Abstract
The microstructure and mineral composition of the gangue play a decisive role in the precipitation of heavy metal elements. In this study, the microstructure, mineral composition, and precipitation of heavy metal elements of coal gangue with different weathering degrees were analyzed through electron microscopy, X-ray diffraction, and static immersion leaching experiments. The following results were derived. (1) After the weathering of the coal gangue, its compactness and integrity changed significantly. The coal gangue structure transformed from relatively dense to relatively loose, and the development of large pores and fractures changed from basically no development to significant development. (2) After weathering, the contents of kaolinite and illite significantly increased, while that of feldspar significantly decreased. Coal gangue contains a small amount of Mn, Cu, Zn, Ti, Ba, Cl, and other elements. After weathering, the contents of each element were reduced. (3) Under the same conditions, a higher number of heavy metal elements precipitated from the weathered coal gangue than from the fresh coal gangue. The results of this research have significant importance in revealing the precipitation mechanism of heavy metals from coal gangue and in perfecting the theory of underground water environmental protection during solid backfilling mining.
Highlights
In addition to containing a large number of major elements including C, Si, Al, Fe, Ca, and Mg, coal gangue contains a variety of trace heavy metal elements
(3) Under the same conditions, a higher number of heavy metal elements precipitated from the weathered coal gangue than from the fresh coal gangue
The overlying cap rock fracture development and coal mining process will result in mine water emission; the coal gangue fillings in the goaf are always immersed in a water environment [1–3]
Summary
In addition to containing a large number of major elements including C, Si, Al, Fe, Ca, and Mg, coal gangue contains a variety of trace heavy metal elements. It is important to study these two features at different weathering degrees to reveal the precipitation mechanism of heavy metal elements in coal gangue and to improve the theory of groundwater environmental protection for solid backfilling in coal mining. Li [9] performed a 40-day static immersion leaching test on coal gangue with different weathering degrees in the Huangling number 1 mine in northern Shaanxi He measured the concentration and pH of seven types of trace elements including Cu, Zn, Cr, and Pb in the leaching solution. Electron microscopy, XRD, and static immersion leaching experiments were performed to reveal the precipitation mechanism of heavy metal elements of coal gangue with different weathering degrees under leaching conditions from two aspects: microstructure and mineral composition of the coal gangue
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