Indispensable role of inherent calcite in coal on activated carbon (AC)’s preparation and applications

Abstract

Calcite (CaCO3) is the main calcium-containing mineral in coal, activated carbons (ACs) were obtained through blending Alxa coal with different content of CaCO3 (2, 4, 6, 8%), molding, carbonization at 600 °C and activation at 900 °C under water–vapor atmosphere. As-derived ACs were investigated physiochemical structure and performance by XRD, SEM, BET, XPS, SO2 and rhodamine-B (RhB) removal test. The results show that: (1) CaCO3 promotes the development of AC’s physiochemical structure and surface chemistry. CaCO3 is beneficial to pore evolution through etching carbon surface, which causing the evolution of micropore/mesopore to mesopore/macropore and/or pores collapse. The total specific surface area and micropore’s specific surface area has decreased from 895 m2/g and 674 m2/g to 671 m2/g and 564 m2/g with CaCO3 addition up to 8%. The total volumes and micropore’s volumes (<2 nm) also decreased from 0.40 cm3/g and 0.33 cm3/g to 0.31 cm3/g and 0.24 cm3/g, respectively. The O/C and π-π* are increased linearly with the addition CaCO3; (2) CaCO3’s addition promotes sulfur capacity through enhancement of pore structure, oxygen-containing functional groups and π-π*. Moreover, the CaO in ACs participates in the desulfurization process and finally forms CaSO4, which further promotes desulfurization, and the mechanism was proposed; (3) CaCO3’s addition slightly decrease the RhB adsorption capacity from 96.7 mg/g to 87.9 mg/g due to competition of OH− with COO−. The results of this work indicate that AC prepared from high-calcium coal is more suitable for desulfurization other than RhB removal.