Metals In Ash Research Articles

Evaluation of Residual Stress in Stir-squeeze Cast Aluminium – Fly Ash Composites Using X-Ray Diffraction Method

Determination of residual stresses in metals, subjected to secondary processing, is necessary from the point of view of their applications and is widely studied in literature. However, residual stresses induced during service is generally ignored when evaluating the performance of the component. The residual stress in a component could be tensile or compressive in nature and eventually affects its service life under external loading. In this regard, industries demand rapid, efficient, and easier methods of non-destructive testing to identify and control the residual stress in such components. The present work aims at evaluation of residual stress in an LM-25 aluminium alloy/fly Ash Metal Matrix Composites (AMC) after subjecting the specimen to dry sliding wear tests. X-ray diffraction technique was used to measure the residual stress in the “pin” specimen of the pin-on-disc set-up. The residual stress was ~ 24 % higher in the composite compared to the un-reinforced alloy after the wear test while the wear rate, measured in terms of weight loss of the pin, was lower by about 50%, under similar test conditions.

Speciation distribution and leaching behavior of heavy metals in coal gasification fine ash: Influence of particle size, carbon content and mineral composition

In this study, the occurrence and distribution of heavy metals in coal gasification fine ash (CGFA) with different particle sizes were investigated to ensure safer disposal and utilization strategies for CGFA. These measures are critical to sustainable industrial practices. This study investigates the distribution and leachability of heavy metals in CGFA, analyzing how these factors vary with particle size, carbon content, and mineral composition. The results demonstrated that larger CGFA particles (>1 mm) encapsulated up to 70 % more heavy metals than smaller particles (<0.1 mm). Cr and Zn were present in higher concentrations in larger CGFA particles, whereas volatile elements such as Zn, Hg, Se, and Pb were found in relatively higher contents in finer CGFA particles. At least 70 % of Hg in CGFA was present in an acid-soluble form of speciation, whereas Cd, Zn, and Pb were mostly present in a reducible form of speciation, which could be attributed to the presence of franklinite. More than 40 % of Cd and Zn in fine CGFA particles exist in an acid-soluble form. With the exception of CGFA_1.18, Se in CGFA mainly existed in an oxidizable form at a ratio of 60 %–80 %. This could be attributed to the presence of bassanite particles as well as the higher affinity of Se for S. In contrast, Cr, Cu, and As were mostly present in residual speciation forms owing to their parasitism in quartz, sillimanite, and amorphous Fe solid solution in CGFA. Additionally, the study revealed that there was no significant relationship between heavy metal content, leaching behavior, and carbon content in CGFA. Based on combined analyses using toxicity characteristic leaching procedure (TCLP) leaching concentrations and risk assessment code (RAC) results, it is recommended to focus on the environmental risks posed by Cd, Cr, Pb, Zn, and Hg in CGFA during their modification and utilization processes.

A study of the stabilization and solidification of heavy metals in co-vitrification of medical waste incineration ash and coal fly ash

Medical waste incineration ash (MWIA) has significant concentrations of heavy metals, dioxins, and chlorine that, if handled incorrectly, might cause permanent damage to the environment and humans. The low content of calcium (Ca), silicon (Si), and aluminum (Al) is a brand-new challenge for the melting technique of MWIA. This work added coal fly ash (CFA) to explore the effect of melting on the detoxication treatment of MWIA. It was found that the produced vitrification product has a high vitreous content (98.61%) and a low potential ecological risk, with an initial ash solidification rate of 67.38%. By quantitatively assessing the morphological distribution features of heavy metals in ashes before melting and molten products, the stabilization and solidification rules of heavy metals during the melting process were investigated. This work ascertained the feasibility of co-vitrification of MWIA and CFA. In addition, the high-temperature melting and vitrification accelerated the detoxification of MWIA and the solidification of heavy metals.

Determination of Concentration of Heavy Metals in Wood Ash

Heavy Metals such as lead, chromium, and arsenic are thought to be present in wood ashes. As many people use wood ash in gardens, we decided to test how easily these metals can be extracted from wood ash. Metals were extracted from 10-gram samples of ash by mixing with 100 ml of 2.0% trace metal nitric acid, gravity filtering, and final filtering with a 0.22 um. nylon syringe. Absorption data for the extracted samples was compared to a calibration curve of absorption versus concentration constructed from data obtained with a Shimadzu AA7000. Initial results indicate that the concentration of the metals are below the lower limit of detection for Cr, As, and Pb which are 0.2 ppm, 2.0 ppm, and 0.5 ppm respectively. However, the laboratory-fortified matrix sample for each metal failed, thus we will need to perform standard addition tests to certify these results. This work was supported by NASA WV Space Grant Consortium training grant number 80NSSC20M0055.

Chemical speciation and environmental risk assessment of heavy metals in ash from smouldering combustion of oily sludge

Smouldering combustion of oily sludge (OS) was carried out to learn the characteristics of heavy metals (HMs) in ash products. Ash collected from four different height layers of the column reactor was analysed for the chemical speciation and environmental risk of six HMs, including Cr, Ni, Cu, Zn, As, and Pb. The results showed that after smouldering combustion, only 21.3–32.2 % of the total HMs was remained in the ash products. The retention of HMs in ash was closely relevant to the carbonaceous destruction efficiency of OS. Smouldering combustion led to the decrease of HMs in acid-soluble/exchangeable fraction from 21.5–49.3 to 0.8–19.8% and oxidizable fraction from 22.6–49.6 to 5.3–21.3, and the increase of reducible fraction from 13.6–38.0 to 30.5–89.1% and residue fraction from 7.8–27.3 to 24.1–63.6%. Upward migration of HMs during smouldering was evidenced by their occurrence in the top clean sand layer, which was dominated in acid-soluble/exchangeable and reducible fractions, accounting for 89.7–99.1% in total. Toxicity extraction and environmental risk studies indicated that smouldering combustion would effectively reduce the toxicity and pollution risk of HMs; however, attention should be paid to the disposal of the top sand layer after smouldering operation due to its high pollution risk of HMs according to the evaluation of Risk assessment code.

Residual, sequential extraction, and ecological risk assessment of some metals in ash from municipal solid waste incineration, Vietnam

Abstract Incineration plants for electricity generation have offered a solution to the challenges of domestic solid waste treatment in many countries. However, their emissions, fly ash (FA) and bottom ash (BA), have had a detrimental impact on environmental quality. This study investigated the morphology, element composition, and concentration of metals in FA and BA from municipal solid waste incineration plants using scanning electronic microscopy/energy-dispersive X-ray and inductively coupled plasma mass spectrometry techniques. It also evaluated the distribution ratios of metal species across five fractions: exchangeable, carbonate-bound, oxide-bound, organic-bound, and sulfide-bound, and residual. The total metal content in both FA and BA was comparable, with calcium having the highest concentration (28,170–135,130 mg·kg−1 dry weight) and silver having the lowest (5.26–19.3 mg·kg−1 dry weight). However, the percentage proportion of metals differed between the extracted fractions. Except for cadmium in FA, ecological risk assessment indicated low direct bioavailability and potential risk of metals in both FA and BA. These findings contribute to the hazard assessment of FA and BA generated from waste incinerators and provide a scientific basis for developing treatment techniques for this type of waste.

Risk control of heavy metal in waste incinerator ash by available solidification scenarios in cement production based on waste flow analysis

Incineration is a common method in municipal solid waste management, which has several advantages such as reducing the volume of waste, but with concerns about exhaust gas and ash management. In this study, heavy metals in bottom ash, secondary furnace ash and fly ash of two waste incinerators in Tehran and Nowshahr were analyzed and its control in cement production was investigated. For this purpose, twelve monthly samples of three types of incinerator ash were analyzed. By combining the studied ashes in the raw materials, the quantity of metals in the cement was analyzed. Finally, by investigating four scenarios based on quantitative variations in the routes of municipal solid waste, ash quantity and the related risk caused by its heavy metals were studied. The results showed that the concentration of heavy metals in the three ash samples of the studied incinerators was 19,513–23,972 µg/g and the composition of the metals included Hg (less than 0.01%), Pb (2.93%), Cd (0.59%), Cu (21.51%), Zn (58.7%), As (less than 0.01%), Cr (15.88%), and Ni (0.91%). The best quality of produced cement included 20% ash and 10% zeolite, which was the basis of the next calculations. It was estimated that the reduction of the release of metals into the environment includes 37 gr/day in best scenario equal to 10.6 tons/year. Ash solidification can be considered as a complementary solution in waste incinerator management.

Purification of lipid oil using ion exchange resins

AbstractOil upgrading technologies for fuel production from second-generation feedstocks require pretreatments, such as the removal of ash metals in crude oil, to improve the catalytic performance in the process. The aim of this work was to purify lipid crude oil, derived from black soldier fly larvae (BSFL), from calcium by dry washing using ion exchange resins. Commercially available ion exchange resins suitable for organic liquids, namely GF 202 and Amberlyst 15DRY (AL 15), were selected for the purification experiments. The lipid material dissolved in nonanoic acid in different concentrations of mixtures was passed through a resin-filled plug-flow reactor at 50 °C and 75 °C with a liquid hourly space velocity (LHSV) of 4 h−1. The oil samples were analyzed for calcium using inductively coupled plasma-optical emission spectrometry, while the resin surfaces were examined by scanning electron microscopy. AL 15 showed a better overall performance and led to a case where over 99% of calcium was removed. Graphical abstract

Quantification of Bioaccessible and Environmentally Relevant Trace Metals in Structure Ash from a Wildland-Urban Interface Fire.

Wildfires at the wildland-urban interface (WUI) are increasing in frequency and intensity, driven by climate change and anthropogenic ignitions. Few studies have characterized the variability in the metal content in ash generated from burned structures in order to determine the potential risk to human and environmental health. Using inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS), we analyzed leachable trace metal concentration in soils and ash from structures burned by the Marshall Fire, a WUI fire that destroyed over 1000 structures in Boulder County, Colorado. Acid digestion revealed that ash derived from structures contained 22 times more Cu and 3 times more Pb on average than surrounding soils on a mg/kg basis. Ash liberated 12 times more Ni (mg/kg) and twice as much Cr (mg/kg) as soils in a water leach. By comparing the amount of acid-extractable metals to that released by water and simulated epithelial lung fluid (SELF), we estimated their potential for environmental mobility and human bioaccessibility. The SELF leach showed that Cu and Ni were more bioaccessible (mg of leachable metal/mg of acid-extractable metal) in ash than in soils. These results suggest that structure ash is an important source of trace metals that can negatively impact the health of both humans and the environment.

Heavy metals behavior of co-combustion ash from sewage sludge and coal slime: Temperature and mixing ratio dependence, interactions and speciation

Co-combustion of municipal sludge (SS) and coal slime (CS) is an effective route to achieve the co-disposal of solid wastes. This work addresses the problem of heavy metal pollution in co-combustion ash, aiming to reveal the effect of interactions in SS-CS co-combustion on the behavior of heavy metals and the control mechanism of minerals using the inductively coupled plasma mass spectrometry (ICP-MS) technique and the Community Bureau of Reference (BCR) method. The residual rate of heavy metals in CS ash monotonically decreased with increasing combustion temperature, while the residual rate of heavy metals in SS tended to increase when it was burned at high temperatures. Increased temperature enhanced the effect of SS-CS interaction on heavy metals. The interaction significantly inhibited the volatilization of As, and the As residue of the blend containing 50% CS (5SS5CS) at 1000 °C was 14.9% higher than the theoretical value. Typical minerals in SS had significant effects on heavy metal migration in CS, and the effects of CaO and Fe2O3 on heavy metals were mainly due to chemical interactions, in which CaO fixed As in the form of Ca3(AsO4). Density functional theory calculations show that the optimal adsorption sites for both As and As2O3 on the CaO(001) surface were O-top sites, and the presence of O defect on the surface led to enhanced interaction of As2O3 with the surface. Co-combustion led to an increase in the residual fractions of heavy metals, but the exchangeable and acid soluble fraction of As in 5SS5CS was still as high as 19.3%, so the ecological impact of As should be considered in further utilization of the co-combustion ash.

Physicochemical characteristics of bottom ash from waste-to-energy incineration pilot plant in Indonesia

Municipal solid waste (MSW) disposal has emerged as a major concern in large cities across Indonesia. Waste-to-energy (WtE) incineration is an attractive method that can significantly reduce volume of waste; however it generates residues, namely bottom ash and fly ash. This study presents the characteristics of bottom ash from the MSW WtE incineration pilot plant in Indonesia. The physicochemical characterization of bottom ash was determined X-ray fluorescence (XRF) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS). The results showed that CaO (46.80%) was the major component, followed by SiO2 (12.30%), Al2O3 (8.80%), and Fe2O3 (8.20%). SEM images showed that the surface morphology of bottom ash appeared flaky, rod-like, and irregular shape. Inert materials, like iron scrap, glass, ceramic, and stone, accounted for 16.7% of the total dry weight of bottom ash. Toxicity characteristic leaching procedure (TCLP) test of 11 heavy metals in bottom ash was carried out, and all of them were detected at very low concentration, indicating that bottom ash possessed a low risk level to human health and environment. This study provides important information on the characteristics of bottom ash from MSW WtE incineration in Indonesia that would be useful in facilitating management and disposal of bottom ash.

Identification and Parametrization of Key Factors Affecting Levoglucosan Emission During Solid Fuel Burning.

Levoglucosan (LG) is a pyrolysis product of cellulose and hemicellulose at low combustion temperatures. However, LG release cannot be determined only by considering the contents of cellulose and hemicellulose exclusively due to the complexity of combustion processes and the physical-chemical properties of the fuel. This study detected the emission factors (EFs) of LG from 22 different solid fuel samples (including coal and biomass) by considering 18 different fuel properties and five combustion parameters. The average LGEFs during solid fuel burning varied in a range of 0.03-136 mg kg-1, with a magnitude difference of 1-4 orders. While the variations in cellulose (59.5-368 mg g-1) and hemicellulose (73.5-165 mg g-1) contents of fuel samples were only one- to 6-fold. A short combustion duration (<150 min) and a medium combustion temperature (200-400 °C) influenced by volatile and ash contents are crucial for the generation and accumulation of LG. A random forest coupled with the Akaike information criterion stepwise regression model successfully explained 96% of the total LG emission variation using three variables (ash content, cellulose content, and modified combustion efficiency). The ash content promoted coke formation and LG chain cracking by increasing the pyrolysis temperature and is considered the most important factor. The alkali metal in ash can reduce the energy barrier of intramolecular ring contraction reactions and inhibit the dehydration reactions, which led to additional heat being utilized by the competitive pathways of LG formation. This study provided a method to address the parametrization and release mechanisms of combustion source emissions.

Emission of nitrogen/sulfur pollutants and migration of heavy metals during combustion of oily sludge from the oil refining process in fluidized bed

Oily sludge is a kind of hazardous waste due to the enrichment of nitrogen, sulfur, and heavy metals. In this work, the combustion of oily sludge from an oil refining factory in a fluidized bed reactor at 850–1050 °C and 0.8–1.2 excess air ratios were studied, with a focus on emission of nitrogen and sulfur pollutants and migration of Cr, Ni, Cu, Zn, Cd, Pb. The emission characteristics of nitrogen and sulfur pollutants were exhibited through monitoring the flue gas. The migration characteristics of heavy metals were clarified by analyzing their retention in bottom and fly ash. Moreover, the BCR (European Community Bureau of Reference) sequential extraction of the heavy metals in bottom ash was also carried out to obtain the migration of heavy metals in different forms. The contents of NOx and SO2 in the flue gas increased with temperature and excess air ratio increasing. High temperature led to less heavy metal retention in the bottom ash. The strong oxidizing atmosphere can weaken the volatilization of heavy metals. The stabilities of the heavy metal in different forms were in the following order: F4 (residual fraction) > F3 (oxidizable fraction) > F2 (reducible fraction) > F1 (exchangeable and acid soluble fraction). F4 was the dominant fraction of heavy metals in the bottom ash. The >60 % content of F3 and F4 led to the high stability of Cu and Ni while the >57 % content of F1 and F2 led to the high volatility of Cd and Pb in bottom ash. The differences in the component map of F1-F4 for the six heavy metals gave rise to their different migration characteristics during combustion.

Changes in the Number of Volatile Components in the Soil Under the Influence of Household Waste

Today, almost all large cities have a landfill for municipal solid waste, where solid waste is dumped, stored and partially disposed. Storage and disposal of household waste (mainly by burning) can negatively impact the structure, productivity indicators, and the agroecological state of the soil cover common around the landfill. Such high levels of heavy metals and metalloids in household waste ash, in turn, lead to soil contamination around the landfill. The reason is that the process of incineration and open storage of waste has a very negative impact on the environment. It should be noted that the level of heavy metal contamination of the soil around the domestic landfill is low. However, failure to fully comply with the measures for storage and disposal of waste can lead to contamination of soils around the landfill with heavy metals since the content of heavy metals in ashes is very high. Soil pollution with household waste affects all processes occurring in it and has a detrimental effect on the activity of living organisms living in the soil. In particular, soil pollution with household waste changes the amount of organic volatile compounds in the organic part of the soil. Studies have shown that benzofuran organic volatile compounds not found in background soils can be found in soils around municipal waste when exposed to pollution. Some compounds, such as carbonic acid-10.99% and di-n-desylsulfone-0.47%, which are noted in the background soils, were not found in soil sample No. 1 taken at the landfill. These compounds are removed from the soil as a result of waste incineration and other processes.

Optimizing abrasive wear loss of Aluminum/Fly Ash and Aluminum/Rice Husk Ash metal matrix composites using AHP-EDAS and AHP-COPRAS techniques for enhanced performance

Lightweight aluminum metal matrix composites (MMCs), Aluminum/Fly Ash and Aluminum/Rice Husk Ash were developed using the stir casting route for automotive applications. As a result of the above consideration, automotive parts such as brake rotor and connecting rod, etc. have been the subject of research in a variety of areas. Finding the right material for the design under consideration requires an effective approach to material selection. Multi-criteria decision-making (MCDM) processes are helpful when dealing with ambiguity in material selection. To rank aluminum-Fly Ash (FA) and Aluminum-Rice Husk Ash (RHA) composites, integrated MCDM methodologies such as Analytical Hierarchy Process (AHP)–Evaluation Based on Distance from Average Solution (EDAS) and AHP–Complex Proportional Assessment (COPRAS) are utilized. The weights for each criterion are determined using the AHP approach, and the EDAS and COPRAS techniques are then used to rank the items. Three different particle sizes (0–53, 54–74, and 75–105 µm) of the reinforcement have been chosen for the selection criteria. Density, hardness, ultimate tensile strength, and compressive strength, and specific wear rate, and coefficient of friction of the manufactured composites evaluated. A thorough examination of the MCDM methods found that Al-FA composites with particle sizes of 54–74 µm were the most effective.

New insight to migration and influence of potassium element on combustion of coal/biomass char-slag interface

Co-combustion of biomass and coal can both support heat requirement of a boiler and reduce carbon emission while the high contents of alkali metals (e.g. Na, K) in ash are key factors in the stable operation. In this study, the migration behavior and influence of K on the combustion of coal/biomass char particles on the slag surface were investigated with visualization experiments and surface analytical techniques. The results showed that the addition of K in the slag can accelerate the combustion process of coal char particles on the slag surface, which proved that K+ was not deactivated as ionic state in the slag. The promotion effect of potassium was mainly reflected in accelerating the combustion rate at the beginning stage, where the carbon conversion was below 0.2, compared to the resting stage. K was proved to migrate from the slag side to the interface of char particles and slag and aggregated with Al during the combustion process, while other elements were enriched on the slag surface outside the combustion zone. Results also showed that the combustion of biomass char particles (rice straw char) on the slag surface with less K was inhibited. However, K was found to aggregate on the interface of biomass char and slag throughout the combustion process with no diffusion. A migration mechanism was proposed that the combustion of char particles on the slag surface caused an increasing temperature and further depolymerization of aluminosilicates, with alumina replacing silicon to form aluminum tetrahedra while adsorbing K+ to the interface and promote the combustion.

Ecological risk assessment of heavy metals in bottom ashes generated by small-scale thermal treatment furnaces for domestic waste in villages and towns of China.

Small-scale Solid Waste Thermal Treatment (SSWTT) is prevalent in remote Chinese locations. However, the ecological threats associated with heavy metals in resultant bottom ash remain undefined. This research study scrutinized such ash from eight differing sites, assessing heavy metal content, chemical form, and leaching toxicity. Most bottom ash samples met soil contamination standards for development land (GB36600-2018). However, levels of As, Cd, Cr, Cu, Ni, Pb, and Zn in some samples exceeded agricultural land standards GB15618-2018) by 1591%, 64,478%, 1880%, 3886%, 963%, 1110%, and 2011% respectively. Additionally, the As and Cd contents surpassed the construction land control limit value by 383% and 13% respectively. The mean values of the combined oxidizable and residual fraction (F3 + F4) for each heavy metal in all samples exceeded 65%, with Cr, Cu, Ni, and Pb reaching over 95%. All sample leaching concentrations, obtained via the HJ/T 299 procedure, were less than limits set by the identification standards for hazardous wastes (GB5085.3-2007). However, only the leaching concentrations of three samples via the leaching procedure HJ/T 300 met the "Solid Waste Landfill Pollution Control Standard" (GB 16889-2008). The results indicate that the location and type of SSWTT equipment play a crucial role in determining an appropriate solution for bottom ash management.

The ecological assessment of the purity of medicinal plant raw materials &lt;i&gt;Thymus serpyllum&lt;/i&gt; L. in the Trans-Urals of the Republic of Bashkortostan

The paper presents the results of the study of heavy metals content in plant raw materials Thymus serpyllum L. growing in the vicinity of the village of Arkaim, Sibay, the Republic of Bashkortostan. The content of mobile forms of Cu, Ni, Mn, Co, Fe, Cd in soils did not exceed the maximum permissible concentrations, with the exception of Zn (1,87 MPC) and Pb (3,16 MPC). It was found that the most mobile element in the soil was Pb (59,4%), while Ni (0,07%) was less mobile. The soils of the studied territory were classified as permissible according to the degree of pollution, and the ecological situation turned out to be relatively satisfactory. The results of the statistical analysis showed that the concentrations of heavy metals in plant ash had a high variability (above 21%), with the exception of Co, which was characterized by an average variability (up to 20%). Cu content in Thymus serpyllum L. plants did not exceed acceptable values. There were exceeding of the maximum permissible levels for Zn (3,889,72 times), Fe (6,457,9 times), Ni (108189 times), Cd (1,162,16 times), Co (3,75,6 times), Pb (4,610,8 times) in all organs of the plant Thymus serpyllum L. Mn concentrations exceeded the norms in the stems and roots of the species by 1,514,48 times, respectively. The most absorbed by plants Thymus serpyllum L. elements turned out to be Fe and Ni. In plants Thymus serpyllum L. Fe (124,3) and Ni (1567,5) belonged to the group of elements of energetic accumulation (IA 10), Zn (8,12), while Cu (8,04), Mn (4,44), Pb (2,08), Cd (1,75), Co (1,31) belonged to the group of elements of strong accumulations (IA 110). In plants of Thymus serpyllum L. Cu, Zn, Ni, Fe, Mn, Pb were distributed by acropetal type (acropetal coefficient 1,0), while Cd, Co were distributed by basipetal type (acropetal coefficient 1,0).

Aluminosilicate Clay Minerals: Kaolin, Bentonite, and Halloysite as Fuel Additives for Thermal Conversion of Biomass and Waste

The current focus on renewable energy sources and the circular economy favors the thermal conversion of low-quality fuels, such as biomass and waste. However, the main limitation of their usability in the power sector is the risk of slagging, fouling, ash deposition, and high-temperature corrosion. These problems may be avoided or significantly mitigated by the application of aluminosilicate clay minerals as fuel additives. In this paper, the three most commonly occurring aluminosilicates are reviewed: kaolin, halloysite, and bentonite. Their application has been proven to minimize combustion-related problems by bonding alkalis in high-melting compounds, thus increasing ash melting temperatures, reducing ash deposition tendencies, and decreasing the particulate matter emission. Due to excellent sorption properties, aluminosilicates are also expected to fix heavy metals in ash and therefore decrease their emissions into the atmosphere. The application of aluminosilicates as fuel additives may be a key factor that increases the attractiveness of biomass and other low-quality fuels for the power sector.

Progress and Challenges of Biological Leaching of Heavy Metal in Coal Ash from a Power Plant

Bioleaching is a technique for reducing the heavy metal content of coal ash by using bacteria, fungi, or yeast. Previous studies in heavy metal bioleaching of coal ash discussed the factors affecting the process, but as yet there is little information on the challenges of using microorganisms. Therefore, this study aimed to obtain comprehensive information regarding the use of microorganisms in heavy metal bioleaching. Heavy metal concentrations in coal ash are low, and the metals are diverse. The components of coal ash are complexes that cannot leach certain heavy metals according to previous studies. These low concentrations and complex components make it difficult to investigate the bioleaching mechanism. The combination of biological and chemical interactions involves various components in this system. The high concentration of iron and heavy metal leached could be toxic for microorganisms. The process is influenced by several factors, such as particle size, pH, and pulp density. Most heavy metal bioleaching studies on coal ash have been conducted on a small scale to control conditions affecting the process. Bioleaching kinetics in coal is a liquid-solid reaction that can be represented by the shrinking core model, which was mainly used in this study.