ChemInform Abstract: ADSORPTION OF CATIONIC PESTICIDES (DIQUAT AND PARAQUAT) FROM AQUEOUS SOLUTION BY ACTIVATED CARBON

Abstract

Abstract Adsorption of diquat and paraquat cationic pesticides from aqueous solution studied on three different activated carbons varying in N2-BET surface area from 660 m2/g to 1280 m2/g suggests that the rate limiting step for removal of these pesticides in agitated non-flow systems is one of intraparticle transport of the solute in the pores and capillaries of the adsorbent. The sorption rates for both adsorbates may be characterized by diffusion coefficients, D, calculated in the usual manner assuming the flux of diffusion to be proportional to the concentration gradient. The resultant values for D vary fairly inversely proportionately with the N2-BET surface area of an activated carbon for an individual adsorbate. Adsorption capacities on active carbon of diquat and paraquat from water vary from ~18 to 36% and ~6 to 14% respectively by weight of active carbon, depending upon the surface area of the carbon. These values are fairly attractive, especially for diquat, from a practical point of view of removing trace quantities of these pesticides. Thermodynamic studies indicate that the rate of removal of these pesticides by active carbon is an endothermic process which is in agreement with a suggested intraparticle transport rate control mechanism; however, the equilibrium position is governed by an exothermic reaction, as is expected for adsorption. Competitive adsorption studies of diquat and paraquat when present as an equimolar mixture, which should indicate the relative affinity of the surface available for each of the two adsorbates, suggest that different sites on the active carbon surface probably adsorb both adsorbates in a different manner.