STUDY OF THE CHROMIUM(VI) REMOVAL FROM AQUEOUS SYSTEMS BY COBALT NANOPARTICLES

The cobalt nanoparticles (NPs-Co) were synthesized and applied in the removal of Cr(VI). The obtained nanomaterials presented magnetic properties and were characterized by the techniques of Transmission Electron Microscopy and X-ray diffraction. The NPs-Co, with a diameter of less than 50 nm, had a composition based on metallic cobalt and cobalt oxide. The NPs-Co were applied in the removal of Cr(VI) being evaluated different parameters such as time of equilibrium, initial pH, dose of NPs-Co, concentration of Cr(VI), and system temperature. The removal of Cr(VI) was favored at lower pH values, being about 100% at pH 2.0. With the increase of Cr(VI) concentration from 40.0 to 300.0 mg L-1 the removal decreased from 80 to 15%. The NPs-Co dose promoted an increase in removal reaching 90% at a dose of 1.0 g L-1. The removal process was spontaneous and endothermic, and the Langmuir isotherm model fit better to experimental data. The maximum removal capacity was approximately 70.0 mg g-1. The removal kinetics followed the pseudo-second order model. The mechanism of Cr(VI) removal occurred through adsorption by electrostatic interactions between CrO42- anion and Co-NPs, followed by reduction of Cr(VI) to Cr(III) and, lastly, co-precipitation of Cr(III) as Cr(OH)3 on the NPs-Co.