L. C. Ram

An appraisal of the potential use of fly ash for reclaiming coal mine spoil

Growing dependence on coal-fired power plants for electrical generation in many countries presents ongoing environmental challenges. Burning pulverized coal in thermal power plants (TPPs) generates large amounts of fly ash (FA) that must be disposed of or otherwise handled, in an environmentally-sound manner. A possible option for dealing with fly ash is to use it as an amendment for mine spoil or other damaged soil. It has been demonstrated through studies in India and other countries that FA alone or in combination with organic or inorganic materials can be used in a productive manner for reclamation of mine spoil. The characteristics of FA, including silt-sized particles, lighter materials with low bulk density (BD), higher water holding capacity, favorable pH and significant concentrations of many essential plant nutrients, make it a potentially favorable amendment for mine spoil reclamation. Studies have indicated that the application of FA has improved the physical, chemical and biological qualities of soil to which it is applied. The release of trace metals and soluble salts from FA could be a major limitation to its application. This is particularly true of fresh, un-weathered FA or acidic FA, although perhaps not a concern for weathered/pond ash or alkaline FA. Some potential contaminants, especially metals and other salt ions, could be immobilized and rendered biologically inert by the addition of certain inorganic and organic amendments. However, in view of the variability in the characteristics of FAs that are associated with location, feed coal, combustion conditions and other factors, the suitability of a particular FA for a specific soil/mine spoil needs to be critically evaluated before it is applied in order to maximize favorable results and eliminate unexpected consequences. FA generated in India tends to be mostly alkaline, with lower levels of trace elements than are often found in FAs from other countries. The concentrations of potential chemical stressors, predominantly metals, in Indian FAs are often less than established or proposed permissible limits and are thus better suited for soil application. A major logistic limitation to the use of FA could be the cost involved in transport of ash from production to utilization sites.

Soil quality index for evaluation of reclaimed coal mine spoil.

Success in the remediation of mine spoil depends largely on the selection of appropriate tree species. The impacts of remediation on mine soil quality cannot be sufficiently assessed by individual soil properties. However, combination of soil properties into an integrated soil quality index provides a more holistic status of reclamation potentials of tree species. Remediation potentials of four tree species (Acacia auriculiformis, Cassia siamea, Dalbergia sissoo, and Leucaena leucocephala) were studied on reclaimed coal mine overburden dumps of Jharia coalfield, Dhanbad, India. Soil samples were collected under the canopies of the tree species. Comparative studies on the properties of soils in the reclaimed and the reference sites showed improvements in soil quality parameters of the reclaimed site: coarse fraction (-20.4%), bulk density (-12.8%), water holding capacity (+0.92%), pH (+25.4%), EC (+2.9%), cation exchange capacity (+46.6%), organic carbon (+91.5%), N (+60.6%), P (+113%), K (+19.9%), Ca (+49.6%), Mg (+12.2%), Na (+19.6%), S (+46.7%), total polycyclic aromatic hydrocarbons (-71.4%), dehydrogenase activity (+197%), and microbial biomass carbon (+115%). Principal component analysis (PCA) was used to identify key mine soil quality indicators to develop a soil quality index (SQI). Selected indicators include: coarse fraction, pH, EC, soil organic carbon, P, Ca, S, and dehydrogenase activity. The indicator values were converted into a unitless score (0-1.00) and integrated into SQI. The calculated SQI was significantly (P<0.001) correlated with tree biomass and canopy cover. Reclaimed site has 52-93% higher SQI compared to the reference site. Higher SQI values were obtained for sites reclaimed with D.sissoo (+93.1%) and C.siamea (+86.4%).

Impacts of opencast coal mine and mine fire on the trace elements’ content of the surrounding soil vis-à-vis human health risk

Coal from its excavation, processing, and utilization creates environmental problems and health hazards. In these processes, the mobilization of potential organic and heavy metal contaminants affects the quality of soil and health of the inhabitants. Soil samples were collected from the nearby areas of an opencast coal mine (OCM) and a coal fire affected area (CFA) located in Jharia coalfield of Dhanbad, India. The control site was an abandoned land approximately 15 km away from the sources of contamination. These samples were analyzed for trace elements including Cr, V, Co, Ni, Cu, Zn, Ga, Rb, Zr, Ba, Th, and U. The soils of OCM were enriched with Cr and Ni and this is attributed to the mining activities in view of the absence of other sources of pollutants. In case of CFA, the soils were enriched with Cr, V, Ni, and Zn. However, the concentrations of Cr, Ni, and Zn in both the soils were well below the USEPA soil screening levels for human health risk assessment. The levels of Co and V exceeded the soil screening limits. Human exposure risks were evaluated for Co and V. The total intake of V concentration exceeded the EPAs reference dose, which may pose adverse health risks.

Evaluation of the co-application of fly ash and sewage sludge on soil biological and biochemical quality

Disposal of sewage sludge (SS) and fly ash (FA) is a multifaceted problem, which can affect environmental quality. FA has the potential to stabilize SS by reducing metal availability and making the SS suitable for application in the agricultural sector. An experiment was performed to evaluate soil biological quality changes with the combined amendment of SS and FA (fluidized bed combustion ash (FBCA) and lignite fly ash (LFA)). SS was amended with 0, 10, 30, 50 and 100%, (w/w) of FA, and then the FA–SS mixtures were incubated with red soil at 1:1 (v/v). Soil quality parameters such as pH, electrical conductivity, N, soil enzyme activities such as dehydrogenase (DHA), urease (URE), and catalase (CAT), and microbial biomass carbon (MBC) were evaluated at 20, 30, and 60 days of incubation. pH and EC increased with FA–SS dose; however, N decreased. DHA and URE were found to be increased with 10% LFA amendment; thereafter it decreased. However, URE increased up to 30% of FBCA. CAT and MBC increased with both FA amendments, even up to addition of 50% FA. Bioavailable Zn, Cu, and Co contents were decreased by the addition of FA. Principal component analysis showed that pH is the most influential factor. MBC appears to be a sensitive soil indicator for the effects that result from the addition of FA–SS. Phytotoxicity studies with Zea mays showed optimum performance at 30% FA. Addition of 10–30% FBCA or LFA to SS has a positive advantage on soil biological quality.

Potentially toxic elements in lignite and its combustion residues from a power plant

The presence of potentially toxic elements in lignite and coal is a matter of global concern during energy extraction from them. Accordingly, Barsingsar lignite from Rajasthan (India), a newly identified and currently exploited commercial source of energy, was evaluated for the presence of these elements and their fate during its combustion. Mobility of these elements in Barsingsar lignite and its ashes from a power plant (Bikaner-Nagaur region of Thar Desert, India) is presented in this paper. Kaolinite, quartz, and gypsum are the main minerals in lignite. Both the fly ash and bottom ash of lignite belong to class-F with SiO2 > Al2O3 > CaO > MgO. Both the ashes contain quartz, mullite, anhydrite, and albite. As, In, and Sr have higher concentration in the feed than the ashes. Compared to the feed lignite, Ba, Co, U, Cu, Cd, and Ni are enriched (10–5 times) in fly ash and Co, Pb, Li, Ga, Cd, and U in bottom ash (9–5 times). Earth crust–normalization pattern showed enrichment of Ga, U, B, Ag, Cd, and Se in the lignite; Li, Ba, Ga, B, Cu, Ag, Cd, Hg, Pb, and Se, in fly ash; and Li, Sr, Ga, U, B, Cu, Ag, Cd, Pb, and Se in bottom ash. Hg, Ag, Zn, Ni, Ba, and Se are possibly associated with pyrite. Leaching test by toxicity characteristic leaching procedure (TCLP) showed that except B all the elements are within the safe limits prescribed by Indian Standards.

The Mineralogical Characteristics of the Ashes Derived from the Combustion of Lignite, Coal Washery Rejects, and Mustard Stalk

With coal being the predominant and limited source of energy, extraction of energy from lignite, coal-washery rejects, and agro-wastes through combustion is being attempted globally. During combustion, minerals in the fuels undergo various transformations with corresponding impact on the process. Lignite fly ash, Jamadoba fly ash, and Kalptaru fly ash and corresponding fuels like lignite, coal-washery rejects, and mustard stalk from pulverized fuel, fluidized bed, and grate system of combustion at Neyveli, Jamadoba, Kalpataru, respectively, were characterized. Lignite has better fuel characteristics than washery rejects and mustard stalk. Of the major phases, SiO2, Al2O3, and CaO are common, besides Fe2O3 in lignite fly ash and Jamadoba fly ash, and K2O in Kalptaru fly ash. Among minor phases, MgO, Na2O, SO3, P2O5, and TiO2 are common, despite K2O in lignite fly ash and Jamadoba fly ash, and Fe2O3 in Kalptaru fly ash. Other minerals are mullite, silicates, sulphates, and carbonates of Ca in lignite fly ash; K-Al-Si species in Jamadoba fly ash; K/Ca-Al-Si species, and sulphates and carbonates of Ca in Kalptaru fly ash. These minerals are the product of mineralogical transformations, where source and composition of the fuels and operating conditions are crucial. Overall the combustion of lignite is more successful than that of washery rejects and mustard.

Status of Some Soil Trace Elements and Their Potential Human Health Risks Around a Coal Beneficiation Plant

The entire coal beneficiation process, starting from unloading the raw coal to the loading of processed coal, liberates particulate matter, which would ultimately settle on the soil at varying distances. This is likely to affect soil quality and possibly the health of the inhabitants. Soil samples collected from the sites of two coal beneficiation plants (CBPs), located in Dhanbad, India, and a control (CNT) site were analyzed for some trace elements like Cr, V, Co, Ni, Cu, Zn, Ga, Rb, Zr, Ba, Th, and U. The results showed that the CBP soils were enriched in Cr and Ni. In the absence of other sources of industrial pollutants, the enrichment of Cr and Ni is attributed to their input from the CBPs. However, the accumulation of Cr and Ni did not appear to reach health-risk levels, as the calculated lifetime human intake levels through different exposure pathways from the soil are within the USEPAs reference dose (RfD). Multivariate analyses like principal component analysis (PCA) and cluster analysis showed that the association between the trace elements in CBP soils is distinctly different than the CNT, thereby suggesting a different origin of some of the trace elements in CBP soils.

Fate of radionuclides present in Indian fly ashes on its application as soil ameliorant

Natural radioactivity depends primarily on the geological and geographical conditions, and appears at different levels in the soils. Coal contains various organic and inorganic substances including trace quantities of the naturally occurring radionuclides, which are of human health concern. The combustion of coals releases natural radioactive elements in the form of their oxides to the environment. In view of the current researches on fly ash (FA) applications as soil ameliorants, the present study deals with the presence of the natural radionuclides ((226)Ra, (232)Th and (40)K) in the coal ash and their mobilisation through the amendment of coal ash to the soil and crop produce. The study shows the variation in the content of radionuclides in soil, FA and crop produce depending on types of soil and FA, mobilisation of the radionuclides from soil/FA to the plant and interactions between radionuclides and soil, etc. The content of the radionuclides in the soil, FA and crop produce is within the permissible limits.

The Impact of Fly Ash Amendment on Soil Carbon

Soils play an important role in carbon cycling. An important approach to terrestrial carbon sequestration is to make use of currently underutilized and waste/degraded lands. The addition of fly ash can ameliorate the adverse conditions of wastelands through a variety of mechanisms, besides helping in stabilization of the soil carbon. Carbon mineralization and humification studies were carried out with soil, fly ash, and their mixtures. Organic monomers included for the humification reactions were resorcinol, p-hydroxybenzoic acid, L-glycine, and L-serine. Results showed that the humification pattern was higher for Associate Cement Companies (0.154 λ485) and Khaparkheda (0.119 λ485) fly ashes, than soil (0.110 λ485). In the carbon mineralization experiment, the soil carbon stabilization enzyme peroxidase activity was higher at soil amended with fly ash (0.052 μM/g/h) than soil alone (0.013 μM/g/h). The dissolved organic carbon was almost two times lower in fly ash amended soil, which revealed the adsorption of carbon in fly ash. The adsorption of soluble organic compounds on the solid surfaces is one of the mechanisms of fixing of soil organic carbon. The cumulative CO2 liberation due to plant litter addition was not affected by fly ash. To conclude, fly ash is abundantly available and is considered as a waste in many thermal power plants, which could be sustainably utilized in the agriculture and forestry sectors, both under arable and waste degraded land for enhancing terrestrial carbon sequestration, besides increasing the plant growth and yield.

Impact of coal industries on the quality of Damodar river water

Increasing demand for water in domestic, agricultural, and industrial sectors necessitates exploitation of water either in the form of groundwater or from natural resources. To safeguard the long-term sustainability of water resources and their utilization, the quality of water has to be periodically monitored and determined for various characteristics, especially when the sources are polluted, such as Damodar river. Central Institute of Mining and Fuel Research (CIMFR), Dhanbad, is carrying out research work on coal and its utilization and associated environmental concerns. The blood stream of life for the whole Jharia Coalfield is none other than the river Damodar. CIMFRs campus also depends exclusively on river Damodar for meeting its demand of drinking water. This study is a general survey toward the characteristics of Damodar river water, with special emphasis on the pollutant parameters, and evaluation of the treatment process being carried out at the institute for potability. Damodar river water is indeed affected by the disposal of the wastes without any pre-treatment by different coal-based industries established in its basin. The quantity of dissolved and suspended solids, total hardness, chemical oxygen demand, and coliform bacterial count are higher in Damodar water due to the disposal of the waste/effluents from coal-washing plants, coke ovens, cement, and other industries, but well within the permissible limit which is probably attributable to the high-carrying capacity of the river. The river is still not that much affected as it is usually apprehended, and it can be well utilized for potable and domestic purposes after simple treatment.