Coal macerals separation technology: current status, mechanism, and development trends of resource utilization

Coal is the most carbon-rich substance in nature, except for diamonds and graphite. Due to its abundant functional groups and defect sites, it is increasingly being utilized as a high-value-added chemical raw material. However, the inorganic mineral components in coal not only hinder its high-value development but also lead to resource waste and environmental pollution. Consequently, a comprehensive analysis of the various methodologies and intrinsic complexities involved in the separation of macerals from coal and rock is imperative to elucidate the future developmental trajectory in this domain. The present article commences with an examination of the sources and physical/chemical properties of each maceral (vitrinite, inertinite, liptinite, and huminite) in coal. A detailed analysis of the properties of each maceral was conducted, forming the basis for subsequent discussions of application methods and mechanisms. The discussions employed physical separation enrichment techniques (density gradient centrifugation (DGC), float-and-sink, dense medium separation (DMS), flotation, and friction electrostatic separation) and chemical separation enrichment techniques (chemical oxidation, chemical leaching, and solvent extraction). Meanwhile, the extant problems and application prospects of the current process separation technology are summarized and projected. Finally, after discussion, an economically feasible technical path was evaluated: The comprehensive processing of one ton of coal can yield a return of 18.7∼ 246.2 US dollars. Under the best conditions, the net profit per ton of coal can reach 246.2 US dollars, indicating a promising economic potential. This review aims to provide a solid theoretical foundation for the high-end, low-carbon, and eco-friendly utilization of coal resources.