Magnetic mesoporous carbon hollow microspheres adsorbents for the efficient removal of Cr(III) and Cr(III)-EDTA in high salinity water

In this study, H2O2 oxidized magnetic mesoporous carbon hollow microspheres (Fe3O4@void@C@H2O2) with core-shell structure, high magnetic properties and abundant oxygen-containing functional groups was synthesized for removal of Cr(III)-EDTA and Cr(III) in high salinity wastewater. Fe3O4@void@C@H2O2 was synthesized at optimum conditions of H2O2 concentration of 20%, oxidation temperature of 40 °C and oxidation time of 4 h, and the determined adsorption amount of Cr(III)-EDTA and Cr(III) on the adsorbent was 9.72 and 10.53 mg g−1 at pH 4.0 and 25 °C, respectively. Adsorption behavior of Cr(III)-EDTA could be better described by Langmuir isotherm and Cr(III) adsorption followed Freundlich isotherm. Cr(III)-EDTA and Cr(III) adsorption on the adsorbent followed pseudo-second-order kinetics, and adsorption rate of Cr(III) adsorption on the adsorbent is higher than that of Cr(III)-EDTA. Fe3O4@void@C@H2O2 showed strong affinity for Cr(III) and Cr(III)-EDTA even in high salinity water. Moreover, Fe3O4@void@C@H2O2 exhibited the high stability in acid solution and Cr(III) saturated adsorbent can be easily regenerated in 0.1 mol L−1 HCl. Cr(III)-EDTA adsorption was described to the surface complexation between the oxygen-containing groups (such as hydroxyl, carbonyl and carboxyl groups) of the adsorbent and Cr(III) in Cr(III)-EDTA, and the hydrogen bonding between oxygen-containing groups of the adsorbent and EDTA of Cr(III)-EDTA, while Cr(III) adsorption on the adsorbent was surface complexation and ion exchange. The results highlighted that Fe3O4@void@C@H2O2 have great potentials for adsorptive removal of Cr(III) and it's chelate from the high salinity wastewater.