TRANSPORT OF HUMIC MATTER-COATED HEMATITE IN PACKED-BEDS

Column filtration experiments, using quartz grains as the bed media, w ere conducted to study the deposition kinetics of hematite particles i n the presence of three well-characterized humic substances. Two pH co nditions, 5.2 and 7.4, were selected such that the humic matter was ad sorbed to an originally positive and negative hematite surface, respec tively. 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 bo th electrostatic and steric repulsive interaction energies. For a give n solution chemistry, values of alpha(exp) exhibited a strong dependen ce on the type of the humic matter, while electrophoretic mobility mea surements were independent of the type of surface coating and were sol ely a function of the pH and NaCl concentration. The lowest values of alpha(exp) were obtained for particles coated with the largest molecul ar size humic material at all solution conditions. Their low attachmen t rates were attributed to greater steric interaction forces. Attachme nt efficiencies of hematite particles coated with two different fulvic acids were determined. It is proposed that differences in the attachm ent rates are related to differences in the surface conformations of t he fulvic acids.