Retention and Release of Copper on Montmorillonite As Affected by the Presence of a Pesticide

The effect of the cationic pesticide chlordimeform ( N ‘-(4-chloro-2 methylphenyl)- N, N -dimethylmethanimidamide hydrochloride) on adsorption−desorption processes of copper onto the clay mineral montmorillonite has been studied. This effect was evaluated when both adsorbates were adsorbed simultaneously and when the pesticide was previously adsorbed on montmorillonite. For different concentrations of pesticide used, copper adsorption decreases (in relation to pesticide-free treatment) when both adsorbates are adsorbed simultaneously, indicating a competition between both cations for interlamellar possitions. In contrast, copper adsorption increases when the pesticide is previously adsorbed. Copper desorption isotherms show a very high hysteresis. The maximum percentage of copper desorbed is only 7%, being lower when pesticide is present and decreasing with pesticide concentration.