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

• Published in: Environmental science & technology Vol. 33; no. 23; pp. 4221 - 4225
• Main Authors: Sannino, F, Filazzola, M. T, Violante, A, Gianfreda, L
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-12-1999
• Subjects: acid soils; Applied sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Chemicals; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Herbicides; Pollution; Pollution, environment geology; simulation; Soil and sediments pollution; Soils; Aluminium hydroxide; Clay; Montmorillonite; Pesticides; Adsorption isotherm; Desorption; Soil pollution; Herbicide; Simazine; Adsorption; Medium effect; Smectite; Model compound; Triazine derivatives; Reaction mechanism; pH; Soil interaction; Kinetics; Ion exchange
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es9813313

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, respectively. Strong electrostatic interactions were involved in the adsorption process. Simazine molecules, arriving at support interfaces mostly as molecular species, dissociated as cations by the microenvironmental pH (“surface acidity”) and were adsorbed by cation-exchange mechanism.