Energy Education Science and Technology Part A: Energy Science and Research 2013 Volume (issues) 31(1): 27-38
Li distribution and mode of occurrences in Li-bearing Coal Seam 9 from Pingshuo Mining District, Ningwu Coalfield, northern China Y. Z. Sun1*, C. L. Zhao2, Y. H. Li1, J. X. Wang1, M. Y. Lin1 1
Hebei University of Engineering, Key Laboratory of Resource Exploration Research of Hebei Province, 05603 Handan, Hebei, China 2
China University of Mining and Technology, 10008 Beijing, China
Received: 20 August 2012; accepted: 12 December 2012
Abstract A total of 58 coal samples of Seam 9 were taken from the Pingshuo Mining District, Ningwu Coalfield, Shanxi Province, northern China. The samples were analysed by optical microscopy, sequential chemical extraction procedure, SEM–EDX analysis, X-ray powder diffraction, and ICP-MS techniques. The results indicate that the average Li content of Seam 9 reaches to 156 mg/kg. The coal reserves of Seam 9 are 3.67 Gt. The Li reserves of the seam amount to 558 kt, that is, 1.195 mt Li2O. The sequential chemical extraction procedure results indicate that the Li concentration is mainly related to inorganic matter, and only about 5.5% lithium has an organic affinity. The minerals are kaolinite, boehmite, chlorite-group minerals, quartz, calcite, pyrite, and amorphous clay-like material. Lithium could be absorbed by clay minerals in the Li-bearing coal seam. According to the paleogeography, the Yinshan Oldland could be the most possible sources of Li of the coal. The bauxite of the Benxi formation, originally derived from the Yinshan Oldland, in the north part of the basin could be another Li source of the coal.
Keywords: Li-bearing coal; Geochemistry; Trace elements; Pingshuo mining district ©Sila Science. All Rights Reserved. ___________
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1. Introduction The Li concentration in coals has been studied by many geologists [1-4]. Ketris and Yudovich [2] estimated average Li content in the world coals to be 18 ± 1 mg/kg for hard coals and 82 ± 5 mg/kg for hard coal ash. Sun et al. [3] estimated that the average Li content is 28.94 mg/kg in 2806 Chinese coal samples. Except for China, the average Li contents in coals is lower than 20 mg/kg. In recent years, high Li contents were found in some Chinese coal samples [3, 5, 6]. Dai et al. [5] found strong enrichment with Li in the no. 6 coal at the Haerwusu Surface Mine, in which the average Li content is 116 mg/kg and the highest Li content reaches 566 mg/kg. Sun et al. [6] found that the Li contents have reached an economic grade, and the total Li2O reserves reaches to 52 kt in the Guanbanwusu Mine, Junger Coalfield, Inner Mongolia. It can be utilized as an associated Li deposits in coal seams according to the Geology and Ore Deposit Standard Specifications for Rare Metal Mineral Exploration of the People’s Republic of China (DZ/T 0203-2002, 2003) [7]. Sun et al. [3] have found that the average content reaches 172 mg/kg and the highest Li content reaches 657 mg/kg in several samples at the Antaibao Surface Mine, Ningwu Coalfield. The purpose of this paper is to study whether Li contents have reached a degree of coal-associated lithium deposits in Coal Seam 9 in the whole Pingshuo mining district, Ningwu Coalfield. 2. Geological setting The Ningwu Coalfield, with an area of 2761 km2, is located in the north part of Shanxi Province. The Pingshuo mine district covers an area of 396 km2 in the north part of Ningwu Coalfield (Fig. 1). The total coal reserves reaches to 13 Gt. Ningwu Coalfield was formed in the Ningwu Syncline Basin. To the west of the basin is Lüliang Palaeohigh and to the east is Wutai Palaeohigh. The north of the basin is Yinshan Oldland (Fig. 1). The base rocks of the basin are plagioclasegneiss and migmatitic gneiss of the Archean Group [8]. The coal-bearing sequences in the Pingshuo mine district include the Benxi and Taiyuan formations (both Pennsylvanian) and Shanxi Formation (Lower Permian) with a total average thickness of 182.8 m [9]. The thicknesses of the Benxi, Taiyuan and Shanxi formations are 9.2-72.8 m (average 46 m), 45.9-99.85 m (average 70 m), and 60.83-136.76 m (average 80 m), respectively. There are 10 coal seams: Nos. 4-1, 4-2, 4-3, 5, 6, 7, 8, 9, 10, and 11 coal seams. The No. 9 Coal Seam with a thickness between 2.4 and 36.5 m, and an average thickness of 13.45 m, is a major seam with reserves in the Pingshuo mine district amounting to 3.67 Gt. The Taiyuan Formation of the study area was formed by the alternation of continental and marine facies. The sedimentary environments are the extensive tidal-flat and partly runnel and sand bar, formed in a regression environment [10].
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Fig. 1. Paleogeographic map of the Late Paleozoic in the study area [11]. 3. Sampling and analytical methods 3.1. Sampling Eighteen bench-coal samples of a seam section and total 41 coalbed channel samples of coal were collected from the No. 9 Coal Seam at Pingshuo Mine District following Chinese Standard Method GB482-1985t (Tables 1 and 2). The bench samples were taken from Anjialing Opencut Coal Mine. Among the 41 mixed coal samples, 12 were collected from Anjialing Opencut Coal Mine; 14 were collected from Antaibao Opencut Coal Mine; five were collected from the No. 1 coal Mine; eight were collected from the No. 2 coal Mine; and two were collected from the No. 3 coal Mine. 3.2. Petrologic analysis The samples were air-dried, crushed to
