Application of an empirical transport model to simulate retention of nanocrystalline titanium dioxide in sand columns

Nanocrystalline titanium dioxide was injected into sand columns to simulate subsurface injection for creation of a permeable treatment barrier. Past usage of this material as an ex situ pilot scale treatment filter has shown that it has a high adsorption capacity for a number of heavy metals and therefore would be a good candidate for injection technology. Three suspension concentrations (50, 75 and 100 mg l−1) were pumped through packed sand columns at different flow velocities (3.0, 6.8 and 14.1 cm min−1). Little to no particles was detected in the effluent. Most of the nanoparticles remained in the sand columns, with an increasing then decreasing retained solids pattern. Application of a one-dimensional advection–dispersion flow model, that included two empirical kinetic terms to account for particle retention in the porous media, produced data fits that followed the general trend of the data, but did not truly capture the concentration maxima in the data sets. Discussion of these results highlights the limited ability of existing models to aid in predicting particle retention of non-ideal materials for engineering purposes.