This paper examines the source rock potential and pore structural framework of Lower Permian shales belonging to Barren Measures and Barakar Formations of Jharia basin, eastern India. The Jharia ...basin contains prolific coking-coal reserves and, consequently, the organic-matter in this basin tends to be mature. Open system pyrolysis analysis reveals that the Barakar Formation shales are thermally more mature and organic-rich than the Barren Measures Formation. Analysis reveals that shales of the Barren Measures possess “fair” to “good” oil generation potential. The more mature shales of the Barakar Formation are gas prone. Detailed pore scale distribution and fractal metrics determined by low-pressure N
2
gas adsorption are observed to be higher for the Barren Measures Formation than the more mature and organically rich Barakar Formation shales possibly due to the inability of N
2
gas to access the ultrafine components of the complex pores in the Barakar Formation shales. Substantial concentration of pores, organic-rich character, and thermal maturity levels indicates that the studied horizons have unconventional source rock properties.
The Rock-Eval technique has been conventionally used for source-rock analysis. In this work we document the importance of Rock-Eval S4 oxidation graphics and S4-
T
peak
as indicators for coal ...reactivity and thermal maturity. Two non-coking coals (lower maturity), one coking coal (higher maturity), and one jhama (intrusion-induced metamorphosed coal), were collected and studied in terms of their reactivity and combustion properties. Our results indicate that Rock-Eval S4-
T
peak
can be convincingly used to decipher the thermal maturity level of a coal sample. The two non-coking coals owing to their higher reactivity and corresponding lower activation energies, combusted at lower temperatures, almost entirely below 650 °C, and showed lower Rock-Eval S4-
T
peak
. The coking coal sample on the other hand due to its higher thermal maturity level and lower reactivity, combusted at higher temperature, showing higher S4-
T
peak
. While the S2
T
max
showed higher maturity for the coking coal than the jhama, the S4 oxidation graphics and S4-
T
peak
clearly revealed higher thermal maturity of the jhama relative to the other samples. With increasing sample weights, the S4CO
2
curves were observed to be broader, and consequently the S4-
T
peak
was observed to be higher and erroneous, the errors being more for the more-mature coking coal and jhama. With lowering sample weights, the curves became tighter and the S4-
T
peak
became lower and more precise. Parameters calculated using TG-DTG-DSC were observed to complement the data from Rock-Eval oxidation-stage, and revealed higher maturity, less reactivity, higher temperatures of ignition and burn out for the jhama, followed by the coking coal. Our results also indicate the suitability of applying Rock-Eval for combustion-profiling of coals, beyond source-rock characterization and CBM reservoir analysis.
Soil pollution due to coal mining and its associative activities has become a serious environmental concern in India. The by-products of coal mining are often disposed directly to the bare lands, ...significantly altering the characteristics of soil up to a considerable extent. These stacks of discarded rock wastes under the influence of various geological agents, viz., wind, running water, etc., undergo leaching and release trace metals into the soil. Consequently, different environmental, geomorphological, and health problems arise. Various remediation techniques are available for soil pollution, which are classified as conventional techniques like soil replacement, thermal desorption, chemical leaching and fixation, etc. and biological techniques, which are bioremediation and phytoremediation. However, the commercial application of these remediation techniques has not gained popularity due to inefficient technologies, unawareness and costlier methods. Recently application of rock dust has emerged as a potential tool for remediating and remineralising the mine soils along with the management of discarded solid waste rocks. This review details the deteriorating effects of coal mining and allied activities, especially in the case of open cast mining, on the physical, chemical and biological characteristics of soil, discusses the different techniques available for remediation of contaminated soil, and how rock dust can be gainfully applied for soil remediation and remineralisation in India and worldwide. Research gaps and conflicts in the utilisation of rock dust have also been presented.
Research Highlights
Soil quality deterioration and contamination in and around coal mining areas.
Available remediation techniques to reduce soil contamination
Emergence of rock dust technique for soil remediation and remineralisation
Benefits of rock dust application for other environmental issues
The Rock-Eval pyrolysis-stage derived parameters such as free hydrocarbons (S1), heavier pyrolysis-hydrocarbons (S2), pyrolyzable carbon (PC) and pyrolysis Tmax (from S2 curve) have received ...considerable interest for source-rock screening and thermal maturity assessment. On the other hand, the Rock-Eval oxidation-stage S4CO2 curve, which gives the amount of residual carbon (RC), only recently has received some interest. While the pyrolysis-stage S2 temperature-peak (Tmax) is conventionally used as a maturity proxy, in this work we show that the temperature-peak of S4CO2 curve (S4Tmax) can also be used as a thermal maturity proxy for shales. For overmature and low-TOC shale samples, showing asymmetric S2 shape and concomitantly producing doubtful Tmax, the S4 curves showed symmetric nature and consequently the S4Tmax was observed to be a reliable thermal maturity estimate. While the S4Tmax clearly resolved immature and overmature shales, for the early mature and peak mature shales the S4Tmax showed overlapping values. S4Tmax of pre-pyrolyzed and pyrolyzed masses showed good positive correlation with differential scanning calorimetry temperature-peak (DSCTpeak), and consequently indicated its applicability as a thermal maturity proxy. When early mature pre-pyrolyzed samples were directly analyzed using the Rock-Eval oxidation stage, the S4 curves showed formation of two sub-peaks, and consequently the Tmax was observed to decrease. It is recommended that analysts and interpreters should thoroughly cross-check S2 curves before reporting data, and in case of asymmetric or unreliable S2 curves, the S4Tmax can be used as a maturity proxy.
•Importance of Rock-Eval oxidation stage.•S4Tpeak as a thermal maturity proxy for shales.•Critical monitoring of Rock-Eval S2 curves.
Trace element pollution of soils surrounding coal-mining areas affects the health of local communities. The increasing coal-mining and associated activities in the Raniganj basin (east India) have ...led to increased soil concentration of certain trace elements. To quantify the elevated trace element (TE) concentrations in the soil surrounding coal-mining areas, 83 surface soil, coal, and shale samples were collected from open-cast mining areas of the eastern Raniganj basin. The soils present are sandy silt, silty sand, and silty in nature, but almost no clay. They are acidic (pH = 4.3) to slightly alkaline (pH = 7.9) with a mean electrical conductivity (EC) of 340.45 µS/cm and a mean total organic carbon (TOC) of 1.80%. The northern and western parts of the study area were found to be highly polluted by certain metallic trace elements. The relevant environmental indices, geoaccumulation index (I
geo
), contamination factors (CF), enrichment factors (EF), and pollution load index (PLI) were calculated and assessed. Analysis revealed that Cr was highly enriched in these soil samples, followed by Pb, Co, Cu, Cd, Fe, Ni, Mn, Zn, As, and Al. Geostatistical analyses (correlation coefficients and principal component analysis) indicated that the occurrence of some trace elements (Al, Cd, Co, Cu, Fe, Mn, Ni, and Zn) is most likely linked to the various coal-mining operations in the study area. However, the anomalous Cr and Pb distributions are likely influenced by other anthropogenic, mainly industrial, inputs besides coal mining. These results justify the adoption of rigorous soil monitoring programs in the vicinity of coal-mining areas, to identify pollution hotspots and to develop strategies to reduce or mitigate such environmentally damaging pollution.
Rock-Eval S2 and S4 curves are commonly used to interpret active source rocks. In this work we report the formation of unusual, uneven, spiky S2 pyrograms from Rock-Eval of manually isolated vitrain ...bands from Mvb and Lvb coals. The spikes and unevenness in the S2 curves for coking-vitrains are interpreted to form from the release of gases or bubbles bursting from the melt during the pyrolysis stage. Crucible swelling numbers measured for these vitrains were observed to be 3 to 4 times higher than the parent coal from which they were separated. Field Emission Scanning Electron Microscope (FE-SEM) images also document formation of three dimensional bubbles due to bursting of gaseous bubbles, in the pyrolysis-residue (using Rock-Eval) of coking-vitrains. For bulk coal samples and vitrains isolated from HvbA coals, the S2 pyrograms were observed to be smooth. At higher sample weights, the formation of spikes for the vitrains from Mvb and Lvb was observed to increase, irrespective of the heating-rates used, owing to the release of greater amounts of gases or bubbles bursting from the melt. The results indicate the importance of cross-examining S2 pyrograms as it offers clues towards the behavior of coals during pyrolysis, and for better interpretation of results.
•Pitfalls for interpreting S2 pyrograms.•Melting during pyrolysis forms gas bubbles, the release of which form spikey S2.•Care needed for comparison of behavior for sample mass as well as composition and rank.
Vitrain is one of the most important lithotype for the end utilization of humic coals in relevant industries. In this work, we examine the thermal, structural and pyrolysis properties of vitrains, ...manually isolated from coals of three distinct thermal maturity levels (rank). The high volatile bituminous (HvbA) vitrain showed highest moisture content and reactivity during combustion, while showing least Rock-Eval S2
T
max
and S4
T
peak
. On the other hand, the low volatile (Lvb) sample showed properties exact opposite to that of the HvbA sample. Thus, the rank of the vitrains was observed to directly control their behaviour. Owing to their inherently lower ash content, all the vitrains during thermogravimetric analysis developed smooth thermograms, indicating easy burning. Interlayer spacing (d
002
), obtained from XRD displayed a strong decrease with increasing coal rank, indicating formation of condensed stacking structures with increasing rank. On the other hand, other XRD parameters, viz., the crystallite height (
L
c
) and the crystallite diameter (
L
a
) were not correlated with the rank of the samples. Rock-Eval S2 pyrograms depicted distinctive responses for the vitrains. While smooth curves were observed for the HvbA vitrain, the pyrograms showed unevenness and spikes for the Mvb and Lvb vitrains. We interpret these spikes or ruggedness to be caused due to melt formation during pyrolysis of Lvb and Mvb vitrains, and concomitant gas/bubble-bursting. We back our results with distinctive observations from the field emission scanning electron microscope (FE-SEM) of the pyrolysis-residues of the vitrains. We interpret that the distinctive S2 signatures shown by coals can be useful in predicting their end usage.
Thermal and chemical properties of coals, and the lithotypes they contain, provide useful insight to their combustion and reaction behaviors. Analysis of thermal properties, proximate parameters, ...Rock-Eval signatures, and petrographic characteristics of vitrain, fusain lithotypes, and bulk coal samples of distinct ranks from Raniganj (high volatile bituminous A rank, HvbA) and Jharia (medium volatile bituminous rank, Mvb) basins (India) reveal contrasting features. The HvbA bulk coal is identified as the most reactive. HvbA and Mvb vitrains display comparable reactivities despite their distinct thermal maturities. Mvb vitrain generates spiky pyrograms, due to melt formation and bubble bursting typical of coking vitrains. Mvb fusian is more prone to self-heating, being characterized by an exothermic thermogram peak due to its greater propensity to adsorb oxygen. In contrast, HvbA fusain, with higher VM and ash, displays least reactivity. These features mean that Mvb coals require higher temperatures for ignition and consume more energy than HvbA coals. Multi-heating-rate Rock-Eval S2 pyrograms show excellent Arrhenius equation simulation fits for the HvbA and Mvb bulk coals and lithotypes, enabling determination of activation energies (E) and pre-exponential factors (A). Distinctive E and A values of the HvbA bulk coal are a consequence of its high liptinite content.
Cyclones and heavy rainfalls are the main reasons for incessant environmental aggravation in the coastal regions and the distribution of pollutants from the contaminated terrestrial areas to the ...offshore regions. Twenty-five surface sediment samples were collected off Kameswaram, SE coast of India, and assessed for their geochemical and sedimentological characteristics post Cyclone Gaja. Sediment texture and various geochemical analyses were carried out to assess the metal distribution in the study area. Environmental impacts caused by heavy metal contamination in the marine sediments were assessed using different sediment pollution indices and it was found that metals such as Cu, Zn, Ni, and Co were moderately contaminated. Fe and Cr were uncontaminated to moderately contaminated, and Mn fall under the uncontaminated category. Multivariate statistical analyses revealed that the enrichment of organic-rich mud helps in entrapping the heavy metals, thus polluting the environment. Moreover, these metals were mainly derived from anthropogenic activities.
•Heavy metal content in marine sediments off Kameswaram was evaluated.•Environmental indices revealed metals of moderately contamination.•Anthropogenic sources influence metal contamination in marine sediments.•Multivariate statistics reveals the role of OM in metal distribution.
In this work, thermal behaviors of ten coal samples (across different thermal maturity levels) collected from five different open cast mines in the Jharia and Raniganj basins, India, were examined ...using differential scanning calorimeter (DSC), thermogravimetry (TG–DTG), Rock–Eval, and organo-petrographic techniques. Rank played a critical factor in controlling their thermal behavior, and with increasing coal rank the combustion parameters shifted towards higher temperatures. The oil-window mature non-coking coals were marked by least ignition and burnout temperatures, least DSC
T
peak
, DTG
T
peak
, and maximum reactivity. In contrast, the coking-coal samples of peak-oil window and condensate wet–gas window stages of maturity, because of their higher thermal maturity level and lower reactivity, required higher temperatures for combustion. Among the peak-oil window mature coking coals, one sample (C4) showed distinct lower combustion parameters relative to others, although vitrinite reflectance (
Ro
; %) and Rock–Eval pyrolysis
T
max
showed similar results as the other coals. This sample was marked by higher reactive maceral content. Highest combustion parameters and least reactivity were shown by the Jhama sample (baked coal), followed by the condensate wet–gas window mature coking coals. The Rock–Eval S4
T
peak
clearly resolved the coal samples with distinct maturities and complemented the results from TG–DTG–DSC thermograms. Our results indicate that Rock–Eval S4T
peak
can be used to decipher convincingly the thermal maturity level of coals.
