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

Tomas Undabeytia*, Shlomo Nir, Tamara Polubesova, Giora Rytwo, Esmeralda Morillo, Celia Maqueda

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

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.

Original languageAmerican English
Pages (from-to)864-869
Number of pages6
JournalEnvironmental Science & Technology
Volume33
Issue number6
DOIs
StatePublished - 15 Mar 1999
Externally publishedYes

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