Gongmin Fu

Adsorption/Desorption hysteresis in organic pollutant and soil/sediment interaction.

Adsorption and desorption of pollutants to soil and sediment materials are major fate mechanisms. The hypothesis that adsorption and desorption are reversible processes has been tested. The organic pollutants naphthalene, phenanthrene, and p-dichlorobenzene have been studied in the laboratory using batch reactors at room temperature from a few hours to over 2 months. The adsorption experiments were at equilibrium within 1-4 days and could be modeled using simple linear isotherms with K p values consistent with published K oc and K ow relationships. Desorption experiments were conducted with the contaminated sediments by successive dilutions

Mechanisms of Mineral Scale Inhibition

An extensive study of adsorption and desorption isotherms of four phosphonates on barite or calcite are tested for a wide range of solution conditions (0 to I M NaCl, 0 to 0.1 M Ca, 0 to 0.33 M sulfate, and 4.6 to 6.4 pH). From these adsorption/desorption observations, it is proposed that the primary driving force for adsorption is related to simple hydrophobic repulsion from solution of a macroneutral molecule and not, as is generally presumed, some specific inhibitor-surface interaction. From the nucleation study, it is observed that the inhibitor needed to completely inhibit barite formation is approximately equal to 16% surface coverage. Air equation to predict minimum inhibitor need is proposed based on this model and is compared with field observations. The range of predicted inhibitor concentrations is quite similar to what is observed in the field as a minimum effective dose even though it was derived by a completely independent calculation method.