<p>Coal is a potential source for many critical elements recovery. This paper investigates the abundances, enrichment, occurrence modes, vertical variations and enrichment influencing factors of selected critical elements (Li, Be, Sc, V, Cr, Ga, Ge, Se, Zr, Nb, Mo, Sb) in eight Carboniferous–Permian coal seams (Nos. 3-2, 6, 7-1, 7-2, 8-1, 8-2, 9, 10) in the Huaibei Coalfield, Anhui, China, which can provide theoretical references for the preference of target areas for strategic resources in regional coal-bearing strata. The results showed that the minerals identified in Huaibei coal samples were mainly kaolinite, illite and calcite, as well as pyrite, ankerite, limonite, gypsum, muscovite, chlorite, quartz and K-feldspar, and the mineral assemblage characteristics of the different coal seams indicated that Nos. 6, 7-2, 8-2 and 10 coals have been affected by magmatic intrusion. The coals in the Lower Shihezi Formation are mainly characterized by higher contents of Si, Al, Ca, Ti, K, Mg, Na and P than the coals in the Upper Shihezi and Shanxi Formations. The Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> ratios suggest that all coal seams have intermediate igneous origin. The studied coal samples were found to be enriched in critical elements, whose abundances are in the order of Zr &gt; V &gt; Li &gt; Cr &gt; Ga &gt; Sc &gt; Nb &gt; Se &gt; Mo &gt; Sb &gt; Ge &gt; Be. By comparison, Se and Sb were more enriched, followed by V and Li, with most elements having the highest contents in No. 6 coal seam. Based on statistical analysis and sequential chemical extraction, it was found that Be, Cr, Zr and Nb were mainly associated with silicates, Li, Sc, V and Ga have inorganic–organic affinities, Ge has significantly organic matter association, while Se, Mo and Sb have sulfide and organic affinities. Vertical variations of critical elements among different coal seams can be categorized into two groups: (1) Li, Be, Sc, V, Cr, Ga, Ge, Zr, Nb; (2) Se, Mo, Sb. The geochemical indicators showed that the Huaibei coal was deposited in a terrestrial environment, and the paleoclimate of the coal-bearing formation changed from an arid condition to a warmer and wetter climate and from aerobic to dysoxic to anoxic during deposition. Principal components analysis indicated that detrital input, igneous intrusion and elemental interactions were major influencing factors of the enrichment of critical elements, and redox conditions and climate had some effect on Mo.</p>

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Geochemistry of Selected Critical Elements in Carboniferous–Permian Coal Seams, Huaibei Coalfield, Anhui, China

  • Mengfei Lu,
  • Guijian Liu,
  • Minglian Shen,
  • Ruijia Liu,
  • Hao Hu,
  • Zhen Yue,
  • Zongfan Xie

摘要

Coal is a potential source for many critical elements recovery. This paper investigates the abundances, enrichment, occurrence modes, vertical variations and enrichment influencing factors of selected critical elements (Li, Be, Sc, V, Cr, Ga, Ge, Se, Zr, Nb, Mo, Sb) in eight Carboniferous–Permian coal seams (Nos. 3-2, 6, 7-1, 7-2, 8-1, 8-2, 9, 10) in the Huaibei Coalfield, Anhui, China, which can provide theoretical references for the preference of target areas for strategic resources in regional coal-bearing strata. The results showed that the minerals identified in Huaibei coal samples were mainly kaolinite, illite and calcite, as well as pyrite, ankerite, limonite, gypsum, muscovite, chlorite, quartz and K-feldspar, and the mineral assemblage characteristics of the different coal seams indicated that Nos. 6, 7-2, 8-2 and 10 coals have been affected by magmatic intrusion. The coals in the Lower Shihezi Formation are mainly characterized by higher contents of Si, Al, Ca, Ti, K, Mg, Na and P than the coals in the Upper Shihezi and Shanxi Formations. The Al2O3/TiO2 ratios suggest that all coal seams have intermediate igneous origin. The studied coal samples were found to be enriched in critical elements, whose abundances are in the order of Zr > V > Li > Cr > Ga > Sc > Nb > Se > Mo > Sb > Ge > Be. By comparison, Se and Sb were more enriched, followed by V and Li, with most elements having the highest contents in No. 6 coal seam. Based on statistical analysis and sequential chemical extraction, it was found that Be, Cr, Zr and Nb were mainly associated with silicates, Li, Sc, V and Ga have inorganic–organic affinities, Ge has significantly organic matter association, while Se, Mo and Sb have sulfide and organic affinities. Vertical variations of critical elements among different coal seams can be categorized into two groups: (1) Li, Be, Sc, V, Cr, Ga, Ge, Zr, Nb; (2) Se, Mo, Sb. The geochemical indicators showed that the Huaibei coal was deposited in a terrestrial environment, and the paleoclimate of the coal-bearing formation changed from an arid condition to a warmer and wetter climate and from aerobic to dysoxic to anoxic during deposition. Principal components analysis indicated that detrital input, igneous intrusion and elemental interactions were major influencing factors of the enrichment of critical elements, and redox conditions and climate had some effect on Mo.