Effects of humic acid on migration of montmorillonite and alumina colloid in a quartz sand column

Effects of humic acid on the migration of montmorillonite and γ-Al2O3 colloid in a quartz sand column were investigated. Breakthrough curves of montmorillonite colloid at pH 8 were very similar in the presence and absence of HA. The breakthrough curve of γ-Al2O3 colloid showed that the amount of γ-Al2O3 colloid migration in a quartz sand column was enhanced by addition of HA. Deposition of montmorillonite colloid on quartz sand in the presence and absence of HA is negligible because of the negative surface charge of montmorillonite. Deposition of γ-Al2O3 colloid on quartz sand was decreased by the addition of HA and increased pH. The surface excess of HA on montmorillonite above neutral pH was negligible, although γ-Al2O3 adsorbed a large quantity of HA. The surface charge of γ-Al2O3 is shifted negatively to a great degree by the addition of HA. These results indicate that HA considerably enhances the amount of γ-Al2O3 colloid migration by coating its surface. However, effects of HA on montmorillonite colloid migration are limited because of their low mutual affinity.