IRREVERSIBLE ADSORPTION OF NAPHTHALENE AND TETRACHLOROBIPHENYL TO LULA AND SURROGATE SEDIMENTS

Several unique features of sorption irreversibility have been investig ated in this paper. Adsorption has been found to be biphasic with abou t 30-50% of the adsorbed mass residing in the irreversibly sorbed comp artment, until this compartment is filled, and the rest of the mass re sides in the labile compartment. Naphthalene in the reversible compart ment follows a linear adsorption isotherm with a normal organic carbon -based partition coefficient. A finite fixed total compartment size is observed for the irreversible fraction, q(max)(irr) (mu g/g), on both natural and surrogate solids. In multiple batch adsorption/desorption experiments, the maximum concentrations that resist desorption are q( max)(irr) approximate to 10 mu g/g for naphthalene on Lula sediment an d q(max)(irr) approximate to 0.36 mu g/g for 2,2',5,5'-tetrachlorobiph enyl (2,2',5,5'-CB) on both Lula and surrogate solids. The concentrati on in the irreversibly sorbed compartment varied with the initial naph thalene concentration available for adsorption. In addition, the amoun t in the irreversibly sorbed compartment increases linearly with the n umber of adsorption steps until the maximum concentration q(max)(irr) is reached. After the maximum concentration of the irreversibly sorbed compartment is satisfied, the adsorption/desorption of naphtha I ene and 2,2',5,5'-CB becomes reversible. The irreversibly sorbed compartme nt appears to be at equilibrium with the aqueous phase when the labile naphthalene or 2,2',5,5'-CB is removed, but the equilibrium concentra tion is much lower than would be predicted with conventional hydrophob ic partitioning theory. The aqueous phase concentration in equilibrium with the irreversibly sorbed compartment is about 2-5 mu g/L for naph thalene and 0.05-0.8 mu g/L for 2,2',5,5'-CB. Similar adsorption/desor ption phenomena are observed with both a natural sediment and a well-c haracterized sorrogate solid.