T. Undabeytia et al., Adsorption-desorption of chlordimeform on montmorillonite: Effect of clay aggregation and competitive adsorption with cadmium, ENV SCI TEC, 33(6), 1999, pp. 864-869
Citations number
29
Categorie Soggetti
Environment/Ecology,"Environmental Engineering & Energy
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 c
oncentration. 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 (approximate to 0.5), chlordimeform exhib
ited low apparent affinity for adsorbing to the SAz-1 clay, due to steric i
nhibition of its penetration between closely opposed clay platelets. The ap
parent 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 Ca-2+-
montmorillonite. An adsorption model which combines electrostatic equations
with specific binding in a closed system is able to account for part of th
is hysteresis by the reduction in the concentrations of the divalent cation
s Ca2+ and Mg2+ in the supernatant. Part of the hysteresis arises from a di
fferent state of aggregation of the Ca2+-clay in the adsorption and desorpt
ion experiments. The model also yields good predictions for the competition
between chlordimeform and Cd in adsorption processes and their consecutive
desorptions.