USE OF A REACTIVE SURFACE-DIFFUSION MODEL TO DESCRIBE APPARENT SORPTION DESORPTION HYSTERESIS AND ABIOTIC DEGRADATION OF LINDANE IN A SUBSURFACE MATERIAL

Desorption hysteresis has been reported frequently in the literature, with several theories advanced to explain the cause of this phenomenon. Several of these theories hypothesize that desorption hysteresis is an experimental artifact. Batch experiments were performed to observe sorption-desorption and transformation of the solute lindane in systems that included a subsurface sand material. Results of these experiments were interpreted with a diffusion and reaction model. Methods were developed to isolate and determine model parameters from experimental data. Rates of dehydrochlorination were determined for lindane in solution and solid phases. A pseudo sorption-desorption equilibrium experiment was performed by allowing 720 h for attainment of sorption equilibrium and 384 h for attainment of equilibrium for each of three desorption steps-longer than most experiments of a similar nature have been allowed to equilibrate. The pseudoequilibrium data showed marked hysteresis. A surface-diffusion model, which accounted for solute degradation from the solution and solid phases, was calibrated with sorption rate data. The model was verified with desorption rate data. Model predictions of the pseudo sorption-desorption experiment showed that slow sorption-desorption rates explained most of the apparent hysteresis.