Surface complexation modelling of uranyl adsorption onto kaolinite based clay minerals using FITEQL 3.2
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Deniz Arda
The aim of this study is to explain how the kaolinite-based clay minerals adsorb hexavalent uranium (uranyl ion), and to model uranyl adsorption based on inner-sphere surface complexation with the kaolinite edge hydroxyl sites and outer-sphere complexation with the permanent charge sites. The adsorption of UO22+ on kaolinite-based clay was modeled with the aid of FITEQL 3.2 code using the single-site binding model of the Langmuir approach. Potentiometric titrations and adsorption capacity experiments were carried out in solutions containing different concentrations of the inert electrolyte NaClO4, however adsorption modeling was deliberately done at low ionic strength (0.01 M electrolyte) for enabling adsorption onto the permanent negatively charged sites of kaolinite. When a ‘two-site’ binding model was adopted, i.e., ≡S1OH sites representing silanol and ≡S2OH sites aluminol, a good fit was not obtained, and therefore the involvement of merely aluminol sites in surface complexation was assumed along with the ion exchange-held X22-–UO22+ species by the NaX permanent charge sites. The uranyl cation was assumed to bind to the clay surface as the sole (unhydrolyzed) UO22+ ion and form monodentate surface complexes. The modeling system comprised of surface complexation and ion exchange was resolved with respect to species distributions and relevant stability constants. Electrostatic effects were accounted for using a diffuse layer model (DLM) requiring the minimum number of adjustable parameters. Metal adsorption onto clay showed a steady increase with increasing pH up to pH 5.5, i.e., the edge pH for bulk precipitation at the studied concentration range.
© Oldenbourg Wissenschaftsverlag
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Articles in the same Issue
- Experimental study of excitation functions of some proton induced reactions on natTi for beam monitoring purposes
- AMS analysis of 36Cl induced in concrete of accelerator facilities
- Ion exchange studies for the removal of plutonium and americium from organic liquid scintillator waste solution
- The interaction of Desulfovibrio äspöensis DSM 10631T with plutonium
- Uranium(VI) sorption onto kaolinite in the presence and absence of humic acid
- Surface complexation modelling of uranyl adsorption onto kaolinite based clay minerals using FITEQL 3.2
- Complex formation of U(VI) with the amino acid L-threonine and the corresponding phosphate ester O-phospho-L-threonine
- Thermoanalytical (TG-DTA-DTG) investigations of uranium (VI) and thorium (IV) complexes of o-hydroxy N, N′-dimethylbenzylamine in static air atmosphere
- Studies on protonation and Th(IV) complexation behaviour of dihydroxybenzenes in aqueous 1 M NaClO4 medium
- Development of [103Pd]-labeled-bis(N4-methylthiosemicarbazone) complexes as possible therapeutic agents
- Potential of Broussonetia papyrifera leaves as biomonitors for atmospheric pollution: use of INAA and AAS techniques
- Appreciation to Referees
