TRANSPORT OF HUMIC MATTER-COATED HEMATITE IN PACKED-BEDS

Column filtration experiments, using quartz grains as the bed media, were conducted to study the deposition kinetics of hematite particles in the presence of three well-characterized humic substances. Two pH conditions, 5.2 and 7.4, were selected such that the humic matter was adsorbed to an originally positive and negative hematite surface, respectively. Background NaCl concentrations ranged from 0.015 to 0.1 M. The particle deposition rates, expressed in terms of initial experimental attachment efficiencies (alpha(exp)), depended on the magnitude of both electrostatic and steric repulsive interaction energies. For a given solution chemistry, values of alpha(exp) exhibited a strong dependence on the type of the humic matter, while electrophoretic mobility measurements were independent of the type of surface coating and were solely a function of the pH and NaCl concentration. The lowest values of alpha(exp) were obtained for particles coated with the largest molecular size humic material at all solution conditions. Their low attachment rates were attributed to greater steric interaction forces. Attachment efficiencies of hematite particles coated with two different fulvic acids were determined. It is proposed that differences in the attachment rates are related to differences in the surface conformations of the fulvic acids.