Yuegang Tang

Distribution, isotopic variation and origin of sulfur in coals in the Wuda coalfield, Inner Mongolia, China

Abstract This paper describes coal petrographic characteristics, sulfur abundance, distribution and isotopic signature in coals in the Wuda coalfield, Inner Mongolia, northern China. Petrographic studies suggest that depositional environment influences petrographic composition. The No. 9 and No. 10 coal seams, which are thought to have formed on a tidal delta plain, have high collodetrinite contents (up to 66.1%) indicating enhanced gelification and bacteria activity during coal accumulation, and also have the highest sulfur content (3.46% and 3.42%). Both organic and pyritic sulfur isotope values (−12.3‰ to 5.8‰ and −18.7‰ to 1.1‰, respectively) are variable and generally tend to be more negative in high-sulfur coals than those in low-sulfur coals in the Wuda coalfield. The negative sulfur isotope values indicate that a large portion of sulfur in the high-sulfur coals has a bacterial origin. Sulfur isotopic compositions and variations within the section were used to propose a model to explain the origin of sulfur in these coals. The presence of pyritized rod-like bacteria, cyanophytes gelatinous sheaths and degraded algae organic matter suggests that bacteria, and perhaps algae, may play an important role in the formation of these high-sulfur coals.

Surface analysis of pyrite in the No. 9 coal seam, Wuda Coalfield, Inner Mongolia, China, using high-resolution time-of-flight secondary ion mass-spectrometry

Abstract The chemical composition of pyrite in coal can be used to investigate its geological and mineralogical origin. In this paper, high-resolution time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to study the chemical composition of various pyrite forms in the No. 9 coal seam (St,d=3.46%) from the Wuda Coalfield, Inner Mongolia, northern China. These include bacteriogenic, framboidal, massive, cell-filling, fracture-filling, and nodular pyrites. In addition to Fe+ (54Fe+, 56Fe+, 57Fe+), other fragment ions were detected in bacteriogenic pyrites, such as 27Al+, Si+ (28Si+, 29Si+, 30Si+), 40Ca+, Cu+ (63Cu+, 65Cu+), Zn+ (64Zn+, 66Zn+, 67Zn+, 68Zn+), Ni+ (58Ni+, 60Ni+, 62Ni+), and C3H7+. TOF-SIMS images show bacteriogenic pyrites are relatively rich in Cu, Zn, and Ni, suggesting that bacteria probably play an important role in the enrichment of Cu, Zn, and Ni during their formation. Intense positive secondary ion fragments from framboidal aggregates, such as 27Al+, 28Si+, 29Si+, AlO+, CH2+, C3H3+, C3H5+, and C4H7+, indicate that formation of the framboidal aggregates may have occurred together with clay mineral and organic matter, which probably serve as the binding substance. The intense ions of 28Si+ and 27Al+ from massive pyrites also suggest that their pores incorporated clay minerals during crystallization. Together with the lowest 28Si+/23Na+ value, the intense organic positive secondary ion peaks from cell-filling pyrites, such as C3H3+, C3H5+, C3H7+, and C4H7+, indicate that pyrite formation may have accompanied dissolution or disintegration of the cell. The intense P+ peak was observed only in the fracture-filling pyrite and the highest 28Si+/23Na+ value of fracture-filling pyrite reflects its epigenetic origin. Together with XRD and REEs data, the stronger 40Ca+ in nodular pyrite than other pyrite forms shows seawater influence during its formation.

Liquefaction reactivity and 13C-NMR of coals rich in barkinite and semifusinite

Coals rich in barkinite and semifusinite were selected to study their liquefaction behavior and chemical structure and to find correlations between the liquefaction product yield and chemical structural parameters. The liquefaction tests were carried out using tubing-bomb reactors in a preheated sand bath. The samples were characterized by ultimate analysis, proximate analysis, petrographic analysis, and 13C-NMR analysis. The results show that barkinite-rich samples contain high hydrogen and volatile matter contents and have high H/C atomic ratios. The chemical structures of the samples used are rich in aromatic carbon. WEST coal had the highest aromaticity. The content of methylene carbons is higher than content of methyl carbon of Leping (LP), Changguang (CG), and Dahebian (DHB) coals and also higher than that in the other three coal samples (YJL, P858, and WEST). The LP, CG, and DHB coals have higher liquefaction conversions and higher yields of oil. Definite correlations between the yield of oil and the content of methylene carbons and between liquefaction conversion and aromaticity have been observed, which indicates that the yield of liquefaction products can be predicted based on the solid-state 13C-NMR spectral data of coal.

Compositional characteristics of sulfur-containing compounds in high sulfur coals

The geochemistry of high-organic-sulfur coals of different ranks from three coalfields in China, Chenxi, Hunan Province, Guiding, Guizhou Province, and Hedong, Shanxi Province have been studied using Soxhlet extraction, gas chromatography and gas chromatography-mass spectrometry. The random vitrinite reflectances of Chenxi, Guiding, and Hedong coals are 0.77%, 1.29% and 1.41%, respectively. Organic sulfur contents, on dry and ash-free basis, are 10.06%, 10.26% and 3.51%, respectively. The So/St ratio is 95%, 93% and 87%, respectively. Three types of sulfur-containing compounds were identified in coals, dibenzothiophene series, benzonaphthothiophene series, and benzobisbenzothiophene series. No benzobisbenzothiophene series was identified in the Guiding and Hedong coal. As the coal rank of a sample increased, so did the content of dibenzothiophene series; in contrast, the benzonaphthothiophene series showed a decreasing trend. The substituent group was mainly methyl. The coal-forming environments, organic sulfur contents and coal rank all played an important role in the types of organic sulfur-containing compounds.

Coal petrology and coal facies interpretations of bark liptobiolith

A detailed analytical study of Leping bark liptobiolith in Jiangxi was conducted to determine its petrographic characteristics and depositional environment based on coal petrography and geochemistry. Results indicate that barkinite mainly occurs in the middle and lower coal sea4ms, whereas less barkinite and more vitrinite occur in the middle and upper coal seams. Coal facies analysis of bark liptobiolith was performed to determine its characteristics under various depositional conditions, such as the presence of a water table and gelification during coal formation. Results indicate that the environmental evolution of bark liptobiolith begins from brackish-marine swamp facies (barkinite-rich coal seam) and ends in back barrier swamp facies (barkinite-poor coal seam).

Fluoride exposure in the endemic fluorosis area of Guizhou, China

The dental and skeletal fluorosis is highly prevalent in Zhijin, Guizhou, especially at Hualuo Village, Hehua Village and Majiazhuang Village. The contents of fuorine in coal, clay used for coal combustion, mixed fuel of coal and clay, corn, and chili from households of the three villages were determined by the pyrohydrolysis-fluorine ion-selective electrode method. The average contents of fluorine in the above samples respectively are 237 mg/g, 2262 mg/g, 828 rag/g, 1419 mg/g, and 110 mg/g. The clay used for coal combustions is the main fluorine source of endemic fluorosis and the inferior coal and weathered coal are the secondary source of fluorine. During the combustion of mixed fuel of coal and clay, about eighty percent of fluorine was volatilized, approximately two thirds of which was from the clay and the other one third from the coal. The occurrence of fluorine in clay used for coat combustion is closely related to apatite and hornblende. The contents of fluorine in corn and chili, dried by coal-clay mixed fuel are about 1400 and 73 times higher than the permitted level of fluorine in foods according to the Chinese Standard. It is worth paying attention to the high-fluorine indoor surroundings, such as coal, clay, corn, and chili, particularly ash from boiler bottom with the fluorine content of 15738 ~g/g. Besides the technologies of fluorine fixation during the combustion, changes in living habits of the residents will help reduce the fluorine absorption, for example, washing the corn and chili before eating and improving the ventilation condition.