Gadolinium, and possibly praseodymium, are relatively enriched in the magnetic fractions of Class F fly ashes from Central Appalachian coal sources. Although the enrichment is evident in the inductively coupled plasma–atomic emission spectroscopy (ICP-AES) determinations of the rare earth content, transmission electron microscopy–energy dispersive x-ray spectroscopy (TEM-EDS) examination of the fly ash fails to show the sites of the Gd or Pr. This apparent lack of correlation could be due to the inability of the EDS to detect low concentrations of the rare earth elements definitively; interferences in the analytics, leading to false positives in the chemical analysis; or the overlap of the energies of Gd and/or Pr with more abundant elements, leading to inaccurate negative results.
High-alumina fly ash is defined to have alumina (Al 2 O 3 ) content of no less than 40%, according to the Chinese power industry standard DL/T 2297. Specification for resource utilization categorization of fly ash from coal-fired power plant (Standard No. DL/T 2297-2021), and is considered a valuable raw material to replace bauxite for making aluminum, refractory materials, and fracking proppants, etc. A low-density and high-strength proppant, conventionally made with bauxite, has been successfully made by high-alumina fly ash and commercially used in the market. This new high-alumina fly-ash–derived proppant has some advantages compared with the bauxite-derived proppant: (1) lower raw material cost, (2) fewer processing steps and less energy consumption, (3) equal or better performance.
Underground coal gasification (UCG) is a coal conversion method that permits coal resources to be exploited in situ using high-temperature conversion reactions. An understanding of the chemical, mineralogical, and petrographic properties of the coal, and resultant unburned carbon, degasified coal, and ash (minerals) in the UCG gasification zone, is fundamental to determining conversion rates, gas composition, and environmental and groundwater risk assessments. This study aims to provide a mineralogical and petrographic characterization of UCG residues obtained from the Eskom Majuba UCG pilot plant site in South Africa. Samples were selected from a verification borehole (VH3) drilled at the site following the pilot trial. The Permian-age Karoo Basin Majuba Gus Seam coal is medium rank C bituminous, inertinite-rich, with variable ash content. All the coal samples extracted from the borehole show evidence of heating and conversion. The volatile matter content is very low, and the mean random vitrinite reflectance values are above 5 (%RoVmr). It is possible to use vitrinite reflectance data to estimate the probable temperatures achieved in the UCG georeactor. The UCG samples in this study were exposed to maximum temperatures of around 1300°C. There is a very slight temperature gradient through the seam, indicative of fairly even heat distribution and release of volatile gases. Cracks within the degasified coals were filled with molten glassy material. Most of the iron sulfide mineralization is the degasified coal samples was transformed to pyrrhotite. The gasified samples show lower levels of sulfur as compared to unheated coal from this seam.
The South African electricity public utility Eskom has embarked on a process to increase utilisation of the ash produced through the electricity generation process at its coal-fired power stations. In the 2014-2015 financial year, 119.2 million tons of coal was consumed, producing 34.4 million tons (28.9%) of ash. About 7% of the Eskom ash is sold from 6 of the 13 coal-fired power stations. Many stations are currently running out of ash storage space, and expansion of the ash disposal facilities is required, which could affect security of supply because of limited ashing areas. Additionally, legislative requirements lead to extra requirements for ash storage facilities, requiring high capital expenditure. Increased utilisation of ash will postpone or ultimately avoid such capital expenditure. The South African legislative framework strictly governs ash utilisation. For this reason, Eskom has rejuvenated its Ash Utilisation Project by submitting an application to the Department of Environmental Affairs on behalf of the industry. Eskom is therefore leading an advocacy campaign for ash utilisation.Ash could play a key role in business development, job creation, skills transfer, and localisation. The development of small brick-making facilities in close proximity to power stations is ideal. It is imperative to develop new markets that consume high volumes of ash, including road construction and agriculture and land rehabilitation. The backfilling of mines with ash provides an opportunity; tied collieries are located in close proximity to power stations and could absorb high volumes of ash and benefit the ability to rehabilitate mines and mine closures cost efficiently. Care needs to be taken for the environmental and health impacts of this application.Multiple benefits can be derived from dealing with ash in an environmentally responsible way. Not only will the environmental footprint be limited, new applications will reduce CO~2~ emissions, acid mine drainage can be treated, and mine rehabilitation will be supported. Eskom cost reduction benefits could eventually filter through to the electricity consumer in terms of electricity price, and satisfactory socioeconomic benefits can be realised.
Groundwater below many basins that have been used to store coal combustion residuals (CCRs) may have concentrations of certain inorganic constituents in excess of applicable regulatory standards. Given that many inorganic CCR constituents are also naturally occurring in the aquifer matrix, their detection may not always be indicative of a release from the CCR unit. Inorganics may be present at elevated levels in groundwater due to natural or background conditions, or due to changes to the aquifer geochemistry resulting from the presence of the CCR basin, which then mobilizes these naturally occurring constituents beneath the CCR unit. Care must be taken to identify the source(s) and the release mechanism(s) of potential CCRrelated impacts. If a link between a CCR unit and an inorganic groundwater exceedance has been established, stakeholders may be faced with the need to evaluate groundwater remedial alternatives to address these impacts. This paper conceptually discusses potentially applicable remedial approaches, including (i) monitored natural attenuation, (ii) hydraulic control using ex situ and in situ methods, (iii) permeable reactive barriers, (iv) slurry walls, and (v) oxidation-reduction–altering approaches. Additionally, this article explores potential water reuse options available at many power generating stations. © 2019 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved.
This article summarizes the use of two fly ashes in the synthesis of Portland/calcium sulfoaluminate (OPC/CSA or A/CSA) clinkers. They are from the Shentou second power plant located in the Shanxi Province and from the Zhungeer power plant located in Inner Mongolia, China. The Zhungeer ash was collected dry, and the Shentou ash is from a pond. Their chemical compositions differ highly, especially the SiO~2~ and Al~2~O~3~ contents. The high contents of silica and alumina make both ashes candidates as a partial or total substitute for bauxite, an expensive source of alumina, in the production of OPC/CSA clinkers. These particular hybrid clinkers are composed mainly of alite (C~3~S) and calcium sulfoaluminate (C~4~A~3~SACUTE), both phases responsible for the high early strength development in OPC and CSA cements, respectively. The production of high-quality OPC/CSA clinkers was produced with both ashes with the additions of hydrated lime, flue gas desulfurization (FGD) gypsum, fluorite, and bauxite at 1250°C for 60 minutes with final composition ranges of 29-41 wt% C~3~S, 20-22 wt% C~2~S, 30-45 wt% C~4~A~3~SACUTE, and 1-4 wt% C~4~AF.
Unburned carbon found in coal conversion ash has the potential to be used in a variety of value-added applications. However, it is first necessary to separate the unburned carbon from the rest of the ash phases. This poses challenges due to the relatively low starting carbon-in-ash values (0.4 to 7.8 wt. % reported for South African sources), and the high carbon grades (ideally ~90 wt. % carbon) and recoveries that need to be achieved. In this paper, a dry method for the separation of unburned carbon from coal ash was developed and assessed using fly, bottom, and gasification ash samples obtained from various South African coal conversion utilities. The idea is to subsequently use the unburned carbon product as a precursor for synthetic graphite manufacturing. The separation consisted of a combination of size, electrostatic (CoronaStat), and magnetic separation steps, and the carbon grades (as loss on ignition - LOI) and recoveries were assessed for each step. Pre-characterisation included X-ray diffraction (XRD), LOI, and petrography (carbon-mineral associations) analyses. The carbon grades increased from 4.01 and 7.04 wt. % to 56.55 and 65.74 wt. % respectively for two fly ash samples. The process was less efficient for the bottom and gasification ash samples, where final carbon grades of 53.21 and 45.10 wt. % were achieved from a starting base of 5.47 and 6.90 wt. % respectively. The carbon recoveries for all samples were low (<35 %), possibly due to the mineral inclusions that form part of the carbon matrix. The suggested separation method is promising but still requires further modification. _Article history: Received 4 February 2019; Received in revised form 15 April 2019; Accepted 7 May 2019_ © 2019 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association. All rights reserved.
On 19 October 2015, the Disposal of Coal Combustion Residuals (CCRs) for Electric Utilities final rule (CCR Rule), issued by the U.S. Environmental Protection Agency (US EPA) under Subtitle D of the Recovery and Conservation Act (RCRA), became effective. The Groundwater Monitoring and Corrective Action subsections of the CCR Rule (40 CFR §§ 257.90-257.98) set out strict requirements for groundwater monitoring at the detection and assessment levels, followed by (if necessary) groundwater characterization in support of corrective measures assessment. Since the federal CCR Rule was implemented, the US EPA has proposed and finalized some amendments, and some states have proposed programs to implement parts or all of the federal CCR Rule, including requirements for groundwater monitoring, assessment, and corrective measures. This article was prepared to highlight the value that can be added to the process from judicious application of the conceptual site model (CSM) approach in progressing through the steps required by the CCR Rule. This article introduces the CSM as a practical, industry-focused project planning tool that can inform project managers, scientists, and engineers on how to collect the right type, quantity, and quality of data, and to leverage statistical, geostatistical, and numerical methods to generate legally defensible information from these data. If implemented properly, the CSM can help assess key data gaps and uncertainty for installing a groundwater monitoring system; meet 90-day implementation periods set forth by the CCR Rule; conceptualize the nature and extent of impacted groundwater; assess cumulative risks, potential alternative sources, and remedies; evaluate the effectiveness of a chosen remedy; manage and handle ponded materials; and successfully communicate site-specific information to stakeholders and regulators.
The study demonstrated that ash composites made from polyurethane and fly ash are able to reduce leaching of coal ash inorganics to less than one-third of the U.S. Environmental Protection Agency\'s maximum containment limit even after being exposed to an accelerated water circulation system for 14 months. Even if these ash blocks are broken, the composite is safe. The concept of encapsulation of fly ash into ash composite by using a polar polymer to bind the fine inorganic particles, as nature has done in the original unburned coal, makes the ash composite safe. The ash composites have compression and flexure strength and surface hardness suitable for many engineering applications such as building products and infrastructure products that are more valuable than the use of ash in concrete. The application examples demonstrated include reusable ash storage blocks, utility pole crossarms, and building products such as chair railings, base boards, and decorative moldings. In addition, there are many more positive attributes of ash composites such as insect and fire resistance, low electrical and thermal conductivities, and low coefficient of thermal expansion. These properties need to be assessed further. This fly ash\--composite technology will be expanded to include pond ash that is very abundant in the United States and worldwide and has very limited use. Other applications such as electric poles, railroad ties, and highway sound barriers are the products for exploration.
The objective of this study was to evaluate the shear strength of a coal combustion product (CCP) by using the vane shear test. A series of small-scale vane shear (SS-VS; diameter = 12.7 mm and height = 25.4 mm) and large-scale vane shear (LS-VS; diameter = 25 mm and height = 50 mm) laboratory tests were conducted. Undrained and drained strength envelopes were determined using consolidated undrained triaxial compression tests, and drained strength was checked via consolidated drained direct shear. In addition, effects of (1) rate of vane rotation, (2) time delay between vane insertion and beginning rotation, and (3) elapsed time under the final vertical effective stress before shear were evaluated via SS-VS. Vane shear strength results were represented in terms of peak shear strength and the initial horizontal effective stress acting on the vertical-oriented failure surface during rotational shear. Both SS-VS and LS-VS yielded shear strengths that plotted between the drained and undrained triaxial strength envelopes. Shear strength of CCP increased with increasing time under load, which was potentially attributed to diagenesis. Peak shear strength in SS-VS was reached after approximately 72 hours of elapsed time under constant vertical effective stress. Peak shear strength in SS-VS and LS-VS compared favorably to the drained strength measured via direct shear testing. © 2019 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved.
This study focuses on mineralogical and geochemical compositions of feed coal (FC) and combustion residues, namely fly ash (FA) and bottom ash (BA) samples, obtained from the Kangal coal-fired power plant in central Turkey. The X-ray powder diffraction data indicate that carbonate and clay minerals are dominant phases in the FC samples. In the FA samples, quartz, hematite, anhydrite, lime, and feldspar are generally dominant and abundant phases, whereas calcite, ettringite, and portlandite are generally more abundant in the BA samples. The elements Mo, Cs, and U are significantly enriched in the studied FC, FA, and BA samples. The statistical analysis and SEM-EDX data show that Ca, Ti, and the vast majority of trace elements are inorganically affiliated, and only Tl and U have prob-able organic affinity in the FC. In addition, the redox conditions in the paleomires presumably resulting in Mo and U enrichment in FC, whereas their enrichment in FA and BA is most likely related to retention by CaO and Ca-sulfate. The Cs enrichment in FA is due to retention by glass. The elements in the FA and BA are distinguished into four groups according to their volatility during combustion. The elements As, Mo, Cd, Tl, and U (Group I) are the most volatile elements during combustion and condensation in the FA. The elements Li, Zn, Ga, Rb, Nb, Cs, Ba, La, and Pb (Group IV) did not become more volatile or less volatile during combustion and are located in BA. Nevertheless, Zn and Pb in the BA seem to be related to the presence of unaffected pyrite and sphalerite, and are due to low combustion efficiency of the boiler during the sampling period. Overall, enriched elements and minerals in FA and BA suggest that their disposal should be undertaken with caution.
The Coal Combustion Residual (CCR) and Effluent Limitations Guidelines(ELGs) rules pose significant technical and economic challenges for ash management and for treatment and discharge of flue gas desulfurization (FGD) wastewater at coal-fired power plants. Beneficial use is always a priority for ash, but only about half is being reused on a national basis, and the rest is destined for disposal. The U.S. Environmental Protection Agency identified biological treatment as the baseline treatment technology for FGD wastewater in the ELGs. However, it is becoming evident that bioreactors exhibit high capital and operating costs, occupy significant space, and are sensitive to changes in temperature and pH. Dense slurry ash management can sequester large quantities of FGD wastewater along with the contained contaminants through hydration, encapsulation, and entrainment for a fraction of the cost of traditional treatment. By using dense slurry sequestration of FGD wastewater, off-site discharge of effluent can be avoided altogether. Dense slurry was employed at (among other plants) the Matra Power Plant near Budapest, Hungary, and this technology played a key role in helping the plant achieve zero liquid discharge (ZLD). The Matra project is summarized and data are presented that show how the technology helped the plant achieve ZLD and other environmental objectives.
The leaching potential of coal fly ash is often approximated with laboratory-based methods that expose columns of compacted material to synthetic precipitation. While this procedure can simulate aspects of the field condition, it remains difficult to replicate site-specific thermodynamic and kinetic constraints on geochemical processes. This article explores one aspect that contributes to the field/laboratory disparity, namely, the influence of flow rate and intermittency. Seven column-based leaching experiments were conducted with the same ash but with different flow rates and intermittency (i.e., infiltration pulsing), and results were evaluated in terms of aqueous sodium, calcium, and chromium concentrations in the effluent. Flow rates ranged by three orders of magnitude, encompassing advection- and diffusion-dominated conditions as determined by Peclet number calculations. With few exceptions, the results revealed diminishing leachate concentrations with continued flushing, consistent with a declining source model. Notwithstanding differences in effluent concentration as a function of pore volume, general mass release followed similar patterns that likely reflected solubility control. Higher liquid-to-solid ratios revealed potentially nonequilibrium behavior at the highest flow rate (2400 mL/day) during intermittent flow conditions for chromium and calcium, and to a modest extent for sodium. The primary conclusion from this work is that for the constituents and ash tested, there was relatively little effect of flow rate or intermittency on leachability patterns.
Fly ash was collected from individual mechanical and electrostatic precipitator (ESP) hoppers at a 130-MW pulverized-coal utility unit burning a southeastern Kentucky moderateto high-S Pennsylvanian Fire Clay coal. The fly ash particle size is generally similar within each row of the mechanical and ESP hoppers, with the mean particle diameter decreasing from >36 μm in the mechanical hoppers to 6 μm in the last ESP row. Rare earth element (REE)–bearing phases occur within fine minerals and, possibly, as part of the fly ash glass phase. Transmission electron microscopy was used to identify Y-Ce-Nd-La–bearing regions within a glassy matrix. Yand U-bearing zircons were also found in the fly ash. Total REE plus yttrium (REY) occupies a narrow range from 719 to 775 ppm, showing an overall lack of partitioning of the REY elements with respect to particle size and temperature in ash collection systems. The heavy REE increase and the light REE/heavy REE ratio decreases from the mechanical hoppers through ESP rows. © 2017 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved. A R T I C L E I N F O Article history: Received 20 February 2017; Received in revised form 12 April 2017; Accepted 14 April 2017
The main objective of this study was to evaluate geopolymer concrete made from coal combustion by-products, disposed of in landfills, as a potential substitute for the ordinary Portland cement (OPC), which is responsible for 5-8% of the total CO~2~ emissions in the world. In this study, a coal fly ash sample from the Carolinas was used in a chemical process known as geopolymerization to produce a \geopolymer binder. The developed geopolymer binder could competently substitute the OPC binder in regular concrete applications. An experimental design program was conducted to optimize parameters of the geopolymerization affecting the strength of the final cementless concrete product. Mortar and concrete samples were made to compare the strength of geopolymer with OPC concrete. The results showed that the compressive strength of geopolymer-based products were more than 6700 psi for mortars and 5750 psi for concrete samples, which could effectively compete with OPC concrete. This paper presents the results of the experiments and discusses the effectiveness of the produced cementless binder.
In response to the U.S. Environmental Protection Agency’s new rule regarding the disposal of coal combustion residuals (CCRs), many utilities need to re-examine their waste disposal practices and make decisions regarding if and how unlined surface impoundments (SIs) should be closed. The two primary options for closing SIs are in-place closure, with capping and engineering controls, and excavation of the CCR for transport to and re-disposal in a lined landfill. To help inform closure option decisions, we supported the Electric Power Research Institute’s development of a practical, science-based decision framework that comprehensively evaluates the potential impacts to human health and the environment associated with SI closure alternatives. We have applied this framework to several sites and have performed a detailed sensitivity analysis of individual parameters on the framework results. Based on these applications, we developed a set of lessons learned that can be used to scope and streamline further SI closure option assessments. © 2017 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved.
Twenty bulk samples were collected from ponded coal combustion ash in Shanxi Province, China, as part of an investigation of their beneficiation potential. The samples were shipped to the University of Kentucky, where they were chemically analyzed. The samples were highly consistent in chemistry, falling within the ASTM C-618 class F compositional range. The particle size of the ponded ash was relatively coarse, with only ,7% by weight on average, falling below 200 mesh (75 mm) particle size. The bulk of the material (.80%) was within 50 by 200 mesh (equivalent to 300 by 75 mm). X-ray diffraction investigation combined with microscopy indicated that the agglomeration was probably due to the presence of small amounts (i.e., ,3.5%) of gypsum. The utilization potential of the ash was assessed in light of its characteristics and location. The presence of sulfate and relatively high alumina concentration, which averaged ,37%, suggested that it may serve as an important ingredient in the fabrication of a Portland–calcium sulfoaluminate (CSA) hybrid cement. Portland-CSA hybrid clinkers were successfully produced from this ponded ash when mixed with hydrated lime, gypsum, fluorite, and bauxite. The raw mixture was fired at 1250uC for 60 minutes twice (sample D) and consisted of approximately 40% alite (C3S), 21% belite (C2S), 3% ferrite (brownmillerite or C4AF), 32% CSA (ye’elimite, Klein’s compound, or C4A3SO3), and no free lime by weight. – 2016 The University of Kentucky Center for Applied Energy Research and the American Coal Ash Association All rights reserved. A R T I C L E I N F O Article history: Received 5 October 2015; Received in revised form 1 December 2015; Accepted 1 December 2015
