Research progress of enrichment characteristics of hazardous mineral matter in coal and their migration and transformation during thermal technology

Low-carbon, zero-emission, and efficiency enhancement are the main themes of clean coal utilization today. The slagging and pollution caused by mineral matter in coal are key bottlenecks in clean coal technologies. To uncover the scientific challenges behind these issues, this study redefines hazardous mineral matter and extensively reviews relevant domestic and international literature, including journals, books, and standards. This paper summarizes the research status of mineral matter and trace elements in coal, categorizing hazardous mineral matter and elements based on their occurrence states. The slagging characteristics of lithophile elements and their minerals, as well as the pollution properties of chalcophile and siderophile elements and their associated minerals, are introduced. A classification of industrial and environmental hazardous elements and their minerals is proposed, with their harmfulness depending on the occurrence mode of the elements and their minerals. The occurrence and enrichment differentiation characteristics of mineral matter in coal are analyzed, generalizing the genesis types of hazardous mineral matter, and exploring the various geological and technological impact factors on the thermal transformation of coal mineral matter, including coal rank, mineral bonding modes, the geochemical affinity of elements, mineral composition, reactive temperature, reactive atmosphere, reactive pressure, and the presence of other components in ash etc. factors. The migrative and transformative mechanism of harmful mineral matter in coal during gasification, liquefaction, pyrolysis, coking and combustion were reviewed, and different volatilization degrees of trace elements during gasification, liquefaction, pyrolysis, and combustion were revealed. Finally, scientific, technique and engineering problems such as amorphous minerals, precise quantification, high-temperature rapid analysis, interactions between alkaline elements and silica elements, slag prediction, geological and technological coupling, and clean degree are put forward. Looking forward to future growth, the basic research of non-crystalline mineraloid in raw coals and molten amorphous substances during thermal technology. The application of tracer isotope techniques in thermal processes should be paid attention to. It is suggested that hazardous mineral matter removal and rare element extraction would be strived to develop for advancing clean coal technologies.