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.
