Leaching characteristics and potential ecological risks of typical heavy metals in coal gangue

Heavy metals in coal gangue can be released in varying degrees in the conditions of soaking，leaching，etc. This behavior poses a threat to the safety of ecological environment. In this study，the coal gangue samples from Xin⁃ glongzhuang Coal Mine in Jining City were collected. The morphology and chemical composition of coal gangue were characterized by scanning electron microscopy energy spectrum analysis technology and X-ray fluorescence spec⁃ trum analysis technology. In order to further understand the release behaviors of heavy metals from coal gangue，the indoor static soaking experiment was conducted to explore the leaching characteristics of typical heavy metals (i.e. Hg， Pb，Cd and As) from coal gangue with extraction solutions in different pH values (i.e. 4.9，5.6 and 7) and differ⁃ ent gangue particle size (i.e. <0.15 mm，0.15-2 mm，2-5 mm and 5-10 mm). The effects of coal gangue leachate on the germination of wheat seeds and early growth of seedlings were studied through seed germination experiment to further verify its threat to the ecological environment. The results show that 1 The coal gangue has an irregular flaky structure and the main components are Si，Al and O，and the main compounds are SiO2 and Al2 O3 . 2 The coal gangue leachate is alkaline. The leaching concent of Hg，Pb and Cd is inversely proportional to the initial pH value of the ex⁃ traction solutions，while the leaching rule of As is opposite. The smaller the particle size of coal gangue is，the high⁃ er the leaching concent of four typical heavy metals is. 3 For water environment，the Hg in coal gangue has the high⁃ est pollution risk to water environment，followed by As and Pb，and the pollution risk of Cd is low. 4 For crop wheat，the coal gangue leachate has ecological toxicity，which significantly inhibits wheat seed germination and root growth. When the initial pH value of the extraction solution is 5. 6 and the coal gangue particle size is the largest (5-10 mm)，the inhibition effect is the weakest. These findings could provide references for the safe stacking and utilization of coal gangue in the coal mining areas.