Role of inherent pyrite in coal on physicochemical structure of activated carbon and adsorption capacity

Abstract

Pyrite is the most common inorganic iron-bearing mineral in coal. In order to reveal the influence of inherent pyrite on physicochemical structure and adsorption performance of AC, in this study, different content of pyrite (0.5%, 1%, 2%, 3%) were physically mixed with Yangcheng coal and briquetted, carbonized and steam activated for activated carbon (AC) preparation. As-obtained ACs’ morphology, pore texture, carbon crystallite structure and surface chemistry were characterized by SEM, BET, XRD and FTIR, respectively. The results show that pyrite (FeS2) transformed into hematite (Fe2O3) during AC preparation. Pyrite promotes the interaction between water vapor and carbon and enhances the rate of gasification reactivity by inhibiting the growth of heavy aromatic structures, catalyzing the graphitization process and enhancing the surface chemical properties. The total specific area and specific surface area of micropore of 2%FeS2/AC are up to 836 m2/g and 644 m2/g, which are 58.6% and 46.9% higher than AC, respectively. The 2 h sulfur capacity of 2%FeS2/AC is up to 65.2 mg/g, which is 18.8% greater than that of AC (54.9 mg/g), the mechanism of which was proposed: absorbed gaseous SO2 finally transformed into H2SO4 in macropores and forming an acid macro-environment where most Fe2O3 attacked by the generated H2SO4 on the AC’s pore surface to form Fe2(SO4)3. Fe3+ can promote the oxidation of SO3 to form H2SO4, and a redox cycle of Fe2+ and Fe3+ was established. Moreover, 1%FeS2/AC shows the highest Rhodamine B (RhB) adsorption, and the capacity of RhB is 168 mg/g, which is 41.2% higher than that of AC.