The Effect of Cation Exchange Capacity on the Retention of Diquat2+ and Paraquat2+ by Three-Layer Type Clay Minerals I. Adsorption and Release
1969
Weed, S. B. | Weber, J. B.
Diquat (1,1′-ethylene-2,2′-dipyridinium dibromide) and paraquat (1,1′-dimethyl-4,4′-dipyridinium dichloride) were equilibrated for thirty minutes with suspensions of three-layer clay minerals varying in CEC from about 1–1.6 meq/g. Maximum adsorption of the divalent organic cations, expressed as percent of CEC, decreased from 100% for a montmorillonite (CEC = 1.03 meq/g) to 13% for a K⁺ -depleted muscovite (CEC = 1.63 meq/g). The exchangeable inorganic cation initially present markedly affected adsorption of diquat²⁺ and paraquat²⁺ by vermiculite but had much less effect on adsorption by montmorillonite. The order of adsorption was Na⁺ -vermiculite > Ca²⁺ -vermiculite ≥ Mg²⁺ -vermiculite. Less than 15% of the adsorbed diquat²⁺ or paraquat²⁺ was released from montmorillonite by a single equilibration with approximately five symmetry of 0.005N chloride salt solutions of Al³⁺, Ca²⁺, Mg²⁺, or K⁺. Similar treatment of vermiculite released up to 70% of the adsorbed organic cation, the order of release being Al³⁺ > Ca²⁺ > Mg²⁺ > K⁺ for diquat²⁺ and Ca²⁺ > Al³⁺ > Mg²⁺ > K⁺ for paraquat²⁺. Three successive treatments of vermiculite released up to 89% of the diquat²⁺ or paraquat²⁺.
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