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This article in SSSAJ

  1. Vol. 33 No. 3, p. 379-382
    Received: Oct 30, 1968
    Accepted: Jan 24, 1969

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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

  1. S. B. Weed and
  2. J. B. Weber2



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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