China is, and in the coming decades should continue to be, the largest producer and user of coal in the world. The high volume of coal usage in China has focused attention not only on the toxic trace elements that may be released from coal combustion but also on the valuable elements that may occur in the coal and associated ash. Valuable elements in several coals (or coal ashes) and some coal-bearing strata in China (e.g. Ge, Ga, U, rare earth elements and Y, Nb, Zr, Se, V, Re, Au, and Ag, as well as the base metal Al) occur at concentrations comparable to or even higher than those in conventional economic deposits. Several factors are responsible for these elevated concentrations: (1) injection of exfiltrational solutions during peat accumulation or as part of later epigenetic activity; (2) injection of infiltrational epigenetic solutions; (3) introduction of syngenetic alkali volcanic ashes into the peat-forming environment or into associated non-coal-forming terrestrial environments; (4) input of terrigenous materials into the coal-forming environment; (5) leaching of non-coal partings by groundwater/hydrothermal solutions; and (6) mixed processes involving both hydrothermal solutions and volcanic ash. The valuable elements in Chinese coals may be associated with either the organic matter or mineral matter, or have a mixed organic- and inorganic-affinity. For example, the Ge and U in coal-hosted ore deposits dominantly occur in the organic matter, with only traces of U-bearing minerals being present; gallium mainly occurs in boehmite and kaolinite, and to a lesser extent, in the organic matter. Rare earth elements and Y occur as carbonate-minerals (e.g. florencite, parisite), phosphate-minerals (e.g. rhabdophane, silico-rhabdophane, and xenotime), and in part are associated with the organic matter. Some metals (e.g. Ge, Al, Ga) have been successfully extracted at an industrial scale from Chinese coals, and others have significant potential for such extraction. Major challenges remaining for coal scientists include the development of economic extraction methods from coal ash, and the control of toxic elements released during the metal extraction process to protect human health and to avoid environmental pollution.

Coal and coal combustion byproducts can have significant concentrations of lanthanides (rare earth elements). Rare earths are vital in the production of modern electronics and optics, among other uses. Enrichment in coals may have been a function of a number of processes, with contributions from volcanic ash falls being among the most significant mechanisms. In this paper, we discuss some of the important coal-based deposits in China and the US and critique classification systems used to evaluate the relative value of the rare earth concentrations and the distribution of the elements within the coals and coal combustion byproducts.

Stone coal is defined as a combustible, low-heat value, high-rank black shale of early Paleozoic (in a few cases, Permian) age, widely distributed in southern China. Attention has been focused on stone coals because (1) they can be used as fuel energy (for power plants and daily use in some villages) mainly in southern China; (2) they are enriched in critical elements and are currently industrially (economic extraction of V) and agriculturally (such as Se) utilized or have such a great potential (e.g. Au, platinum group elements, Mo, and Ni); (3) they are the sources for some toxic elements that have caused environmental pollution (e.g. SO₂ emission during their combustion) and endemic diseases such as selenoisis and fluorosis; and (4) they can provide useful information for geological events and regional geological setting (e.g. hydrothermal activities). This article reviews stone coal’s definition; occurrence and distribution; petrologic properties, mineralogy, and geochemistry; adverse impacts on environment and human health; and by-products of critical elements as well as major challenges remaining from point of view of determining element enrichment mechanisms, utilization of critical elements, and control of toxic elements released during stone coal utilization.

Each year China burns as much coal as the rest of the world. The coal use results in many benefits such as electricity, industrial heat, coke for steel manufacturing, and many valuable chemical products. Unfortunately, coal use also results in environmental degradation and widespread and severe health problems. China is especially vulnerable to these problems because of the abundant coal deposits occurring in every Chinese province, the predominantly rural population, and the widespread use of domestic coal burning. The health problems are attributed to exposure to fine particulate air pollution (PM_2.5), mobilization of trace elements such as arsenic, fluorine, selenium, and possibly mercury and the release of organic compounds from incomplete combustion of domestic coal fires. Inhalation of minerals such as quartz and pyrite has deleterious health impacts contributing to lung cancer in women and black lung disease in coal miners. The extensive uncontrolled coal fires in China may also be a source of health problems. The overall situation has improved in recent years as uncontrolled fires have been extinguished, improved coal-burning stoves are being introduced, and people are switching to alternative fuel sources. Nevertheless, more needs to be done to minimize the health consequences of coal use in China.

China is the largest coal gasification market in the world. The gasifiers have been commercialized for producing syngas for coal-to-liquids, coal-to-olefin, and coal-to-substitute natural gas. During coal gasification at high temperature and pressure, the differences in reactivity of organic matter in coal are almost negligible; however, the transformation behaviour of minerals is important to the stability of the process. Detailed knowledge of the mineralogical properties of ash and slag is essential for optimizing the operational parameters. It is also significant for determining the influence of the solid wastes on the environment: for example, trace elements carried in bottom slag, fly ash, condensate water, and gaseous products migrate to natural water and soil and into the atmosphere. With this in mind, the mineralogy of ash and slag from typical coal gasification processes in China are reviewed, including the transformation of minerals typically found in coal, and the effects of operating conditions on mineral transformation and melting/slagging behaviour of minerals during gasification process. In addition, trace element migration behaviour in commercialized gasifiers is discussed.