TWO-REGION LINEARfNONLINEAR SORPTION MODELING BATCH AND COLUMN EXPERIMENTS

摘要

Batch and column experiments were conducted to assist in elucidation of the mechanism and rates of slow diffusion of 1,2,4-trichlorobenzene into Borden sand. Batch rate experiments were conducted at three concentration levels, and a full isotherm was developed over 550 d. The equilibrium isotherm showed significant nonlinearity (Freundlich exponent = 0.75). Three column experiments were conducted--two at low velocity (each at a different input concentration) and one at high velocity. The data were analyzed with four different models; the two most successful are described in detail here. These two models divided sorption between instantaneously equilibrating and diffusion-limited domains, with either a linear or nonlinear sorption isotherm assumed for the instantaneously equilibrating fraction of sorption sites. Either model could simulate any single data set by adjustment of two parameters, however, no single parameter set could simulate all data sets. The model with a linearly sorbing instantaneous fraction described the batch data better than the model with a nonlinearly sorbing instantaneous fraction; however, a nonlinearly sorbing instantaneous fraction described the slow column experiments much better than a linearly sorbing instantaneous fraction. The high-flow-rate column experiment indicated that the assumed instantaneous fraction is actually influenced by rate limitations, suggesting that more complex models are needed in order to simulate this shorter time scale behavior. Overall, our work illustrates how one needs to include a wide variety of experimental conditi