Enhanced removal of Cr(III) in high salt organic wastewater by EDTA modified magnetic mesoporous silica

EDTA-modified magnetic mesoporous microspheres (Fe3O4@nSiO2@mSiO2/EDTA) was synthesized and was employed to remove Cr(Ш) from water with high salinity and organic matter. The adsorbents were characterized by means of N2 adsorption-desorption, TEM, XRD, TGA, FTIR, and XPS. Characterized results exhibit that EDTA functionalized Fe3O4@nSiO2@mSiO2 with average pore diameter of 2.1 nm, the BET surface area of 337.02 m2 g−1 and the pore volume of 0.19 cm³·g−1 was successfully synthesized. The adsorbent shows high adsorption capacity for aqueous Cr(III), and the maximum adsorption amount in tested experiment was 30.59 mg L−1 at pH 3.0 and 25 °C. The Freundlich isotherm model can be better fitted with the adsorption results for Cr(III) adsorption than Langmuir isotherm model. The fast Cr(III) adsorption was observed within 10min and the adsorption kinetics can be fitted by the pseudo-second-order kinetic model. No obvious reduce of Cr(III) adsorption on the adsorbent in presence of foreign cations (Na+, K+ and Ca2+) and complex agents (EDTA, citric acid and formic acid) was observed, reflecting that the synthesized adsorbents can be used for Cr(III) removal from high salinity organic wastewater. XPS analysis showed that the ion exchange and surface complexation mechanism contributed to the enhanced Cr(III) adsorption. The Cr(III) saturated adsorbent can be regenerated and reused. The present results suggest Fe3O4@nSiO2@mSiO2 can be used as a promising adsorbent for the removal of heavy metals from aqueous solution with high salinity and organic matter.