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Adsorption of Fenuron and Monuron (Substituted Ureas) by Two Montmorillonite Clays¹

ABSTRACT

The effect of the type of clay mineral, exchangeable cation, temperature, and electrolyte concentration on the adsorption of two substituted ureas was investigated.

The adsorption was greater on a Bentonite than on a Camp Berteau montmorillonite, possibly because the lattice charge in the former originates from tetrahedral and octahedral layers whereas in the latter only from octahedral layers. The adsorption increased with the polarizing power of the exchangeable cation. Normal adsorption isotherms were exothermic but when the temperature effect on solubility was accounted for, the adsorption reaction tended to be more and more temperature independent as the electronegativity of the exchangeable cation increased. Relative thermodynamic data suggest that the favorable contribution to the adsorption energy arises mainly from enthalpy changes.

The effect of salt concentration was almost negligible up to 1.0N and for a given electrolyte good agreement was obtained between the heat of solution of the herbicide and its adsorption.

¹ Contribution from the Dep. of Soil Science, Univ. of Louvain, Belgium. This research was supported by the "Institut pour l'Encouragement de la Recherche Scientifique dans l'Industrie et l'Agriculture" (I.R.S.I.A.). Laboratory assistance by Mrs. Ch. Parvais is appreciated.

² Associate-Professor and Research-Assistant, respectively, Univ. of Louvain, 42, de Croylaan, 3030 Heverlee, Belgium.

Received for publication July 6, 1973. Accepted for publication November 26, 1973.