Adsorption of paraquat from aqueous medium by Amberlite XAD-2 and XAD-4 resins using dodecylsulfate as counter ion

A study is reported about the adsorption of the herbicide paraquat (PQT(2+)) by the polymeric resins Amberlite XAD-2 and XAD-4, in a medium containing sodium dodecylsulfate (SDS). The strategy employed in this study was based on the adsorption of the ion-associate complex, formed between the cationic PQT(2+) and the dodecylsulfate anion, which presents high affinity by the hydrophobic resins. The effect of several parameters that could affect the efficiency of adsorption (SDS concentration, pH, mass of adsorbent and initial concentration of PQT(2+)) was investigated. Also, a detailed kinetic characterization of the system was performed. The SDS concentration added to the medium affected the adsorption efficiency, while the pH of the solution did not present any effect on the efficiency in the range of 2-9.5. The mass of adsorbent was studied in the range of 100-500 mg and did not influence the adsorption efficiency, changing only the adsorption rate. The kinetic evaluation of the system indicated that the adsorption of the PQT(2+) followed a pseudo first-order model and that the adsorption rate was controlled by an intraparticle diffusion mechanism. (C) 2012 Elsevier B.V. All rights reserved.