Adsorption of humic acid fractions by a magnetic ion exchange resin

Abstract

Natural organic matter in waters varies in different fractions. To better understand the removal of different fractions by a magnetic ion exchange (MIEX) resin and the mechanism behind it, this study investigated adsorption kinetics, equilibrium and thermodynamics of humic acid (HA) fractions with different hydrophilic-hydrophobic properties and molecular weights on MIEX resin through a series of batch experiments. MIEX resin can effectively remove approximately 40% of hydrophilic and 30% of hydrophobic HA components, as well as approximately 44% of molecular weight (MW) <10 kDa to some degree. The removal efficiency of HA fractions by MIEX resin reduced with the increase of pH from 6 to 9. Adsorption kinetics of different HA fractions on MIEX resin fitted the pseudo-second-order model well. With the increase of MW of HA from <1 kDa to >10 kDa, the time to reach adsorption equilibrium reduced from 180 to 120 min. It took more time for the hydrophilic fractions (140 min) to reach the equilibrium than for hydrophobic HA fractions (120 min). The Sips model fitted the adsorption equilibrium data of HA fractions on MIEX resin well. It was revealed that the adsorption of HA fractions on MIEX resin was spontaneous, endothermic and an entropy driven process, and the chemisorption might dominate the adsorption of HA components on MIEX resin. This study is of great significance to the design of magnetic ion exchange resin reactors and the optimization of operational parameters for the removal of natural organic matter with different hydrophilic-hydrophobic properties and molecular weights in different water sources.

Revealing the effect of anion exchange resin conditioning on the pH and natural organic matter model compounds removal mechanisms

“…column) on the other hand. Nevertheless, the effect of different pH values on the NOM removal efficiency and mechanisms is widely investigated [29,57,58]. Whether the pH of the water during the resin treatment is caused by migration of ions from the resin-water phase or by the pH of the feed water, the degree of protonation, activity, repulsion or attraction, hydrodynamic volume of the NOM compounds will be the same.…”

“…Ding et al explained the decrease in the HA removal efficiency of an acrylic SBA type I resin with an increase in pH (from 6 to 9). The authors assigned this observation to competition of OHions for IEX on the one hand and the electrostatic repulsion between the HA in solution and the HA adsorbed on the resin and the HA, impeding HA diffusion onto the resin surface on the other hand [57].…”