SPECTROSCOPIC EVIDENCE FOR THE RATE LIMITED ACCUMULATION OF A PERSISTENT FRACTION OF 1,2-DICHLOROETHANE SORBED ONTO CLAY-MINERALS

Diffuse reflectance infrared spectra are collected in situ as a function of time during the sorption/desorption of 1,2-dichloroethane on montmorillonite and kaolinite. The spectra indicate that the sorptive becomes associated with the clay minerals in both a liquid and a labile vapor state, confirming previous results obtained with illite as the sorbent. They also provide evidence for an additional sorbed species that accumulates at a rate quite different from those of the other two. Features characteristic of this species persist in the spectra for periods of days after desorption is initiated. The results are interpreted in the context of sorbent porosity and the existence of a network of narrow pores that limits the rates of both sorption and desorption for the persistent species.