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Sorption and Desorption of Acetonitrile on Montmorillonite from Aqueous Solutions

Delaware Agric. Exp. Stn., Dep. of Plant and Soil Sciences, College of Agric. Sciences, Univ. of Delaware, Newark, DE 19717-1303

R. A. Pease

Engineering Dep., E.I. DuPont de Nemours & Co., Inc., Newark, DE 19714

* Corresponding author.

ABSTRACT

The sorption and desorption of acetonitrile on K, Na, Ca, and Mg montmorillonite from aqueous solutions were determined using a ¹⁴C isotope tracer method. The heat of sorption of acetonitrile on K, Na, and Ca montmorillonite at two concentrations was determined using a Calvet microcalorimeter. The infrared spectra of the clay-water-organic systems were recorded on a Fourier-transform infrared spectrometer and the c-axis spacings of K, Ca, and Mg montmorillonite in the acetonitrile solutions were determined by x-ray diffraction. It was found that the sorption and desorption of acetonitrile on the four homoionic montmorillonites are reversible, and that the sorption of acetonitrile is exothermic on K and Ca montmorillonite, but endothermic on Na montmorillonite. Further, it was found that the wavenumbers of the CN band and the C-H band for the acetonitrile molecules on the clay surfaces do not differ from those in the solution. It was also observed that the sorption of acetonitrile affected the c-axis spacing of the various homoionic montmorillonites differently. These results led to the conclusion that the sorption of acetonitrile on montmorillonite is not due to any specific bonding between the organic molecules and the clay surfaces, but rather to a distribution or partition between the interfacial phase and the bulk-solution phase. Analysis was provided to show that a partition mechanism does not necessarily yield a linear isotherm, especially when the concentration of the organics is high.

Published as Miscellaneous Paper no. 1297 of the Delaware Agric. Exp. Stn.

Received for publication April 28, 1989.