Hydrothermal chemical modification of red mud for efficient adsorption of methylene blue.

Red mud (RM) is the industrial solid waste produced after alumina extraction from bauxite, and most RM is directly discharged to the landfill yards without any treatment. In this study, modified red mud (MRM) was synthesized by a hydrothermal chemical modification method as an efficient adsorbent for methylene blue (MB) removal. The prepared MRM was characterized by X-ray fluorescence spectroscopy, X-ray diffraction, scanning electron microscope, transmission electron microscope, and Fourier transform infrared spectrometer. The effects of reaction time, initial MB concentrations, MRM dosage, temperature, and system pH were investigated in the MB batch adsorption experiments. The results showed that the modification method increased the specific surface area of RM material from 16.72 to 414.47 m²/g. The maximum adsorption capacity of MRM for MB was 280.18 mg/g under the conditions of initial MB concentration of 1000 mg/L, reaction time of 300 min, temperature of 25 ℃, and natural pH of 6.06. Meanwhile, the adsorption kinetics and equilibrium isotherms were demonstrated to fit well with the pseudo-second-order kinetic model and Temkin isotherm, respectively. This study provides a new method for the valorization of RM and demonstrates that MRM can be used as a low cost and environmentally friendly potential adsorbent for the removal of MB from wastewater.