Development of a surrogate sediment to study the mechanisms responsible for adsorption/desorption hysteresis

A surrogate sediment was developed to reduce some of the complexity in the structural aspects of the adsorbed organic carbon phase. Layers of an anionic surfactant were sorbed to colloidal anatase to produce an organic carbon phase that had hydrophobic regions and resisted desorption. The surrogate is verified as a model sediment by comparing the results of contaminant [2,2',5,5'-tetrachlorobiphenyl (PCB) and naphthalene] adsorption and desorption batch experiments to the results of similar experiments performed an a well-studied natural sediment. The surrogate exhibited adsorption of contaminants via a hydrophobic interaction in the same magnitude as to a natural sediment for the two different hydrophobic organic contaminants in 0.1 or 0.15 M NaCl solution. The sorption of PCB to the surrogate at varied organic carbon contents was observed to follow a linear adsorption isotherm. Desorption experiments were conducted by successive dilutions. Both the surrogate and natural sediment were observed to exhibit similar desorption behavior. The solution concentration during desorption was lower than predicted by the adsorption isotherm and remained unchanged from 4 h to 168 days. The heterogeneous nature of sediments should be greatly reduced in the surrogate yet desorption still appears to be low.