The sorption and desorption kinetics of polycyclic aromatic hydrocarbons in methanol/water mixtures

The sorption and desorption kinetics of polycyclic aromatic hydrocarbons (PAHs) by soils in mix-solvent systems were studied The rate of PAH uptake or desorption from the solid phase was dependent upon the composition of the co-solvent/water mixture. Generally, higher co-solvent volume fractions resulted in a significant increase in rates of PAH sorption/desorption. A simplified retarded-radial diffusion model. (RRDM) was applied to model the effects of co-solvents on the sorption kinetics of hydrophobic organic compounds. This approach assumes that the diffusion of an organic molecule into soil aggregates is retarded by tortuosity effects and partitioning between the porefluids and sorbent organic matter. In the presence of co-solvents, the diffusional mobility of hydrophobic organic contaminants would presumably be enhanced The RRDM was calibrated using sorption/desorption rate data collected for one PAH (phenanthrene), and was capable of estimating the effects of co-solvents on the sorption/desorption kinetics of the other two analytes. In all cases the RRDM was able to show that both sorption and desorption rates were significantly enhanced with increasing amounts of co-solvent in the solution phase.