ADSORPTION OF ORGANIC CATIONS TO NATURAL MATERIALS

The factors that control the extent of adsorption of amphiphilic organic cations on environmental and pristine surfaces have been studied. The sorbents were kaolinite, montmorillonite, two aquifer materials, and a soil; solutions contained various concentrations of NaCl and CaCl2, at various pH values. The distribution ratio of the dodecylpyridinium was strongly dependent on the nature and concentration of the inorganic cations in solution, but virtually independent of solution pH. The adsorption isotherms were distinctly nonlinear, even at very low surface concentrations of organic cations. A multisite adsorption model has been developed to describe adsorption over a wide range of dodecylpyridinium, NaCl, and CaCl2 concentrations. Two types of adsorption reactions were found to be significant: exchange of pyridinium with an alkali-metal cation, and adsorption of pyridinium with chloride counterion. © 1990, American Chemical Society. All rights reserved.