Makum Coalfield Research Articles

Sedimentology, palynostratigraphy and palynofacies of the late Oligocene Makum Coalfield, Assam, India: A window on lowland tropical vegetation during the most recent episode of significant global warmth

The sedimentology, palynofacies and pollen and spore assemblages, together with observations on the preserved megaflora, from the Tirap coal mine, Assam, India (27° 17′ 20″ N, 95° 46′ 15″ E) provide important insights into the composition and distribution of plant communities in a late Oligocene tropical delta (palaeolatitude approximately 18°N). These insights take on additional significance because the late Oligocene included the last significantly warm interval in Earth's history before progressive Neogene cooling to the present day ‘icehouse’. The lower two thirds of a 188m studied section represents lower delta plain environments with only a small degree of brackish water (marine) influence. Raised mires, autochthonous swamps and allochthonous organic matter accumulations comprise the vitrinite-rich high volatile bituminous B coals. The upper third of the section represents upper delta plain environments with high sediment pass-through. Here standing fossil ‘forests’ attest to frequent inundation and recovery of the arborescent interfluve vegetation. Throughout the period of deposition of the studied section (several 100kyr) sediment supply exceeded increases in accommodation space afforded by basin subsidence/relative sea level rise.A dominance of spores attributed to cyatheaceous and other fern taxa indicates that tree ferns and other pteridophytes were a major component of the vegetation throughout the environments represented by the section, despite the absence of ferns in the megafossil record. Nypa and mangrove megaremains together with mangrove pollen and Acrostichum spores attest to the presence of a mangrove community similar in composition to those of modern Southeast Asia. Palms and megathermal tree taxa such as those belonging to the Malvaceae, Meliaceae, Alangiaceae, Anacardiaceae and Pellicieraceae inhabited the interfluve and swamp forests. Perennial herbs of the family Gunneraceae occur throughout the section.Palynofacies analysis shows a dominance of anoxic/dysoxic environments with a small part of the lower part of the section exhibiting more oxic conditions associated with circumstantial evidence for mild marine, possibly tidal, influence. Most palynodebris fluoresce only weakly consistent with the relatively high rank for coals of this age. A small number of reworked Gondwanic (Permian) grains suggest sediment erosion from the highlands to the north.The late Oligocene tropical delta vegetation has much in common with modern lowland wet megathermal forests from Southeast Asia. However tree ferns appear more prevalent in the late Oligocene.

493 Late Oligocene flora from the Makum Coalfield, Assam, India and its palaeoclimatic and palaeogeographic significance

493 Late Oligocene flora from the Makum Coalfield, Assam, India and its palaeoclimatic and palaeogeographic significance

Hydrogeochemical characteristics of acid mine drainage and water pollution at Makum Coalfield, India

Acid mine drainage (AMD) is one of the severe environmental problems that coal mines are facing. Generation of AMD in the northeastern part of India due to the coal mining activities has long been reported. However detailed geochemical characterization of AMD and its impact on water quality of various creeks, river and groundwater in the area has never been reported. Coal and coal measure rocks in the study area show finely disseminated pyrite crystals. Secondary solid phases, resulted due to oxidation of pyrite, occur on the surface of coal, and are mainly consisting of hydrated sulphate complexes of Fe and Mg (copiapite group of minerals). The direct mine discharges are highly acidic (up to pH 2.3) to alkaline (up to pH 7.6) in nature with high concentration of SO 4 2−. Acidic discharges are highly enriched with Fe, Al, Mn, Ni, Pb and Cd, while Cr, Cu, Zn and Co are below their maximum permissible limit in most mine discharges. Creeks that carrying the direct mine discharges are highly contaminated; whereas major rivers are not much impacted by AMD. Ground water close to the collieries and AMD affected creeks are highly contaminated by Mn, Fe and Pb. Through geochemical modeling, it is inferred that jarosite is stable at pH less than 2.5, schwertmannite at pH less than 4.5, ferrihydrite above 5.8 and goethite is stable over wide range of pH, from highly acidic to alkaline condition.

Notes on elements of the Oligocene flora from the Makum Coalfield, Assam, India

A new species Daphnogene makumensis sp. nov. (Lauraceae), plus Equisetum sp. both new to the flora, and Mesua antiqua Awasthi et al. are described from the Tikak Parbat Formation of the Makum Coalfield, Assam, India. The formation is considered Late Oligocene in age. The fossil assemblage indicates the existence of tropical evergreen to moist deciduous forest in the region during the Late Oligocene.

Scanning electron microscopy of Assam coals, India

An examination on the structural features of some coal samples from Makum coalfield, Assam (India) were carried out by using scanning electron microscopy. The morphological characteristics of the macerals were recognized. Collinite was recognizable by its angular shape with characteristic fracture patterns and striated or laminated surfaces. Sporinite particles showed no well-defined shape. Fusinite was remarkable in having a chunky needle form. Chemical and petrographic characteristics of these coals also have been reported. These findings have shown prime importance in fingerprinting the physical structure of these coals.

Radon exhalation rate studies in Makum coalfield area using track-etched detectors

Radon exhalation rates were studied using LR-115 (II) nuclear track detectors in and around the Makum coalfield, which has significant geological features. Exhalation rates (mass and surface) from coal and soil samples were studied with reference to the geological features. The mass and surface exhalation rates from coal samples ranged from 6.1–16.2 mBq/kg/h and 201.6–535.7 mBq/m2/h, respectively. The mass and surface exhalation rates from the soil samples collected from the Margherita Thrust area of the coalfield and the coalfield area lying in between the Margherita Thrust and Disang Thrust of the coalfield were found to be 10.7 mBq/kg/h and 354.2 mBq/m2/h, and 9.5 mBq/kg/h and 314.2 mBq/m2/h, respectively.

Upgradation of High Sulfur NE Region Indian Coals by Pyrolysis in Presence of Hydrogen

In order to utilize high sulfur (3-6%) coals in various industries which otherwise cannot be utilized directly or even as a blend, studies on pyrolysis of four high sulfur NE regions Indian coals viz. 60ft Tikak, 20ft Tikak, Surupi and Bapung coal from Makum Coalfields of Meghalaya in presence of hydrogen were carried out at 900 0 C. The steam was generated by heating waste water followed by its super heating in the steam zone at a temperature of 400±5 0 C. Hydrogen was produced from this super heated steam, copper-iron scrap reaction at 900 0 C in the promoter zone. This hydrogen was passed into reaction zone where high sulfur coal was kept at 900±5 0 C. It was found that a reduction of about 58.7 - 91.1% in organic sulfur and 75.7 - 93.8% in inorganic sulfur (pyrites + sulfates) leading to total sulfur reduction from 68.6 - 90.2% was achieved. After reduction in sulfur on pyrolysis, the low sulfur coke/char thus formed can be used directly as such in case where the coke/char has about 1% sulfur or the same may be used as a blend with low sulfur coke/char in different industries giving value addition to the coal.

Occurrence of some hazardous metals in Indian coals

Studies on hazardous metals pollution through various processes of utilization of the Assam (India) coals suffer from the lack of reliable information on the level of trace and heavy metals in them. Four representative coal samples with high sulphur from Ledo, Tikak, Tipong and Baragolai collieries of Makum coalfield, Assam, India were studied for the occurrence of Al, Bi Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Se, V, and Zn by Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES) methods. Six of the metals (Cd, Cr, Co, Mn, Ni, and Pb) found to be present in low to moderate concentrations were identified as Hazardous Air Pollutants (HAPs) in the 1990 Clean Air Act Amendments (CAAA) USA. The concentration of Fe, Mg and Al was observed to be higher than the rest of the metals. Significant variation of these metal contents in the four coals samples was observed with no noteworthy statistical relationship with the ash and carbon contents of the coals. The concentrations of metals in the samples are within the average world coal range. It was also observed that there is no definite trend of metal concentration with reference to different collieries of Assam. The association of some metals in the coal matrix was also discussed. XRD and FT-IR patterns of the coals also supported the presence of these metals.

A X-ray diffraction analysis on graphene layers of Assam coal

The so-called turbostatic structure of carbons in coal with randomly oriented stacking of the lamellae (graphene) produces intense peaks, which are the dominant features in its X-ray diffraction profiles. The diffractogram may be conveniently divided into two regions of reciprocal space, the medium S region (1 < S < 3 Å) and a high S region (S > 3 Å) where S = 4πλ −1sinθ. To better understand the molecular level structure of high sulphur Assam coal, two coal samples (Tirap-1 and Tirap-2) from Tirap colliery of Makum coalfield, Assam (India) has been interpreted in this study by using the X-ray diffraction profiles. Random layered (graphene) structural parameters of these coals were determined by using X-ray diffraction technique, which showed that the L a and L c are 64·99 Å and 22·63 Å for Tirap-2 and 55·54 Å and 23·80 Å for that of Tirap-1 coals respectively. The position of γ band was found to be at 4·34 Å and 4·13 Å for Tirap-2 and Tirap-1 coals respectively. The number of layers and average number of carbon atoms (N) per aromatic graphene were found to be 21 and 8 for both the coal samples. Proximate, ultimate and ash analysis of the two coal samples were also carried out in this investigation.

A thermal investigation on coals from Assam (India)

A thermal characterization of two coal samples from Ledo and Tikak collieries of Makum coalfield, Assam, India using XRD, FT-IR, and TGA was reported in this paper. The coal samples were heated for 20, 40 and 60 min in a 1000-watt heater (temperature ∼ 250 °C) in presence of air and characterized by XRD and FT-IR spectroscopy. Both the coals contain amorphous and crystalline phases. The raw coals also contain very small peaks due to quartz, calcite, gypsum, pyrite, and chlorite. The XRD patterns were found to change upon heating. In the coals heated for 20 and 40 min, it was observed that both amorphous and crystalline parts are common in them; crystalline part being the major one in the 40 min heated samples. The XRD patterns of the samples heated for 60 min indicate the presence of major quantities of α-quartz, hematite, and chlorite in them. They also show some new peaks, which are assigned to be kaolinite, illite, magnetite and very small in comparison to the amorphous portion in raw coals. α-quartz was found to be most stable crystalline phase of silica in the coals. The crystallinity % (X-ray) of the coals heat-treated for different times was determined and found to be increasing with time of heating. The FT-IR spectra of raw and heat-treated coal samples at 250 °C were also recorded and compared. The spectra were observed to be almost similar and it was observed that few functional groups disappear on heating at 250 °C. The same coal samples were also characterized by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) techniques. On heat treatment in air atmosphere up to 800 °C, 20–27% weight loss occurs due to removal of various volatile materials. DTA results indicate the chemical reactivity of the coal sample initially at 80–110 °C due to loss of water, and two other major reactions at around 420 and 530 °C due to primary and secondary volatization.

X-ray scattering study of the average polycyclic aromatic unit in Ledo coal

This report is an attempt to understand the short-range structural features, to determine the relationship(s) between the aryl/alkyl carbon ratio, and to determine the size of the average polycyclic aromatic unit in Ledo coal from Makum coalfield, Assam, India. An X-ray scattering analysis of the average polycyclic aromatic unit in the coal indicates that the aromatic fraction in this coal is 74% with the aliphatic fraction correspondingly estimated to be 26%. The average carbon atom has 2.3 nearest carbon atom neighbours at an average bond distance of 1.50 (1) Å. The average stacking height of the parallel aromatic layers and the average diameter of the aromatic layers are estimated to be 7.58 Å and 4.86 Å, respectively. For this coal, the average number of stacking layers and the average number of atoms per layer are estimated to be 2 and 8, respectively. In addition, the Gamma band is observed at advalue of 4.42 Å.

FT-IR and XRD analysis of coal from Makum coalfield of Assam

High sulphur coal sample from Ledo colliery of Makum coalfield, Assam, India was studied using FT-IR and XRD methods. FT-IR study shows the presence of aliphatic -CH, -CH2 and -CH3 groups, aliphatic C-O-C stretching associated with -OH and -NH stretching vibrations and HCC rocking (single and condensed rings). XRD pattern of the coal shows that it is amorphous in nature. Function of Radial Distribution Analysis (FRDA) indicates that coal is lignite in type and there is no evidence of graphite-like structure. The first maximum in the G(r) plot of FRDA at r = 0.14 nm relates to the aliphatic C-C bond (Type C-CH=CH-C), the second maximum at r = 0.25 nm relates to the distance between carbon atoms of aliphatic chains that are located across one carbon atom. The curve intensity profiles obtained from FRDA show quite regular molecular packets for this coal. The coal was found to be lignite in nature.

XRD and FT-IR investigations of sub-bituminous Assam coals

Two coal samples collected from Makum coal field, Assam, India were studied by XRD and FT-IR techniques. The X-ray diffractogram shows the existence of some crystalline carbons in Assam coals as proven by the appearance of peaks. The radial distribution functional (RDF) method was applied for the determination of structural aspects of the coals. The study indicates that the coals are lignite in type and there is no evidence of graphite-like structures. The maximum in the G(r) plots of function of radial distribution of atoms (FRDA) relates to different distances between carbon atoms of aliphatic chains. The first significant maximum relates to the C-C bond (type C-CH=CH-C), the second maximum relates to the distance between carbon atoms of aliphatic chains that are located across one carbon atom. The curve intensity profiles obtained from FRDA show quite regular molecular packets for this coal. The coals were found to be lignite in nature. FT-IR study shows the presence of aliphatic carbon, C=O and C-O stretching associated with -OH and -NH stretching vibrations. Kaolinite and quartz were also found to be major minerals in Assam coals by FTIR spectroscopy. The difference in intensities of carbonyl groups of the coal samples is likely to relate with the rank.

Aqueous Leaching on High Sulfur Sub-bituminous Coals, in Assam, India

Aqueous leaching of high sulfur sub-bituminous coals from Ledo and Baragolai collieries of Makum coal fields, in Assam, India, has been investigated with respect to time at different temperatures. Leaching at 25 °C up to 120 h showed that the physicochemical characteristics viz., conductivity, acidity, TDS, and SO4-2 ions, increase with the increase in time of leaching. The generation of highly acidic leachates at 1−1.5 h (pH 2.5) and 2 h (pH 3.1) for Ledo and Baragolai coals was observed, respectively. However, it remains stable up to 120 h. The concentration of major, minor, and trace elements and their mobility along with the loss of pyritic sulfur or depyritization were also reported. The release of metals (Fe, Mg, Bi, Al, V, Cu, Cd, Ni, Pb, and Mn) above the regulatory levels during leaching was evidenced. Depyritization was found to be 79.8, 82.9, 84.7, and 89.7% for Ledo and 70.49, 73.77, 75.41, and 77.05% for Baragolai coal at 15, 25, 35, and 45 °C, respectively. A pseudo-first-order kinetic relationship with activation energies (E) of 8.1477 and 5.2378 kJ mol-1 with frequency factors (A) of 8.8405 × 10-4 and 2.6494 × 10-4 dm3 mol-1 s-1 was attributed to aqueous oxidation of pyrites in Ledo and Baragolai coals, respectively. The X-ray diffraction analysis and Fourier transform infrared spectroscopy patterns indicate the presence of illite, α-quartz, hematite, chlorite, rutile, calcite, and albite as mineral phases. This investigation justifies the formation of acid mine drainage by weathering of pyrites from coal during the mining of high sulfur Makum coal fields, in Assam, India, and demonstrates one of the possible routes for its formation.

Minerals Transformations in Northeastern Region Coals of India on Heat Treatment

Studies on transformations of minerals in Baragolai, Ledo, and Tipong coals of the Makum coalfield of the northeastern region of India on heat treatment in the presence of air at 350 and 850 °C have been carried out using XRD, FTIR, DTA, TGA, and DTG. XRD patterns of the above three coals show that the samples contain both amorphous and crystalline phases. The coal samples exhibit a number of peaks. The most dominant peaks in all the coal samples are due to quartz. The coal samples also exhibit very small peaks assigned to calcite, gypsum, pyrite, marcasite, and chlorite. The XRD patterns of the coal samples are found to change on heating in the presence of air until ash is prepared at 350 °C. These samples show some new peaks assigned to kaolinite, illite, and feldspar. These are present in raw coals too but could not be detected due to the presence of these minerals in small amounts in comparison to that of the amorphous material. The large amount of amorphous carbonaceous material possibly envelops the minerals which slowly get oxidized on heating in the presence of air at 350 °C resulting in an increase in the concentrations of the minerals kaolinite, illite, and feldspar. The XRD patterns of the 350 °C heated ash sample exhibit peaks due to quartz, calcite, and marcasite. Thus, these are not affected by heat treatment of coal in the presence of air at 350 °C. There was no peak present due to gypsum because the water of crystallization was lost. Some of the peaks observed in the raw coal and the ash produced at 350 °C were found to disappear in the ash prepared at 850 °C. The XRD patterns of ash prepared at 850 °C exhibit some new peaks due to iron oxide which might have been formed as a product of thermal transformation reactions of some phases present in the coal. The sample did not show peaks due to pyrite, marcasite, and calcite. Pyrite undergoes oxidation at 370 °C and marcasite at 430-480 °C forming iron oxide and sulfur dioxide. Calcite decomposes in the range of 675-750 °C yielding calcium oxide and carbon dioxide. The 850 °C heated ash sample also did not exhibit peaks due to kaolinite and illite. Kaolinite transforms into metakaolin at 550-600 °C, and illite undergoes dehydroxylation at 450-550 °C. Quartz is the dominant phase in the coal and its ash prepared at 350 and 850 °C, i.e., no change. This is expected as α-quartz is the best known most stable crystalline form of silica, and it transforms to another crystalline form, cristobalite, through an amorphous transition phase when heated above 1470 °C for a considerable time. The FTIR spectra of the raw coal samples, ash obtained at 350 °C, and ash prepared at 850 °C were recorded and compared. The general characteristics of the FTIR spectra of all the coal samples are almost similar. On comparison of the spectra, it was observed that on heating the coal samples in the presence of air all the stretching, bending bands due to coaly matter functional groups disappear. The FTIR peaks due to presence of different functional groups of minerals support the findings of XRD summarized above. Similarly the TGA, DTA, and DTG results support our XRD findings too as stated above.

Trace Elements in High-Sulfur Assam Coals from the Makum Coalfield in the Northeastern Region of India

The trace-element contents in several high-sulfur Assam coal samples from the Baragolai colliery of the Makum coalfield were estimated using inductively coupled plasma−atomic emission spectroscopy (ICP-AES). The coals are relatively rich in gallium (8−122 ppm) and poor in arsenic (0.04−0.24 ppm), boron (0.02−0.11 ppm), selenium (0.04−0.24 ppm), germanium (0.19−1.19 ppm), and barium (0.38−2.39 ppm), relative to most of the world coal. The contents of copper (9.86−30.35 ppm), manganese (15.27−63.81 ppm), antimony (0.22−1.19 ppm), tin (0.18−1.43 ppm), lead (5.06−24.13 ppm), and vanadium (5.92−64.29 ppm) are in the same range as those for world coal. The mode of occurrence of all the aforementioned trace elements present in these coals have been determined. Assam coals have the following trace elements: arsenic, boron, lead, and selenium of great concern; copper and vanadium of moderate concern; barium, germanium, and manganese of minor concern; and tin of concern but present in negligible concentration in c...

Effects of alkali treatment on ash and sulphur removal from Assam coal

The effects of leaching subbituminous coal samples from Boragolai and Ledo collieries of Makum coal field, Assam, India, with aqueous sodium hydroxide solution on removal of ash and sulphur, were investigated. Mild alkali treatment for relatively short period leads to removal of ash from the coal samples. Increase of alkali concentration and treatment time has negative effect on ash reduction due to formation and accumulation of insoluble sodium aluminosilicate. Boragolai coal is less demineralized than Ledo coal and is attributed to presence of higher amount of alkali-soluble silica and alumina. Alkali treatment leads to over 70% removal of the inorganic sulphur in the coal samples. Desulphurization increases with increase in alkali concentration and treatment time.

Demineralization of subbituminous high sulphur coal using mineral acids

The effect of HCl, HNO 3 and H 2SO 4 at different concentrations on demineralization of high sulphur coal from Boragolai and Ledo colliery of Makum Coalfield, Assam, India was investigated at ambient and 95 °C. The acids, depending on type and concentration, can reduce the mineral matter in the range of 22.6–32.0% at ambient temperature and 24.8–40.1% at 95 °C from Boragolai coal. The acids at 10% concentration level can remove 7.6–22.6% and 13.6–38.6% sulphur from Boragolai coal at ambient and 95 °C, respectively. HNO 3 leads to maximum and H 2SO 4 minimum desulphurization of the coal samples. The low desulphurization ability of H 2SO 4 is attributed to high viscosity of the acid at ambient temperature and sulphonation of the coal samples. The demineralization and desulphurization of Ledo coal with the acids are relatively low and is attributed to its higher hydrophobicity.

Demineralization and Desulfurization of High-Sulfur Assam Coal with Alkali Treatment

Demineralization and desulfurization of high-sulfur coal from Assam (Makum coalfield), India, was investigated using aqueous solutions of sodium hydroxide, potassium hydroxide, and their mixtures (...

Effect of leaching high sulphur subbituminous coal by potassium hydroxide and acid on removal of mineral matter and sulphur ☆

The effect of leaching coal samples from Boragolai and Ledo collieries of Makum coal fields, Assam, situated in north eastern region of India with potassium hydroxide solution alone at 95 and 150 °C as well as followed by mild acid on demineralization and desulphurization was investigated. Potassium hydroxide alone leads to 2–19% demineralization and 16–30% desulphurization of the coal samples at 95 °C. Demineralization of the coals decreases to 1–11 and desulphurization increases to 26–43% on increasing the temperature to 150 °C. The decrease in demineralization is due to increased precipitation of potassium aluminosilicates. Demineralization of the coal may be enhanced to 28–45 and 39–68% and desulphurization to 22–35 and 34–53% at 95 and 150 °C, respectively, by leaching the potassium hydroxide treated coal with 10% hydrochloric acid which decomposes the potassium aluminosilicates to certain extent. The treatment almost completely remove the inorganic and up to 37% organic sulphur from the coal samples.