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The Effect of Cation Exchange Capacity on the Retention of Diquat²⁺ and Paraquat²⁺ by Three-Layer Type Clay Minerals I. Adsorption and Release¹

ABSTRACT

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⁺.

¹ Paper no. 2748 of the Journal Series of the North Carolina State University Agr. Exp. Sta., Raleigh. This investigation was supported by Public Health Service Research Grant CC 00282 from the National Communicable Disease Center, Atlanta, Ga.

² Professor of Soil Science and Associate Professor of Soil Science and Crop Science, North Carolina State University, Raleigh.

Received for publication October 30, 1968. Accepted for publication January 24, 1969.