Deyi Ren

Distributions of minor and trace elements in Chinese coals

The concentrations of forty-five elements in 137 Chinese coals collected from the main coal fields and representing the main coal-forming periods were determined using instrumental neutron activation analysis (INAA), atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP-AES), and atomic fluorescence spectrometry (AFS). Among the elements determined are the following minor and trace elements which are important to environmental protection and human health: As, Cd, Pb, Hg, Se, Mn, Ni, Cu, Zn, Sb, Co, Mo, F, Cl, V, Ba, U and Th. The ranges and means of concentrations of these elements are given. Comparison with world averages and geometric means of concentrations in American coals shows that the concentrations of most elements are higher in Chinese coals. However, it is necessary to point out that although the samples are representative, the number of samples is small. Hence, these are only preliminary results. Finally, five major genetic types of enrichments of minor and trace elements in Chinese coals are proposed on the basis of Chinese coal geology, namely, source-rock-controlled type; sedimentation-controlled type; magmatic/hydrothermal-controlled type; fault-controlled type; and groundwater-controlled type.

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.

Trace element abundances in major minerals of Late Permian coals from southwestern Guizhou province, China

Abstract Fourteen samples of minerals were separated by handpicking from Late Permian coals in southwestern Guizhou province, China. These 14 minerals were nodular pyrite, massive recrystallized pyrite, pyrite deposited from low-temperature hydrothermal fluid and from ground water; clay minerals; and calcite deposited from low-temperature hydrothermal fluid and from ground water. The mineralogy, elemental composition, and distribution of 33 elements in these samples were studied by optical microscopy, scanning electron microscope equipped with energy-dispersive X-ray spectrometer (SEM-EDX), X-ray diffraction (XRD), cold-vapor atomic absorption spectrometry (CV-AAS), atomic fluorescence spectrometry (AFS), inductively coupled-plasma mass spectrometry (ICP-MS), and ion-selective electrode (ISE). The results show that various minerals in coal contain variable amounts of trace elements. Clay minerals have high concentrations of Ba, Be, Cs, F, Ga, Nb, Rb, Th, U, and Zr. Quartz has little contribution to the concentration of trace elements in bulk coal. Arsenic, Mn, and Sr are in high concentrations in calcite. Pyrite has high concentrations of As, Cd, Hg, Mo, Sb, Se, Tl, and Zn. Different genetic types of calcite in coal can accumulate different trace elements; for example Ba, Co, Cr, Hg, Ni, Rb, Sn, Sr, and Zn are in higher concentrations in calcite deposited from low-temperature hydrothermal fluid than in that deposited from ground water. Furthermore, the concentrations of some trace elements are quite variable in pyrite; different genetic types of pyrites (Py-A, B, C, D) have different concentrations of trace elements, and the concentrations of trace elements are also different in pyrite of low-temperature hydrothermal origin collected from different locations. The study shows that elemental concentration is rather uniform in a pyrite vein. There are many micron and submicron mosaic pyrites in a pyrite vein, which is enriched in some trace elements, such as As and Mo. The content of trace element in pyrite vein depends upon the content of mosaic pyrite and of trace elements in it. Many environmentally sensitive trace elements are mainly contained in the minerals in coal, and hence the physical coal cleaning techniques can remove minerals from coal and decrease the emissions of potentially hazardous trace elements.

Geochemical and mineralogical anomalies of the late Permian coal in the Zhijin coalfield of southwest China and their volcanic origin

Abstract This paper describes the influence of volcanic ash on the concentrations and occurrences of associated elements in coal in the Zhijin Coalfield in western Guizhou Province, China. Our studies reveal that the No. 9 coal seam in the Zhijin Coalfield has very high content of Fe (4.34%), Cu (369.90 μg/g), U (49.6 μg/g), Mo (63.10 μg/g), Zn (33.97 μg/g), and Zr (841.80 μg/g). The studies have also found that elements, such as Fe and Cu, do not occur as sulfides in this coal seam, in sharp contrast to many other coal seams in China. The geochemical and mineralogical anomalies of the coal seam are attributed to synsedimentary volcanic ash. In addition to normal macerals and minerals in coal, a volcanic-influenced material (VIM) derived from volcanic ash, detrital material of terrigenous origin and organic matter was identified under polarized-light reflectance microscopy and scanning electron microscopy equipped with energy-dispersive X-ray (EDX) analyzer. The volcanic-influenced material is the main carrier of the above elements in this coal. Six types of the volcanic-influenced material (VIM-1, VIM-2, VIM-3, VIM-4, VIM-5, and VIM-6) are further distinguished on the basis of their structures and compositions. To the best of our knowledge, this is the first report that presents a detailed classification of coal components with a high content of volcanic ash.

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.

Comparative leaching experiments for trace elements in raw coal, laboratory ash, fly ash and bottom ash

Abstract Samples of raw coal, fly ash and bottom ash have been collected from a Chinese power plant together with laboratory ash obtained by ashing of the coal under 850°C. Comparative-leaching experiments were carried out on each fraction under various pH conditions. A mathematical model for leaching of trace elements has been developed and leaching intensity (Il) has been calculated for each element. The results show that pH of the solution, leaching time, and particularly, properties and occurrence of the elements, have a strong influence on leaching behavior.

Valuable elements in Chinese coals: a review

ABSTRACT China is, and in the coming decades should continue to be, the largest producer and user of coal in the world. The high volume of coal usage in China has focused attention not only on the toxic trace elements that may be released from coal combustion but also on the valuable elements that may occur in the coal and associated ash. Valuable elements in several coals (or coal ashes) and some coal-bearing strata in China (e.g. Ge, Ga, U, rare earth elements and Y, Nb, Zr, Se, V, Re, Au, and Ag, as well as the base metal Al) occur at concentrations comparable to or even higher than those in conventional economic deposits. Several factors are responsible for these elevated concentrations: (1) injection of exfiltrational solutions during peat accumulation or as part of later epigenetic activity; (2) injection of infiltrational epigenetic solutions; (3) introduction of syngenetic alkali volcanic ashes into the peat-forming environment or into associated non-coal-forming terrestrial environments; (4) input of terrigenous materials into the coal-forming environment; (5) leaching of non-coal partings by groundwater/hydrothermal solutions; and (6) mixed processes involving both hydrothermal solutions and volcanic ash. The valuable elements in Chinese coals may be associated with either the organic matter or mineral matter, or have a mixed organic- and inorganic-affinity. For example, the Ge and U in coal-hosted ore deposits dominantly occur in the organic matter, with only traces of U-bearing minerals being present; gallium mainly occurs in boehmite and kaolinite, and to a lesser extent, in the organic matter. Rare earth elements and Y occur as carbonate-minerals (e.g. florencite, parisite), phosphate-minerals (e.g. rhabdophane, silico-rhabdophane, and xenotime), and in part are associated with the organic matter. Some metals (e.g. Ge, Al, Ga) have been successfully extracted at an industrial scale from Chinese coals, and others have significant potential for such extraction. Major challenges remaining for coal scientists include the development of economic extraction methods from coal ash, and the control of toxic elements released during the metal extraction process to protect human health and to avoid environmental pollution.

Distribution of potentially hazardous trace elements in coals from Shanxi province, China

Shanxi province, located in the center of China, is the biggest coal base of China. There are five coal-forming periods in Shanxi province: Late Carboniferous (Taiyuan Formation), Early Permian (Shanxi Formation), Middle Jurassic (Datong Formation), Tertiary (Taxigou Formation), and Quaternary. Hundred and ten coal samples and a peat sample from Shanxi province were collected and the contents of 20 potentially hazardous trace elements (PHTEs) (As, B, Ba, Cd, Cl, Co, Cr, Cu, F, Hg, Mn, Mo, Ni, Pb, Sb, Se, Th, U, V and Zn) in these samples were determined by instrumental neutron activation analysis, atomic absorption spectrometry, cold-vapor atomic absorption spectrometry, ion chromatography spectrometry, and wet chemical analysis. The result shows that the brown coals are enriched in As, Ba, Cd, Cr, Cu, F and Zn compared with the bituminous coals and anthracite, whereas the bituminous coals are enriched in B, Cl, Hg, and the anthracite is enriched in Cl, Hg, U and V. A comparison with world averages and crustal abundances (Clarke values) shows that the Quaternary peat is highly enriched in As and Mo, Tertiary brown coals are highly enriched in Cd, Middle Jurassic coals, Early Permian coals and Late Carboniferous coals are enriched in Hg. According to the coal ranks, the bituminous coals are highly enriched in Hg, whereas Cd, F and Th show low enrichments, and the anthracite is also highly enriched in Hg and low enrichment in Th. The concentrations of Cd, F, Hg and Th in Shanxi coals are more than world arithmetic means of concentrations for the corresponding elements. Comparing with the United States coals, Shanxi coals show higher concentrations of Cd, Hg, Pb, Se and Th. Most of Shanxi coals contain lower concentrations of PHTEs.

Concentrations and origins of platinum group elements in Late Paleozoic coals of China

The platinum group elements (PGEs) in 63 samples collected from the Late Paleozoic coal-bearing strata in western Guizhou Province and North China were determined using high-resolution inductively coupled plasma-mass spectrometry (HR ICP-MS). The study shows that PGEs in coal have five different sources: magmatic hydrothermal inputs, low-temperature hydrothermal fluids, synsedimentary volcanic ash, detrital minerals of terrigenous origin, and seawater. This study indicates that the first three sources can lead to enrichment of PGEs in these Chinese coals. The typical low contents of PGEs in most of the studied coals, defined as background contents in this work, mainly originate from detrital minerals. The background content of Pd (150 ng/g) is higher than that of Pt (30 ng/g), and much higher than that of Ru (5 ng/g), Rh (14 ng/g), and Ir (1 ng/g). The Pd content is nearly 15-fold higher than the crustal abundance. In contrast, Pt content is lower than its crustal abundance. The relatively good correlation between Pd, Pt, and ash contents suggests that the PGEs are associated with minerals.

Late Permian coal-bearing carbonate successions in southern China: coal accumulation on carbonate platforms

Abstract Late Permian coal-bearing carbonate successions are extensively developed in southern China. Microfacies analyses show that these coal-bearing carbonate successions were deposited in shallow-water carbonate settings comprising restricted platform tidal-flat, restricted platform subtidal, open-platform, marginal shoal, marginal organic reef, and basin facies belts. Coal seams are directly intercalated with carbonate or silicified carbonate rocks in these successions. The microfacies of the roof and floor of coal seams are typically tidal-flat facies laminated clayey algal-clast packstones which suggest that the coal-forming peat swamps were developed on or adjacent to tidal-flats. Three settings for coal accumulation can be recognised, including shallow flat platform, platform interior bank and platform marginal shoal. The coal-forming materials were most likely derived from mangrove-like plants which tolerated variable mixtures of alkaline, brackish and fully marine seawater in tide-influenced swamps which were similar to modern intertidal mangrove swamps. This interpretation is further supported by high organic sulphur contents (6–9%), together with elevated concentrations of Na 2 O (up to 4.36%), MgO (up to 1.6 to 2.6%) and CaO (up to 2 to 4%). The occurrence of dolomite, calcite and marine fossils within the coals and their partings demonstrates a close marine association.