Adsorption and desorption of Ni2+ on Na-montmorillonite: Effect of pH, ionic strength, fulvic acid, humic acid and addition sequences
ABSTRACT Humic substances and clay minerals have been studied intensively because of their strong complexation and adsorption capacities. In this work, adsorption of Ni2+ on Na-montmorillonite was studied using batch technique under ambient conditions. Effect of pH, ionic strength, solid content, humic acid (HA), fulvic acid (FA) and the addition sequences of fulvic acid/Ni2+/montmorillonite on Ni2+ adsorption was also investigated. The results indicate that adsorption of Ni2+ on montmorillonite are strongly dependent on pH and ionic strength. The adsorption of Ni2+ is mainly dominated by surface complexation and ion exchange. The adsorption–desorption hysteresis suggests that the adsorption of Ni2+ is irreversible. The thermodynamic parameters (ΔH, ΔS, and ΔG) are calculated from the temperature dependence, and the results suggest that the adsorption reaction is endothermic and spontaneous. The presence of FA and the addition sequences of FA/Ni2+/montmorillonite do not influence the adsorption of Ni2+ on FA bound montmorillonite hybrids. Montmorillonite is a suitable candidate for pre-concentration and solidification of Ni2+ from large volume of solutions.
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ABSTRACT: The association of organic–inorganic colloid-borne trace elements was investigated. Radionuclide 152+154Eu(III) was chosen as a representative and chemical homologue for trivalent lanthanide and actinide ions present in radioactive nuclear waste. Effect of pH and contact time of organic–inorganic/Eu(III) on the kinetic dissociation of Eu(III) from HA–Al2O3 colloids was studied. The kinetic desorption behavior of sorbed 152+154Eu(III) from humic acid–γ-Al2O3 colloids was studied at pH values of 4.5 ± 0.2, 5.3 ± 0.2 and 6.5 ± 0.2, respectively, by the addition of the chelating resin. The experimental results suggest that the fractions of irreversible sorption of radionuclide 152+154Eu(III) to HA–Al2O3 colloids increase with increasing pH values, and are independent of aging time. At least two different species, “weak” and “strong” dissociation fractions, are required to simulate the kinetic desorption of 152+154Eu(III) from HA–Al2O3 colloids. The species of Eu(III) sorbed on HA–Al2O3 colloids move from “weak” sites to “strong” sites with increasing aging time, whereas the fractions of irreversible sorption are independent of aging time. The results are important for the evaluation of radionuclides’ behavior in the environment.Surface Science 01/2006; · 1.84 Impact Factor
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ABSTRACT: Sorption of metal ions by clay minerals is a complex process involving different mechanisms, and controlled by different variables that can interact. The aim of this work was to study the retention mechanisms of Pb2+ ions on illite. We obtained Pb2+ sorption isotherms at constant pH, sorption edges as a function of pH, sorption isotherms at 5, 25 and 45 °C (pH = 5.5), and response surfaces of the simultaneous effect of pH, initial concentration, ionic strength, and temperature on the retention of Pb2+ ions on illite. Surface topography and atomic composition of illite samples doped with Pb2+ were studied by scanning electron microscopy and X-ray fluorescence microanalysis. Below pH 4.5, sorption of Pb2+ ions on illite is via ion exchange with H3O+ and Na+ ions that saturated the exchange sites, where the exchange with Na+ is the main mechanism between pH 3.5 and 4.5. Al3 + ions whose concentration in solution increases with decreasing pH can also compete with Pb2+ ions. For pH above 5.0, proton stoichiometry was higher than 1.0, and the effect of ionic strength on the amount of Pb2+ retained decreased with pH; in fact, at pH 6.8, the amount adsorbed was practically 100% and independent of ionic strength. The pronounced decrease in the intensity of the OH-stretching band for Pb–illite sample at pH 7.0 suggests that Pb2+ ions had lost the inner hydration sphere. The analysis of images obtained by SEM from 3 mM Pb2+ solutions with and without illite showed particles with the same morphology, which indicate a homogenous lead precipitation from the solution. For pH values higher than 4.5, increase in the temperature favored the retention of Pb2+ ions.Applied Clay Science. 01/2005;
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ABSTRACT: Thorium is considered as a chemical analog of other tetravalent actinides. Herein, the sorption of Th(IV) on TiO(2) in the presence or absence of soil fulvic acid (FA)/humic acid (HA) as a function of pH, ionic strength and FA/HA concentration has been studied by a batch method. The morphology was characterized by scanning electron microscopy (SEM). The results indicate that sorption of Th(IV) on TiO(2) increases from 0% to approximately 94% at pH 1 approximately 4, and then maintains level with increasing pH values. Both FA and HA have a positive effect on Th(IV) sorption at low pH values and the contribution of FA on Th(IV) sorption is rather higher than that of HA at pH<4. The sorption is weakly dependent on the concentration of KNO(3) in solution, but the cations K(+), Na(+) and Li(+) influence Th(IV) sorption more obviously. The batch results indicate that the inner sphere complex formation is formed at bare surfaces or FA/HA-bound TiO(2) particle surfaces. Results of SEM analysis show that the particle sizes of TiO(2), Th-TiO(2) and Th-HA-TiO(2) colloids are quite different. Surface complexation may be considered as the main sorption mechanism.Applied Radiation and Isotopes 04/2007; 65(4):375-81. · 1.18 Impact Factor