Preparation of efficient adsorbent for methylene blue and Congo red by co-hydrothermal of red mud with food waste compost

Herein, a novel red mud-carbon composite (RFBC) was prepared through co-hydrothermal treatment of red mud with food waste compost, and its adsorption property was evaluated on Methylene blue (MB) and Congo red (CR), selected model dyes in aqueous solution. The adsorption process conformed to pseudo-second-order kinetic, intraparticle diffusion, and the Redlich-Peterson isotherm models. RFBC exhibited a maximum sorption of 124.06 mg·g -1 for MB and 2959.35 mg·g -1 for CR at 298 K. Isothermal and thermodynamic studies demonstrated that adsorption of MB and CR by RFBC were spontaneous and exothermic, governed by physisorption and chemisorption. Furthermore, the possible adsorption mechanisms are pore filling, electrostatic attraction, hydrogen bonding, and π-π interactions. After five consecutive adsorption-desorption cycles were completed, the RFBC demonstrated an adsorption efficiency exceeding 70 % in relation to dyes, affirming its exceptional reusability. This study suggested this red mud-carbon composite had high potential as a novel and promising adsorbent for dye removal from wastewater.