Leaching Behavior and Potential Environmental Effects of Trace Elements in Coal Gangue of an Open-Cast Coal Mine Area, Inner Mongolia, China

Abstract

Abstract:In order to better understand the role of coal gangue in potential environmental and ecological risks, the leaching behavior of trace elements from coal gangue has been investigated in an open-cast coal mine, Inner Mongolia, China. Four comparative column leaching experiments were conducted to investigate the impacts of leaching time, pH values and sample amount on the leaching behavior of trace elements. Enrichment factors (EF), maximum leached amount (L am ), maximum leachability (L rm ), effects range low (ERL) and effects range median (ERM) were employed to evaluate potential environmental and ecological hazards resulting from the leaching behavior of environment-sensitive trace elements from coal gangue. Leaching time and sample amount display important effects on trace element concentrations, leached amounts and leachability. The pH values exhibit a weak influence on the leaching behavior of the selected trace elements (e.g., As, V, Cr, Co, Ni, Cu, Zn, Se, Cd, Sn, Pb and Hg). The coal gangue are enriched in As, Co, Se and Pb and, in particular, show higher environmental pollution levels of As and Se (EF > 2). L am values suggest that all of the elements investigated do not show potential risk to soils and vegetation, but have a high hazard risk for ground water. Elements including Ni, As, Cr and Zn are inclined to show high or moderate biological toxicity.

Trace Elements in Coal Gangue: A Review

“…Meanwhile, the content of Ga, Se, As, and Sn are much higher in the Huainan Coalfield coal gangue compared with the Clarke values, while the content of other trace elements are lower [38]. The coal gangue in the Wulantuga open-cast coal mine area is enriched in Co and depleted in Se, Cd, and Hg, and the other trace elements are close to the concentrations of the world Clarke values [37].…”

“…Therefore, some studies about the leaching behavior of trace elements from coal gangue, especially from coal gangue piles, have been done by some authors [37,56]. The leaching behavior of the trace elements from coal gangue indicated that leaching is a very complex process, which might be affected by many factors.…”

“…Also, leaching time is another important impact factor on the leaching behavior of trace elements from coal gangue [57][58][59]. Meanwhile, the concentration of the trace elements in coal gangue can influence the leaching behavior [37].…”

“…Therefore, some researches regarding of the content of the total trace element in coal gangue have been conducted. For [37]. Also, 20 trace elements, including Ba, Co, Cr, Cu, Ga, Mn, Ni, Li, Se, Zn, V, As, etc., were selected by Zhou et al for the study of trace element in coal gangue at the Huainan Coalfield in China [38].…”

“…The mineral and chemical composition of coal gangue Generally, the main mineral phases of coal gangue are kaolinite, quartz, pyrite, illite, calcite, ankerite, and montmorillonite [36,37]. The coal gangue samples are usually dominated by silicon dioxide and aluminum oxide, followed by ferric oxide and potassium oxide accompanied with some trace elements [37]. For example, it is reported that the mineral phases in the Huainan coal gangue samples are kaolinite, quartz, illite, calcite, pyrite, siderite, and muscovite.…”