Petrographical and thermo-chemical investigation of some North East Indian high sulphur coals

The Tertiary North East Indian coals, classified as sub-bituminous rank, have found less industrial application owing to their physico-chemical attributes. These coals are characterized by low ash (<15%), high volatile matter (>35%) and high sulphur (2.9-4.46%). Majority of the sulphur occurs in organic form affixed to the coal matrix owing to marine influence, is difficult to remove. The coal maceral analysis shows the dominance of vitrinite (>75%) with lesser amounts of liptinite and inertinite. Reflectance measurements (Rmax) of these sub-bituminous coals fall in the range of 0.57 to 0.65. In this study, the petrographical (maceral), thermal and other physico-chemical analyses of some low rank Tertiary sub-bituminous coals from north-east India were carried out to assess their potential for combustion, liquefaction and coal bed methane formation. The petrofactor, conversion (%) and oil yield (%), combustion efficiency of the coal samples were determined. The respective linear correlations of conversion (%) of the coals with their vitrinite contents, petrofactor and oil yield values have been discussed. The relative combustion efficiency of the coals was measured from the thermo gravimetric analysis (TGA) of coals. The influence of maceral composition upon gas adsorption characteristics of these high volatile coals showed the increase in methane adsorption with vitrinite enrichment. Both the maceral and mineral matter contents were observed to have important influence on the gas adsorption characteristics.     

A study of trace elements in lithotypes of some selected Indian coals

Ashes of the lithotypes from some Indian coals were analyzed by emission spectroscopy for some selected elements. Based on the combined concentration and differential fixation, the elements Pb and Co appear to be supplied by the woody portion of the proto-coal material whereas Ga, Nb, Ni, Cr and In can be attributed to the non-woody portions of the proto-coal. On the other hand, Cu, Mo and part of the available Cr appear to come from both organic and inorganic sources, whereas V, Mn, Sr, La and Ba have been attributed to an extraneous inorganic source. The differential fixation of the trace elements appears to be mainly dependent on the physicochemical environment of the basin.     

Preliminary investigation on the metamorphism of Chinese coals

The fact that most Chinese coals are of a relatively high degree of coalification indicates that the metamorphism of Chinese coals has its own characteristics. As contact metamorphism and dynamic metamorphism have influenced the coals only to a restricted extent, they are not the causes of this distinguishing feature. Though geothermal metamorphism of coal occurs universally in China, the maximum subsidence as reflected by the thickness of coal measures and their overlying rock series is so small that the palaeo-temperature to which most Chinese coals were subjected was low and only low-ranking coals were formed. Hence, geothermal metamorphism is also not the principal cause of the higher ranking Chinese coals. Next to temperature, time is an important factor in geothermal metamorphism; the degree of coalification is dependent on the temperature and duration of heating that the coal has undergone.It is inferred that palaeogeothermal anomalies ought to be held responsible for most of the higher ranking Chinese coals. They are principally caused by magmatic intrusions, or by deep-seated faults, or by the uplift of the Moho with the corresponding uplift of the asthenosphere, and these three causes are interrelated. Telemagmatic metamorphism has so widely influenced Chinese coals that it accounts mainly for the majority of higher-rank Chinese coals. Consequently Chinese coals have first and universally been coalified by geothermal alteration to lower rank and then partially promoted by telemagmatic metamorphism to medium and high ranks. Based upon the patterns of magmatic intrusions and associated hydrothermal processes, the telemagmatic metamorphism of Chinese coals can be tentatively divided into the following types: (1) type a, produced mainly by hypabyssal or meso-epimagmatic intrusions; (2) type b, produced mainly by hydrothermalism from blind intrusive bodies; (3) type c, produced mainly by mesoepimagmatic and epimagmatic intrusions; and (4) type d, produced mainly by hydrothermalism and epimagmatic intrusions. Characteristics of coalification zones, wall rocks and coal itself may be used as criteria to differentiate the telemagmatic metamorphism from other kinds of metamorphism. Magmatic activities which caused the telemagmatic metamorphism and its extent are controlled by structural systems, especially by the latitudinal structural systems and other structural systems associated with the former.     

Geochemistry and origin of elements in some UK coals

Twenty-four UK coals ranging in rank with 4.6%–37.6% volatile matter were analysed for 46 major and trace elements. The samples were obtained from the UK Coal Bank and are representative of the major UK coal fields. The major element distributions are interpreted in terms of the mineralogical variations—quartz and kaolinite are largely responsible for the Si and Al, carbonates for Ca and Mg and pyrite for Fe. Also exerting an influence in some samples are siderite, Al-phosphate minerals and illite. Based on statistical relationships with the major elements, Rb, Cr, Th, Ce, Zr, Y, Ga, La, Ta, Nb and V are thought to be mainly present in the clay minerals, and As, Mo, Sb, Tl, Se and Bi and Pb are probably present in pyrite. Strontium and Ba are concentrated in a restricted number of samples related to the phosphate minerals. Germanium is the only element for which a major organic association can be demonstrated. Elements with an indirect association with the organic matter are Na, Cl, and Br in porefluids and possibly Te. The ash content is controlled mainly by the detrital input and the trace elements related to the ash content are therefore those elements associated with the clay minerals. Variations with rank would appear to be mainly related to the moisture content (porefluids). The trace elements associated with the quartz and clay minerals are thought to be dominantly detrital in origin. The non-detrital elements, essentially those contained in pyrite, are thought to have been incorporated in the depositional environment from waters with enhanced salinities through seawater ingress, hence there are positive relationships between S and trace element concentrations.     

Structure and origin of terpenoid hydrocarbons in some German coals

Hydrocarbon extracts of coal samples from major coal fields in West Germany have been investigated by gas chromatography-mass spectrometry (GC/MS). The samples are of Carboniferous and Tertiary age and derive from limnic and paralic environments, the Saar District, the Ruhr Area and the Lower Rhine Basin.Differences in facies, maturity and age reflected in the distribution patterns of the extracted alkylcyclohexanes. An unexpected occurrence of cyclic diterpenoid hydrocarbons in some samples of Carboniferous age has been found. The tetracyclic compounds mainly show phyllocladane type structures and can serve as source indicators.Hydrocarbons obtained from chemical degradation of the macromolecular material of the samples also revealed phyllocladane-type compounds which are normally associated to resins of modern and extinct familes of conifers. Origin and structural variations of this class of hydrocarbons are discussed in terms of maturity and palaeobotanical implications.     

Mineral matter in coals: cleat minerals and their origin in some coals from the english midlands

In four coal seam profiles from the Cannock Coalfield, West Midlands, the cleat (joint) frequency is a function of lithotype (greatest in vitarin) and is inversely related to bed thickness. The cleat minerals were studied: (1) under the microscope (optical and electron); (2) by X-ray diffraction; and (3) chemically. The minerals present are pyrite, marcasite, sphalerite, galena (sulphides), quartz, kaolinite (silicates), ankerite, calcite (carbonates) and apatite. This sequence has features in common with diagenetic sequences recorded in other rock types and it is concluded that the cleat minerals in coal form in response to pore fluid evolution and movement during burial diagenesis. The elements are thought to originate from both the coal and the associated sediments, mainly mudrocks. Similarities in diagenetic sequences are in part a reflection of the importance of organic maturation reactions in all the rock types in the sequence, whereas differences are attributed to the dominance of these reactions in the coal itself.     

A review of chlorine and bromine in some United Kingdom coals

In the UK there is a longstanding interest in the Cl content of coals because of the adverse effects associated with high-Cl coals during combustion. An average Cl content of a representative suite of coal samples is 0.44 wt.%, but the range is from near zero to over 1%. Several lines of evidence show that in the high-Cl coals the Cl is associated with the coal moisture and that other sources, such as the silicate minerals, are negligible. Although the Cl is moisture associated there is anion exchange with the organic matter, which means that Cl is less than 100% water- soluble unless the Cl is exchanged with other anion species. This occurs if carbonates are present and calcite in particular. The Cl and Br are closely related and the location within the coal is thought to be common to both. These two elements differ from nearly all other trace elements in UK coals in that they are not present in significant concentrations in the mineral matter or bound within the organic matter. Whereas there is a good understanding of the geochemical behaviour of these other elements this is not the case for Cl and Br in the coal moisture. Chlorine and Br are thought to be conservative elements in the diagenetic evolution of the porewaters, in which an original marine depositional imprint could have been preserved. In some areas the porewaters may have fully evolved pre-Permian, whereas in other areas the diagenetic evolution could be much longer.     

Resino-inertinites of Indian Permian coals — their origin, genesis and classification

Variously shaped discrete bodies with reflectance higher than the associated vitrinite occur in Permian coals in India, Australia and Africa and the Carboniferous coals of the United States, Canada and Europe. These bodies have been variously named by different authors. In the present paper they are described as ‘resino-inertinites’ as suggested by Lyons et al. (1982).Based on available information and our observations on Carboniferous and Permian coals, it is presumed that resino-inertinites were formed mainly from the resinous (resinite) and to some extent from the phlobaphinitic or corpocollinitic substances. Various morphological patterns developed on resino-inertinites have been interpreted to be governed by the chemical composition of their precursors and the degree of oxidation or fusinization during coalification. Influences of other vvariables viz., paleoenvironmental, paleodepositional, tectonic set up etc. on resino-inertinites are not clearly recognizable probably because all the previous effects were masked by subsequent fusinization.Different morphological features of resino-inertinites associated with early diagenetic and secondary mineralization have caused much confusion in their proper identification and classification. In order to resolve this problem, an attempt has been made to ascertain the source of resins in Indian Permian coals and their subsequent mode of transformation into resino-inertinites during coalification.Further, by critically evaluating morphological features of resino-inertinites and keeping the chemical nature of their precursors in view, a classification scheme has been proposed categorizing them into 3 types. The classification proposed may prove as a useful means for coal-seam correlation.     

Striking liptinitic bark remains peculiar to some Late Permian Chinese coals

An unusual liptinite coal component has been reported in the Chinese literature over the past sixty years. It has been described as a maceral in the Chinese National Standard (1991), but it has not been named internationally. In Chinese literature it is called “barkinite”, on the basis of its morphological features and because it is believed to have originated as bark tissue.“Barkinite” occurs in Late Permian, marine-influenced coals and is best represented in the Changguang, Leping and Shuicheng Basins of southern China.The material originates from plant periderm or the bark of higher plants. However, “bark” contains a variety of substances, including resin and suberin, which are recognised as the precursors of the resinite and suberinite macerals. “Barkinite” is distinguished by (i) its thickness; individual pieces can be more than ten cells thick and several centimetres long and (ii) it fluoresces strongly at 0.6% vitrinite reflectance and loses its fluorescence at about 1.1% vitrinite reflectance.The reporting of “barkinite” from only Chinese coals may be due to its origin from Lepidodendron and Psaronius flora, which was common in the Northern Hemisphere during the Carboniferous, but which was isolated to China by the Late Permian. It is proposed that the remnant flora evolved into unique forms in China by the Late Permian. Lepidodendron and Psaronius remains, coupled with a strongly marine-influenced, peat-forming environment have given rise to “barkinite” and to its restricted distribution.     

Concentration and distribution of trace elements in some coals from Northern China

The concentration, distribution and modes of occurrence of trace elements in thirty coals, four floors and two roofs from Northern China were studied. The samples were collected from the major coalfields of Shanxi Province, Shaanxi Province, Inner Mongolian Autonomous Region, and Ningxia Hui Autonomous Region. The concentrations of seventeen potential hazardous trace elements, including Hg, As, Se, Pb, Cd, Br, Ni, Cr, Co, Mo, Mn, Be, Sb, Th, V, U, Zn, and five major elements P, Na, Fe, Al, and Ca in coals were determined.Compared with average concentration of trace elements in Chinese coal, the coals from Northern China contain a higher concentration of Hg, Se, Cd, Mn, and Zn. They may be harmful to the environment in the process of combustion and utilization. Vertical variations of trace elements in three coal seams indicated the distributions of most elements in coal seam are heterogeneous. Based on statistical analyses, trace elements including Mo, Cr, Se, Th, Pb, Sb, V, Be and major elements including Al, P shows an affinity to ash content. In contrast, Br is generally associated with organic matter. Elements As, Ni, Be, Mo, and Fe appear to be associated with pyrite. The concentrations of trace elements weakly correlate either to coal rank or to maceral compositions.     

淮北煤中几种具有环境意义的微量元素分布

通过中子活化法,对淮北煤田主采煤层中和相对应的灰中几种具有环境意义的微量元素含量进行了测试,分析了它们在煤中和灰中的含量分布,并与中国和华北煤田煤中的平均值进行了对比,以便为煤和煤灰的综合利用提供基础资料。     

An expert system based on hybrid ICA-ANN technique to estimate macerals contents of Indian coals

Coal, as an initial source of energy, requires a detailed investigation in terms of ultimate analysis, proximate analysis, and its biological constituents (macerals). The rank and calorific value of each type of coal are managed by the mentioned properties. In contrast to ultimate and proximate analyses, determining the macerals in coal requires sophisticated microscopic instrumentation and expertise. This study emphasizes the estimation of the concentration of macerals of Indian coals based on a hybrid imperialism competitive algorithm (ICA)–artificial neural network (ANN). Here, ICA is utilized to adjust the weight and bias of ANNs for enhancing their performance capacity. For comparison purposes, a pre-developed ANN model is also proposed. Checking the performance prediction of the developed models is performed through several performance indices, i.e., coefficient of determination (R ²), root mean square error and variance account for. The obtained results revealed higher accuracy of the proposed hybrid ICA-ANN model in estimating macerals contents of Indian coals compared to the pre-developed ANN technique. Results of the developed ANN model based on R ² values of training datasets were obtained as 0.961, 0.955, and 0.961 for predicting vitrinite, liptinite, and inertinite, respectively, whereas these values were achieved as 0.948, 0.947, and 0.957, respectively, for testing datasets. Similarly, R ² values of 0.988, 0.983, and 0.991 for training datasets and 0.989, 0.982, and 0.985 for testing datasets were obtained from developed ICA-ANN model.     

Solid state 13C-NMR spectroscopy of some oligocene coals of Assam and Nagaland

Five representative sub-bituminous coals from NE part of India have been analyzed with respect to their distribution of carbon functional groups through ¹³C solid state NMR experiments. The ¹³C Cross Polarised/Magic Angle Spinning NMR spectra of the coal samples were recorded at temperatures of 23°C, 50°C and 70°C respectively and the changes on their structures were interpreted. The NMR spectra of low rank coals were found to exhibit varying degrees of fine structures. The aromaticities of the coal were also determined from the C/H ratios of coal. Some changes in the peak positions along with the formation of simple aromatic units were observed on mild heating.     

贵州煤中某些金属元素异常富集研究进展

煤层能在特定的地质条件下富集多种关键金属元素,形成具有综合利用价值的“煤型关键金属矿床”,随着煤中共伴生金属元素提取技术日益成熟,研究煤中金属元素的富集与分布特征、查明具有成矿潜力的富集区具有十分重要的资源意义。本研究基于近20年以来前人发表的有关贵州煤地球化学的研究成果及作者自测数据,统计了贵州省23个主要产煤县(市)的1002个样品数据,揭示了贵州煤中Li、Zr、Hf、Nb、Ta、U和稀土元素(REY,即REE+Y)等关键金属元素的总体分布富集特征。研究表明,贵州煤中Li、Zr、Nb、REY等关键金属元素较为富集并具有共伴生成矿潜力的区域为黔北煤田和黔西南兴义煤田两个区域。其中,金沙、桐梓、普安等地煤中Li平均含量换算为灰基Li₂O分别为1254μg/g、1214μg/g和724.4μg/g,务川和正安煤种Zr平均含量换算为灰基ZrO₂分别为4749μg/g和4168μg/g,务川煤中Nb平均含量换算为灰基Nb₂O₅为484.4μg/g,金沙、桐梓、务川及凯里煤中REY含量换算为灰基稀土氧化物R...     

Tetracyclic diterpenoid hydrocarbons in some Australian coals,sediments and crude oils

Tetracyclic diterpenoid hydrocarbons (diterpanes) based on the ent-beyerane, phyllocladane and ent-kaurane skeletons have been identified in the hydrocarbon extracts of some Australian coals, sediments and crude oils. Structures were assigned to the geological diterpanes by comparison with synthetically prepared reference compounds. Studies of a sample suite consisting of low-rank coals and sediments indicate that the ratios of C-16 epimers of phyllocladane and ent-kaurane are maturity dependent, and that the relative proportion of the thermodynamically preferred 16β (H)-compounds increases with increasing thermal maturity. Thermodynamic equilibrium for the interconversion reactions is attained in sediments before the onset of crude oil generation.The most likely natural product precursors for the tetracyclic diterpanes are considered to be the tetracyclic diterpene hydrocarbons which occur widely in the leaf resins of conifers. Tetracyclic diterpanes have been identified in sediments and coals of Permian age or younger, suggesting that these compounds are markers for both modern and extinct families of conifers. In particular, phyllocladane is proposed as a marker for the Podocarpaceae family of conifers.     

The relationship between macerals and sulphur content of some South African Permian coals

There is a positive correlation between sulphur concentration and the vitrinite maceral group content in Permian Vryheid Formation coals in South Africa; the reverse is true for the inertinite maceral family. This relationship is evident at intraseam, interseam and intercoalfied levels. Vitrinite precursors formed where the water table in peat-forming environments was high and Eh low. These conditions favoured bacterial sulphate reduction and resulting H₂S reacted with Fe²⁺ and organic peat compounds to form pyrite and organic sulphur components. Inertinite precursors formed when the water table was low and Eh high; aerobic respiration prevailed and little H₂S was produced. Organic sulphur derived from peat-forming plant tissue is dominant in intertinite-rich low-sulphur coal; pyritic sulphur exceeds organic sulphur in high-sulphur coals dur to preferential reaction of H₂S with Fe²⁺.     

贵州煤中某些金属元素异常富集研究进展

煤层能在特定的地质条件下富集多种关键金属元素,形成具有综合利用价值的“煤型关键金属矿床”,随着煤中共伴生金属元素提取技术日益成熟,研究煤中金属元素的富集与分布特征、查明具有成矿潜力的富集区具有十分重要的资源意义。本研究基于近20年以来前人发表的有关贵州煤地球化学的研究成果及作者自测数据,统计了贵州省23个主要产煤县（市）的1002个样品数据,揭示了贵州煤中Li、Zr、Hf、Nb、Ta、U和稀土元素（REY）等关键金属元素的总体分布富集特征。研究表明,贵州煤中Li、Zr、Nb、REY等关键金属元素较为富集并具有共伴生成矿潜力的区域为黔北煤田和黔西南兴义煤田两个区域。其中,金沙、桐梓、普安等地煤中Li平均含量换算为灰基Li2O 分别为1254 μg/g、1214 μg/g和724.4 μg/g,务川和正安煤种Zr平均含量换算为灰基ZrO2分别为4749 μg/g和4168 μg/g,务川煤中Nb平均含量换算为灰基Nb2O5为484.4 μg/g,金沙、桐梓、务川及凯里煤中REY含量换算为灰基稀土氧化物REO含量分别为2175 μg/g、2429 μg/g、2875 μg/g和2604 μg/g,这些含量均超过了相应矿种的最低工业品位或文献建议的可回收利用指标。贵州煤中多种金属元素具有较高的含量背景值,尤其以黔西南兴义煤田和黔北煤田最为显著,作者建议应进一步加强对上述两个区域的煤地球研究,查清煤中微量元素的时空分布与富集规律,为煤型关键金属矿床的找矿勘查提供更可靠科学依据。贵州晚二叠世煤中异常富集的Li、U、Nb、Ta、Zr、Hf和REY等元素的富集主要受峨眉山玄武岩风化产物的供给、同沉积火山灰的混入以及成煤期后低温热液作用的影响。其中REE的富集,不仅与玄武岩风化产物有关,还可能受到长英质—中性物质输入的影响。     

Sedimentology of Fraser River delta peat deposits: A modern analogue for some deltaic coals

On the Recent lobe of the Fraser River delta peat accumulation has actively occurred on the distal lower dilta plain, the transition between upper and lower delta plains, and the alluvial plain.Distal lower delta plain peats developed from widespread salt and brackish marshes and were not influenced appreciably by fluvial activity. Lateral development of the marsh facies were controlled by compaction and eustatic sea level rise. The resulting thin, discontinuous peat network contains numerous silty clay partings and high concentrations of sulphur. Freshwater marsh facies formed but were later in part eroded and altered by transgressing marine waters. The peats overlie a thin, fluvial, fining-upward sequence which in turn overlies a thick, coarsening-upward, prodelta—delta front succession.Lower delta plain—upper delta plain peats initially developed from interdistributary brackish marshes and were later fluvially influenced as the delta prograded. The thickest peats occur in areas where distributary channels were abandoned earliest. Sphagnum biofacies replace sedge-grass-dominated communities except along active channel margins, where the sedge-grass facies is intercalated with overbank and splay deposits. The peats are underlain by a relatively thin sequence of fluvial deposits which in turn is underlain by a major coarsening-upward delta front and pro-delta sequence.Alluvial plain peats accumulated in back swamp environments of the flood plain. Earliest sedge-clay and gyttjae peats developed over thin fining-upward fluvial cycles or are interlaminated with fine-grained flood deposits. Thickest accumulations occur where peat fills small avulsed flood channels. Overlying sedge-grass and Sphagnum biofacies are horizontally stratified and commonly have sharp boundaries with fine-grained flood sediments. At active channel margins however, sedge-grass peats are intercalated with natural levee deposits consisting of silty clay. These levees reduce both the number and size of crevasse splay deposits.Coal originating from peats of the different environments of the Fraser delta would vary markedly in character. Peats of the lower delta plain will form thin lenticular coal seams with numerous splits and have a high ash and sulphur content. Peats from the lower to upper delta plain will be laterally extensive and of variable thickness and quality. Basal portions of the seams will contain numerous splits and have a high sulphur content whereas upper portions will be of higher quality. Peats from the upper delta plain—alluvial plain will form thick, isolated and laterally restricted coal seams characterized by low ash and sulphur contents.     

Mineral matter and the nature of pyrite in some high-sulfur tertiary coals of Meghalaya, northeast India

Coal samples collected from four different sources in the Jaintia Hills of Meghalaya, northeast India, have been investigated for their sulfur content, mineral matter, and to assess their potential behavior upon beneficiation. These coals contain high sulfur which occurs both in organic and inorganic forms. The organic sulfur content is much higher than the inorganic sulfur. Studies on different size and gravity fractions indicated that the mineral phases are concentrated in higher density fractions (d > 1.8) and in general are fine grained (<50 μm). Data of reflected-light optical microscope and electron probe micro-analysis (EPMA) revealed that minerals in these coals are sulfides-pyrite, marcasite, sphalerite, pentlandite; sulfates-barite, jarosite; oxides-hematite, rutile; hydroxides-gibbsite, goethite; phosphate-monazite; carbonate-calcite, siderite and silicates-quartz, mica, chlorite, and kaolinitic clay. The disulfides of iron occur in two modes — mainly pyrite and occasionally marcasite with wide size ranges and in various forms, such as: framboid, colloidal precipitate, colloform-banded, fine disseminations, discrete grains, dendritic (feathery), recrystallized, nuggets, discoidal, massive, cavity-fracture- and cleat-fillings. Framboidal pyrite has formed primarily due to biological activities of sulfur reducing bacteria in the early stages of coalification. Massive and other varieties have formed at later stages due to coalescence and recrystallization of the earlier formed pyrites. Sulfur isotopic values indicate a biogenic origin for the pyrites. Association of trace metals, such as Ni, and Zn has been recorded in these pyrites. Given the large fractions of organic sulfur present, these coals can be upgraded only partially to reduce the sulfur content by beneficiation.