Application of the mass transfer model for describing nonequilibrium transport of HOCs through natural geosorbents

Column experiments of nonsorbing and sorbing solutes were conducted in sandy aquifer material. Results of the column experiments were analyzed using a numerical nonequilibrium mass transfer model (designated as dispersed flow, film and particle diffusion model, DF-FPDM), an equilibrium advection–dispersion model (designated as dispersed flow, local equilibrium model, DF-LEM) as well as a nonequilibrium two region (mobile–immobile) advection–diffusion model (designated as homogeneous solid diffusion model, HSDM). Results of the analyses revealed that in all experiments the experimental BTCs are much better predicted by the DF-FPDM than by DF-LEM and HSDM. The relative influence of different processes (film diffusion, intraparticle diffusion and dispersion) can be identified by dimensionless mass transfer parameters NF, NS and ND. Their plausibility can be compared with the well-known advection–dispersion-based equilibrium model. In general, spreading and asymmetry of sorbing solute BTCs can be explained with the DF-LEM and HSDM, but the identification of different processes and their influence on the total transport processes can only be ascertained with a model like DF-FPDM.