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Título: | Adsorption-desorption of chlordimeform on montmorillonite: effect of clay aggregation and competitive adsorption with cadmium |
Autor: | Undabeytia López, Tomás CSIC ORCID ; Nir, Shlomo; Polubesova, T.; Rytwo, Giora; Morillo González, Esmeralda CSIC ORCID ; Maqueda Porras, Celia CSIC | Fecha de publicación: | 1999 | Editor: | American Chemical Society | Citación: | Environmental Science and Technology 33: 864-869 (1999) | Resumen: | 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. | 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. | URI: | http://hdl.handle.net/10261/62053 | DOI: | 10.1021/es980822k | Identificadores: | doi: 10.1021/es980822k issn: 0013-936X e-issn: 1520-5851 |
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