Coal Combustion Fly Ash Research Articles

Gold Nanoparticle Conjugated Water Soluble Multiwall Carbon Nanotubes

The poor solubility and dispersibility of carbon nanotubes in both aqueous and organic solvents restrict their applications in biological science. Herein, a simple and cheap method for synthesizing and purification of water soluble multiwall carbon nanotubes from coal combustion fly ash and characterization of this water soluble multiwall carbon nanotubes after conjugation with gold nanoparticles has been described.

Fly ash based geopolymeric foams using silica fume as pore generation agent. Physical, mechanical and acoustic properties

The aim of this work is the development of a porous geopolymeric foam with sound absorbing properties using silica fume as the pore generation agent. The samples were manufactured using a coal combustion fly ash as source material for the geopolymerization reaction, an alkaline solution as activating solution and silica fume as pore forming agent. Three parameters were studied: silica fume proportion (0, 20 and 40 wt%), activating solution (potassium silicate and potassium hydroxide) and setting temperature (40 and 70 °C). Once the samples were prepared, the experimental study of the most important physical, mechanical and acoustic features were carried out. The increase in the proportion of silica fume in the mixture and setting temperature produced a reduction in setting time and a raise of open void porosity, reducing the compressive strength at 28 days up to a half but increasing the sound absorption. The influence of activating solution in open porosity and sound absorbing properties was not very important.

Aqueous acid and alkaline extraction of rare earth elements from coal combustion ash

The recovery of rare earth elements (REEs) from coal combustion fly ash has recently gained attention as a possible beneficial reuse application that could provide an alternative, low-grade source of REEs in an unstable global supply market. To economically recover REEs, an efficient process needs to be developed to remove them from the ash. This study investigated different methods of leaching REEs from fly ash and other coal combustion ashes. Aqueous acid and alkaline leaching were employed on multiple types of coal fly ash samples (representing coals from three major U.S. coal basin sources) with variable leaching parameters that include extractant type (HCl, NaOH), extractant concentration, leachate-to-ash ratio, and addition of CaO during the leaching process. Acid leaching of high calcium-containing fly ashes such as samples derived from Powder River Basin coals had the highest recoveries of REEs (near 100% of total REE contents), while leaching efficiencies were much lower (<40%) for low calcium fly ashes from Appalachian and Illinois Basin coals. If the fly ashes were subjected to aqueous NaOH (to decompose alumunosilicates) and followed with dilute acid to maintain solubility of metal cations, recoveries of the REEs was up to 85% for Appalachian ashes. Overall, these results demonstrate that REEs in the Powder River Basin-based coal fly ashes are more easily leached into acidic solution than the other ashes tested. While the Appalachian Basin-based coal ashes contained the highest total REEs concentrations out of all regional coal ash sources, these ashes required more complex leaching methods that first decompose the aluminosilicate glassy matrix of the ash (e.g. alkaline digestion) prior to acid leaching.

Application of nanofiltration for Rare Earth Elements recovery from coal fly ash leachate: Performance and cost evaluation

This work evaluated nanofiltration (NF) as a potential step in the recovery process of Rare Earth Elements (REEs) from leachates of coal combustion fly ashes. A pre-treatment step, by pH adjustment and microfiltration (MF), has been studied to separate REEs by major elements. The individual and combined effects of applied pressure (12–24 bar) and NF feed acidity (pH 1.5–3.5) on rejection of six critical REEs and permeate flux have been investigated via response surface methodology (RSM). The resulting model equations were used to develop a cost model for the recovery chain, in order to select the optimum NF operating conditions. The optimization of the REE recovery chain, including pre-treatment and NF, was done with respect to the objective of maximizing the difference between NF concentrate economic value and treatment cost. NF with an appropriate MF pre-treatment has been effective in concentrating REEs from fly ash leachate, reaching the maximum potential gain at the optimum operating conditions of 12 bar and pH 3.5.

Experimental study on the recovery of sodium in high sodium fly ash from thermochemical conversion of Zhundong coal

Zhundong (ZD) coal gasification/combustion fly ash is a high Na content residual product and contains a large quantity of harmful elements, including as Cl, S, and Na that must be removed and recovered. Water-soluble Na is the predominant Na form in ZD coal fly ash, accounting for 34.7–92.8% of the total Na. The main minerals of Na identified were NaCl and Na2SO4. Most of the water-soluble Na in the ZD coal fly ash can be effectively removed by water washing, the removal yields have been found to be 31–93%. Increasing the washing time, water temperature, liquid–solid ratio and acid concentration can increase the Na removal yield. For the ZD coal combustion fly ash (SEHcf) and gasification fly ash (SEHf), NaCl particles are present on the fly ash surface, most water-soluble Na was washed by water in 5 min at 30 °C. However, the removal of Na by water washing was inhibited by the water insoluble calcium oxides and sulfides that covered the surface of the ZD coal gasification fly ashes (TCf and SHf), Na removal required higher wash water temperatures and longer washing times. It is feasible to recover Na from ZD coal fly ash by water washing, and the recovered Na products are primarily NaCl and Na2SO4. The recovery yields of Na in the SEHcf, SEHf and TCf were 49.4%, 81.2%, and 65.4%. But the recovery yield of Na in SHf was 16.6%. SEHcf, SEHf and TCf were more suitable for recovering Na. the recovery of Na from ZD coal fly ash is economically feasible.

Fly ash from coal combustion: Dependence of the concentration of various elements on the particle size

The dependence of the distribution of various elements on the particle size of coal combustion fly ash is of special interest for use of the fly ash in ultrafine cement, or for recovery of valuable elements from fly ash. Therefore, electrostatic precipitator fly ash from a coal fired power plant was split into particle size classes with mass median diameters of 2.2 µm, 5.4 µm, 9.7 µm, 19 µm and 43 µm by means of an air classifier. The size dependence for the elements Al, As, Ba, Br, Ca, Ce, Cl, Co, Cr, Cu, Fe, Ga, Ge, Hg, K, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Rb, S, Sb, Se, Si, Sn, Sr, Ta, Ti, Th, Tl, U, V, W, Y, Yb, Zn, Zr, and for total carbon, was determined. For several components a considerable dependence of the concentration on the particle size was observed, which can be approximated by power functions. Substantially higher concentration with decreasing particle size was found for total carbon, As, Cu, Ga, Ge, Hg, Sn, Pb, Tl, V and Zn, whereas the concentration of the main mineral components Si, Al, Fe, Ca, K, Na, Mg, Mn and Ti was slightly lower in the fine particles. The increased concentrations have to be considered for critical elements like Pb and Cu when air classified ultrafine fly ash is used in ultrafine cement. Air classification might also be an important pre-processing step in a recovery process for trace elements like Ga, Ge and V.

Differences in bulk and microscale yttrium speciation in coal combustion fly ash.

Coal combustion ash is a promising alternative source of rare earth elements (REE; herein defined as the 14 stable lanthanides, yttrium, and scandium). Efforts to extract REE from coal ash will depend heavily on the location and speciation of these elements in the ash. This study sought to identify the major chemical forms of yttrium (Y), as a representative REE in coal fly ash samples selected from major coal sources in the United States. Y speciation was evaluated using both bulk scale analyses (sequential extractions, Y K-edge X-ray absorption near-edge spectroscopy - XANES) and complementary analyses at the micron scale (micro-focus X-ray fluorescence and micro-XANES). Sequential selective extractions revealed that the REE were primarily in the residual (unextracted fraction) of coal fly ash samples. Extraction patterns for yttrium resembled those of the lanthanides, indicating that these elements were collectively dispersed throughout the aluminosilicate glass in fly ash. Bulk XANES analysis indicated that Y coordination states resembled a combination of Y-oxides, Y-carbonate, and Y-doped glass, regardless of ash origin. However, in the microprobe analysis, we observed "hotspots" of Y (∼10-50 μm) in some samples that included different Y forms (e.g., Y-phosphate) not observed in bulk measurements. Overall, this study demonstrated that yttrium (and potentially other REEs) are entrained in the glass phase of fly ash and that microscale investigations of individual high-REE regions in fly ash samples do not necessarily capture the dominant speciation.

Accelerated Carbonation of Coal Combustion Fly Ash for Atmospheric Carbon dioxide Sequestration and Soil Amendment: An Overview

Fly ash is one of the major solid by-products generated by coal combustion for power generation. At present most fly ash generated all over the world is dumped as waste material without any beneficial use. Only a small proportion of the total fly ash production is used in applications such as cement production, mineral wool production, recovery of metals, road sub-base construction, mine reclamation, and in agriculture. In addition, fly ash is a material that can be used to capture and store atmospheric CO2 through mineral carbonation both in situ and ex situ of the source of CO2 emissions. As a means of increasing the rate of mineral carbonation, accelerated carbonation has been researched by scientists in the recent past. In addition to achieving the benefits of carbon sequestration, accelerated carbonation can make the fly ash chemically stable, which is beneficial in overcoming problems associated with the leaching of toxic elements when using it as a soil amendment. Therefore, through accelerated carbonation followed by addition to soil this solid waste material can be successfully managed. The efficacy of the mineralization reaction depends on the mineralogy, and the physical and chemical properties of fly ash and the reaction conditions, such as CO2 partial pressure, temperature, relative humidity and the contact time of gas and the material. In order to achieve higher CO2 sequestration efficiency it is vital to select material with the required properties and to supply it with the optimum reaction conditions. This paper reviews the main issues related to the accelerated carbonation of coal combustion fly ash under different reaction conditions and its effects on CO2 sequestration efficiency. It also identifies the potential application of carbonated fly ash to soil in order to improve soil’s physical and chemical properties.

高砷燃煤燃烧飞灰中砷粒径分布及健康风险评价

高砷燃煤燃烧飞灰中砷粒径分布及健康风险评价

Optical Property Measurements of Mixed Coal Fly Ash and Particulate Carbon Aerosols Likely Emitted during Activated Carbon Injection for Mercury Emissions Control

The most mature technology for controlling mercury emissions from coal combustion is the injection into the flue gas of powdered activated carbon (PAC) adsorbents having chemically treated surfaces designed to rapidly oxidize and adsorb mercury. However, carbonaceous particles are known to have low electrical resistivity, which contributes to their poor capture in electrostatic precipitators (ESPs), the most widely used method of particulate control for coal-fired power plants worldwide. Thus, the advent of mercury emissions standards for power plants has the potential for increased emissions of PAC. Our previous analyses have provided estimates of PAC emission rates resulting from PAC injection in the U.S. and extrapolated these estimates globally to project their associated climate forcing effect. The present work continues our examination by conducting the first comparative measurements of optical scattering and absorption of aerosols comprising varying mixtures of coal combustion fly ash and PAC. A pa...

The fungistatic properties and potential application of by-product fly ash from fluidized bed combustion

The article deals with the evaluation of antifungal effect of Fluidized Bed Combustion Fly Ash (FBCFA) and Bottom Ash (FBCBA) by-products compared with the performance of conventional pulverized coal combustion fly ash (FA). The antifungal effects were evaluated using the procedure given in the Czech standard ČSN 72 4310. A blend of the Aspergillus niger, Chaetomium globosum, Penicillium funiculosum, Paecilomyces variotii and Gliocladium virens fungi was used in the experiments. The scale for the evaluating of mould resistance was from 0 to 5 depending on the degree of fungi growth, where a value of 0 means that there is zero growth of fungi and so the product possesses the fungistatic properties. Contrary to “conventional” FA which demomstrated the highest fungi growth degree of 5, the study confirms the attainment of fungistatic propeties by FBC by-products. I tis expected, that the incorporation of fungistatic ash can increase the antimicrobial properties of construction materials.The literature review has revealed a number of potential applications for FBC ash in the construction industry including the production of cement mixtures, binders, geopolymers, mortars, concretes. However, there are no relevant standards for utilization of FBC ash in such applications.

Distribution of rare earth elements in coal combustion fly ash, determined by SHRIMP-RG ion microprobe

During coal combustion for electric power generation, rare earth elements (REE) are strongly retained in the ash fraction leading to significant enrichment compared to the REE content of the respective feed coals. Knowing how the REE are distributed in coal ash is essential to devising effective approaches for REE extraction from this potential resource. To better understand the distribution of REE in coal ash, we used the Stanford-USGS SHRIMP-RG ion microprobe to determine grain-scale REE partitioning in a suite of 19 U.S. and international coal fly ash samples. SHRIMP-RG microanalysis used a nominal spot size of 15μm and an oxygen negative-ion primary beam. NIST multi-element glass standards SRM 611 and SRM 613 were used for REE calibration. Prior to SHRIMP-RG analysis, samples were characterized by backscattered electron imaging and wavelength-dispersive elemental mapping to delineate constituents of interest for REE microanalysis. Results confirm the occurrence of REE in aluminosilicate glasses consistent with previous results that showed a strong positive correlation between Al and REE content in a larger group of U.S. and international coal fly ash samples. Among these glasses, aluminosilicates consisting of Al and Si and lacking other major constituents tend to have REE contents similar to, or slightly lower than the bulk sample REE content, whereas Ca- and/or Fe-enriched aluminosilicate glasses are similar to, or more REE-enriched than the bulk sample. Co-occurring quartz and/or high-silica glass is almost always the most REE depleted fly ash constituent, having much lower REE contents than the aluminosilicate glasses. Fe-oxide magnetospheres have REE content with relative proportions of light (LREE) to heavy (HREE) rare earths that are more variable than in the aluminosilicate glasses. Results suggest that extraction of REE from the aluminosilicate glass fraction in coal ash will yield a significant portion of the REE present and therefore, this fraction should be targeted in ongoing efforts to recover REE from coal fly ash.

48 微粉炭燃焼フライアッシュからのヒ素溶出挙動(灰・微量金属(2))

48 微粉炭燃焼フライアッシュからのヒ素溶出挙動(灰・微量金属(2))

Synthesis and characterization of hydrotalcite from South African Coal fly ash

The synthesis of adsorbents such as hydrotalcites (HT) from mineral waste (e.g. blast furnace slag) is receiving increasing attention. This study reports a novel procedure to prepare HT from a South African coal-combustion fly ash, an ubiquitous waste generated by coal-fired power stations. The second point of novelty is the optimization process, which highlights the boundary conditions for crystallization of this mineral phase. The parameters investigated for the optimization of HT synthesis from fly ash included HCl concentration, aging time and temperature, pH during the aging step, and crystallization time and temperature. The most suitable synthesis conditions were: HCl concentration of 3M, aging time of 30min, aging temperature of 65°C, pH of 11.5 during aging, crystallization time of 12h, and crystallization temperature of 70°C. HT had a large external surface area and very low microporosity. Morphologically, synthesized HT was mostly made up of sub-micron plate-like particles. The structural characteristics of HT synthesized from fly ash were similar to those of HT produced from analytical grade chemicals, except for the presence of calcite. A novel use of the waste South African Class F fly ash was a suitable feedstock for the synthesis of high quality HT under the optimized process conditions that minimized the formation of secondary undesired mineral phases such as calcite or hydrogarnet.

Impact of coal source changes on mercury content in fly ash: Examples from a Kentucky power plant

Mercury capture by coal combustion fly ash is a function of the chemistry of the feed coal, including halogens; the amount and type of carbon in the fly ash; and the type of fly ash collection and the flue gas temperature at the point of fly ash collection. In this study of fly ash collected at different points in time from a five-row electrostatic precipitator (ESP) system at a Kentucky power plant, relationships were seen between the amount of fly ash carbon and the concentration of Hg in the ash. Coincident with the burning of low-S coal at two collection times, a better correlation between Hg and C was seen in the relatively cooler 3rd and 4th ESP rows than in the first two rows. This was particularly evident in the 2007 collection where the fly ash carbon was higher than in the 2004 collection. In 2013, following the installation of flue-gas desulfurization and the resulting switch to high-S coal and the installation of a hydrated-lime injection system between the 2nd and 3rd ESP rows, no significant Hg vs. C trend was observed.

ADVERSE AGRICULTURAL CONSEQUENCES OF WEATHER MODIFICATION

For at least fifteen years, with ever increasing frequency and extent, weather modification and/or climate alteration investigations have been conducted without public disclosure to perfect a covert methodology for inhibiting rainfall to deliberately damage a sovereign nation’s agri-cultural economy. This research discloses methodology for inhibiting rainfall, the evidence of coal combustion fly ash utilization, the adverse consequences on agriculture, and the adverse health implications on biota, including humans. The harm to agriculture comes primarily from aluminum addition to soil, changing soil pH and changing historic weather patterns. Aluminum in a chemically mobile form, not only harms plants, but is toxic to most biota, including humans. The micron and submicron particulates are used for weather modification contain heavy metals and radioactive elements which pose potentially grave human health threats including, but not limited to, cardiovascular disease, diabetes, respiratory diseases and reduced male fertility. Understanding that methodology and its adverse consequences by the agricultural community is crucial to identify and stop covert operations aimed at damaging the agricultural economy of a sovereign nation.

Characterization of supplementary cementitious materials by thermal analysis

Working Group 1 of RILEM TC 238-SCM ‘Hydration and microstructure of concrete with supplementary cementitious materials (SCMs)’ is defining best practices for the physical and chemical characterization of SCMs, and this paper focusses on their thermal analysis. Thermogravimetric analysis (TGA) can provide valuable data on the chemical and mineralogical composition of SCMs. Loss-on-ignition (LOI) testing is a commonly used, standardized, but less sophisticated version of TGA that measures mass at endpoints only, with heating generally in air. In this paper we describe the use of TGA and LOI to characterize Portland cement with limestone additions, coal combustion fly ashes, ground-granulated blast furnace slag, calcined clays, and natural pozzolans. This paper outlines the value and limitations of TGA and LOI (in the formats defined in different standards regimes) for material characterization, and describes testing methods and analysis. TGA testing parameters affect the mass loss recorded at temperatures relevant for LOI measurements (700–1000 °C) of slags and fly ashes, mainly associated with oxidation reactions taking place upon heating. TGA of clays and natural pozzolans is utilized to identify optimal calcination conditions leading to dehydroxylation and consequent structural amorphization, particularly for kaolinite. However, dehydroxylation and amorphization do not occur at similar temperatures for all clays, limiting the applicability of TGA for this purpose. Although TGA is widely utilized for characterization of SCMs, the testing parameters significantly affect the results obtained, and TGA results require careful interpretation. Therefore, standardization of TGA testing conditions, particularly for LOI determination of slags and fly ashes, is required.

Geopolymerisation of fly ashes with waste aluminium anodising etching solutions

Combined management of coal combustion fly ash and waste aluminium anodising etching solutions using geopolymerisation presents economic and environmental benefits. The possibility of using waste aluminium anodising etching solution (AES) as activator to produce fly ash geopolymers in place of the commonly used silicate solutions was explored in this study. Geopolymerisation capacities of five European fly ashes with AES and the leaching of elements from their corresponding geopolymers were studied. Conventional commercial potassium silicate activator-based geopolymers were used as a reference. The geopolymers produced were subjected to physical, mechanical and leaching tests. The leaching of elements was tested on 28 days cured and crushed geopolymers using NEN 12457-4, NEN 7375, SPLP and TCLP leaching tests. After 28 days ambient curing, the geopolymers based on the etching solution activator showed compressive strength values between 51 and 84 MPa, whereas the commercial potassium silicate based geopolymers gave compressive strength values between 89 and 115 MPa. Based on the regulatory limits currently associated with the used leaching tests, all except one of the produced geopolymers (with above threshold leaching of As and Se) passed the recommended limits. The AES-geopolymer geopolymers demonstrated excellent compressive strength, although less than geopolymers made from commercial activator. Additionally, they demonstrated low element leaching potentials and therefore can be suitable for use in construction works.

Trends in the Rare Earth Element Content of U.S.-Based Coal Combustion Fly Ashes.

Rare earth elements (REEs) are critical and strategic materials in the defense, energy, electronics, and automotive industries. The reclamation of REEs from coal combustion fly ash has been proposed as a way to supplement REE mining. However, the typical REE contents in coal fly ash, particularly in the United States, have not been comprehensively documented or compared among the major types of coal feedstocks that determine fly ash composition. The objective of this study was to characterize a broad selection of U.S. fly ashes of varied geological origin in order to rank their potential for REE recovery. The total and nitric acid-extractable REE content for more than 100 ash samples were correlated with characteristics such as the major element content and coal basin to elucidate trends in REE enrichment. Average total REE content (defined as the sum of the lanthanides, yttrium, and scandium) for ashes derived from Appalachian sources was 591 mg kg(-1) and significantly greater than in ashes from Illinois and Powder River basin coals (403 and 337 mg kg(-1), respectively). The fraction of critical REEs (Nd, Eu, Tb, Dy, Y, and Er) in the fly ashes was 34-38% of the total and considerably higher than in conventional ores (typically less than 15%). Powder River Basin ashes had the highest extractable REE content, with 70% of the total REE recovered by heated nitric acid digestion. This is likely due to the higher calcium content of Powder River Basin ashes, which enhances their solubility in nitric acid. Sc, Nd, and Dy were the major contributors to the total REE value in fly ash, based on their contents and recent market prices. Overall, this study shows that coal fly ash production could provide a substantial domestic supply of REEs, but the feasibility of recovery depends on the development of extraction technologies that could be tailored to the major mineral content and origins of the feed coal for the ash.

Study on Type C Coal Fly ash as an Additive to Molding Sand for Steel Casting

Study of physio-chemical properties studies such as granulometric analysis, moisture, X ray fluorescence etc. were performed with Type C coal—combustion fly ash to investigate their potential as a distinct option for molding sand in foundry, thereby reducing the dependency on latter. Technological properties study such as compressive strength, tensile strength, permeability and compaction of various compositions of fly ash molding sand (10, 20 and 30 % fly ash substitute to chemically bonded sand) were performed and compared with silica molding sand. Steel casting production using this fly ash molding sand was done and the casting surface finish and typical casting parameters were assessed. It was noted that a good quality steel casting could be produced using type C fly ash molding sand, which effectively replaced 20 % of traditional molding sand and binders thereby providing greater financial profits to the foundry and an effective way of fly ash utilization (waste management).