Use Of Coal Combustion By-products Research Articles

Minimising Coal Mining’s Impact on Biodiversity: Artificial Soils for Post-Mining Land Reclamation

Coal mining and the energy industry generate large amounts of solid waste, which must be disposed of in landfills and lead to numerous environmental problems. This paper presents a method for creating artificial soil mixtures based on an EU-funded international research project called RECOVERY. The main idea behind the proposed solution is the safe use of coal combustion by-products (energetic slag and decarbonation lime), mining waste (aggregate and sealing material) and spent mushroom compost as components for creating artificial soils. Laboratory tests of the soil substitutes showed low concentrations of heavy metals and high macronutrient content, adequate for proper plant growth. As a result of a two-year study on the application of soil cover on a 4000 m2 testing ground, species characteristics for the mesotrophic, dry meadow, ruderal and segregated vegetation were found. In the second year of the in situ study, an apparent reduction in soil salinity was observed. The principal component analysis confirmed that decreasing soil salinity positively affected ruderal and dry meadow species. In contrast, high salinity levels showed no adverse effect on mesotrophic meadow vegetation. The results demonstrated that applying soil covers elaborated from industrial by-products is valuable for recovering high-acidity coal mine waste heaps.

The evolution of waste into a resource: Examining innovation in technologies reusing coal combustion by-products using patent data

The reuse of waste begins with the development of new technologies for ways to use waste. Despite the critical role of innovation in waste reuse, innovation for waste reuse technologies has been largely overlooked in innovation studies. This paper presents the first patent study examining the innovation process for a specific waste reuse technology, to elucidate how waste evolves into a resource with a greater possibility of being used. This study specifically analyzes how innovation occurs, what drives it, and the consequences of this innovation. Coal combustion by-products (CCBs), which are solid residues generated from coal-fired utilities, are specifically examined as a test case because they have been promoted as a resource through century-long innovative efforts for use in construction, mining, and agricultural applications. Having examined more than 700 patents from the United States Patent and Trademark Office database, the results of this study show that innovation has primarily occurred: (1) to reuse CCBs, particularly fly ash, in various building, construction, and structural products; (2) by businesses, particularly those that need to use CCBs; and (3) since 1967, and the number of CCB-related patents peaked during the early 1980s and 1990s. For the drivers of innovation, this study identifies the impact of some market factors, such as cement and lime price, and institutional activities, such as the establishment of industrial associations that support CCB reuse, on patent filings. The role of regulation in innovation, however, is ambiguous with regard to CCB reuse. Although more CCBs have been used as more innovation occurs, the use of CCBs has increased with a lag, due to variation in the values of individual technologies and barriers to the implementation of technologies in the reuse market.

The application of coal combustion by-products in mine site rehabilitation

Abstract Coal combustion by-products (CCBs) generated from coal-fired power plants have been considered in some circumstances and in some applications as alternatives for natural materials. This review focused on the beneficial use of CCBs for mine sites. The alkaline pH of CCBs has been shown to play a neutralising role for acid mine drainage and the consequent precipitation of metals from solution, mainly as metal hydroxides. Coal combustion by-products have also been used for soil restoration, having been shown to improve one or more of the physical, chemical and biological properties of degraded soils which in turn has led to improvements in revegetation outcomes. In addition, fly ash has been used as a one of the materials in engineered covers that are constructed to encapsulate and isolate potentially hazardous mine wastes. The use of CCBs for mine void backfilling has been considered an opportunity for the bulk utilization of CCBs. Backfilling of underground mine voids with these materials presents the potential to reduce acid mine drainage, limit the risk of land subsidence and minimise and control the likelihood of mine fires. Even though the proactive use of CCBs may eliminate or reduce an environmental burden that remains if separate storage or disposal of these otherwise ‘waste’ materials is required, there may be adverse side effects that could occur through such uses of CCBs, such as the leaching of deleterious elements. Therefore, in the case of their use in mine backfilling, for example, possible environmental impacts need to be assessed and monitored during a testing phase in the context of other variables, and before backfilling with such materials is used on a large-scale. There is still a lack of well-researched information on the practical use of CCBs, and their potential environmental and health effects, and in their use for mine site rehabilitation purposes, effective guidelines and regulations are also limiting factors. In most countries, government regulations regard CCBs as a waste but not a hazardous waste. However, given the high potential CCBs have in a number of roles and functions relating to mine rehabilitation and mine closure, more research at the practical level, and more engagement at a government level, is required.

English

Coal combustion byproducts (CCBs) have potential as structural fill and capping materials in abandoned mine land (AML) reclamation because of their acid-neutralization capacity. However, the potential for these materials to leach constituents of potential concern (COPCs) into groundwater hinders their use by AML program managers. In 1996, the Midwestern AML site in southwestern Indiana was reclaimed using fixated scrubber sludge (FSS) cap composed of flue gas desulphurization sludge, fly ash, and lime. The cap was placed over a pyritic refuse deposit, an unreclaimed spoil ridge, and highwall lakes that were filled with ponded ash. Post reclamation analyses of groundwater chemistry showed that alkalinity and pH levels increased below the cap, indicating that the CCBs helped to neutralize the preexisting acid mine water. Concentrations of COPCs initially increased below the cap, but dropped back to near or below pre-reclamation values over the past 10 years. For example, boron that initially increased to 13,000 µg/L decreased to pre-reclamation values (300 μg/L) with time. X-ray diffractometry was conducted on core samples containing FSS and ponded ash collected from the site in 2011 to identify mineralogical changes since emplacement. Oxidation of hannebachite (calcium sulfite hemihydrate) produced gypsum and calcite in the upper 1 to 4 cm of the 1 to 3 m thick FSS cap. No oxidation zone was observed at the bottom of the cap. Sediment cores of ponded ash reveal little change with depth, possibly because leaching had already occurred as a result of stockpiling at the power plant. The results of this study indicate that FSS did contribute COPCs, including boron, molybdenum, chromium, and arsenic, to groundwater for short periods and in the immediate vicinity of emplacement. Nevertheless, a lack of significant oxidation and declining trends in groundwater contamination represent long-term favorable outcomes for use of CCBs in AML reclamation.

Use of coal combustion by-products in mine reclamation: review of case studies in the USA

With the continued use of coal to generate electricity for the world's power needs, coal combustion by-products (CCPs) will be produced in greater quantities during the ensuing decades. About 130 million tons of CCPs are produced annually from the 600 coal-fired power plants currently operating in the USA, with estimates of 500 million tons produced worldwide. Five major types of CCPs exist: bottom ash; boiler slag; fly ash; fluidized bed ash; flue gas desulfurization ash. Bottom ash does not generally constitute a disposal problem because it is extensively used as aggregate fill material for construction projects, filler in construction materials (wall board and dry wall) and de-icing solids for roads. Boiler slag is used for similar purposes as bottom ash, but it can be used as a glassy grit material for sand blasting. Fly ashes constitute 70% of the by-products generated and these ashes are produced in several ways in a power plant depending on the boiler type and the emission control system employed at the power plant. These fine-textured ash materials may be dry fly ash from conventional coal-fired boilers, dry ashes collected in flue-gas desulfurization or other collection devices (bag houses or scrubber filters), or they may be collected in wet scrubber systems producing a fly ash slurry.Coal combustion by-products can be beneficially used as: (1) an alkaline seal or fill material to contain acid producing materials and to prevent the formation of acid mine drainage; (2) an agricultural amendment to create artificial soil on abandoned mine lands where native soils are not available; (3) an alkaline amendment added to spoils to neutralize acid producing materials in the spoil; (4) a flowable fill that seals and stabilizes abandoned underground mines to prevent subsidence and the production of acid mine drainage (5) a non-toxic fill material for final pits within the spoil area to reduce reclamation costs. Case studies in this paper demonstrate that CCPs can be used to improve reclamation, revegetation and water quality on reclaimed areas. Results to date have shown the effective neutralizing capacity of these ashes and stabilization of reclamation sites.

English

The use of coal combustion by-products (CCBs) in mine reclamation has been advocated by some because of their low permeability and potential to generate alkalinity. However, others have argued that these benefits are outweighed by the potential for leaching of trace elements that can enter ground and surface waters. In 1996, an abandoned mine land (AML) site in southwestern Indiana was reclaimed using ponded ash as structural fill in highwall cuts, and fixated scrubber sludge (FSS) as capping material over pyritic refuse. Pre- reclamation and post-reclamation monitoring of surface water discharge from the site, groundwater elevations and chemistry, as well as soil moisture fluctuations in the unsaturated zone have provided a basis for evaluating the effects of CCBs on the hydrochemistry of the site and potential for off-site impacts. Limited recharge through the FSS is supported by barometric efficiency changes in the refuse aquifer, the presence of perched water measured in monitoring wells installed on the cap, and minimal fluctuations in soil moisture within and immediately below the cap. Reductions in oxygenated rainwater reaching the refuse are indicated by groundwater chemistry data, collected from the refuse aquifer between 1995 and 2007, which show an increase in pH along with decreasing trends in total acidity, specific conductivity (SpC), and arsenic. Concentrations of boron, a trace element commonly associated with CCBs, have declined to near pre-reclamation levels at most sites (~1 mg/L) after an increase immediately following reclamation. Although arsenic concentrations at 14 µg/L (EPA maximum contaminant level, or MCL, is 10 µg/L) along with boron (14 mg/L) remain slightly elevated in groundwater associated with ash-filled lakes, improvements in surface water quality leaving the site include significant reductions in total mineral acidity and total iron concentrations, while trace metal concentrations remain below EPA MCLs.

Beneficial Use of Coal Combustion By-products in the Rehabilitation of Failed Asphalt Pavements

� Abstract—This study demonstrates the use of Class F fly ash in combination with lime or lime kiln dust in the full depth reclamation (FDR) of asphalt pavements. FDR, in the context of this paper, is a process of pulverizing a predetermined amount of flexible pavement that is structurally deficient, blending it with chemical additives and water, and compacting it in place to construct a new stabilized base course. Test sections of two structurally deficient asphalt pavements were reclaimed using Class F fly ash in combination with lime and lime kiln dust. In addition, control sections were constructed using cement, cement and emulsion, lime kiln dust and emulsion, and mill and fill. The service performance and structural behavior of the FDR pavement test sections were monitored to determine how the fly ash sections compared to other more traditional pavement rehabilitation techniques. Service performance and structural behavior were determined with the use of sensors embedded in the road and Falling Weight Deflectometer (FWD) tests. Monitoring results of the FWD tests conducted up to 2 years after reclamation show that the cement, fly ash+LKD, and fly ash+lime sections exhibited two year resilient modulus values comparable to open graded cement stabilized aggregates (more than 750 ksi). The cement treatment resulted in a significant increase in resilient modulus within 3 weeks of construction and beyond this curing time, the stiffness increase was slow. On the other hand, the fly ash+LKD and fly ash+lime test sections indicated slower shorter-term increase in stiffness. The fly ash+LKD and fly ash+lime section average resilient modulus values at two years after construction were in excess of 800 ksi. Additional longer-term testing data will be available from ongoing pavement performance and environmental condition data collection at the two pavement sites.

Field tests on drilled shafts made with coal combustion by-products based concrete composites

Drilled shaft foundations are used commonly to resist compression, pull-out, and lateral loads from all kinds of structures ranging from single story buildings to multi-span heavy bridges. Recently, a field study involving testing of small diameter drilled shafts was completed to investigate the use of coal combustion by-products in the construction of drilled shaft foundations. The goals of this study were accomplished by conducting a series of laboratory tests to develop concrete composites containing pulverized coal combustion (PCC) by-products suitable for use in the construction of drilled shafts and field tests on drilled shafts. Based on the results of extensive laboratory investigation, two concrete composites and an equivalent conventional concrete were used to construct 330 mm diameter and 7.6 m long drilled shafts in the field and tested under field loading conditions. The drilled shafts were tested in compression using conventional top-down static load test and Osterberg Cell (O-Cell) tests, conventional axial pull-out tests, and lateral load tests. Results from the field tests on the drilled shafts are presented

Coal fly ash as an amendment to container substrate for Spathiphyllum production

Coal fly ash, possessing alkalinity and containing some essential mineral elements, could be an alternative to lime amendment and a nutrient source of container substrates for ornamental plant growth. This study examined physiochemical properties of three fly ashes collected from Florida, Michigan, and North Carolina and container substrates formulated by incorporating commercial dolomite and the three fly ashes, respectively into a soilless basal substrate. The basal, dolomite- and fly ash-amended substrates were used to grow peace lily ( Spathiphyllum Schott ‘Ty’s Pride’), a popular ornamental foliage plant, in 15-cm diameter containers in a shaded greenhouse. Electrical conductivities and pH of the substrates were monitored monthly. Plant canopy heights and widths, shoot fresh and dry weights were recorded five months after transplanting, and tissue nutrient contents were measured. Three fly ashes and the commercial dolomite were able to raise pH of the basal substrate from 3.8 to about 6.8. Canopy heights and widths as well as shoot fresh and dry weights of plants produced from fly ash-amended substrates were comparable to those produced from dolomite-amended substrate but significantly different from those produced from the basal substrate. On an average, five necrotic leaves appeared from plants produced in the basal substrate; however, less than one necrotic leaf occurred on plants produced in either dolomite- or fly ash-amended substrates. As a result, the quality grade of plants grown in the basal substrate was low, and plants were not marketable. Additionally, electrical conductivities of fly ash-amended substrates were consistently higher during the course of plant growth, suggesting that, in addition to neutralizing pH, the amended fly ashes provide nutrients for peace lily growth, which was confirmed by high nutrient contents in plant shoots. This study demonstrates that the three fly ashes can be alternatives to commercial dolomites used as amendments to soilless substrates for ornamental plant production. Utilization of fly ashes as container substrate amendments should represent a new market for the beneficial use of coal combustion byproducts.

Assessment of groundwater quality impacts due to use of coal combustion byproducts to control subsidence from underground mines

Coal combustion byproducts are to be placed in an underground coal mine to control subsidence. The materials were characterized to determine potential groundwater impacts. No problems were found with respect to heavy or toxic metals. Coal combustion byproduct leachates are high in dissolved solids and sulfates. Chloride and boron from fly ash may also leach in initially high concentrations. Because the demonstration site is located beneath deep tight brine-bearing aquifers, no problems are anticipated at the demonstration site.

Changes in the quality of coal combustion by-products produced by Kentucky power plants, 1978 to 1997: consequences of Clean Air Act directives

The original US Clean Air Act (CAA), implemented by the Environmental Protection Agency in 1971, and the amendments to the act in 1977 and 1990 have required a considerable evolution of the quality of coal burned by utilities and in the type pollution control equipment needed to reduce SO 2 and NO x emissions. Any change in coal quality or emission’s control implies a change in the amount, type, and quality of coal combustion by-products (CCB). CCB is a collective term for fly ash, bottom ash and boiler slag, and flue-gas desulfurization (FGD) or fluidized-bed combustion produced in coal burning. Studies by the University of Kentucky in 1978, 1992, and 1997, the latter two conducted by the Center for Applied Energy Research, have focussed on the amount, quality, and end use of CCBs from Kentucky power plants, with particular emphasis on fly ash. The evolution of clean air standards has impacted the quality and volume of CCBs in a variety of ways: (1) switching from high sulfur to lower sulfur coal generates lower quantities of spinel phases and greater amounts of alumino-silicate glasses; (2) switching to Powder River Basin subbituminous coals produces Class C fly ash, compared to Class F fly ash from the combustion of the typical eastern bituminous coals; (3) the wider use of beneficiated coals reduces the amount of fly ash and bottom ash produced; (4) use of a wider rank range into the coal blend increases the potential of unburned carbon caused by inefficient combustion of non-design coals; (5) the inclusion of non-coal fuels, such as petroleum coke and with tire-derived fuel, in the coal blend; (6) reduction of NO x emissions has generally meant an initial increase in the amount of carbon in the fly ash; (7) addition of FGD means an added CCB stream, either a calcium sulfite which in generally mixed with fly ash and landfilled, or a calcium sulfate, which is sold for wallboard manufacture. The modification of the petrology and chemistry of the fly ash impacts the potential for utilization.

Using FBC and Stoker Ashes as Roadway Fill: A Case Study

Approximately 100,000 m3 of atmospheric fluidized bed combustion (FBC) ash and stoker ash were used as structural fill in the construction of a large roadway embankment. The embankment is ∼200 m long and 10 m high, and it supports an extension of a street across a gravel quarry in West Lafayette, Ind. The use of coal combustion by-products on this project was motivated by the need to find cost-effective alternatives to the disposal of these materials in solid-waste landfills. Similar projects have been completed using the more common bottom ash and fly ash. However, little information is available related to the performance of FBC and stoker ashes in this application. An overview of the project and construction operations is described, and the results of geotechnical laboratory tests and field monitoring are presented. Instruments used in the monitoring of fill behavior include settlement plates, vertical and horizontal inclinometers, seismic cross-hole tests, and postconstruction standard penetration tests. The compacted FBC material exhibited significant swell stresses and strains and is still expanding 2 years after construction.

Maize growth and mineral acquisition on acid soil amended with flue gas desulfurization by‐products and magnesium

The large amounts of coal combustion by‐products (CCBs) generated by coal burning power plants must be utilized or discarded, and beneficial use of these materials are desired. One beneficial use of CCBs could be application to agricultural land. Information about the use of one kind of CCB (flue gas desulfurization by‐product, FGD‐BP) on soil is limited. Maize (Zea mays L.) was grown (greenhouse) on an acid soil [Umbric Dystrochrept, pHCa (1:1, soil: 10 mM CaCl2) 4.2] amended with two high CaSO4 FGD‐BPs (5 and 15 g#lbkg‐1 soil) and CaCQ3 (2.5 and 5.0 g#lbkg‐1 soil) at varied calcium/magnesium (Ca/Mg) equivalency ratios (0/0, 1/0, 1/0.01, 1/0.05, 1/0.1, and 1/0.5) to determine treatment effects on growth traits [shoot and root dry matter (DM) and total and specific root length (RL)], mineral concentrations in leaves, and soil pH and electrical conductivity [(EC) 1:1, soil:water]. Magnesium deficiency symptoms were induced on leaves of plants grown with and without low Mg, and the Mg to Ca ratio in each amendment needed to be about 1 to 20 to alleviate Mg deficiency. Shoot and root DM and total RL of plants grown with FGD‐BPs became higher as Mg increased. Specific RL (total RL/root DM, root fineness) was not affected by FGD‐BP and only slightly by Ca/Mg ratio. Shoot concentrations of Mg increased; Ca, phosphorus (P), and manganese (Mn) decreased; and potassium (K), sulfur (S), iron (Fe), zinc (Zn), and copper (Cu) remained relatively constant as amendment and Mg increased. On unamended soil, aluminum (A1) and Mn concentrations in shoots were above normal. Enhancement of growth was closely related to increased soil pH compared to added Mg for CaCO3 amended soil and to increased Mg compared to increased soil pH for FGD‐BP amended soil. Except at the highest level of Mg where soil pH increased, added FGD‐BPs and Mg had only limited effect on increasing soil pH. Soil EC increased from added FGD‐BPs but not from added Mg, and EC was not sufficiently high to be detrimental to plants. Maize grown on this acid soil amended with FGD‐BPs received benefits when caution was used to alleviate mineral deficiencies/toxicities inherent in the soil.

Boron availability to plants from coal combustion by-products

Agronomic use of coal combustion by-products is often associated with boron (B) excess in amended soils and subsequently in plants. A greenhouse study with corn (Zea mays L.) as test plant was conducted to determine safe application rates of five fly ashes and one flue gas desulfurization gypsum (FDG). All by-products increased soil and corn tissue B concentration, in some cases above toxicity levels which are 5 mg hot water soluble B (hwsB) kg−1 soil and 100 mg B kg−1 in corn tissue. Acceptable application rates varied from 4 to 100 Mg ha− for different by-products. Leaching and weathering of a high B fly ash under ponding conditions decreased its B content and that of corn grown in fly ash amended soil, while leaching of the same fly ash under laboratory conditions increased fly ash B availability to corn in comparison to the fresh fly ash. Hot water soluble B in fly ash or FDG amended soil correlated very well with corn tissue B. Hot water soluble B in fly ash amended soil could be predicted based on soil pH and B solubility in ash at different pH values but not so in the case of FDG. Another greenhouse study was conducted to compare the influence of FDG and Ca(OH)2 on B concentration in spinach (Spinacia oleracea L.) leaves grown in soil amended with the high B fly ash. The Ca(OH)2 significantly decreased tissue B content, while FDG did not affect B uptake from fly ash amended soil.

Evaluation of coal combustion byproducts as soil liming materials: their influence on soil pH and enzyme activities

There is considerable interest in the use of coal combustion byproducts as soil liming materials in agricultural production, but there is concern that such use may be detrimental to the quality of agricultural soils. To evaluate these byproducts as liming materials and address issues related to soil quality, we compared the influence of different amounts of four combustion byproducts [fly ash and bed ash from a fluidized bed combustion furnace, lime-injected multistage burner residue, and spray dryer residue] and CaCO3 on soil pH and activities of urease, phosphatase, arylsulfatase, and dehydrogenase in an acidic soil. Studies comparing the influence of the combustion byproducts and CaCO3 on soil pH showed that on a weight basis of application, substantial differences were observed in the ability of these materials to influence soil pH but that such differences decreased markedly after the data were transformed to a CaCO3 equivalent basis of application. Analysis of covariance for these transformed data indicated that whereas the liming abilities of fly ash and CaCO3 were not significantly different when compared on the CaCO3 equivalent basis, those of bed ash, multistage burner residue, and spray dryer residue were less than that of CaCO3. Studies comparing the influence of the byproducts and CaCO3 on soil enzyme activities showed that the effect of these liming materials on the enzyme activities studied was largely due to their influence on soil pH. The relationships obtained between soil pH and enzyme activities in soil amended with the liming materials generally demonstrated the marked similarities in the influence of the combustion byproducts and CaCO3 on these activities when observed within the domain of soil pH. These studies showed that the combustion byproducts tested functioned as soil liming materials in a manner similar to that of CaCO3 and seemed to have little adverse effect on soil quality.