INTERACTIONS OF 2 ACETANILIDE HERBICIDES WITH CLAY SURFACES MODIFIED WITH FE(III) OXYHYDROXIDES AND HEXA-DECYLTRIMETHYL AMMONIUM

The adsorption at 22-degrees and 5-degrees-C of two acetanilide herbicides (Alachlor and Metolachlor) on montmorillonite saturated with HDTMA+ cation or coated with Fe (III) oxyhydroxides (modified clays) was studied. The isotherms were of L, S and C type depending on the type of the adsorbent. The calculated values of isosteric adsorption heat (DELTAH) and desorption experiments suggest that weak bonds take place. FT-IR analyses showed that both molecules are adsorbed on clays by hydrogen bond between the C=O group and OH groups of Fe(III) oxyhydroxy cation coating the clay. Also on HDTMA-Montmorillonite the C=O group is involved in the adsorption but with lower strenght. Alachlor is only partially decomposed to 2-chloro-2',6'-diethylacetanilide when the dirty clays complexes are heated at 70-degrees-C for 18 h. X-ray analyses showed that both herbicides were unable to penetrate into the inter-layers of the clays.