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Title

Adsorption-desorption of chlordimeform on montmorillonite: effect of clay aggregation and competitive adsorption with cadmium

AuthorsUndabeytia López, Tomás ; Nir, Shlomo ; Polubesova, T.; Rytwo, Giora; Morillo González, Esmeralda ; Maqueda Porras, Celia
Issue Date1999
PublisherAmerican Chemical Society
CitationEnvironmental Science and Technology 33: 864-869 (1999)
AbstractEffect of the aggregation state of montmorillonite clays of types SAz-1 and SWy-1 on the adsorption of the monovalent organic cation chlordimeform was studied. The shapes of the adsorption isotherms were related to the degree of dispersion of the clay, changing from S- to L-type by decreasing clay concentration. Unlike monovalent organic cations denoted dyes, chlordimeform adsorption did not exceed the cationic exchange capacity of the clay (CEC). At larger Ca2+/Na+ charge ratio (≃0.5), chlordimeform exhibited low apparent affinity for adsorbing to the SAz-1 clay, due to steric inhibition of its penetration between closely opposed clay platelets. The apparent affinity increased dramatically at smaller Ca2+/Na+ charge ratios (<0.06) for Ca2+-montmorillonite, or by switching to Na+- montmorillonite. The desorption process of chlordimeform shows an apparent hysteresis in Ca2+-montmorillonite. An adsorption model which combines electrostatic equations with specific binding in a closed system is able to account for part of this hysteresis by the reduction in the concentrations of the divalent cations Ca2+ and Mg2+ in the supernatant. Part of the hysteresis arises from a different state of aggregation of the Ca2+-clay in the adsorption and desorption experiments. The model also yields good predictions for the competition between chlordimeform and Cd in adsorption processes and their consecutive desorptions. | Effect of the aggregation state of montmorillonite clays of types SAz-1 and SWy-1 on the adsorption of the monovalent organic cation chlordimeform was studied. The shapes of the adsorption isotherms were related to the degree of dispersion of the clay, changing from S- to L-type by decreasing clay concentration. Unlike monovalent organic cations denoted dyes, chlordimeform adsorption did not exceed the cationic exchange capacity of the clay (CEC). At larger Ca2+/Na+ charge ratio (≈0.5), chlordimeform exhibited low apparent affinity for adsorbing to the SAz-1 clay, due to steric inhibition of its penetration between closely opposed clay platelets. The apparent affinity increased dramatically at smaller Ca2+/Na+ charge ratios (<0.06) for Ca2+-montmorillonite, or by switching to Na+-montmorillonite. The desorption process of chlordimeform shows an apparent hysteresis in Ca2+-montmorillonite. An adsorption model which combines electrostatic equations with specific binding in a closed system is able to account for part of this hysteresis by the reduction in the concentrations of the divalent cations Ca2+ and Mg2+ in the supernatant. Part of the hysteresis arises from a different state of aggregation of the Ca2+-clay in the adsorption and desorption experiments. The model also yields good predictions for the competition between chlordimeform and Cd in adsorption processes and their consecutive desorptions.
URIhttp://hdl.handle.net/10261/62053
DOI10.1021/es980822k
Identifiersdoi: 10.1021/es980822k
issn: 0013-936X
e-issn: 1520-5851
Appears in Collections:(IRNAS) Artículos
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