Transport behavior and deposition kinetics of humic acid under acidic conditions in porous media

The transport behavior of humic acid in porous media was studied from the viewpoint of colloidal stability. Column experiments were performed with a large molecular weight fraction of purified Aldrich humic acid over a wide range of monovalent (NaCl) and divalent (CaCl2) electrolyte concentrations at pH 3. The ratio of the humic acid effluent to influent concentration was analyzed using the colloid filtration theory to determine attachment efficiencies (α) of the humic acid that deposited onto the surface of glass beads. In a log–log plot, the obtained value of α increased linearly with an increase in the electrolyte concentrations up to a threshold value and remained constant above the threshold value for both NaCl and CaCl2. This threshold value represented the critical deposition concentration (CDC). The ratio of the CDC of NaCl to that of CaCl2 was reasonable as a prediction of the Schulze–Hardy rule. These findings suggest that the transport behavior of humic acid under acidic conditions depends on its colloidal stability.