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 Ba 2+ ions in a concentration range 10 −3 to 10 −6 M. Throughout the study, 133 Ba 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.
a b s t r a c tIn this study, the sorption behavior of two important fission product radionuclides ( 137 Cs and 140 Ba) onto sodium form of insolubilized humic acid (INaA) were investigated as a function of time, cation concentration and temperature, utilizing the radiotracer method. The sorption processes are well described by both Freundlich and Dubinin-Radushkevich type isotherms. Thermodynamic constants such as; free energy ( G ads ), enthalpy ( H ads ), entropy ( S ads ) of adsorption were determined. It was found that Ba 2+ was adsorbed five times more than Cs + onto structurally modified humic acid and kinetic studies indicated that adsorption behavior of both ions obey the pseudo second order rate law. The effect of pH change on sorption was also examined. FTIR and solid-state carbon NMR ( 13 CNMR) spectroscopic techniques were used to understand the structural changes during insolubilization process. Quantitative determination of adsorption sites was carried out using potantiometric titration.
The sorption of Ba 2+ ion on natural kaolinite and chlorite-illite clays was investigated at different initial concentrations and temperatures using the radiotracer method. The sorption data were well described by Freundlich and Dubinin-Radushkevich isotherms. Ba 2+ sorption on both clays showed an exothermic behavior with H° (kJ/mol) values being -7 and -5 for sorption on kaolinite and chlorite illite mixed clay, respectively. The G° values indicate that the sorption was spontaneous with sorption energies corresponding to ion-exchange type sorption. X-ray diffraction studies showed that no significant change in the matrix of the clays occurred upon Ba 2+ sorption.
The natural bentonite used in this study contained montmorillonite in addition to low cristobalite. The uptake of aqueous Co 2+ ions was investigated as a function of time, concentration, and temperature. In addition, the change in the interlayer space of montmorillonite was analyzed using XRPD, and the distribution of fixed Co 2+ ions on the heterogeneous clay surface was recorded using EDS mapping. The sorbed amount of Co 2+ appeared to closely follow Freundlich isotherm, with the sorption process showing apparent endothermic behavior. The relevance of the apparent H o values is briefly discussed. Analysis of the Co-sorbed bentonite samples using SEM/EDS showed that the montmorillonite fraction in the mineral was more effective in Co 2+ fixation than the cristobalite fraction. XRPD analysis demonstrated that the interlayer space of montmorillonite was slightly modified at the end of sorption.
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