ACETONITRILE AND ACRYLONITRILE SORPTION ON MONTMORILLONITE FROM BINARY AND TERNARY AQUEOUS-SOLUTIONS

The main objective of this study was to gain mechanistic information on clay-organic interactions in aqueous environments containing multiple organics. Three different measurements were made to achieve this objective. The sorption of acetonitrile and acrylonitrile on K, Na, Ca, and Mg montmorillonite from binary and ternary aqueous solutions were determined using a C-14 isotope tracer method. The infrared spectra of acrylonitrile in solution and adsorbed on montmorillonite were recorded on a Fourier-transform infrared (FTIR) spectrometer and the c-axis spacings of montmorillonites in the acrylonitrile solutions were determined by x-ray diffraction. It was found that the sorption of acetonitrile and acrylonitrile from tenary solutions on K montmorillonite was competitive across the entire concentration range. The sorption was slightly competitive at lower concentrations on Na, Ca, and Mg montmorillonite, but enhanced at higher concentrations. The competitive sorption on K montmorillonite was probably associated with the decrease in the interfacial volume, since the layers of K montmorillonite were collapsed at higher concentrations, while the enhanced sorption on Na, Ca, and Mg montmorillonite appeared to be caused by an increase in the partition coefficient as more organic molecules entered the interfacial phase. These results led to the conclusion that the sorption of acetonitrile and acrylonitrile on montmorillonite was not due to specific bonding between the organic molecules and the clay surfaces, but rather to a partition between the interfacial phase and the bulk solution phase.