Removal of chromium from laboratory wastewater using preparation–adsorption technology with a Mg/Al/Cr layered compound

Abstract

A Mg/Al/Cr layered compound (Mg/Al/Cr(III)–LDH) was prepared using laboratory wastewater containing Cr(III), and the calcined Mg/Al/Cr(III)–LDH compound (Mg/Al/Cr(III)–CLDH) was applied to remove Cr(VI) from laboratory wastewater. The present work simultaneously treats Cr(III) and Cr(VI) pollution using preparation–adsorption technology with the Mg/Al/Cr layered compound. The preparation conditions of Mg/Al/Cr(III)–LDH and the removal process of Cr(VI) were optimized. The maximum adsorption capacity and regenerative properties of Mg/Al/Cr(III)–CLDH were also studied. The physicochemical properties of the materials were analyzed using a combination of X-ray diffraction, FT-IR spectroscopy, TG-DTG, N₂ adsorption–desorption, pore size distribution and SEM. The results show that Mg/Al/Cr(III)–LDH performs better when the molar ratio of Mg : Al : Cr(III) is 10 : 4 : 1, the reaction temperature is 45 °C and the aging time is 24 h. The optimal absorption conditions for Cr(VI) are as follows: a pH value of 8–9, a solid–liquid ratio of 1 : 250, and a reaction time of 80 min at room temperature. The maximum adsorption capacity of Mg/Al/Cr(III)–CLDH for Cr(VI) is 237.80 mg g⁻¹. When the concentration of Cr(III) or Cr(VI) in simulated laboratory wastewater is below 300 mg L⁻¹ or 60 mg L⁻¹, the remaining concentration of Cr(III) or Cr(VI) is below to 0.5 mg L⁻¹ after the preparation–adsorption process which is in line with the Chinese National Integrated Wastewater Discharge Standard (GB8978-1996). In addition, Mg/Al/Cr(III)–CLDH could effectively remove Cr(VI) in practical laboratory wastewater, and the treated wastewater could be discharged directly.