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Evaluation of Leachates from Coal Refuse Blended with Fly Ash at Different Rates

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Abstract

There is great interest in returning coal combustion products to mining sites for beneficial reuse as liming agents. A column study examined the effects of blending two coal fly ashes with an acid-forming coal refuse (4% pyritic S). Both fly ashes were net alkaline, but had relatively low neutralizing capacities. One ash with moderate alkalinity (CRF) was bulk blended with coal refuse at 0, 20, and 33% (w/w), while another lower alkalinity ash (WVF) was blended at 0, 5, 10, 20, and 33% (w/w). The columns were leached (unsaturated) weekly with 2.5 cm of simulated precipitation for >150 wk. Where high amounts of ash alkalinity (>20% w/w) were mixed with the coal refuse, pyrite oxidation was controlled and leachate pH was >7.0 with low metal levels throughout the study. At lower rates of alkalinity loading, trace metals were sequentially released from the WVF ash as the 5, 10, and 20% treatments acidified due to pyrite oxidation. Lechate metals increased in proportion to the total amounts applied in the ash. In this strongly acidic environment, metals such as Mn, Fe, and Cu were dissolved and leached from the ash matrix in large quantities. If ash is to be beneficially reused in the reclamation of acid-producing coal refuse, the alkalinity and potential acidity of the materials must be balanced through the appropriate addition of lime or other alkaline materials to the blend. Highly potentially acidic refuse material, such as that used here, may not be suitable for ash/refuse codisposal scenarios.
... However, fly ash also contains a number of potentially toxic trace elements (e.g. Mn, Zn and Cu), which are leachable under certain conditions, particularly if the ash is exposed to highly acidic drainage (Stewart et al., 2001;see Fig. 1). Thus, our overall findings from work in the 1990's were generally positive with respect to the beneficial reuse potential of coal fly ash, but they did contain significant cautionary results. ...
... Thus, the pressure for land application and/or mine utilization would be expected to increase. On a positive note, however, both of these additives could substantially improve the soil amendment properties of CCP's. Figure 1: Effects of alkaline fly blending rate on leachate pH from acid forming coal refuse over three years as reported by Stewart et al. (2001). The CRF ash was high alkalinity while the WVF ash was moderately alkaline. ...
... We utilized (with minor modifications) the leaching column design developed by and Stewart et al. (2001) to equilibrate and subsequently obtain the leachates. The columns were 20cm diameter, 75cm long, ABS plastic drainage pipes with a flexible PVC endcap to hold the material. ...
... Short term leach tests (batch tests) are a simple means to compare the dissolution behavior of various components in considerably shorter interaction periods thus providing critical information [26, 28, & 38]. The column studies using synthetic water, can simulate the surface leaching from fly ash dumps to predict the natural weathering actions on the fly ashes to a considerable extent [55,56] the actual environment on field; however, the generated data provides a relatively fair idea of the dissolution characteristics of different materials in the waste. There are 143 coal based [1] thermal power plants in India but with respect to this large number very few studies [31-33, 37, 40, 42, 43, & 50-52] have been done. ...
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This paper presents the results of short-term leach tests conducted on slightly alkaline fly ash collected from Suratgarh Super Thermal Power Plant (SSTPP), Sri Ganganagar, Rajasthan, India. ASTM D3987-85 (ASTM) and toxicity characteristic leaching procedure (TCLP) test methods were applied on fresh fly ash (FA-1) and weathered fly ash (FA-2), to understand the leaching characteristics of the elements Cu, Zn, Mn, Fe, Ba, Ca, Co, Cr, Ni, Si, Pb, Sr, Cd, Al, Mg, V, Ti, and As inherent in the SSTPP fly ash. Morphological, quantitative and qualitative elemental as well as mineralogical analyses of fly ash samples were done using XRD, FEG-SEM and ICP-AES techniques. The results showed that both the fly ashes comprise mainly of Bavenite, Silicon Oxide Quartz and Berlinite minerals. The concentration of V (in both FA-1 and FA-2) and Cr (only in FA-1) exceeded the acceptable limit prescribed by New-Zealand waste acceptance criteria for class-A landfill. The TCLP test rendered more mobility to almost all the elements. The concentrations of As (in FA-1), Fe, Cr (not in ASTM FA-2), Mn, Pd and Se (not in ASTM FA-2) in the leachates exceeded the WHO drinking water standards for both TCLP and ASTM tests whereas Ni and Ba surpassed only in TCLP test. The high elemental concentrations of various elements in the leachates thereby suggest a fair amount of pollution potential of SSTPP fly ash.
... The dissolution behaviour of different constituents in a short time frame can be identified by batch leaching tests (de Groot et al., 1989;Fleming et al., 1996;Wang et al., 2008). However, the column leaching test is used to simulate leaching phenomena owing to the weathering impact on fly ash dumps by natural forces using artificial leachant (Chichester and Landsberger, 1996;Stewart et al., 2001). Though the conditions under which leaching tests are performed in the laboratory are different from the real environment at the disposal site, the results obtained from these tests provide an insight into the dissolution behaviour of different trace elements in the waste. ...
Article
The fly ash, generated at the coal-based thermal power plant, is always a cause of concern to environmentalists owing to its adverse impact on air, water and land. There exists a high environmental risk when it is disposed to the environment. Thus, two different type of fly ash samples (FA-1 and FA-2) have been considered in this study to examine the leaching potential of the elements magnesium, aluminium, silicon, calcium, titanium, vanadium, chromium, manganese, iron, nickel, cobalt, copper, zinc, arsenic, selenium, strontium, cadmium, barium and lead for different types of leachant. Toxicity characteristics leaching procedure and ASTM tests have been performed in the laboratory to simulate different natural leaching scenarios. Characterisation of samples have been done through X-ray diffraction and field emission gun scanning electron microscope. The effect of different liquid to solid ratios (i.e. 5, 10, 20 and 50) on the mobilisation of elements has been analysed. The results indicated that the maximum leaching of all elements occurred at a liquid to solid ratio of 5 except for arsenic, barium and silicon. The groundwater analysis has also been done to understand the actual effects of leachate. The elements presenting the highest leachability in the two fly ash samples under all tested conditions were magnesium, aluminium, silicon and calcium. It has been observed that calcium exhibits greater leaching effects than all other constituents. The study presented here has been found very useful for assessing contamination levels in groundwater owing to leaching effects of fly ash under different scenarios, which can be helpful to prevent spreading of the contaminants by efficient management of fly ash.
... Therefore, drainage from coal waste, which is initially alkaline, remains alkaline for a certain period of time and then tends to become acidic. This period can be extended by addition of alkaline materials which is a widely accepted mine reclamation practice (Dreher et al. 1994;Nawrot and Gray 2000;Stewart et al. 2001). Chugh et al (2007a, b) and others have suggested that differential AP and NP rates could be used advantageously in waste management operations to allow for improved placement and compaction practices, and reduction of SO 4 discharges. ...
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Management of coal mining and coal processing wastes, particularly of high sulfur coals, can generate excessive amounts of sulfate (SO42−) and chloride (Cl−) in mine drainage that are known to negatively impact quality of both surface and ground water. The U.S. Environmental Protection Agency provides guidance to states on allowable SO42− and Cl− discharges from mine sites. This research evaluates the hypothesis that co-disposal of CCPW and FCPW with appropriate compaction can result in improved geochemical and geotechnical environments that will minimize acid mine drainage formation and SO42− and Cl− discharges. Addition of ground limestone (ag-lime) to the mix was also evaluated as a drying agent and for improvement in overall geochemistry by buffering higher pH values within the coal waste. These objectives were to develop and implement innovative concepts for engineered co-management of CCPW and FCPW at coal mining sites. The authors performed long-term field column leaching studies to analyze improvement in SO42− and Cl− in water quality. Requirements for stricter standards in some states led to the need for development of potentially improved environmental practices. This paper presents the overall encouraging results of the field kinetic studies.
... The column leaching method employed here is described in greater detail by Orndorff et al. (2015) and was based upon an earlier design utilized by Stewart et al. (2001) for studying temporal leaching response in coal refuse materials. Leaching columns were built from PVC pipe (inside diameter ¼ 7.4 cm, length ¼ 40 cm) with a concave endcap fitted with a PVC pipe nipple and Tygon tube to drain leachate to a nalgene sample bottle. ...
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Chapter
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Chapter
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