ABSTRACT
The adsorption capacity of decylammonium-montmorillonite (C10-M) and decylammonium-vermiculite (C10-V) for the anionic pesticide 2,4-dichloro-phenoxyacetic acid (2,4-D) has been measured from the adsorption isotherms and compared with those of the inorganic clays (Na+-M and Na+-V). 2,4-D adsorption capacity was larger for C10-V (high layer charge mineral) than for C10-M (low layer charge mineral). The uptake of 2,4-D by organoclays was probably due to lyophilic interactions between the alkyl chains of the adsorbents and the aromatic ring of the herbicide, this adsorption being similar to a partitioning process between water and the organic phase of organoclays. The organic phase of C10-M behaved similarly to the soil organic matter, but the organic phase of C10-V (even being the same) adsorbed five times more 2,4-D than soil organic matter did. The higher adsorption capacity of C10-V, as compared with C10-M, was related to the different arrangement of organic cations in the interlayer spaces of these clays, which was determined by their layer charge. Successive desorption results showed also that 2,4-D binding to C10-V was stronger than to C10-M. The results of this study suggest the possibility of using these organoclays for removing 2,4-D from contaminated waters (C10-V) and for a possible slow-release formulation (C10-M).
