Performances and Mechanism of Methyl Orange and Congo Red Adsorbed on the Magnetic Ion-Exchange Resin

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.