Charging mechanism analysis of macerals during triboelectrostatic enrichment process: Insights from relative dielectric constant, specific resistivity and X-ray diffraction

With increasing need for coal liquefaction, the separation and enrichment of active maceral (vitrinite) in feed coal has become the research focus for increasing liquefaction yield from coal. Vitrinite and inertinite could be separated and enriched in negative coal flow and positive coal flow, respectively by triboelectrostatic method. In order to analyze the tribo-charging mechanism of macerals, their relative dielectric constant (RDC) and specific resistivity were measured in this work. Lower RDC of vitrinite corresponds to its positive charge during separation while inertinite has the opposite actions. The wider RDC and closer specific resistivity gaps between the two macerals could form more distinct separation track and achieve better yield and enrichment of vitrinite. X-ray diffraction characterization results show that inertinite with high L_a (12.18 Å) is harder to lose electrons and charges negative compared with vitrinite (L_a 9.57 Å) in the separation, this also matches their different RDCs. Besides, the active small groups represented by largerγband area and higher amorphous carbon content of vitrinite could be a reason for its lower specific resistivity.