Sorption studies of cesium and barium on magnesite using radiotracer and x-ray photoelectron spectroscopy

Ankara : The Department of Chemistry and the Institute of Engineering and Sciences of Bilkent Univ., 1997.Thesis (Master's) -- Bilkent University, 1997.Includes bibliographical references leaves 74-79As the consumption of the radioactive materials is continuously increasing, the problem of disposing the resulting v^^astes safely is becoming more challenging. One way through which these radioactive wastes could be isolated from the biological environment is by disposing them in deep geological formations. Clay minerals are proposed as backfill buffering materials that can delay the migration of the radionuclides and thus decrease the contamination of underground waters. The extent of retardation of the radionuclide migration is dependent on factors like time of contact, pH and Eh of groundwater, concentration, temperature and grain size of the mineral particles. Up to now, several studies were carried out to examine the effect of such parameters on the sorption behavior of different radionuclides on various kinds of minerals. This study was conducted to investigate the effects of time, concentration and temperature on the sorption behavior of cesium and barium ions on magnesite. Cesium 137 140 and barium have the radioactive isotopes Cs (t^^^ = 30.1 y) and Ba (t^^^ = 12.8 d) 1/2 produced in high yields during the fission process which are important in radioactive waste considerations. Magnesite is a mineral composed mainly of magnesium carbonate 2+ together with minor amounts of quartz and has a single exchangeable cation. Mg . The radiotracer method and x-ray photoelectron spectroscopy, which is a powerful surface sensitive tool, were used in this study. The results obtained from both methods complemented each others and were in good agreement. Kinetic studies of the sorption process show that equilibrium was approached within one day of contact for both of cesium and barium ions. The data of the sorption of both cations using different concentrations at various temperatures were most adequately described by the Freundlich type isotherms which correspond to multilayer adsorption on heterogeneous surfaces. The values of the Freundlich constants k and n imply that barium ions have slightly larger adsorption affinity and adsorption intensity than cesium ions. The adsorption data at low concentrations were also observed to obey the Dubinin-Radushkevich type isotherms which describe monolayer adsorption on heterogeneous or homogeneous surfaces. The adsorption data were very poorly described by the Langmuir type isotherms. Thermodynamic parameters such as enthalpy change, AH°, entropy change, AS° and free energy change of adsorption, AG°, were calculated from the sorption data of cesium and barium ions at different temperatures. The values obtained for AH° and AS° were -37 kJ/moL, -0.09 kJ/moL.K and -13 kJ/moL, -0.009 kJ/moL.K for cesium and barium ions respectively. The negative AH° values indicate the exothermic nature of adsorption which means that low temperatures are favored. The decrease in entropy upon adsorption implied by the negative AS° values is indicative of the stability of adsorption for both cations. The values of AG° at different temperatures were all negative indicating the spontaneity of the adsorption process for both cesium and barium ions. The magnitudes of AG° were seen to be within the 8-16 kJ/moL range which is the energy range of ion- exchange type processes.Shahwan, TalalM.S

Kinetic and thermodynamic investigations of strontium ions retention by natural kaolinite and clinoptilolite minerals

The current study was devoted to the determination of various thermodynamic and kinetic parameters resulting from the fixation of Sr2+ 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 Sr2+ 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 ΔH° 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.İYTE: 2003 İYTE 0

Effect of magnesium carbonate on the uptake of aqueous zinc and lead ions by natural kaolinite and clinoptilolite

Adsorption behavior of Zn2+ and Pb2+ ions on kaolinite and clinoptilolite, originating from natural resources, was studied as a function of contact time and concentration. Zn2+ and Pb2+ ions are quickly adsorbed on both minerals and the uptake of the latter is more favored. The uptake of both ions was then examined on kaolinite–MgCO3 and clinoptilolite–MgCO3 mixtures over a metal ions range from 1 to 10 000 mg/L. The sorption behavior of Zn2+ and Pb2+ on pure MgCO3 was also studied. MgCO3 is much more effective in the retention of Zn2+ and Pb2+ ions, in particular at higher concentrations. The large increase in the retarded amounts of both ions was associated with formation of the hydroxy-carbonate phases; namely hydrozincite for Zn2+, and cerussite and hydrocerussite in the case of Pb2+

A radiotracer study of the adsorption behavior of aqueous Ba2+ ions on nanoparticles of zero-valent iron

Recently, iron nanoparticles are increasingly being tested as adsorbents for various types of organic and inorganic pollutants. In this study, nanoparticles of zero-valent iron (NZVI) synthesized under atmospheric conditions were employed for the removal of Ba2+ ions in a concentration range 10-3 to 10-6 M. Throughout the study, 133Ba was used as a tracer to study the effects of time, concentration, and temperature. The obtained data was analyzed using various kinetic models and adsorption isotherms. Pseudo-second-order kinetics and Dubinin-Radushkevich isotherm model provided the best correlation with the obtained data. Observed thermodynamic parameters showed that the process is exothermic and hence enthalpy-driven.2006 İYTE 1

ToF-SIMS depth profiling analysis of the uptake of Ba2+ and Co2+ ions by natural kaolinite clay

The sorption behavior of Ba2+ and Co2+ ions on a natural clay sample rich in kaolinite was studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Depth profiling at 10-Å steps was performed up to a 70-Å matrix depth of the clay prior to and following sorption. The results showed that Co2+ is sorbed in slightly larger quantities than Ba2+, with significant numbers of ions fixed on the outermost surface of the clay. Depletion of the ions K+, Mg 2+, and Ca2+ from the clay lattice was observed to accompany enrichment with Co2+ and Ba2+ ions. The data obtained using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) indicated insignificant structural and morphological changes in the lattice of the clay upon sorption of both Ba2+ and Co2+ ions. Analysis using energy dispersive X-ray spectroscopy (EDS) showed that the average atomic percentage (±S.D.) of Ba and Co on kaolinite surface were 0.49±0.11 and 0.61±0.19, respectively, indicating a limited uptake capacity of natural kaolinite for both ions

Radiochemical and spectroscopic studies of cesium, barium, and cobalt sorption on some natural clays

Ankara : The Department of Chemistry and the Institute of Engineering and Sciences of Bilkent Univ., 2000.Thesis (Ph.D.) -- Bilkent University, 2000.Includes bibliographical references leaves 153-161Shahwan, TalalPh.D

Corrigendum to "Modification of a montmorillonite-illite clay using alkaline hydrothermal treatment and its application for the removal of aqueous Cs+ ions" [J. Colloid Interface Sci. 295 (2006) 303-309] (DOI:10.1016/j.jcis.2005.12.008)

Unfortunately, we noticed that Ref. [8], which was cited three times in our article, was mistakenly not cited also in the experimental part as the reference on which we based our hydrothermal treatment process. In light of this, the first paragraph of the experimental section (pages 303 and 304) should read..

Modification of a montmorillonite-illite clay using alkaline hydrothermal treatment and its application for the removal of aqueous Cs+ ions

A montmorillonite-illite clay was modified using alkaline hydrothermal treatment (reflux method) and applied to the removal of aqueous Cs+ ions. The alkaline solutions were prepared by dissolving NaOH in seawater and in distilled water, and the effect of the two alkaline media on the sorption capacities of the modified clay was discussed. The modified materials were characterized using XRD, SEM/EDS, and FTIR. As a result of the modification, the original mineral was partially transformed into a zeolitic material with spherical morphology. The results showed that the modification improved the Cs+ uptake capacity of the starting clay, with the clay modified in distilled water medium demonstrating higher sorption capacity. The sorption data were adequately described using the Freundlich and Dubinin-Radushkevich isotherm models

Study of the scavenging behavior and structural changes accompanying the interaction of aqueous Pb2+ and Sr2+ ions with calcite

The uptake of Pb2+ and Sr2+ ions from aqueous solutions by calcite was studied at various initial concentrations and pH conditions using the batch method under ambient conditions. XRPD, SEM/ EDS, AAS/AES, and DRIFT techniques were used in characterizing the sorption process. The results indicated that the retention mechanism of Ph2+ and Sr2+ ions ranged from ion incorporation to precipitate overgrowth (cerussite, hydrocerussite for Pb, strontianite for Sr) depending on the concentration and pH conditions. The calcite structure seemed to be entirely vanishing upon formation of cerussite and hydrocerussite while partial dissolution of calcite occurred upon strontianite formation. The formation of precipitates showed rapid kinetics, and equilibrium seemed to be reached within about an hour from the start of mixing. SEM analysis showed that cerussite, hydrocerussite, and strontianite had columnar prismatic-like, tabular hexagonal-like, and needle-like morphologies. Based on a nine-month observation period, dry samples of hydrocerussite seemed to show more morphological stability than cerussite. EDS analysis indicated that Pb2+ sorption is more favored than that of Sr2+, particularly in the phase of precipitate overgrowth. DRIFT analysis indicated a change in the symmetry of the carbonate groups in calcite matrix upon uptake of Pb2+ and Sr2+ cations