Fly Ash Leachate Research Articles

An H3O-Alunite Method for Production of Smelter Grade Alumina from an Ammonium Alum Solution after High-Pressure Acid Leaching of Coal Fly Ash

An H3O-Alunite Method for Production of Smelter Grade Alumina from an Ammonium Alum Solution after High-Pressure Acid Leaching of Coal Fly Ash

Selective separation and recovery of rare-earth elements (REEs) from acidic solutions and coal fly ash leachate by novel TODGA-Impregnated organosilica media

Rare-earth elements (REEs) are essential in a wide range of applications including magnets and satellite technology, with demand driven by geopolitical factors. While multiple techniques exist for REE recovery including solvent extraction and selective precipitation, solid–liquid extraction offers key advantages in selectivity, scalability, and recyclability. N, N, N′, N′-tetraoctyl diglycolamide (TODGA) is a tridentate ligand widely used in solvent extraction, but the incorporation in a solid support to separate individual lanthanides from acid solutions remains largely unexplored. A novel TODGA-organosilica sorbent material was developed and tested to evaluate recovery of 17 elements (REEs and thorium) in terms of selectivity, kinetics, and equilibrium isotherms in 0.01 to 15.9 M nitric acid. Characterization of the new sorbent was performed before and after sorption using FTIR, XPS, and SSA techniques to help elucidate sorption mechanisms and limiting variables. REE adsorption increased from 1.26 mg g−1 to 10 mg g−1 with nitric acid concentrations of 0.01 M and 15.9 M, respectively. TODGA-organosilica exhibits high selectivity towards heavy REEs (Dy to Lu), with minimal sorption of lighter REEs (Ce to Gd). Batch adsorption experiments confirm pseudo-second-order kinetics and a Langmuir adsorption isotherm with TODGA binding to REEs in a 3:1 complex. A packed bed column study confirmed the high selectivity of TODGA-impregnated organosilica towards heavy REEs and a proof-of concept experiment with coal fly ash leachate shows high selectivity for REEs over Al, Fe, and Ca present in several orders of magnitude higher concentrations. Fractionation was observed where loading cycle effluent contained 84 % light REEs while strip cycle effluent contained 80 % heavy REEs. More than 90 % of loaded REEs were successfully stripped with water as the stripping agent.

Optimization of Culture Conditions for Microalgae Treatment Fly Ash Leachate System

In order to explore the feasibility of using algae to treat the fly ash leachate from a safe landfill site, leachate samples taken from a certain safe landfill site in Wenzhou City were treated with two different microalgae, Chlorella vulgaris and Scenedesmus obliquus, and the effectiveness of each treatment was evaluated in terms of its efficiency of pollutant removal. The effects of conditions such as pretreatment of leachate by sterilization, the initial concentration of leachate, and the addition of nutrients on pollutant removal efficiency and algae growth were studied. Sterilization of the leachate was found to have a relatively small impact on the growth of C. vulgaris and S. obliquus, as well as the removal of pollutants from the leachate. Therefore, sterilization treatment may not be necessary for engineering applications. Algal growth and the removal of pollutants were optimal when the leachate was used at a concentration of 10%, but when the leachate concentration was 30% or higher, the growth of both algae was weakened. The inclusion of 0.2 g/L K2HPO4·3H2O and 0.06 g/L ammonium ferric citrate in the system led to higher algal growth and pollutant removal. The chlorophyll a levels of C. vulgaris and S. obliquus were 555.53% and 265.15%, respectively, and the nitrogen removal rates were also the highest, reaching 59.51% and 56.69%, respectively. This study optimized the cultivation conditions of a microalgae treatment leachate system, providing technical support and a theoretical basis for the practical engineering of a harmless treatment of leachate.

Coupled physicochemical dual-crosslinking Ti3C2Tx composite aerogels for the selective adsorption of gallium ions in acid fly ash leaching

Herein, in order to extract Ga3+ from acid fly ash leaching, we propose a functionalized Ti3C2Tx-based MXene composite aerogel adsorbent for Ga3+ adsorption. The prepared physicochemical dual-crosslinking network aerogel MPHG-40 possesses good Ga3+ adsorption performance (132.52 mg g−1) at the pH of 3 and Ga3+ initial concentration of 50 mg L−1 within 6 h. After five adsorption-desorption cycles, the material shows good mass retention and a 95.65 % retention of its initial adsorption capacity, compared to most reported adsorbents. The optimized adsorbent realized good selective adsorption of Ga3+ against Cu2+, Zn2+, Fe3+, and Al3+ in a simulated acid fly ash leaching with the selective coefficient of 8.63, 96.10, 4.49, and 28.30, respectively. The adsorption may comply with a combined mechanism of physical adsorption, electrostatic interactions, ion-exchange mechanism, and ligand chelation, dominated by chemical adsorption, as identified by theoretical calculations based on density functional theory and experimental data. The three-dimensional solid adsorbent constructed in this study provides a new strategy for selective adsorption of Ga3+, making it possible to be applied to solid waste utilization of fly ash.

Reactive Transport Modeling to Predict Leaching of Coal-Derived Fly Ash

Reactive Transport Modeling to Predict Leaching of Coal-Derived Fly Ash

Efficient recovery of aluminum, lithium, iron and gallium from coal fly ash leachate via coextraction and stepwise stripping

The recovery of critical metals from industrial waste is very important and challenging. This work proposed an efficient process for recovering aluminum, lithium, iron and gallium from coal fly ash leachate. Firstly, 98.1 %, 86.6 % and 99.8 % of iron, lithium and gallium are coextracted by tributyl phosphate (TBP), facilitating the subsequent use of the aluminum raffinate. The spectroscopic analysis verifies the formation of [Li(TBP)2][FeCl4] and [Li(TBP)2][GaCl4]. Afterwards, the effective separation of lithium, iron, gallium in TBP is achieved by stepwise stripping. Lithium can be almost completely stripped using 6 mol/L HCl with free iron and gallium of loss. An extremely high separation factor of iron and gallium (αFe/Ga, 1175) can be achieved through reduction stripping by precisely controlling pH value and oxidation–reduction potential. Finally, about 99.5 % of gallium can be stripped with 0 ∼ 1 mol/L HCl. This work realizes the synergistic recovery of valuable metals from waste resources.

Study on semi-dynamic leaching and microstructure characteristics of MSWI fly ash solidified sediment

municipal solid waste incineration (MSWI) fly ash partially replaces cement to solidify sediment, and then can be used as intermediate cover materials in landfill as one of the resources utilization ways of MSWI fly ash and sediment. The strength and the semi-dynamic leaching characteristics of MSWI fly ash solidified sediment under hydrochloric acid attack at different pH were studied by means of unconfined compressive strength (UCS), semi-dynamic leaching, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA). Results revealed that the UCS strength increased as the curing age and cement content increased. When the curing content is 50% and the replacement ratio of MSWI fly ash is 75% and 80%, the UCS of 7 d can be greater than 50 kPa. The primary contribution to the strength development was from silicic acid gels such as calcium silicate hydrate (C–S–H) and carbonates. Notably, the leaching behavior of Zn and Cu within the solidified sediment underwent substantial alterations. The leaching amount of heavy metals in a strong acidic environment (pH = 2) is significantly greater than that in a weak acidic (pH = 4) and neutral (pH = 7) environment. Conversely, minimal disparities were observed in the leaching characteristics of Zn and Cu between the weakly acidic and neutral environments. Ca(OH)2, C–S–H and carbonate exhibits a remarkable acid-resistant buffering capacity in the solidified sediment. The obvious diffusion coefficient (Dobs) was less than 10−9 m2/s in semi-dynamic leaching tests. Moreover, the mobility of Zn and Cu surpassing 12.5, coupled with a leaching index exceeding 8, further attests to the favorable S/S outcome achieved. Based on these findings, the solidified material is confidently recommended to be used as suitable landfill middle soil cover material.

Leaching kinetics and reactivity evaluation of fly ash based on the synergistic effect of alkali and sulfate

This work evaluates the reactivity of various minerals of fly ash based on the backscattered electron images analysis (BSE-IA) method and discusses the influencing factors and kinetics of Si and Al selective leaching of fly ash in alkali solution and alkali-sulfate composite solution, respectively. The relationships among the physicochemical properties, dissolution behavior, and reactivity of fly ash have been revealed. There are three typical phases in fly ash, namely the Si–Al phase, Ca–Si–Al phase, and Fe phase. The Ca–Si–Al phase is more soluble and preferentially participates in the reaction process than the other two phases. The dissolution process is greatly affected by temperature. Alkali and sulfate have a compound synergistic effect and SO42− further promotes the dissolution of Si and Al mainly by changing the gel property wrapped on the surface of fly ash particles. The leaching kinetics results indicate that the internal diffusion controls the reaction process. The research method and system in this work can be applied to other solid waste, providing reference significance for quickly exploring its reaction activity. Moreover, the synergistic effect of alkali and sulfate can be used to establish an alkali-sulfate composite cementitious system, guiding the application of fly ash as a supplementary cementitious material.

Agro-Waste Biochar to Reduce the Leaching of Heavy Metals from Coal Fly Ash Amended Soil

The soils added with coal fly ash may contain heavy metals potentially up to the levels of toxicity. Biochars have been successfully used in the past to reduce the bioavailability and leaching of heavy metals in contaminated soils. Therefore, the co-application of biochar together with coal fly ash could positively change the bioavailability and leaching characteristics of heavy metals in sandy soils through various fixing mechanisms. In the present study, the authors investigated the effect of agro-waste biochar in modifying the leaching loss of heavy metals from coal fly ash contaminated soils. Column leaching tests with simulated rainfall conditions were conducted for sandy Ultisol soils mixed with coal fly ash and avocado branch cut biomass biochar at 5 tons/ha rate. The results showed the presence of heavy metals in the leachate of fly ash added soil. Application of biochar significantly reduced the leachability of all the tested heavy metals in the study. The reduction rates were up to 55% compared to non-amended samples. Therefore, the agro-waste biochar can effective be used in stabilizing the heavy metals in coal fly ash contaminated soils, to minimize the risk of environmental contamination.

Catalytic pyrolysis of biomass using fly ash leachate to increase carbon monoxide production and improve biochar properties to accelerate anaerobic digestion

Biomass-derived biochar is attracting growing interest as an effective additive for anaerobic digestion (AD). To improve energy yield and digestion performance through an integrated process of biochar production and AD, biochar upgrading using biomass fly ash leachate as a sustainable metal catalyst was investigated. The results indicate that the bark soaked in the leachate improved the pyrolysis reactivity of biomass with CO2 and reduced the temperature at which the reaction rate reached its maximum from 943 °C to 801 °C. This resulted in a doubling of CO production during CO2-assisted pyrolysis at 800 °C. In addition, the combined use of fly ash leachate and CO2 in bark pyrolysis improved not only the porosity of the resulting biochar but also its wettability and liming potential. Moreover, biochar amended with fly ash leachate and CO2 significantly reduced the lag time in the anaerobic digestion of grease trap waste.

Preparation of graphene-based surface ion-imprinted adsorbent for Ga(Ⅲ) selective extraction from acid leaching of fly ash

To meet the requirements of Ga(Ⅲ) selective adsorption from acid leaching of fly ash, a grapheme-based Ga(Ⅲ) imprinted polymer is developed by combining adsorption method with surface ion imprinting technology. The obtained Ga(Ⅲ) imprinted polymer can effectively adsorb Ga(Ⅲ) with a maximum adsorption capacity of 221.56 mg g−1 at an initial concentration of 200 mg/L within 240 min. The pseudo-second order model (R2 = 0.9882) and Langmuir isotherm (R2 = 0.9628) fitted the Ga(Ⅲ) adsorption data well. In addition, the imprinted adsorbent exhibits significant selectivity towards Ga(Ⅲ) in a simulated acid leaching of fly ash. The selectivity coefficients of Ga(Ⅲ) with respect to Al(Ⅲ), Fe(Ⅲ), Mg(Ⅱ), and Ca(Ⅱ) are 10.09, 3.36, 18.50, and 55.50, respectively. The synthesized imprinted adsorbent exhibits excellent regeneration ability, maintaining 85.71% of its initial adsorption capacity after 5 adsorption-regeneration cycles. The binding energy of Ga(Ⅲ) to functional monomers is calculated as −16.79 kJ mol−1, which confirms that Ga(Ⅲ) can be effectively adsorbed. The theoretical simulated calculation results are basically in consistence with the experimental results, which confirms the selective adsorption mechanism of Ga(Ⅲ). Therefore, it provides a new idea for the extraction of Ga(Ⅲ) from acidic environments.

Physical properties, chemical composition, and toxicity leaching of incineration fly ash by multistage water washing.

Incineration fly ash contains a large amount of chloride, which limits the scope of its resource utilization. Water washing effectively removes chlorides and soluble substances, increasing the ability to dispose of them. The properties of incineration fly ash after multi-level water washing have been studied, providing theoretical guidance for the safe disposal of water-washed ash at all levels. Taking a practical project as an example, this paper analyzed the impact of three-stage countercurrent water washing on the physicochemical properties and toxicity leaching of incineration fly ash with different washing grades by XRD, BET, XRF, SEM, and ICP-MS. The results showed that with the improvement of washing grade, the removal rate of chloride ions was more than 86.96%. However, due to the removal of soluble substances, dioxins enriched from 98ng-TEQ/kg of raw ash to 359ng-TEQ/kg of tertiary washed incineration fly ash. Cr, Cu, and Zn also increased from 40.35mg/L, 356.55mg/L, and 3290.58mg/L of raw ash to 136.30mg/L, 685.75mg/L, and 5157.88mg/L, respectively. Pozzolanic activity had increased from 40.56% of the raw ash to 74.12% of the tertiary-washed incineration fly ash. There was no risk of excessive heavy metal leaching, and the dioxin content was lower than the raw ash in the primary washed incineration fly ash. After multi-stage water washing, incineration fly ash accumulated heavy metals, so more attention must be paid to the issue of heavy metal content in the safe disposal process.

From ash to oxides: Recovery of rare-earth elements as a step towards valorization of coal fly ash waste

Coal fly ash (CFA) is both a valuable waste material and a potential source of environmental contamination. The inclusion of metals such as rare-earth elements offer a possible incentive towards waste valorization if the metals can be extracted and recovered in an economical manner. Rare-earth elements (REEs) have many technological applications and are critically important in the manufacture of electric vehicles, communication devices, and industrial magnets. However, the global supply of rare-earth elements has faced shortages and price shocks. Current methods for separating and isolating individual rare-earth elements use large amounts of energy and organic solvents, raising concerns over environmental impacts. These factors have led to the investigation of nontraditional sources and separation techniques for these elements. We describe a column-based system that uses a newly developed ligand-associated organosilica sorbent to concentrate and separate rare-earth elements from fly ash leachate. The fly ash used in this study originally contained 0.024 wt% rare-earth elements and the final oxide powder after enrichment contained > 10 wt% rare-earth elements, which is a enrichment of > 400 times. This process requires no additional organic solvents after the sorbent media has been synthesized, offering an alternative to the current standard using solvent extraction for rare-earth element recovery.

Removal of heavy metals from fly ash using electrodialysis driven by a bioelectrochemical system: a case study of Pb, Mn, Cu and Cd

ABSTRACT Municipal solid waste incineration (MSWI) fly ash is classified as hazardous waste due to high leachable heavy metals, and incineration leachate belongs to organic wastewater with high biodegradability. Electrodialysis (ED) has shown potential for the removal of heavy metals from fly ash, and bioelectrochemical system (BES) employs biological and electrochemical reactions to generate electricity and remove contaminants from a wide range of substrates. In this study, the ED-BES coupled system was constructed for the co-treatment of fly ash and incineration leachate, where the ED was driven by BES. The treatment effect of fly ash by varying additional voltage, initial pH and liquid-to-solid (L/S) ratio was evaluated. Results showed that the highest removal rates of Pb, Mn, Cu and Cd were 25.43%, 20.13%, 32.14% and 18.87% after 14 days treatment of the coupled system, respectively. These values were obtained under 300 mV of additional voltage, L/S 20 and initial pH3. After the treatment of the coupled system, the fly ash leaching toxicity was lower than the threshold of GB5085.3-2007. The highest energy saving for removed Pb, Mn, Cu and Cd were 6.72, 15.61, 8.99 and 17.46 kWh/kg, respectively. The ED-BES can be considered a cleanliness approach to treating fly ash and incineration leachate simultaneously.

Lanmodulin-Functionalized Magnetic Nanoparticles as a Highly Selective Biosorbent for Recovery of Rare Earth Elements.

Recovering rare earth elements (REEs) from waste streams represents a sustainable approach to diversify REE supply while alleviating the environmental burden. However, it remains a critical challenge to selectively separate and concentrate REEs from low-grade waste streams. In this study, we developed a new type of biosorbent by immobilizing Lanmodulin-SpyCatcher (LanM-Spycatcher) on the surface of SpyTag-functionalized magnetic nanoparticles (MNPs) for selective separation and recovery of REEs from waste streams. The biosorbent, referred to as MNP-LanM, had an adsorption activity of 6.01 ± 0.11 μmol-terbium/g-sorbent and fast adsorption kinetics. The adsorbed REEs could be desorbed with >90% efficiency. The MNP-LanM selectively adsorbed REEs in the presence of a broad range of non-REEs. The protein storage stability of the MNP-LanM increased by two-fold compared to free LanM-SpyCatcher. The MNP-LanM could be efficiently separated using a magnet and reused with high stability as it retained ∼95% of the initial activity after eight adsorption-desorption cycles. Furthermore, the MNP-LanM selectively adsorbed and concentrated REEs from the leachate of coal fly ash and geothermal brine, resulting in 967-fold increase of REE purity. This study provides a scientific basis for developing innovative biosorptive materials for selective and efficient separation and recovery of REEs from low-grade feedstocks.

Converting Catalytic Palm Oil (MEPO) to Produce Biogasoline Using Zeolite Faujasite Catalyst From Fly Ash with Nickel Impregnation (Ni)

The process hydrocracking methyl ester of palm oil into fractions biogasoline by faujasite cata-lyst of fly ash impregnated with nickel have been made. Preparation for faujasite synthesis of fly ash can bedone by removing organic compound and refluxing HCl. Synthesis do by melting the fly ash which has beenprepared with NaOH 1: 1.2 and in aging for 8 hours and in the hydrothermal autoclave for 24 hours. The char-acter faujasite using XRD and Si / Al ratio produces crystallinity main peak of 67% and Si / Al ratio of 1.65.Hydrocracking process using a variety of 4 catalyst used fly ash leaching results, faujasite, Ni-Faujasite 2%, andNi-Faujasite 4%. Test the activity and selectivity of the catalyst to produce liquid product analyzed by GC-MSwith the best catalyst was Ni-Faujasite 4% to yield 42.34% of the activity and selectivity of biogasoline frac-tion of 7.12%. The impregnation of the nickel catalyst is made by soaking in salt of nickel and then oxidationusing O2 gas and reduction using H2 gas. The impregnation of nickel will affect the character of the catalystso that the activity and selectivity of the catalyst is changed. The impregnation of nickel 4% on faujasite suc-cessfully done with nickel content of 3.71%, increasing Si / Al ratio of 2.27 and an acidity of 0.0035 mol/g.

Effect of Chelating Agent Type and Addition Amount on Heavy Metal Leaching of Fly Ash in Municipal Solid Waste Incineration

Effect of Chelating Agent Type and Addition Amount on Heavy Metal Leaching of Fly Ash in Municipal Solid Waste Incineration

Circular indirect carbonation of coal fly ash for carbon dioxide capture and utilization

Mineral carbonation of alkaline wastes is a promising route for carbon dioxide (CO2) capture and utilization. An exploration of the carbonation potential of relatively inert alkaline wastes is important to develop mineral carbonation. Large amounts of coal fly ash are generated from coal-fired power plants and must be treated. A fundamental study of the circular indirect carbonation of coal fly ash was proposed and fly-ash leaching, calcium carbonate (CaCO3) precipitation, and solution regeneration with bipolar membrane electrodialysis (BPED) stages were investigated. In the leaching stage, the nitric acid/calcium ratio affected the solution pH and impurity concentration. The leaching behavior of impurities was related mainly to colloidal precipitation. Approximately 97.3% calcium in solution reacted to form precipitated CaCO3, and a higher-purity CaCO3 precipitate was obtained when a lower nitric acid/calcium ratio was used in the leaching stage. The CO2 conversion was 92.9% and the CO2 uptake efficiency was ~0.011 g-CO2/g-fly ash, which can be improved by optimizing the liquor purification process. Fundamental liquor purification was performed. Solution regeneration by BPED was evaluated by investigating the effect of electric potential and current density on the regeneration yield, current efficiency, and power consumption. A comprehensive assessment, including cost and CO2 balance, was conducted, and future interesting research on circular indirect carbonation was suggested.

Intrinsic characteristics of coal combustion residues and their environmental impacts: A case study for Bangladesh

This study has focused on petrography, geochemistry, radiochemical, and leaching properties of coal combustion residues (CCRs), their leachates and nearby waters from the Barapukuria coal-fired power-plant (BCPP) to evaluate the potential environmental impacts and human health hazards for the first in Bangladesh. The CCRs, used in this study are predominantly comprised of Al-Si-rich glassy materials (94.8%) followed by crystallites (3.6%), notably quartz, mullite, and spinel with rock-fragments (0.3%); and un-burnt organic constituents (1.3%) such as anisotropic coke (0.8%) and slightly altered inertinite (0.5%). Hematite, magnetite, cristobalite, monazite, zircon, rutile, tourmaline and sillimanite were also identified as trace minerals. Elemental contents are found to be elevated (2.1–14.2 times) in the fly ash (FA) and bottom ash (BA), as compared to world coal-ash average with the exceptions of Ni in FA; and of Zn, As, Cu, and Hg in BA. The sum of detected rare earth elements is significantly high as compared to the world FA, Indian and Chinese ash residues. The specific activities of CCR are comparatively higher by a factor of 3.7 (226Ra) to 6.2 (232Th) than those of the world average. The examined spheres, particles, and agglomerates of FA are predominantly comprised of C, Al, and Si as major while, K, Ca, Mg, Fe, W and Ti as minor elements. On the other hand, extractable amounts of soluble potentially toxic elements in FA leachates are 7.7% for Se, 4.8% for Zn, and in BA 5.7% for As and 3.1% for Se and others are < 1%. Metals are substantially released from FA in the range of 8.5 (for Cr) to 9650 (for Zn) ppb and 0.002% (for Cr) −7.7% (for Se), while from BA below detection level (for Cr) to 940 ppb (for Mn). The concentration of hazardous metals in the discharged waste water and water ash pond were higher than those were found in nearby pond- and ground-water sources around the BCPP. Ecological and radiological risk indices suggest moderate-risk derived from FA and low-risk from BA.

Simultaneous and clean separation of titanium, iron, and alumina from coal fly ash in one spot: Electrolysis-hydrolysis method

Large amounts of heavy-metal-containing coal fly ash can cause serious environmental hazards. The separation and extraction of titanium, iron, and alumina from coal fly ash can provide economic and environmental benefits. This work presents an electrolysis-hydrolysis method to alter the precipitation order of iron and alumina by changing the ion charge sequence to extract iron and alumina in an orderly manner while recovering the waste heat to polymerize the precipitated titanium. The separation and extraction of titanium, iron, and alumina in one spot can shorten the process and make full use of the electric energy. Under optimal conditions, the efficiencies of iron, titanium, and alumina were 97.6%, 93.1% and 88.5%, respectively. The iron product had a composition of 95.8% Fe2O3, 0.5% Al2O3, 0.3% CaO, 0.1% SO3, and 0.4% TiO2. The alumina product had a composition of 88.7% Al2O3, 0.1% Fe2O3, 0.2% CaO, 9.1% SO3 and 0.2% TiO2. The titanium product had a composition of 63.78% TiO2, 3.11% Al2O3, 8.15% Fe2O3, 0.28% CaO, 4.12% SiO2, and 9.6% SO3. Moreover, in the entire electrolysis process, no expensive membranes or chemical additives were required, avoiding the limitations of membranes and high costs. Fe, Al(OH)3, Ti(OH)4, O2, and H2 were generated during the electrolysis-hydrolysis process; therefore, no harmful substances were produced. Thus, this study proposes an alternative electrolysis-hydrolysis process for the simultaneous separation and extraction of titanium, alumina, and iron from coal fly ash leachate in one spot.