Assam Coal Research Articles

Geochemical variations of major, trace, rare earth elements in some Gondwana and Eocene coals of India with a comparison of their germanium, lithium, and mercury content

The geochemistry of major, trace, rare earth elements (REEs), with special reference to Ge, Li, and Hg in selected Gondwana and Eocene coals, has been studied. Major oxide and trace element ratios have been utilised to compare the tectonic setting, provenance of source rocks, and paleoweathering conditions that prevailed the during formation of these coals. The Gondwana coals have a higher mean mercury and ash content (244.5 μg/kg and 17.2 %, respectively) than the Eocene coals (142.1 μg/kg, 8.9 % respectively). The major oxides, SiO2, Fe2O3, and Al2O3, in Gondwana and Eocene coals, are enriched relative to the upper continental crust (UCC), Chinese and American coals. The UCC normalized trace element concentration coefficients of the Gondwana and Eocene coals show enrichment in Ge, Se, Th, Co, Mo, Sn, W, and Li. The mean Ge and Li concentrations (mg/kg) in Gondwana (106.7, 154.7) and Eocene (120.0, 252.6) exceed the corresponding values in world coal (2.2, and 12). The Rajmahal coals have the highest mean Ge concentration (168.8 mg/kg) among the Gondwana coals while Eocene coals from East Jaintia Hills have the highest mean value (343.7 mg/kg). The Gondwana coals have a higher mean As concentration (3.5 mg/kg) in comparison to the Eocene coals (1.9 mg/kg). The mean of the rare earth elements in Gondwana (24.1 mg/kg) is higher than that in Eocene coals (11.3 mg/kg) and these values are less than the World coals (68.5 mg/kg). Both the Gondwana and Eocene coals are enriched in light rare earth elements (LREEs). However, among the Eocene coals, the Meghalayan coals show REE enrichment in comparison to Assam coals. Both the Gondwana and Eocene coals were formed in warm and humid climates under oxic conditions with moderate weathering of the source rocks.

Mineralogical Control on Ash Fusion Temperatures of some High Sulfur Indian coals by oxides generated during combustion

ABSTRACT Four different sulfur-containing coals (from low to high) (A, B, C and D) obtained from three different geographical locations of the North Eastern Region (NER) of India were studied for the control of ash fusion temperature (AFT) by oxides, generated via in-situ process, during coal combustion. The Meghalaya (B and C) and Nagaland (D) coals were found to contain high ash content in comparison to that of Assam coal (A). Meghalaya coals (B and C) were found to be better as they produce ash in greater quantity of acidic components (Al2O3 and SiO2) and lower amount of basic components (Fe, Ca, Mg, Na and K oxides). This results in lower value of slagging and fouling indices of the Meghalaya coals, and hence increases their AFT. X-ray diffraction studies (XRD) and atomic absorption spectroscopy (AAS) were also performed for qualitative mineralogy and elemental analyses. Statistical tools. such as correlation coefficient and principal component analysis (PCA), confirmed that the low-to-medium AFTs of the coal samples are due to the presence of various fluxing agents (such as K, Fe, Mg and Ca). Ternary phase diagram indicates the fact that the Meghalaya coals (B and C) have higher amount of Aℓ2O3 with lower Fe2O3 contents, resulting in increased fusion temperature.

Acidophilic biodesulphurization of calcined pet coke and coal samples in iron and iron-free leaching media

Mineralogically distinct coal samples respond differently to microbial attack. In the present study, a mixed meso-acidophilic bacterial consortium predominantly comprising of Acidithiobacillus ferrooxidans strain was investigated for its biodesulphurization abilities for three distinct sulphur bearing samples (Goa CPC, Rajasthan Lignite, Assam Coal) of Indian origin in iron (9K+) and iron-free (9K−) media. A media devoid of Fe (II) iron was more effective for sulphur removal with maximum desulphurization of 45.19% for Assam coal followed by 36.8% for Rajasthan Lignite and 23.38% for CPC respectively. The proximate analysis, FTIR patterns and XRD analysis of the samples provided better insights into understanding the mineralogical and compositional changes in the coal matrix. Owing to the higher efficiency, Assam coal was additionally subjected to further optimization studies and characterization of the treated coal through TGA. The study indicated that the gross calorific values for all the samples increased following microbial treatment in 9K− media thereby providing a scope for further scale-up studies.

Studies on removal of arsenic in contaminated water by using Assam coal

Studies on removal of arsenic in contaminated water by using Assam coal

An investigation on the heterogeneous nature of mineral matters in Assam (India) coal by CCSEM technique

This is a very first preliminary investigation on the distribution of heterogeneous nature of mineral matter in one of the industrially important Assam (India) pulverized coal using computer-controlled scanning electron microscopy (CCSEM). The results show that clay minerals, quartz, pyrite, and pyrrhotite form the bulk of the mineral matter. Minor minerals, such as calcite, dolomite, ankerite, barite, oxidized pyrrhotite, and gypsum, are also observed in the sample. The particle size distribution (PSD) of the included minerals is generally observed to be finer than that of the excluded ones in the coal. As a consequence, the coal rich in included minerals has more small mineral particles, which may affect its reactivity. Regarding the association of individual mineral species, the proportion of included to excluded is found to be higher in major cases. With regard to the modes of occurrence of major inorganic elements, it is found that Si mostly occurs as quartz and clay minerals, while Al mostly occurs as silicate minerals. Fe is primarily present as iron sulfides, iron oxide, and Fe–Al-silicate. S is partitioned into iron sulfides and gypsum. Most Ca occurs as carbonates and gypsum, with a minor fraction associated with clay minerals. Mg is mainly present as dolomite and clay minerals, with a very minor fraction present as ankerite. The majority of alkali elements are associated with aluminosilicates. P is mostly associated with kaolinite and/or present as more complex compounds containing Al, Si, and other elements as apatite is found to be absent in the coal studied. Ti is mainly present as rutile and kaolinite.

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.

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.

Laser-Induced Fluorescence Spectra of Some High-Sulphur Assam Coals, India

Coal is a carbonaceous material of sedimentary origin, whichoccurs as an intimate mixture of complex organic mass andinorganic matter. The product of partial decomposition of livingmaterials laid down in sediments on death makes coal verycomplex. The use of laser radiation as an excitation source hasa major impact on the study of the complex material, such ascoal.

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.

Studies on the Reaction Engineering of Combustion and Carbonization of Indian Coals, Depolymerized Coals and Residual Coal Obtained After Organo-Refining

Kinetics of the combustion of original and depolymerized Assam, Raniganj and Talcher coals and Neyveli lignite has been studied under non-isothermal conditions in a thermogravimetric analysis apparatus by employing Coats and Redfern kinetic modeling. Depolymerization of coals through acidic phenoation was found to improve the reactivity of the coals for combustion. Similarly, depolymerization reaction also led to the improvement in the pyrolysis behavior of coals. The order and activation energy of the reactions have been reported. The kinetics studies of the residual coal obtained after the successive solvent extraction of coal has also been studied. The present studies on the reaction engineering of coal conversion and utilization technologies may help in the reactor design and in the process development engineering.

05/01395 Extent of lead in high sulphur Assam coals: Baruah, M. K. et al. Fuel Processing Technology, 2005, 86, (6), 731–734

05/01395 Extent of lead in high sulphur Assam coals: Baruah, M. K. et al. Fuel Processing Technology, 2005, 86, (6), 731–734

Biological elimination of sulphur from high sulphur coal by Aspergillus-like fungi

An attempt was made to desulphurise the coal from North Eastern coalfields of Assam in India, characterized by high total concentration of sulphur (2.13%) and high concentration of organic sulphur (1.21%) by using the indigenous fungal culture( Aspergillus sp.) isolated from coal. While using this natural fungal strain, the best results were obtained when desulphurisation was carried out on coal sample of size of −74 μm, making 2 wt% of extraction mixture for a process duration of 10 days. Final total sulphur content of the desulphurised coal was 0.47%. An elimination, as high as, 70–80% of total sulphur demonstrated the convenience of using the indigenous culture of Aspergillus sp. for desulphurisation. The results advocate an attack of the fungal strain on the organic sulphur component as the sulphur present in Assam coal mainly exist in organic form. In reference to immediate analyses of the coal, it was observed that the ash content was lowered due to acidic conditions imposed by the experimental process.

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...

Extent of lead in high sulphur Assam coals

This study has been undertaken to understand the precise nature of association of lead in high sulphur Assam coal. Sequential extraction of lead with ammonium acetate, HCl and RuCl 3 solutions have been carried out. RuCl 3 has been used as a suitable reagent for the extraction of lead. It is found that treatment of sample with CCl 4 increases the extraction of lead by RuCl 3 solution. The amount of lead in the coal studied varies between 43.2 and 50.4ppm. It has been found that lead is predominantly occurring in coals in association with organic matter and needs concerted attention to understand its bio-availability. The chemical principles involved therein are also discussed.

04/01178 Distribution and nature of organic/mineral bound elements in Assam coals, India: Baruah, M. K. et al. Fuel, 2003, 82, (14), 1783–1791

04/01178 Distribution and nature of organic/mineral bound elements in Assam coals, India: Baruah, M. K. et al. Fuel, 2003, 82, (14), 1783–1791

04/00613 Demineralization and desulfurization of high-sulfur Assam coal with alkali treatment: Mukherjee, S. Energy & Fuels, 2003, 17, (3), 559–564

Coal desulfurization and deashing are the common challenges that the coal industry worldwide is facing. A new technique is presented in this paper using high voltage pulse (HVP) selective breakdown of mineral matter that exhibits higher electric conductivity/permittivity than coal, followed by size-based separation to reject the pyritic sulfur-bearing and ash-bearing mineral matter. Part 1 of this study demonstrates HVP selective breakdown of mineral matter, and Part 2 reports the optimization of the HVP treatment to minimize coal loss during the coal desulfurization and deashing process. Two coal samples, one bituminous and one anthracite, were collected from two coal mines in China and used to assess the viability of this new HVP technique for the coal industry. In the paired-particle tests with one low-density (<1.47 RD) particle and one high-density (greater than1.77 RD) particle in each batch subjected to one HVP discharge, over 75% of probabilities were observed that the high-density particles broken and the low-density particles remained intact, resulting in distinct product size distributions of the two density groups. In the multi-particle tests to treat the as-received Coal B sample without prior density-fractionation, the particles remaining on the parent size fraction (19–26.5 mm feed) after HVP treatment contained 0.49% sulfur, 13.4% ash, and 87.6% carbon, changing from 1.92% sulfur, 30.1% ash, and 78.5% carbon contents in the feed. The HVP treatment with <1 kWh/t specific energy (spark) resulted in 89.8% sulfur, 82.2% ash, and 55.6% carbon reporting to the −19 mm stream.

04/00605 Organic affinity of silver in subbituminous Assam coals: Baruah, M. K. et al. Fuel, 2003, 82, (10), 1291–1293

04/00605 Organic affinity of silver in subbituminous Assam coals: Baruah, M. K. et al. Fuel, 2003, 82, (10), 1291–1293

Microbial desulfurization of different coals.

Coal is the most important nonrenewable energy source of fossil origin. It is also the most common fuel in thermal power plants. However, during coal incineration in power plants, high sulfur content of coal poses serious environmental problems owing to sulfur dioxide emission. We studied the application of microbial methods for removal of sulfur from three types of high sulfur coals-two samples collected from Assam and Rajasthan in India and one from Libiaz, Poland. These coal samples were desulfurized using indigenous Acidithiobacillus sp. After investigation of the effect of various parameters, the conditions optimized for the maximum removal of total sulfur (91.87% for lignite, 63.13% for Polish coal, and only 9.44% for Assam coal) were as follows: initial pH of 1.5 (2.5 in the case of Assam coal), particle size of 45 micro, pulp density of 2% (w/v), incubation period of 30 d at -35 degrees C in presence of 44.2 g/L of ferrous sulfate in the media with shaking at 140 rpm. Poor removal of sulfur in the case of Assam coal was owing to extensive precipitation of jarosites. In addition, the sulfur in Assam coal is mostly found in organic form, which is difficult to remove with Acidithiobacillus sp. The removal of sulfur from the three coal samples was demonstrated with photomicrographic studies.

Correlation for estimating solubility of oxidized coal in ethanolamine

The effect of reaction time in aerial oxidation of Assam coal on variation in moisture with wt% solubility in ethanolamine is presented. The effects of variation in helium density, specific energy, carboxyl acidity, and acid equivalent values on wt% solubilities of oxidized coal in ethanolamine are also highlighted. It is observed that progressive increase of oxidation time caused an increase in the moisture content and wt% solubility of oxidized coal in ethanolamine. The solubility of oxidized coal is found to correlate linearly with helium density, specific energy, acid equivalents, and carboxyl acidity on univariate basis with correlation coefficients of 0.88, 0.996, 0.992, and 0.995, respectively.