Adsorption-desorption of 2,4-D by hydroxy aluminium montmorillonite complexes

✍ Scribed by Sannino, Filomena; Violante, Antonio; Gianfreda, Liliana

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 257 KB
• Volume: 51
• Category: Article
• ISSN: 1526-498X
• DOI: 10.1002/(sici)1096-9063(199712)51:4<429::aid-ps619>3.0.co;2-j

✦ Synopsis

AdsorptionÈdesorption characteristics of 2,4-dichlorophenoxyacetic acid (2,4-D) on pure montmorillonite and synthetic chlorite-like complexes complexes, obtained by coating montmorillonite sur-[Al(OH)

x -montmorillonite faces with di †erent amounts of were investigated. The equilibrium Al (OH) x ] adsorption of 2,4-D was described by both Langmuir and Freundlich type isotherms. The extent of adsorption as well as the type of interaction between adsorbate and adsorbent was a †ected by the nature of incubation bu †er and the charge characteristics of supports. At pH 5É6 and in acetate bu †er, 2,4-D was negatively adsorbed by montmorillonite and herbicide adsorption capacity increased with increasing amounts of species loaded on montmorillonite Al(OH) x surfaces. When adsorption experiments were performed at the same pH but in phosphate bu †er, strong reductions of both the amount of adsorbed pesticide and its affinity for the adsorbents were measured. Evidently, phosphate anions competed strongly with 2,4-D anions for the sorption site on chlorite-like complexes. Furthermore, desorption tests revealed that a large amount (about 60%) of the pesticide was Ðrmly bound to the clay and was not removed even after repeated washings or 24 h exposure to desorption solution. Both electrostatic interactions between the negative COO~moieties of 2,4-D and the positive sites on clays, and ligand exchanges of COO~groups with [ OH or water at the clay surface were probably involved in the adsorption process.