Adsorption−Desorption of Simazine on Montmorillonite Coated by Hydroxy Aluminum Species

Abstract

Adsorption−desorption of simazine on model systems which closely simulate those encountered in soils [i.e., pure montmorillonite and montmorillonite covered by different amounts of OH−Al species (chlorite-like complexes)] was investigated. The adsorption data were analyzed according to Langmuir and Freundlich equations. Results obtained indicate that the adsorption of simazine was strongly influenced by the charge characteristics of clay minerals and the pH of buffer (3.7 and 5.6). At pH 3.7, simazine was adsorbed in large amounts on montmorillonite, whereas adsorption significantly decreased with increasing amounts of Al(OH)x species on montmorillonite surfaces. When experiments were carried out at pH 5.6, the adsorption of the herbicide on montmorillonite drastically decreased, whereas no severe differences were observed with AM18 (a montmorillonite loading 18 mequiv g-1 M). Desorption tests showed that negligible and very little amounts of simazine were desorbed from montmorillonite and AM18, respectiv...