Comparative study of various magnetic nanoparticles for Cr(VI) removal

In this study, various magnetic nanoparticles were prepared by chemical co-precipitation method and used for the removal of Cr(VI) from synthetic electroplating wastewater. The size of these magnetic nanoparticles was measured using transmission electron microscopy (TEM) and found to be about 20 nm. Their magnetic properties were characterized by vibrating sample magnetometer (VSM). The technical feasibility of magnetic nanoparticles for Cr(VI) removal was investigated in batch studies in acidic synthetic solution using 5 g/L of different magnetic nanoparticles and 100 mg/L of Cr(VI). The Cr(VI) removal performances were compared and the adsorption capacities followed the order: MnFe2O4 > MgFe2O4 > ZnFe2O4 > CuFe2O4 > NiFe2O4 > CoFe2O4. Contact time required by all types of ferrite particles was relatively short, ranging from 5 to 60 min. Factors affecting adsorption including solution pH, shaking rate, and magnetic properties were further investigated. In addition, the desorption of Cr(VI)-adsorbed magnetic nanoparticles were conducted using 0.01 M NaOH as eluent and the desorption efficiency was found to be more than 90%. While much lower amount of Cr(VI) desorbed from Cr-loaded MnFe2O4 nanoparticles using the same eluent due to a chemical redox occurred during adsorption.