Adsorption and Desorption of Picloram, Trifluralin, and Paraquat by Ionic and Nonionic Exchange Resins

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Abstract
We investigated the forces involved in the adsorption and desorption of 4-amino-3,5-6-trichloropicolinic acid (picloram), 1,1-dimethyl-4,4′-bipyridinium ion (paraquat), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) using cationic, anionic, and nonionic exchange resins. The anionic resin (Cl-form) adsorbed 375, 0.08, and 0.67 mg of picloram, paraquat, and trifluralin, respectively, per gram of oven-dry resin. The nonionic resin adsorbed 4.0, 0.34, and 10.0 mg of picloram, paraquat, and trifluralin, respectively, per gram of oven-dry resin, while the cationic resin (H-form) adsorbed 2.3, 226, and 0.17 mg of picloram, paraquat, and trifluralin, respectively. Other cationic resins (Na-form and Ca-form) performed similarly to the hydrogen form. Desorption studies indicated that picloram was adsorbed mainly in the anionic form by coulombic forces (electrostatic) and to a lesser degree by weak physical bonding (van der Waal's forces). Paraquat was adsorbed as a cation through coulombic forces. Trifluralin was mainly absorbed by physical bonds at sites on the resins where there were no coulombic forces.