Preparation of magnetically separable mesoporous activated carbons from brown coal with Fe_3O_4

Magnetically separable mesoporous activated carbon was prepared from brown coal in the presence of Fe₃O₄ as a bi-functional additive. Magnetic activated carbon (MAC) was characterized by low-temperature nitrogen adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM). The evolution behaviors and transition mechanism of Fe₃O₄ during the preparation of MAC were investigated. The results show that prepared MAC with 6 wt% Fe₃O₄ addition having a specific surface area and mesopore ratio of 370 m²·g^?1 and 55.7%, which meet the requirements of adsorption application and magnetic recovery. Highly dispersed iron-containing aggregates with the size of 0.1 μm in the MAC were observed. During the preparation of MAC, Fe₃O₄ could enhance the escape of volatiles during the carbonization. Fe₃O₄ could also accelerate burning off the carbon wall during activation, which leads to enlarging micropore size, then resulting in the generation of mesopore and macropore. As a result, a part of Fe₃O₄ converted into FeO, FeOOH, α-Fe, γ-Fe, Fe₂SiO₄ and compound of Aluminum-iron-silicon. The prepared activated carbon, which was magnetized by both of residual Fe₃O₄, reduced α-Fe and γ-Fe, can be easily separated from the original solution by external magnetic field.