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

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 degrees 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 m(2)/g and 674 m2/g to 671 m(2)/g and 564 m(2)/g with CaCO3 addition up to 8%. The total volumes and micropore's volumes (<2 nm) also decreased from 0.40 cm(3)/g and 0.33 cm(3)/g to 0.31 cm(3)/g and 0.24 cm(3)/g, respectively. The O/C and pi-pi* are increased linearly with the addition CaCO3; (2) CaCO3's addition promotes sulfur capacity through enhancement of pore structure, oxygen-containing functional groups and pi-pi*. 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.

Automated summary

The study shows that the addition of calcium carbonate can promote the development of the physiochemical structure and surface chemistry of activated carbon, enhance pore evolution, and increase sulfur capacity. However, the addition of calcium carbonate slightly decreases the adsorption capacity of RhB due to competition with COO-.