COUPLING ADSORPTION AND PARTICLE AGGREGATION - LABORATORY STUDIES OF COLLOIDAL PUMPING USING FE-59 LABELED HEMATITE

Fe-59-labeled, spherical hematite particles not retained by filters because of their size coagulated to form aggregates, which were filter-retained. Batch systems containing hematite particles and a suite of radionuclides showed that, as the hematite coagulated, colloid-adsorbed radionuclide species were transferred from the colloid pool to the filter-retained particle pool. Sorptive equilibrium was rapidly achieved; thus, the rate-limiting step for the appearance of the radionuclides in the filter-retained particle pool was coagulation. The results indicate that, in many instances, slow "sorption" kinetics may be due to a combination of particle aggregation and artifacts of incomplete phase separation. It is evident that what is an artifact in experimental systems can be an important process in natural aquatic systems. The results of this study therefore provide a framework for a better understanding of the role of coagulation coupled to sorption in regulating the fate of trace metals in natural systems.