Feasible low-cost conversion of red mud into magnetically separated and recycled hybrid SrFe12O19@NaP1 zeolite as a novel wastewater adsorbent

Red mud (RM), a byproduct of the alumina industry, poses serious environmental issues owing to its strong alkalinity and high salinity. A novel process for the synthesis of magnetic SrFe12O19@NaP1 (SFO@NaP1) zeolite using RM industrial waste was proposed. The optimum conditions for RM pretreatment, which consisted of acid leaching (time, temperature, liquid-to-solid ratio, and HCl concentration) and alkali fusion (time, temperature, and acid-leached RM/NaOH mass ratio), were systematically analyzed. SFO@NaP1 zeolite was synthesized from RM for the first time without using additional aluminum and silicon sources, and SFO was initially applied to the magnetic matrix of zeolite. The methylene blue (MB) adsorption parameters revealed that the removal efficiency and adsorption capacity of 2.5 wt% SFO@NaP1 were 95.4% and 47.9 mg/g, respectively, under the following adsorption conditions: adsorbent dosage of 1 g/L, initial pH of 7, dye concentration of 50 mg/g, and reaction temperature of 25 degrees C. Furthermore, the adsorption of MB on SFO@NaP1 was an exothermic process that followed the pseudo-second-order kinetic and Langmuir isotherm models. After three adsorption cycles under an external magnetic field, the adsorption capacity of SFO@NaP1 for MB still reached 33.2 mg/g, which suggested that SFO@NaP1 is a green, low-cost, and eco-friendly adsorbent with excellent adsorption capacity.