Infrared investigation of the sequestration of toluene vapor on clay minerals.

The Ca-exchanged clays were used to investigate the sorption of toluene under both high and low relative humidity conditions. According to the observed rates of sorption and desorption and the Fourier transform infrared (FTIR) spectra of sorbed toluene, the sorbate molecules on clays can be divided into three categories: labile (gaslike) phase, slow sorption (liquidlike) phase, and resistant-to-desorption phase with sorption/desorption time scales of less than 30 min, several hours, and several weeks, respectively. Aging changed the spectroscopic characteristics of the sorbed sorbates and contributed to the irreversibility of the sorption under both high and low relative humidity. Irreversibly sorbed portions of the sorbates and new characteristic peaks identified with FTIR spectrometry suggest the existence of chemical transformation of sorbed species under both high and low relative humidity conditions. It is suggested that the clay minerals, acting as catalysts, may contribute to abiotic natural attenuation of volatile organic aromatic hydrocarbons in soils.