Ash Leachate Research Articles

On the characterization and leaching of rare earths from a coal fly ash of Indian origin

ABSTRACT Fly Ash from a lignite coal-based power plant was spotted in southern India to contain economic concentration of total Rare Earth Elements (TREE) in the order of 2100 mg/kg, of which 20% are heavier rare earth elements (HREE). Optical microscopy revealed that the portion of Lighter rare earth elements (LREE) occurs in the form of Zircon and Monazite minerals. Direct leaching of the fly ash yielded differential solubilization LREE(50%) and HREE(90%), equivalent to 60% recovery of TREE, under the optimum conditions: Sulfuric acid (1.5 M initial concentration), 20% solids (by wt.), Room Temperature (25°C), 5 h contact time.

Assessment of leachable elements in volcanic ashfall: a review and evaluation of a standardized protocol for ash hazard characterization

Volcanic ash presents a widespread and common hazard during and after eruptions. Complex interactions between solid ash surfaces and volcanic gases lead to the formation of soluble salts that may be mobilized in aqueous environments. A variety of stakeholders may be concerned about the effects of ash on human and animal health, drinking water supplies, crops, soils and surface runoff. As part of the immediate emergency response, rapid dissemination of information regarding potentially hazardous concentrations of soluble species is critical. However, substantial variability in the methods used to characterize leachable elements makes it challenging to compare datasets and eruption impacts. To address these challenges, the International Volcanic Health Hazard Network (www.ivhhn.org) organized a two-day workshop to define appropriate methods for hazard assessment. The outcome of this workshop was a ‘consensus protocol’ for analysis of volcanic ash samples for rapid assessment of hazards from leachable elements, which was subsequently ratified by leading volcanological organizations. The purpose of this protocol is to recommend clear, standard and reliable methods applicable to a range of purposes during eruption response, such as assessing impacts on drinking-water supplies and ingestion hazards to livestock, and also applicable to research purposes. Where possible, it is intended that the methods make use of commonly available equipment and require little training. To evaluate method transferability, an interlaboratory comparison exercise was organized among six laboratories worldwide. Each laboratory received a split of pristine ash, and independently analyzed it according to the protocol for a wide range of elements. Collated results indicate good repeatability and reproducibility for most elements, thus indicating that the development of this protocol is a useful step towards providing standardized and reliable methods for ash hazard characterization. In this article, we review recent ash leachate studies, report the outcomes of the comparison exercise and present a revised and updated protocol based on the experiences and recommendations of the exercise participants. The adoption of standardized methods will improve and facilitate the comparability of results among studies and enable the ongoing development of a global database of leachate information relevant for informing volcanic health hazards assessment.

Utilization of biomass ash for upgrading petroleum coke gasification: Effect of soluble and insoluble components

In this paper, the catalytic effect of different components in biomass ash on petroleum coke (PC) gasification was studied. Cotton straw ash with high content of AAEMs and low content of silica, was prepared and pretreated by washing to obtain the soluble (ash leachate) and insoluble (washed ash) components. These ash-based catalysts were added to PC via physical mixing or impregnation. The catalytic gasification performance and kinetics were investigated using a thermal-gravimetric analyzer (TGA), and the carbon structure evolution was determined by Raman spectroscopy. The results showed that all of these ash-based catalysts, even for the washed ash, had catalytic effect on PC gasification. The soluble component, mainly containing K, could speed up the gasification rate especially at the late stage. The catalytic activity of the soluble component was sensitive to temperature and conversion, while that of the insoluble component was steady. Moreover, the modified random pore model and nucleation and growth method were applied to analyze the gasification kinetics. In addition, the washed ash could inhibit the graphitization during gasification, whereas the ash leachate and original ash could enhance the generation of amorphous carbon. Possible mechanisms of catalytic gasification were proposed to explain these phenomena.

Pressured carbon dioxide hydrothermal leaching of catalytic gasification ash for dealkalization of solid waste, sodium catalyst recovery and carbon dioxide utilization

Abstract The alkali catalysts are easy to deactivate, causing low catalysts recovery. Meanwhile, the alkali in the gasification residue also poses potential hazard to the environment if improperly handled. So alkali recovery and alkali residue dealing hinder the progress of catalytic gasification. In this study, pressured carbon dioxide (CO2) hydrothermal leaching catalytic gasification ash to recover sodium (Na) catalyst as sodium carbonate (Na2CO3) and CO2 mineralization was studied, and the re-catalytic performance of recovered Na was evaluated as well. When gasified at 900 °C, the catalytic gasification ash is composed of sodium aluminum silicates [(Na2O)0.33NaAlSiO4]. By hydrothermal leaching at 180 °C with 2 MPa of CO2, 93.6% of Na can be leached, and the leaching residue is composed of amorphous Si and Al matters. At the same time, 138 g of CO2 can be mineralized by dealing with 1 Kg of catalytic gasification ash. Moreover, the recovered Na even shows better catalytic performance than fresh Na2CO3 with the same Na loaded amount, due to calcium (Ca) in the recovered Na can also enhance gasification reactivity. By pressured CO2 hydrothermal leaching, the catalyst can be recovered, the alkali in the gasification residue can be dealkalized, and CO2 can be mineralized as well, thus making catalytic gasification cleaner. Therefore, it is an economical and environmental-friendly way for alkali recovery and CO2 utilization.

Mineralogy Characteristic Study and Exploration on the Valuable Metals Enrichment of Coal Fly Ash

The separation and enrichment can be targeted to enrich in fly ash and reduce the cost of leaching and recovering of fly ash. Regarding their different properties, the single-component separation was used to obtain uncompleted burned carbon, glass microbeads, minerals, and other characteristic components from the ash. Also, the mineral composition of each component was analyzed by electron microscopy. The metal minerals were mainly concentrated in the mineral components. Besides, the electron probe microanalysis shows that the Pt content in the minerals of fly ash was significantly correlated with the metal contents of Ni and Cu. After the obtainment of the characteristics of fly ash metal enrichment, the heavy minerals with Cu, Ni, Pt, Pd, and other target metal elements were enriched by gravity separation and flotation. The enrichment coefficients of Cu, Ni, Pt, and Pd were 1.45, 1.33, 1.90, and 1.60, respectively, and the recovery rates were 77%, 81%, 97%, and 88%, respectively. Since the yield of heavy minerals obtained by separation was 62.24%, it indicated the physical separation method could significantly reduce the cost of leaching and recovering of fly ash metal resources.

Effect of Cooking Methods on the β-carotene Content of Jute Mallow Leaves (Corchorus olitorius)

The objective of this study was to evaluate the effect of different cooking methods on the β-carotene content of jute mallow (Corchorus olitorius) leaves. Three cooking methods have been experimented. Jute mallow raw leaves was respectively boiled for 15 and 30 minutes in water (CW), in water containing ash leachate (CWA) and frying for 5 minutes followed by cooking with water (CWF) for 15 and 30 minutes. The -carotene content of raw Corchorus olitorius (jute mallow) leaves were 9774.90 µg/100g dry matter basis. The -carotene content decrease significantly (p=0.00) during the different types processing. However, the -carotene content on leaves cooked using ash leachate (3604.00 µg/100g and 3768.80 µg/100g) was significantly (p=0.00) higher that on leaves cooked in water (2285.50 µg/100g and 2365.00 µg/100g) respectively for 15 minutes and 30 minutes. The highest loss (86.42%) of -carotene was observed for leaves fried for 5 minutes followed by 30 minutes cooking. These results demonstrated that any of the cooking methods used lead significantly (p=0.00) to a decrease of the β-carotene content of jute mallow leaves, but addition of ash leachate during cooking improves significantly (p=0.00) the β-carotene retention.

Simultaneous removal of As(III) and Cu(II) from real bottom ash leachates by manganese-oxidizing aerobic granular sludge: Performance and mechanisms

Manganese-oxidizing aerobic granular sludge (Mn-AGS) is a novel extension of AGS technology to treat arsenic (As) in organic wastewater. In this study, Mn-AGS was first applied to treat real wastewater (bottom ash leachates) containing high levels of As(III) and Cu(II) in a sequencing batch reactor (SBR) for 91 days. Influent and effluent As(III), As(V), Cu(II), as well as pH and chemical oxygen demand (COD) were monitored daily, and sludge was collected regularly for morphological observation, chemical characterization, and microbial analysis. The results indicated that As(III) and Cu(II) could be efficiently removed from wastewater (∼83% and ∼100%, respectively), but the performance was sensitive to pH variation, especially for As(III). The removed As and Cu were mostly bound to carbonates (60.2 ± 2.0% and 70.0 ± 0.6%, respectively) and Fe/Mn oxides (28.2 ± 1.6% and 14.6 ± 0.5%, respectively) in the final sludge. Influent As(III) was partially oxidized into As(V), and high fractions of As(V) were obtained in the Fe/Mn oxide-bound phase. Unexpectedly, microbial analysis revealed that community richness was only slightly changed when the influent was acidized (pH 4.0) but greatly reduced after the influent pH back to 6.0. It could be explained by that acid-fast bacteria rapidly grew after pH recovery and eliminated non-acid-fast bacteria. This work further supported the practical application of Mn-AGS to treat As(III)-containing organic wastewaters.

Assessment of water-quality parameters of groundwater contaminated by fly ash leachate near Koradi Thermal Power Plant, Nagpur.

Thermal power generating industries affect the surrounding environment in various ways. Fly ash escapes along with flue gases and can be found in undesirable quantities in soil and water sources in the region. The water quality of an area must be evaluated regularly to ensure the quality of potable water. The present study evaluates the pre-monsoon and post-monsoon concentrations of several important physico-chemical parameters and heavy-metal contents of groundwater samples collected from sites near the Koradi Thermal Power Plant, a major source of power generation in the Nagpur Region. The maximum amount of total dissolved solids observed during the two seasons studied were 1571mg/l and 1591mg/l which is within the desirable limit implying that fly ash contamination did not affect this water quality parameter. The total hardness of samples from GW-3, GW-5 and GW-9 were 844mg/l, 775mg/l and 675mg/l during pre-monsoon season, while GW-3 and GW-5 along with GW-4 continued to show high levels of total hardness at 1015mg/l, 741mg/l and 650mg/l, respectively. These values are higher than the permissible limit due to the high levels of ions of bicarbonate, calcium, sodium and sulphate derived from fly ash leachate. Statistical analysis showed that sulphides, total hardness, electrical conductivity and total dissolved solids were the significant water quality parameters of the region. The evaluation of the parameters found that the three water sources (GW-3, GW-5 and GW-9) out of 10 are the most affected groundwater sources of fly ash pollution.

Increased Peatland Nutrient Availability Following the Fort McMurray Horse River Wildfire

Northern peatlands are experiencing increased wildfire disturbance, threatening peatland biogeochemical function and ability to remain major stores of carbon (C) and macronutrients (nitrogen—N, and phosphorus—P). The impacts of climate change-driven drying on peatland nutrient dynamics have been explored previously; however, the impacts of wildfire on nutrient dynamics have not been examined when comparing burned and unburned areas in a post-fire fen. This study assessed the impact of wildfire on N and P bioavailability, change in CNP stoichiometric balance and feedback on plant nutrient limitation patterns in a fen peatland, one-year post-wildfire, by comparing Burned and Unburned areas. Water extractable P increased up to 200 times in shallow leachate, 125 times in groundwater and 5 times in peat. Surface ash leachate had increased concentrations in Ammonium (NH4+) and Nitrate (NO3−), and through groundwater mobility, increased extractable N concentrations were observed in peat throughout the entire fen. The net mineralization of N and P were minimal at the Burned areas relative to Unburned areas. Fire affected plant nutrient limitation patterns, switching from dominantly N-limited to NP co-limited and P-limitation in moss and vascular species respectively. The top 20 cm of the Burned area C concentrations was higher relative to the Unburned area, with increased CN and CP ratios also being found in the Burned area. These findings suggest that the long-term effects of elevated C, N, and P concentrations on plant productivity and decomposition must be re-evaluated for fire disturbance to understand the resiliency of peatland biogeochemistry post-wildfire.

Cross-Layer Leaching of Coal Fly Ash and Mine Tailings to Control Acid Generation from Mine Wastes

Coal fly ash can be used in in various configurations (e.g. as cap, bottom liner, or blending) at a mine site, but comparative studies investigating their capacity to control acid mine drainage are limited. Batch and column leaching experiments were conducted to investigate the effects of fly ash-mine tailings mix ratios and system configurations on leachate chemistry. Acidic mine tailings (pH 2.72) were obtained from waste piles at a former gold and pyrite mine. Mixing the fly ash with the tailings in a 1:1 (w/w) ratio decreased Zn, Ni, Fe, Mn, Pb, and Cu leaching by 90 ± 6%, increased the pH from extremely acidic (2.9) to alkaline (8.0), and decreased electrical conductivity from 4 to 2.5 mS cm−1 due to solute precipitation. Using the fly ash as a ‘chemical liner’ beneath the tailings, applying the fly ash as both a cap and bottom liner, or blending the fly ash with tailings produced significantly less acidity, salinity, and metal leaching than using the fly ash as a cap. The capacity of fly ash to control acid generation is attributed to its acid neutralizing capacity and high pH (11.1).

Recovery of zinc from zinc ash by leaching in sulphuric acid and electrowinning

Oxide fraction of zinc ash originating from hot dip galvanizing plant was investigated. Chemical and phase compositions of the material were characterized in details. The zinc ash contained simonkolleite, zinc oxide and metallic zinc as main phases. Influence of solid to liquid ratio (150–500 kg/m3) and sulphuric acid concentration (20% and 25%) on dissolution of zinc and metallic impurities was investigated. 95–97% zinc recovery was obtained for 150–200 kg/m3 in 20% H2SO4, but the solutions were contaminated mainly by Mn(II) and Fe(II, III) ions. Acid leaching of the zinc ash was accompanied by exothermic effects. Precipitation purification of the leach liquor from iron ions was followed by zinc electrowinning. Final product of 99.5% purity at a current efficiency of 92% was obtained.

Chemical Characteristics of Ash Formed from the Combustion of Shoe Manufacturing Waste in a 2.5 MWth Circulating Fluidized Bed Combustor

The ash formation behaviour and associated compositional characteristics of the combustion of shoe manufacturing waste (SMW) in a 2.5 MWth pilot-scale circulating fluidized bed combustor (CFBC) were investigated to better understand the combustion behaviour and to find effective management strategy for the disposal of the ash streams produced. The compositional characterisations for the ashes produced from the pilot demonstrations showed the presence of a variety of trace heavy metals both in the fly ash and bottom ash. A pronounced uneven partitioning behaviour was observed on the distribution of these heavy metals between the fly ash and bottom ash, and it was found that all the heavy metals except chromium were preferentially enriched in the fly ash, with the contents of lead and cadmium in the fly ash being over 11 and 6 times higher than in the bottom ash. Leaching tests demonstrated that the concentrations of most of the aforementioned metals present in the leachates from the fly ash and bottom ash could meet the permissible limits for landfill disposal but with lead as an exception with its concentration in the fly ash leachates being over 2 times higher than the limit. The total PCDD and PCDF contents both in the fly ash and bottom ash were also much below the legal limit. To further understand the ash behaviour, the slagging and fouling tendency during SMW combustion in the CFBC was examined by use of the characterisation of the ash mineralogy and the results indicated that the SMW ash likely had low tendencies for slagging and fouling. The best two valorization routes for the SMW bottom ash and fly ash were recommended, one being to use them to produce colloidal silica medium to obtain safe inert filler and the other being to use them as the raw materials in the cement industry.

Speciation of major and trace elements leached from coal fly ash and the kinetics involved

The combustion of coal in thermal power plants may result in high concentrations of elements in the coal fly ash remaining that may be toxic to living organisms or pose a risk to the environment. This study was aimed at determining the concentrations of potentially toxic elements in coal fly ash leachates, in an attempt to simulate natural processes that influence the environment. Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and elemental composition studies were employed to characterize the physicochemical properties of the parent coal fly ash. The effect of various leaching parameters, including the pH of leaching solutions, the volume ratio of leaching solutions to the mass of coal fly ash, leaching time and temperature, were investigated. Moreover, the kinetics of the leaching of toxic elements from coal fly ash was also investigated by considering that the leaching process is governed by dissolution. Zero order, pseudo-first order, pseudo-second order, power function, simple Elovich and parabolic diffusion kinetic models were used to evaluate the leaching process. The experimental results indicate that the pH and leaching time had the most significant effect on the leaching behavior of elements from coal fly ash.

A Case Study of Environmental Policies and Guidelines for the Use of Coal Ash as Mine Reclamation Filler: Relevance for Needed South Korean Policy Updates

The South Korean government is pursuing a national project to use the complex carbonates found in coal ash to capture CO2 and promote coal ash recycling. One possible approach is the use of coal ash as fill material in mine reclamation, but environmental concerns have so far blocked the implementation of this procedure, and no relevant regulations or guidelines exist. In this study, we review international approaches to the environmental management of coal ash recycling and consider how the lessons learned can be applied to South Korea. Each studied country was proactively using coal ash for beneficial uses under locally suitable conditions. The United States, European Union, United Kingdom, Australia, and Japan are all putting coal ash to beneficial use following thorough analyses of the environmental impact based on several considerations, including bulk concentration, coal ash leachate concentration, field inspections, and water quality monitoring. Our findings can contribute to the development of proper regulations and policies to encourage the use of recycled coal ash in South Korea as an approach to managing carbon emissions and climate changes. There are currently no relevant regulations in South Korea, so we consider the adoption of the strictest standards at each stage of the other cases at the time of introduction. Based on our findings, detailed and appropriate management guidelines can be developed in the future. Establishing management plans for complex carbonates, verifying their environmental stability, and using them as fill material will provide clear benefits for South Korea in the future.

Bio-electrochemical treatment of food wastewater and copper recovery from copper-contaminated plant with electricity production using biomaterial anode

A lab-based H-type microbial fuel cell (MFC) was developed for the recovery of copper (Cu) accumulated in harvested biomass ash leachate with simultaneous electricity generation and treatment of real food wastewater from cocoa processing (C1), cassava processing (C2) and bakery (C3) at low and high ionic strengths using activated wood (AW) char and activated bamboo (AB) char as anodes. The optimum Cu concentration of 85.37% and 82.14% was recovered for C1 and C3, respectively, with high ionic intensity. The least Cu (23.15%) was recorded for C2 with low ionic strength. The maximum chemical oxygen demand (COD) removal of 79.3% was obtained for C1 with high conductivity in MFCs, whereas C2 with low conductivity gave the lowest COD removal of 47.5%. Maximum power density of 249.88 mW/m2 was attained in C1 at high ionic strength and 65.70 mW/m2 is achieved C2 with low ionic strength. AW char is a cost-effective and sustainable anode material alternative to carbon and graphite-based electrode in MFC. Findings from this study suggested MFC as a feasible low-cost and ecofriendly technology for copper recovery to limit the toxicity effects associated with disposal of harvested copper phyto-accumulated biomass with simultaneous treatment of real wastewater.

A geochemical weathering profile of a fine ash tailings dam and its impact on the underlying aquifers

A weathering profile of an unlined fine ash tailings dam was established with the aid of static and kinetic tests to determine the leachate composition across a tailings dam profile and to evaluate its impact on the underlying aquifers. Kinetic leaching results indicated that SO42−, Ca2+, Na+, Cl−, Mg2+ and K+ ions were highly soluble in both, fresh and weathered fine ash. Leaching rates of elements including Ca, B, Ba and Al decreased with depth and age of the fine ash while V, Mo, Cu, Mn, Si, Li, Cr and SO4 had an increasing leaching rate. A constant leaching rate was measured for Se, Fe, Na, Mg, K, NO3 and Zn. At shallow depth, a weathering zone was identified by a decrease in leaching rates of most elements. Although the hydraulic conductivity of the fine ash dam was low (0.0067 m/d and 0.0367 m/d), long-term hydrochemical monitoring around the tailings dam showed alterations in groundwater types of the underlying aquifers due to seepage. Downstream of the tailings dam, the groundwater type of the shallow weathered aquifer changed from Ca/MgSO4/Cl to NaSO4/Cl and from Na-bicarbonate to Ca/MgSO4/Cl upstream. A reverse trend was observed in the deeper fractured aquifer indicating that the fine ash leachate plume migrated laterally and vertically from the shallower to the deeper aquifer. Hence, the natural clay layer below the tailings dam was insufficient in retaining soluble elements leached from the fine ash over two decades. Therefore, an impermeable liner is recommended prior to the tailings dam construction.

Limitations of the toxicity characteristic leaching procedure for providing a conservative estimate of landfilled municipal solid waste incineration ash leaching

ABSTRACTLimitations of the toxicity characteristic leaching procedure (TCLP) for simulating pollutant leaching from wastes disposed of in full-scale landfills are well understood in the waste management profession; the TCLP solution has a lower pH and greater organic acid content than typical landfill leachate. The TCLP serves its intended regulatory objective, however, as long as a conservative estimate of leaching is provided. Here, we examine TCLP’s ability to represent worst-case leaching conditions for monofilled municipal solid waste incineration (MSWI) ash. A critical examination of TCLP’s applicability to MSWI ash is especially relevant, as ash management at MSWI facilities often centers on passing TCLP, regardless of environmental risk posed by the ash or its recyclability. Multiple batch leaching tests were conducted on different MSWI ash streams: mixed ash, fly ash, and different size fractions of bottom ash. Batch-test results were compared with leachate simulating MSWI ash monofills. The TCLP did not consistently provide the most conservative estimate of leaching, supporting the need to consider alternative methodologies in future regulatory development.Implications: This paper analyzes the existing hazardous waste regulatory testing requirement for municipal solid waste incinerator (MSWI) ash management to evaluate whether the TCLP serves its intended purpose in providing the most conservative estimate of landfilled MSWI ash. The results will serve as guidance and motivation for policy makers and the regulatory community to reevaluate the TCLP’s application for characterizing MSWI ash leaching in certain disposal scenarios and could promote consideration of alternative testing procedures based upon results of this study. This study serves to promote representative and accurate quantification of leaching risk from MSWI ash.

Selective Recovery of Rare Earth Elements from Coal Fly Ash Leachates Using Liquid Membrane Processes.

Coal combustion residues and other geological waste materials have been proposed as a resource for rare earth elements (REEs, herein defined as the 14 stable lanthanides, yttrium, and scandium). The extraction of REEs from residues often generate acidified leachates that require highly selective separation methods to recover the REEs from other major soluble ions in the leachates. Here, we studied two liquid membrane processes (liquid emulsion membranes, LEM, and supported liquid membranes, SLM) and compared them to standard solvent extraction techniques for selective recovery and concentration of REEs from a leachate of coal fly ash. All separation methods involved an organic solution of di(2-ethylhexyl)phosphoric acid dissolved in kerosene or mineral oil and an acid strippant solution of 5 M nitric acid for the liquid-based separations. The LEM configuration, which separated REEs by immersing an acid-in-oil emulsion in the ash leachate, resulted in similar recovery percentages of individual REEs as the conventional solvent extraction approach. The recovery of REEs in the SLM configuration, which involved the impregnation of the solvent in a hydrophobic membrane, was slower than the LEM process. However, the SLM process was notably more selective for the heavy (and higher value) REEs, while the conventional extraction and LEM processes were more selective for the light REEs. A flux-based model of the extraction processes suggested that recovery rates were limited by REE affinity for the solvent chelator in the SLM, while the rates of REEs separation via LEM were limited by diffusive mass transfer across the liquid membrane. Altogether, these results help to identify specific steps in the recovery process that future work should target in the development of scalable liquid membrane separations for REE recovery.

The study on determination of Fluoride in Aluminum Ash Leachate

The content of fluoride ion in aluminum ash leaching solution was measured by using the ion selective electrode method accurately. The measure conditions were also studied. Theoretical and experimental results show that pH, temperature, instrument performance and coexisting ions have an important influence on the measure of fluoride ions in aluminum ash leaching solution. Hydrochloric acid was added to adjust pH closing to the neutral and adding 10 mL total ionic strength adjustment buffer solution, Controlling the pH between 5-6. The temperature was consistent with the standard solution, and the measurement result was the most accurate. The fluoride ion content in the aluminum ash leaching solution reaches 446mg/L, far exceeding the national standard.

Rare earth elements and yttrium in coal ash from the Luzhou power plant in Sichuan, Southwest China: Concentration, characterization and optimized extraction

Coal ash is considered as a promising alternative resource for rare earth elements and yttrium (REE + Y or REY) recovery. Coal ash samples (fly ash and bottom ash), as well as corresponding feed coals, collected from the Luzhou coal-fired power plant in Sichuan, southwestern China were analyzed for their chemical and mineralogical characteristics. The fly ash was further tested for its feasibility of REE extraction. The feed coals are characterized as a low-volatile bituminous, medium‑sulfur, and high-ash coal, sourced from the Guxu coalfield (Late Permian Longtan Formation) in Sichuan, SW China. REE and Y, along with high-field-strength elements Zr(Hf) and Nb(Ta), and Li, F, Sc, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Sr, Cd, In, Sn, Hg, Th, U, are all enriched in the feed coal. The mineralogical compositions of the feed coals are dominated by kaolinite and illite/smectite (I/S) mixed layers, followed by the carbonate minerals including calcite, siderite, ankerite, and minor amounts of anatase and jarosite.The combustion of the feed coals produces a Class F fly ash, characterized by an aluminosilicate composition with a low CaO content. The bottom ash is compositionally similar to the fly ash, except that it is more enriched in high-density elements (Fe and Mn), and more depleted in volatile elements. REY are enriched in both the fly ash and bottom ash, although heavy REY (HREY) are notably more enriched in the fly ash. Mineralogical analysis shows that the fly ash consists of >70% amorphous glass and <30% mineral phases such as mullite, quartz and iron oxides. The bottom ash is composed of ~60% amorphous glass but with a more complex mineralogical composition than the fly ash. Dissolution of the fly ash and bottom ash with 4% hydrofluoric acid (HF) showed that ~90% of all the REY are associated with the amorphous glass in the fly ash, whereas <50% of REY in the bottom ash is contained in the glassy component. An alkaline-acid-combined (NaOH-HCl) sequential leaching process was employed to test the extractability of REY in the Luzhou fly ash. The experimental variables, including extractant concentration, liquid-to-solid ratio, leaching temperature and leaching time, were optimized by an orthogonal array design. The optimal NaOH leaching conditions results in 41.10% of active silica removal from the fly ash and 39.43% of REY enrichment. The HCl leaching of desilicated fly ash achieves 88.15% of REY extraction efficiency under the optimal conditions, which is a dramatic increase as compared to the same leaching of raw fly ash. Even though the extraction efficiency may vary between different coal ashes from various sources, a complete REY extraction procedure from fly ash is suggested for future use.