Removal of heat stable salts from industrial lean methyldiethanolamine using magnetic alginate/iron oxide hydrogel composite

Heat Stable Salts (HSS) are undesirable contaminates that are generated due to the degradation of the amine solvent. This study deals with the development of a new process for the removal of HSS from amine solvent using magnetic calcium alginate hydrogel composites. The magnetic calcium alginate hydrogel composites was prepared by encapsulating freshly prepared maghemite nanoparticles (γ-Fe₂O₃) synthesized using a conventional precipitation technique in the calcium alginate beads. The developed magnetic hydrogel composites (CA-Fe₂O₃) characterized by XRD, SEM and FTIR showed that γ-Fe₂O₃ are retained homogeneously in the composites matrix. Kinetic and equilibrium batch adsorption experiments revealed that maximum HSS removal of 29.24% was achieved in 240 min with 3.0 g of onto CA-Fe₂O₃ composites at 25 °C and sorption efficiency increased with an increase in temperature. Adsorption kinetic study was performed using three kinetic models and the pseudo-second order kinetics very well correlated with the experimental data; demonstrating the chemisorption and endothermic nature of sorption. The reusability experiments showed no significant loss in absorption capability even after eight cycles. Additionally, the superparamagnetic behavior showcased by the magnetic composites allowed easy separation of the composites from lean MDEA using an external magnet. Therefore, such magnetic alginate–Fe₂O₃ hydrogel composites can work as a simple and cost-effective adsorbent for the reclamation of industrial lean MDEA, with the additional advantages of good efficiency, eco-friendliness and being easy to fabricate and recover.