Effective removal of azo dyes is a stringent issue. In this study, the adsorption behaviors of methyl orange (MO) and congo red (CR) on the magnetic ion-exchange (MIEX) resin were investigated by batch experiments. Attaining adsorption equilibrium of MO and CR takes 90 and 150 min, respectively. The equilibrium adsorption capacity of MO (42.32 mg mL −1 ) on the MIEX resin is much larger than that of CR (30.57 mg mL −1 ). The kinetic processes of MO and CR adsorbed on the MIEX resin follows the Elovich model. At 288 K, the Langmuir model can simulate the equilibrium adsorption data of MO and CR. However, the equilibrium data can be well fitted by the Freundlich model at 293 and 303 K. The thermodynamic parameters show that the adsorption of MO and CR are both thermodynamically spontaneous, endothermic processes. The MIEX resin can well remove MO (80%) and CR (50%) at pH 5.0−9.0. Ion exchange dominates the mechanism of CR adsorbed on the MIEX resin. For MO, however, physical adsorption plays a role to some extent besides ion exchange. Sodium chloride (187 mg) is needed to regenerate per milliliter of spent the MIEX resin. After eight times adsorption−desorption cycles, The MIEX resin retains still efficient adsorption. As a summary, the MIEX resin can be considered as a promising adsorbent to remove azo dyes from water and wastewater due to its high adsorption capacity, short adsorption time, and simple regeneration.

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.