The interaction of organic matter with clays and soils has been extensively studied 1, 2. It has been reported that this interaction with siliceous and ~tur~inous surfaces in dilute suspensions is affected by several factors such as the, nature of the organic substance, its solubility and concentration in the solvent, the solvent itself, the lattice configuration of the adsorption, its saturating cations, CEC, pH, organic matter and orientation of the molecules. Adsorption isotherms have been used to explain some of the interactions 3'4. In spite of these studies the mechanism of these interactions is doubtful. The confusion arises mostly as a result of the presence of a large number of chemically active spots in clays in the form of exchangeable cations, sorbed water around cations, hydroxyl groups, lattice surface oxygens and the electrical double layer at the edges of the clays. The situation is further complicated by environmental factors which often simultaneously interact in these reactions. Information on the mechanism of clay-organic matter interaction is thus very meagre so far as the mineral illite is concerned.
Illite occurs on a large scale in the alluvial soils of India and is an important clay mineral. That this mineral may have chemically reactive sites at the edges, corners, interlayer and inter-lattice positions has been visualised by several workers 5-6. The work of Mitra and Rajagopalan 7 and Khan and Singhal 8 on the tribasicity of illites is significant in this regard. Nicotine and other heterocyclic materials have been used as pesticides.
The present study was designed to investigate the adsorption of nicotine on acid-and base-saturated illites, to study the stoichiometry of the reaction under differing conditions of pH and hence to obtain a clearer understanding of the mechanism of adsorption and the specificity of the different types of sites existing in illitic clays.
Methods
The clay mineral illite used in the studies was obtained from Wards Natural Science Establishment, Inc. The mineral was from Morris, Illinois and was a monomineralic standard of the Clay Mineral Standards Project No. 49 of the American Petroleum Institute. The < 2#m clay fraction was separated by sedimentation and centrifugation. Sodium-and hydrogen-saturated illites were prepared by the method of Aldrich and Buchanan 9. The clay suspension was treated with sodium chloride and dilute hydrochloric acid until the concentration of the supernatant liquid was * BEC = base exchange capacity.