In-situ magnetic activated carbon produced from sludge, straw and steel slag for the effective adsorption of methylene blue

In order to achieve the goal of green and sustainable development, solid waste of sludge, straw and steel slag were used as raw materials for the preparation of in-situ magnetic activated carbon (MAC) by chemical activation and co-pyrolysis, and was then used to remove methylene blue (MB). The MAC with the highest specific surface area (359 m2/g) was obtained at 750 degrees C, and the in-situ magnetization was achieved by reducing the iron oxides in steel slag to Fe3O4 and Fe0, resulting in a saturated magnetization of 8.69 emu/g, this allowed for easy separation using a magnet. Batch adsorption of MB onto MAC was studied, indicating the removal efficiency of methylene blue was higher than 95% under room temperature at pH = 8 while the dosage of MAC was 1 g/L. Adsorption kinetic and isotherm studies indicated the adsorption of methylene blue onto MAC involved multilayer physisorption with intraparticle diffusion and chemisorption as the rate limiting steps. The maximum calculated adsorption capacity of MB was 283 mg/g; thermodynamic analysis showed the adsorption was spontaneous and endothermic. The adsorption mechanism of methylene blue onto MAC involved electrostatic attraction, formation of hydrogen bonds and the interaction of pi electron system.