SOME PHYSICO-CHEMICAL INTERACTIONS OF PARAQUAT WITH SOIL ORGANIC MATERIALS AND MODEL COMPOUNDS

Summary. The adsorption equilibria of paraquat were investigated on a range of organic materials including an organic soil, various humic fractions of that soil, model polymers prepared by the oxidative coupling of benzoquinone, ion-exchange resins (Zeo-Karb 216 and 226) and a polystyrene resin (Amberlite XAD-2). Isotherms were prepared for adsorption on the H⁺ and on some of the Ca²⁺ saturated materials. Measurement of the counter-ion in solution at equilibrium, and correlation of the adsorption with exchange capacity for H⁺ adsorbents showed that ion exchange was the primary adsorption mechanism. Significant amounts of non-exchange adsorption were also detected, especially at low concentrations, but generally the results followed the Rothmund-Kornfeld isotherm equation fairly accurately. The Rothmund-Kornfeld plots for the Ga²⁺ forms were complicated by the hydrolysis by water of some of the exchange sites. Other types of isotherm equations were tested and found to be unsatisfactory.
Desorption of paraquat with HCl from organic soil preparations was less than expected, and the isotherms did not conform to the Rothmund-Kornfeld or to the mass action equations. The probable reasons for this behaviour arc discussed.
Quelques interactions physico-chimiques du paraquat avec des matériaux de sol organique et des composés modèles
II. Adsorption, désorption et équilibre dans les suspensions aqueuses