Bimala P. Baruah

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.

Water-soluble organic compounds (WSOCs) in PM 2.5 and PM 10 at a subtropical site of India

PM2.5 and PM10 samples collected at a suburban site of northeastern part of India have been analysed for particle mass, total carbon (TC), water-soluble total carbon (WSTC), water-soluble organic carbon (WSOC), water-soluble inorganic carbon (WSIC), organic acids (formic, acetic, proponoic and oxalic acids) along with inorganic ions (NO3−, SO42− and NH4−). Most of the PM10 consists of PM2.5 in the present site (ratio 54–74%). WSTC content in PM2.5 and PM10 corresponds to 21% and 16%, respectively, of their total particle masses. Thermo gravimetric analysis showed the presence of humic-like substances (16–22%) in particulate samples. Domestic heating and stagnant atmospheric conditions enhanced the levels of these carbonaceous compounds in PM2.5 and PM10 in winter. Qualitative estimation of various functional groups by Fourier transform infrared (FTIR) analysis indicates the presence of carboxylic, hydroxyl, aliphatic and aromatic hydrocarbons, amines and sulphurous compounds in these aerosols. Absolute principal component analysis applied on the aerosol data resolves four factors. These factors are associated with carbonaceous aerosols released from combustion of coal and wood, secondary inorganic and organic aerosols and water-soluble inorganic fraction

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.

Structural Parameters of Perhydrous Indian Coals

Higher hydrogen content of perhydrous coals exhibits a different composition and physicochemical properties in comparison with normal coals. In the present investigation, a structural study of perhydrous coals and coke was done using FTIR and HPLC data. These coals have high volatile matter with high-calorific values and low-moisture content. The structural study suggests that the major structural units of these coals are simple phenols with para-alkyl substituted derivatives. They have high alkyl substitution groups and low aromatic compounds. The structural studies reveal that these coals contain high amounts of low-molecular weight PAH compounds with 1-2 ring structures. These 1-2 ring structures have high H/C ratios as compared to large ring polyaromatic hydrocarbons (PAHs). It may also be one of the reasons for high H/C ratios in these coals. The alkyl groups contribute significantly to their high volatile matter (VM) contents. The presence of alcoholic groups found in pyrolytic products may also be due to the conversion of catechol-like structures to those of cresols. Coal properties, such as moisture, VM, H/C ratio, and CV, do not correlate with the rank as normally classified. A definite relationship has been found between the characteristics of these coals, char/cokes, and aromatic characters (f a , Har).

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.

Comparative study of thermal properties of bio-coal from aromatic spent with low rank sub-bituminous coals.

In present investigation, biocoal samples were prepared from aromatic plant waste of two perennial grasses, i.e. Cymbopogon flexuosus (lemongrass) and Vetiveria zizanioides (khus) after oil extraction, root of Rosa damascene (rose), bark of Eucalyptus citriodora. These biocoals were characterized by proximate, ultimate, metal, thermogravimetric analysis (TGA), Fourier Transform Infra Red (FTIR) spectroscopy and ash analyses. Activation energies, initial temperature of devolatilization, maximum rate of weight loss (Rmax), fouling, slagging and alkali index were determined on the basis of TGA and ash analysis. These biocoals have good calorific values. There is possibility of slagging and fouling in combustion system but it is not severe. Owing to their similar fuel properties as high sulphur sub-bituminous coal, they can be good candidates for co-firing. Blending of these biocoals with high sulphur coals will serve dual purpose as (i) alternate fuel, and (ii) reduction in SO2 emission.

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.

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.

Characterizations of Humic Acid Isolated from Coals of Two Nagaland Coalfields of India in Relation to their Origin

In the present study, the humic acid isolated from coals of two coalfields of Nagaland, India has been characterized by Ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), thermal analysis (TGA-DTA), and scanning electron microscopy (SEM) in relation to their origin. The humic acid reveals a high degree of humification with predominantly aromatic content, which is considered to be type-A humic acid.

Chemical kinetics of oxidative desulphurisation of Indian coals

The high sulphur coals of North Eastern region (NER) of India have 70%–80% of organic sulphur affixed to the coal structure due to the influence of marine sources during its formation. The per-acid (H2O2/HCOOH) medium is used here to see its effect in removing the organic sulphur from this coal. The rate of the oxidation was studied for 60, 120, 180 and 240 minutes at room temperature. The oxidised coals are also extracted with dimethyl formamide and treated with alkali. Total sulphur removal has been found to be 38.09 wt% during oxidation while, alkali treatments after the oxidation showed 46.5 wt% desulphurisation. The kinetic studies on this removal of organic sulphur from coal showed that the reaction is of second order and found to be faster in nature. The FTIR and physico-chemical properties of oxidised, alkali treated coals are also reported.