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

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 coalforming 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.