Influence of herbicide structure, clay acidity, and humic acid coating on acetanilide herbicide adsorption on homoionic clays

摘要

Adsorption of chloroacetanilide herbicides on homoionic montmorillonite was studied by coupling batch equilibration and FT-IR analysis. Adsorption decreased in the order metolachlor > acetochlor > alachlor > propachlor on Ca2+- or Mg2+-saturated clays and in the order metolachlor > alachlor >. acetachlor > propachlor on Al3+- or Fe3+-saturated clays. FT-IR spectra showed that the carb,onyl group of the herbicide molecule was involved in bonding. For,the same herbicide, adsorption,of alachlor, acetachlor, and metolachlor on clay followed the order Ca2+ approximate to Mg2+ < Al3+ less than or equal to Fe3+, which coincided with the increasing acidity of homoionic clays. Adsorption of propachlor, however, showed an opposite dependence, suggesting a different governing interaction. In clay and humic acid mixtures, herbicide adsorption was less than that expected from independent additive adsorption by the individual constituents, and the deviation was dependent on the clay-to-humic acid ratio, with the greatest deviation consistently occurring at a 60:40 clay-to-humic acid ratio. [References: 25]