Behavior of Minerals and Trace Elements during Cleaning of Three Coals with Moderately High Ash Yields

Abstract

The removal rate of minerals and 17 trace elements during coal cleaning, as well as their cleaning potential, were investigated based on selection of washing products from three coal washeries and raw coal samples. The petrological, mineralogical, and chemical characteristics of the samples were investigated using an optical microscope, a scanning electron microscopy with energy dispersive X-ray spectroscopy, and an inductively coupled plasma mass spectrometer. The minerals derived from raw and clean coals of the Fenghuang (FH), Huangling (HL), and Gaoyang (GY) coal mines consisted mainly of clay minerals and pyrite. Pyrite and clay minerals occurred in five main forms; moreover, we observed three different types of pyrite and four types of clay mineral dissemination. Depending on the type of dissemination, the removal of these minerals can be more or less difficult to achieve. The removal rate of trace elements from the clean coals of FH and HL is >70% and it increases with decreasing coal particle size. In addition, the removal rate of trace elements from the clean coals of GY is low. FH and GY belong to a marine peat flat coal-forming environment, while HL belongs to a terrestrial mire coal-forming environment. This environmental difference explains the varying removal efficiency of mineral matter during coal cleaning.

Spatial Macroscale Variability of the Role of Mineral Matter in Concentrating Some Trace Elements in Bituminous Coal in a Coal Basin—A Case Study from the Upper Silesian Coal Basin in Poland

“…This was confirmed by the results of numerous studies of the botanical, geochemical, mineralogical, palynological, and petrological composition [3]. Recently, an important role of the new chronometric indicator of marine sediments and carbon age has been demonstrated; it is expressed by the ratio of strontium isotope content 87 Sr/ 86 Sr and the presence of syngenetic gypsum in coal [6]. The mineral matter in coal also provides a range of useful information on the depositional conditions of coal-bearing sequences [4,5].…”

“…In turn, chalcophile elements, occurring in >50 µm epigenetic grains of sulfides, can be removed from coal with satisfying effectiveness (approximately 80%), applying gravity separation and/or flotation [24,81,85,86]. The removal rate of thalassophile elements (Ca, Mg, Na, Fe, Mn, Zn, B, and Sr) is high, while that of continental elements (Al, Pb, Ba, and Th) is low [87]. Still, the best solution for the environment is avoiding combustion of ecotoxic elements-rich coal, preceded by monitoring their content in raw coal.…”

Occurrence of Minerals in Coal and Its Geological Controlling Factors—Significance in Evaluation of Coal Washability

“…The existing methods are satisfactory for coal preparation technology but make coalfield prediction, washability exploitation, and the evaluation and prediction of coal seams formed in different coal-accumulating environments complex and difficult . From a geological viewpoint, the minerals in coal that have been formed in different environments have different occurrence forms, assemblage characteristics, and dissemination of minerals with macerals, which can directly lead to different mineral removal rates. − In view of the depletion of high-quality coal resources and the urgent need for green utilization of difficult washability coal resources in China, research on the geological control of minerals in the washing process identifies the fundamental factors that affect the selectivity of coal and guides coal industrial washing technology, and improving the removal rate of minerals in coal has very important practical significance. This study uses coal seams in the same region to assess the influencing factors of coal-forming environments on coal washing and analyzes the internal changes from a geological perspective.…”