Effects of nonvolatile organic contamination on the surface areas and adsorption energetics of porous media

Surface areas and pore-size distributions of natural and model porous media were measured before and after contamination by naphthalene, a nonvolatile organic compound (NVOC). The contaminant was added to the solids in a solvent (pentane) which was subsequently volatilized (a scenario meant to mimic field behavior of mixed solvents). The Brunauer-Emmett-Teller (BET) and Frenkel-Halsey-Hill (FHH) models were used to interpret the measured adsorption isotherms. Also, the Barrett-Joyner-Halenda (BJH) model was used to calculate pore-size distributions and pore properties of the samples. The results indicate that contamination of the porous media results in a reduction of surface areas and pore areas and volumes. For the Moffett sand (natural media), the surface area was reduced from 1.57 m(2)/g to 0.81 m(2)/g and 0.65 m2/g for the 0.1% and 1.0% contaminated samples, respectively. For the silica gel (model media), the area was reduced from 397 m(2)/g to 248 and 238 m(2)/g for the 0.1% and 1.0% contaminated samples, respectively. This reduction is also apparent in the pore-size distributions, where all pore areas and volumes are reduced significantly (for pores between 2.5 and 35 nm). Moreover, adsorption energetics are affected by the presence of the contaminant, although the results are difficult to interpret. It is postulated that the contaminant precipitates into the pores of the solids, reducing the pore and overall areas. Residence in these pores would render the contaminants inaccessible to mobile fluids and difficult to remove during remediation of contaminated soils.