ASSESSING THE EFFICIENCY OF MODIFIED CLAYS FOR DECONTAMINATE AGRICULTURAL WASTE WATER BY PESTICIDE RESIDUES

Sorption of three pesticides (chlorpyrifos, metalaxyl and penconazole) has been measured on a commercial clay montmorillonite and on the same mineral modified with either of two cationic-surfactant micelles. Both micelle–clay complexes, commercial names Cloisite 20A and Cloisite 30B, showed a good capacity to sorb all three pesticides from water, whereas their sorption on the natural montmorillonite was not described by an isotherm. Modelling sorption on both micelle–clay complexes showed that the Freundlich sorption constant (KF) was higher for chlorpyrifos on Cloisite 20A (KF = 7.76) than on Cloisite 30B (KF = 5.91), whereas the sorption of metalaxyl was stronger on Cloisite 30B (KF = 1.07) than on Cloisite 20A (KF = 0.57). Moreover the micelle–clay complex Cloisite 20A showed also a good affinity for penconazole, the maximum quantity adsorbed (qm) of 6.33 mg g being 45% more than that on Cloisite 30B. Single-batch adsorption of each pesticide onto both micelle–clay complexes was studied using the Freundlich isotherm for chlorpyrifos and metalaxyl and the Langmuir isotherm for penconazole. The Cloisite 20A micelle–clay complex was predicted to require 23% less adsorbent to treat certain volumes of wastewater containing 30 mg L chlorpyrifos, 43% more to treat metalaxyl similarly and 57% less to treat penconazole compared with Cloisite 30B.