Summary of Studies for

Michael Sander, Fiessinger Scholarship Winner 2003

(Report - summer 2004)

Mr. Sander's Ph.D. research focuses on irreversible sorption of organic contaminants in soils and sediments. Irreversibility is manifested by (i) hysteresis in which the contaminant shows stronger affinity for the solid during a desorption event than it did during the initial sorption, and (ii) the ‘conditioning effect’ in which the contaminant shows stronger affinity for a solid in a second sorption cycle. Over the last year, he tested the hypothesis that sorption irreversibility in macromolecular natural organic matter results from irreversible expansion of micropores in the solid by entering contaminant molecules.

Sander derived a thermodynamically based index to calculate irreversibility. This index quantifies the partial molar free energy of contaminant that is irreversibly lost to deformation of sorbent micropores. While indices to quantify hysteresis have been published, their use is restricted because they are empirical and require specific model assumptions.

He developed a ¹⁴C-isotope exchange technique to differentiate between artificial hysteresis (i.e., due to experimental artifacts) and true hysteresis. The technique involves monitoring the uptake of a minute amount of ¹⁴C-labeled chemical following both bulk contaminant sorption and desorption. The technique was applied to the hysteresis of naphthalene, a common pollutant, to a low-rank coal reference standard, which represents hard organic matter in soils and sediments. The results show that hysteresis is true and are consistent with irreversible deformation of the sorbent without the formation of an entrapped fraction.

Further supportive of the micropore-deformation hypothesis was Sander's observation of conditioning effects in a peat soil, a humic acid, and a glassy synthetic organic polymer using chlorinated benzenes as model compounds. In a subsequent experiment, he exposed the conditioned peat soil and humic acid to elevated temperatures. In both cases, heat-treatment anneals (i.e., diminishes or –depending on the temperature and exposure time - even eliminates) the conditioning effect. This can be explained by assuming that the macromolecular backbone undergoes thermal relaxation towards structural equilibrium by reducing internal (micropore) volume. Synthetic organic polymers show the same behavior.

Mr. Sander expressed  gratitude for the financial support of EREF, which allowed him to present his work at several international conferences.