Binoy K. Saikia

Nano-mineralogical investigation of coal and fly ashes from coal-based captive power plant (India): an introduction of occupational health hazards.

Coal derived nano-particles has been received much concern recently around the world for their adverse effects on human health and the environment during their utilization. In this investigation the mineral matter present in some industrially important Indian coals and their ash samples are addressed. Coal and fly ash samples from the coal-based captive power plant in Meghalaya (India) were collected for different characterization and nano-mineralogy studies. An integrated application of advanced characterization techniques such as X-ray diffraction (XRD), High Resolution-Transmission Electron microscopy (HR-TEM)/(Energy Dispersive Spectroscopy) EDS/(selected-area diffraction pattern) SAED, Field Emission-Scanning Electron Microscopy (FE-SEM)/EDS analysis, and Mössbauer spectroscopy were used to know their extent of risks to the human health when present in coal and fly ash. The study has revealed that the coals contain mainly clay minerals, whilst glass fragments, spinel, quartz, and other minerals in lesser quantities were found to be present in the coal fly ash. Fly ash carbons were present as chars. Indian coal fly ash also found to contain nanominerals and ultrafine particles. The coal-fired power plants are observed to be the largest anthropogenic source of Hg emitted to the atmosphere and expected to increase its production in near future years. The Multi Walled Carbon Nano-Tubes (MWCNTs) are detected in our fly ashes, which contains residual carbonaceous matter responsible for the Hg capture/encapsulation. This detailed investigation on the inter-relationship between the minerals present in the samples and their ash components will also be useful for fulfilling the clean coal technology principles.

Effective removal of sulfur components from Brazilian power-coals by ultrasonication (40 kHz) in presence of H2O2

The present investigation reports a preliminary attempt of using ultrasonic energy (40kHz) to clean some low rank high sulfur Brazilian power-coal samples in presence of H2O2 solution. All types of sulfur components (i.e. pyritic, sulfate and organic) could be removed from the coal samples by this process. The raw and ultrasonicated coal samples were characterized by chemical analysis, Fourier Transformation Infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), focused ion beam (FIB), high-resolution transmission electron microscope (HR-TEM) with selected area electron diffraction (SAED) and/or microbeam diffraction (MBD), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectrometer (EDS), and Thermogravimetry (TG-DTG) techniques to evaluate the clean-coal quality. The FT-IR spectroscopic analysis demonstrated the formation of oxidized sulfur species (SO and -SO2) and their subsequent removals after ultrasonication. The XRD profiles supported the presence of mineral matters in the coals. The TG-DTG profiles of the beneficiated coals revealed their improved quality for using in thermal plants with better combustion efficiency.

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.

Ambient air quality and emission characteristics in and around a non-recovery type coke oven using high sulphur coal

The objective of this study is to determine the concentrations of gaseous species and aerosols in and around a non-recovery type coke making oven using high sulphur coals. In this paper, physico-chemical properties of the feed coal sample are reported along with the collection and measurement of the emitted gases (SO2, NO2, and NH3) and aerosol particles (PM2.5, PM10) during the coal carbonization in the oven. The coals used are from northeast India and they are high sulphur in nature. The concentrations of the gases e.g., SO2, NO2 and NH3 emitted are observed to be within the limit of National Ambient Air Quality Standard for 24h. The mean PM10 and PM2.5 concentrations are found to be 125.4 μg/m(3) and 48.6 μg/m(3) respectively, as measured during three days of coke oven operations. About 99% of the SO2 in flue gases is captured by using an alkali treatment during the coke oven operation. A Principal Component Analysis (PCA) after Centred Log Ratio (clr) transformation is also performed to know the positive and negative correlation among the coal properties and the emission parameters.

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) A. The average stacking height of the parallel aromatic layers and the average diameter of the aromatic layers are estimated to be 7.58 A and 4.86 A, 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 a d value of 4.42 A.

Nanominerals, fullerene aggregates, and hazardous elements in coal and coal combustion-generated aerosols: An environmental and toxicological assessment

Studies on coal-derived nanoparticles as well as nano-minerals are important in the context of the human health and the environment. The coal combustion-generated aerosols also affect human health and environmental quality aspects in any coal-fired station. In this study, the feed coals and their combustion-generated aerosols from coal-fired boilers of two tea industry facilities were investigated for the presence of nanoparticles/nano minerals, fullerene aggregates, and potentially hazardous elements (PHEs). The samples were characterized by using X-ray diffraction (XRD), Time-of-flight secondary ion mass spectroscopy (TOF-SIMS), High resolution-transmission electron microscopy/energy dispersive spectroscopy (HR-TEM/EDS) and Ultra Violet-visible spectroscopy (UV-Vis) to know their extent of environmental risks to the human health when present in coals and aerosols. The feed coals contain mainly clay minerals, whilst glass fragments, spinel, quartz, and other minerals occur in lesser quantities. The PM samples contain potentially hazardous elements (PHEs) like As, Pb, Cd and Hg. Enrichment factor of the trace elements in particulate matters (PMs) was calculated to determine their sources. The aerosol samples were also found to contain nanomaterials and ultrafine particles. The fullerene aggregates along with potentially hazardous elements were also detected in the aerosol samples. The cytotoxicity studies on the coal combustion-generated PM samples show their potential risk to the human health. This detailed investigation on the inter-relationship between the feed coals and their aerosol chemistry will be useful for understanding the extent of environmental hazards and related human health risk.

Formation of onion-like fullerene and chemically converted graphene-like nanosheets from low-quality coals: application in photocatalytic degradation of 2-nitrophenol

The formation of coal-derived carbon nanomaterials (CNMs) consisting of onion-like fullerene and chemically converted graphene-like nanosheets from the low-quality coals were observed during an oxidation-cum-extraction (OCE) process. Detailed characterization of these CNMs was examined by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), solid-state 13C NMR, UV-visible spectroscopy, and fluorescence spectroscopy (FL) techniques. The size of the coal-derived onion-like fullerenes was found to be in the size range of 5–20 nm and composed of 5–20 nm concentric shells. The outer diameter of the onion-like structures was estimated to be in the range of 3–15 nm. The presence of clusters of chemically converted graphene-like nanosheets was also observed in the coal-derived CNMs obtained by this novel OCE process. The method reported in this paper could be an inexpensive and simple chemical process for the preparation of CNMs from coals. These low-quality coal-derived CNMs were utilized as an efficient photocatalyst for the degradation of hazardous 2-nitrophenol under natural sunlight irradiation.

Petro-chemical Investigation of some Perhydrous Indian Coals

An attempt has been made to study the petro-chemical characteristics of some high sulphur sub-bituminous coal samples from Makum coalfield, Assam, India. The proximate and ultimate analyes were carried out and forms of sulphur were determined and their relationships with the Maceral constituents (vitrinite, liptinite, and inertinite) were investigated. The macerals (vitrinite+liptinite+inertinite) have significant relationships (R2>0.500) with volatile matter and carbon, whereas weak correlations were seen with rest of the physico-chemical characteristics of the coals. The study reveals that these coals are rich in vitrinites and sulphur and are aromatic in nature. These coals have good hydrocarbon potential.

X-ray (Radial Distribution Function, RDF) and FT-IR analysis of high sulphur Tirap (India) coal

AbstractA preliminary study has been performed on high sulphur coals from Tirap colliery of Assam, India, using X-ray (RDF) technique and FT-IR spectroscopy. 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 structures. The first maximum in the FRDA at R=0·133 nm relates to the C–C aliphatic bond (type C–CH=CH–C), and 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. 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).

Study on physico-chemical properties, mineral matters and leaching characteristics of some Indian coals and fly ash

Six high sulphur coal samples along with two fly ash samples were characterized by using X-ray diffraction (XRD), Energy Dispersive x-ray Fluorescence (EDXRF), Atomic Absorption Spectroscopy (AAS), Fourier Transform Infrared (FT-IR) and Scanning Electron Spectroscopy (SEM) techniques to interpret their mineral matters and inorganic constituents. The proximate, ultimate and sulfur analyses of the coal and fly ash samples were also performed to know their possible aspects of utilization. Significant amount of silicate/clay minerals along with other elements are found to be present in these coals and fly ash samples. The SEM micrographs showed the presence of pyrite and marcasite in different forms including clusters of pyrites in the coals. The leaching characteristics of the coal and fly ash samples showed the mobilization of some potentially hazardous elements (PHEs) from them. Mercury was found to be leached out with ~0.50 ppm from fly ash samples in water.