Temperature effect on chromium(VI) removal by Mg/Al mixed metal oxides as adsorbents

Temperature plays a major role in Cr(VI) adsorption although the underlying mechanisms are still unclear. The aim of this study was to determine the relationship among the temperature, adsorption properties and microstructure characteristics. In this work, the calcined Mg/Al hydrotalcites (MMO) as adsorbents were investigated for the Cr(VI) removal in aqueous solution. The effect of calcination and adsorption temperatures on the Cr(VI) removal of the MMO was studied based on the aspects of the microstructure characteristics and adsorption properties. The results showed that the sample calcined at 500 °C (MMO500) had the largest adsorption capacity of 94.64 mg·g− 1 for Cr(VI). For MMO500 as an adsorbent, the experiment data were fitted well into Langmuir isotherm model and pseudo-second-order kinetic model. Combined with thermodynamic analysis, the activation energy (22.42 kJ·mol− 1) suggested that the adsorption process was chemisorption nature and diffusion was the rate limiting step. The further research showed that the film diffusion was more dominant than the intra-particle diffusion. The results demonstrated that the MMO500 was a promising adsorbent in the Cr(VI) pollution control.