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Mineral Release Processes And Mechanisms Of Raw Coal From Feicheng, China

Congress: 2015
Author(s): Lou junpeng (Beijing, China, Peoples Republic), Lou Huajun
Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences1

Keyword(s): Sub-theme 13: Non-conventional sources of water,
Abstract1、Introduction Abandoned coalmine pollution results from the underground structural damage that results from decades of mining and the release of multiple contaminants that pose long-term and continuous threats to groundwater sources in mining areas. Abandoned coalmines threaten the safety of water environments and pose serious problems worldwide (Pokhrel and Dubey 2013). Thus, current studies have focused on the effects of mine water rebound on external environments (rivers, groundwater and other water systems) after coalmine closure (Environment Canada. 2004). Here, we consider mine water as a potential resource that has been polluted. Therefore, studies on flooded mine water from abandoned coalmines that restore the original resource value of mine water and increase the usable water source are important for the increasingly severe global crisis of water scarcity (Fanfani and Ardau 2011, Ordonez, Jardon et al. 2012). Many researchers have studied the use of mine water and abandoned coalmines (Sevenster 1959, McCutcheon, Barton et al. 2001). However, few researchers have studied the characteristics and patterns of mineral release in abandoned coalmines. The release of related ions from abandoned coal in abandoned coalmines determines the investments and profits of mine water treatment. Thus, this process is considered by many decision-makers. Therefore, the characteristics and patterns of mineral release from residual coal in underground spaces and groundwater environments after coalmine closure were discussed in this study. Specifically, indoor leaching experiments were conducted with the coal samples. Our results provide a theoretical basis for the use of mine water resources from closed coalmines. 2、Methods/Materials Coal samples collected from 3 major mining seams at the Caozhuang Coalmine of the Feicheng Mining Bureau were used as the experimental samples in the present study. The coal samples come from the 3rd seam (Sample 1), 8th seam (Sample 2) and 9th seam (Sample 3). The still water leaching method was used here to investigate the characteristics and patterns of mineral release to water from coal samples with different particle diameters. The release process was also studied. The degree of mineralisation was used as an index for quantifying mineral release. The experimental steps are listed below. 1) Standard experimental samples with particle diameters of 5, 2, 0.6, 0.25 and ≤0.05 cm (pulverised coal with the smallest particle diameter) were prepared from coal samples 1, 2 and 3. The samples with a particle diameter of 0.25 cm weighed 800 g and the other samples weighed 400 g. 2) Still water leaching experiment. Distilled water was added to the samples with different particle diameters (400 g of each sample) based on a coal:water ratio of 1:5. The coal samples were immersed in distilled water for 24 h. Then, the distilled water was replaced with clean distilled water, and the coal samples were immersed for an additional 24 h. The distilled water was replaced 5 times. After each immersion, the leachate was added to a flask before chemically analysing the leachate. 3) Still water leaching extension experiment. Distilled water was added to samples with a particle diameter of 0.25 cm at a coal:water ratio of 1:5. The coal samples were immersed in distilled water for 72 h before the distilled water was replaced by clean distilled water, and the coal samples were immersed for an additional 72 h. The distilled water was replaced 8 times. After each immersion, the leachate was added to a flask before leachate analysis. The experiments were conducted exclusively at the Shandong Geological Environmental Monitoring Station and were performed according to their requirements. The leachates were analysed at the Shandong Geological Environmental Monitoring Station laboratory. 3、Results and Discussion We obtained the cumulative amounts of leached minerals from the coal samples with different particle diameters by chemically analysing the coal leachates. The particle diameter (using y=axb) was suitable for describing the correlations between the cumulative amounts of mineral leaching and the particle diameters. During the mineral release process, we discovered a layer of soft residues on the surfaces of the coal particles that became thicker with leaching time. This layer of surface residue on the coal particles acted as a "protective membrane" and prevented the release of minerals. In addition, the thickness of this "protective membrane" continued to increase and became more effective at preventing the release of minerals, resulting in stable, low amounts of released minerals from the coal samples. 4、Conclusion In this study, the characteristics and patterns of mineral releases from coal samples in a aqueous environment were investigated through still water leaching experiments. A significant correlation occurred between the amount of minerals leached from the coal sample and the particle diameter. The particle diameter was described by the following equation: y=axb. When the coal samples released minerals to the water, a layer of the residues on the coal surface gradually increased. This residue layer acted as a "protective membrane" on the surfaces of the coal particles, preventing additional mineral release and decreasing the mineral release rate. Eventually, the amounts of minerals released gradually stabilised (WANG Lai-gui 2008). When treating an abandoned coalmine, the mean particle diameter and volume of the abandoned coal should be measured according to the fitting equations of the amount of leaching versus particle diameter. Next, we can predict the approximate cumulative amount of leaching based on the regression equations of the cumulative amounts of mineral leaching and the particle diameter to treat the mine water of an abandoned coalmine. Decision-makers can estimate their investments and profits from treating the mine water. Therefore, the present study provides a theoretical basis for comprehensively treating and utilising mine water in abandoned coalmines and is promising for turning abandoned coalmines into "underground water reservoirs". In addition, this study is important for addressing water scarcity issues that are becoming more severe. Environment Canada. (2004). Threats to water availability in Canada. Burlington, Canada: Environment Canada. http://www.ec.gc.ca/inre-nwri/default.asp?lang=En&n=0CD66675-1&off Fanfani, L. and C. Ardau (2011). A Worldwide Emergency: Arsenic Risk in Water. Case Study of an Abandoned Mine in Italy. Water Security in the Mediterranean Region: An International Evaluation of Management, Control, and Governance Approaches. A. Scozzari and B. ElMansouri. Dordrecht, Springer: 177-189. McCutcheon, A., W. Barton and M. Wilson (2001). "Kinetics of water adsorption/desorption on bituminous coals." Energy & fuels 15(6): 1387-1395. Ordonez, A., S. Jardon, R. Alvarez, C. Andres and F. Pendas (2012). "Hydrogeological definition and applicability of abandoned coal mines as water reservoirs." Journal of Environmental Monitoring 14(8): 2127-2136. Pokhrel, L. R. and B. Dubey (2013). "Global Scenarios of Metal Mining, Environmental Repercussions, Public Policies, and Sustainability: A Review." Critical Reviews in Environmental Science and Technology 43(21): 2352-2388. Sevenster, P. (1959). "Diffusion of gases through coal." Fuel 38(4): 403-418. WANG Lai-gui, L. X.-l., LIU Ling, HAN Liang (2008). Research on mechanism of groundwater pollution from mine water in abandoned mines.
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