchange.

The kinetic behaviour of Cl(-), Br(-) and SCN(-) exchanges on hydrous tin oxide have been investigated under conditions of particle diffusion and the limited bath technique. Values for the diffusion coefficients, energy of activation and entropy of activation have been calculated. The data obtained have been compared with those reported for other organic and inorganic exchangers.