Magnetically assisted coagulation using iron oxide nanoparticles-Leucaena leucocephala seeds' extract to treat synthetic Congo red wastewater

This study focused on utilization of Leucaena leucocephala seeds' extract and iron oxide nanoparticles (IONPs) under magnetic field to provide effective coagulation process. Leucaena seeds' extract was obtained using 3 M NaCl solution as solvent at feed-to-solvent mass ratio of 1:20. IONPs were synthesized using co-precipitation method. The obtained IONPs were analyzed using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. Based on analysis results, the obtained IONPs were the agglomerate of Fe3O4 phase with average particle diameter of 14.6 nm. The extract and IONPs were used as natural coagulant at various pHs (3-12), coagulant dosages (4-40 mL extract/L), and IONPs concentrations (0.5-3 mg/mL extract) under external magnetic field. It was obtained that pH 3 was the best pH because positively charged Leucaena protein at pH 3 acts to neutralize negatively charged Congo red molecules. The highest removal was obtained at coagulant dosage of 20 mL/L, and further increase in dosage was decreasing the removal due to colloid re-stabilization effect. The variation of IONPs concentration did not give any effect on the %removal and sludge volume. However, further investigation using pseudo-second-order kinetic model showed that the increase in IONPs concentration gave increase to the kinetic constant, signifying faster settling kinetics. The best condition was obtained at pH 3, coagulant dosage 20 mL/L, and IONPs concentration of 3 mg/mL extract that gave 90% Congo red removal, 30 mL/L sludge volume, and 30 min settling time.