Solid Fly Ash Research Articles

Alkali-activated binders – A sustainable alternative to OPC for stabilization and solidification of fly ash from municipal solid waste incineration

This research aims to evaluate the sustainability of alkali-activated binders for the stabilization/solidification (S/S) of municipal solid waste incineration fly ash (MSWI FA). A detailed environmental assessment of different alkali-activated mixtures was conducted using life cycle assessment (LCA) to identify the factors affecting their environmental burden. Ground granulated blast-furnace slag (GGBS) and metakaolin (MK) were used as the precursors. Results showed that all the alkali-activated blocks fulfilled the requirements for landfill and reuse as fill materials. Adopting alkali activation for S/S of MSWI FA instead of OPC allowed up to 70% reduction of global warming potential. However, in other impact categories such as human toxicity and land use, the alkali mixtures recorded higher values than the mix with OPC (+60–70%), primarily because of the impacts related to the production of chemical activators. The sensitivity analysis demonstrated that alternative production methods for sodium silicate and sodium hydroxide could enormously reduce the impacts related to the alkali solution. When the hydrothermal method for sodium silicate and the ODC method for sodium hydroxide were adopted, a reduction of 71%, 22%, and 24% was recorded in global warming potential, fossil resource scarcity, and human toxicity categories, respectively, compared with the mix with OPC. Therefore, this study sheds light on alkali-activated materials as sustainable S/S alternative to OPC for hazardous waste management to promote carbon neutrality.

Dioxin emission and distribution from cement kiln co-processing of hazardous solid waste.

Cement kiln collaborative disposal technology can not only dispose of hazardous waste but also provide energy for the cement industry. However, the addition of hazardous waste may promote the formation of dioxins in cement kilns. In this study, typical hazardous solid wastes, such as solidified fly ash, electroplating sludge, and industrial residue, were co-processed in a cement kiln with different feeding positions and different feeding amounts. The concentrations of dioxins in the flue gas, clinker, and precalciner furnace slag were investigated. The effect of adding mixed hazardous solid waste on the formation of dioxin was also studied. The results showed that the concentration of dioxin in the flue gas without added hazardous waste was 1.57ng/m3, and the concentration varied from 1.03 to 6.49ng/m3 after the addition of hazardous waste. In addition, the concentration of dioxin in the flue gas and solid samples increased substantially when the co-processing ratio doubled. The large amount of Cu in solidified fly ash promoted the formation of dioxins, while the higher S content in the electroplating sludge suppressed the formation of dioxins. Compared with the addition of single hazardous waste, the concentration of dioxin in precalciner furnace slag increases by about 300%. Furthermore, the distributions of isomers in the clinker and precalciner furnace slag were similar. 1,2,3,4,6,7,8-HpCDD and OCDD accounted for a large proportion of the mass concentration, and the contribution rate ranged from 48.7 to 82.0%. Most importantly, correlation analysis showed that the concentration of dioxin was closely related to the copper content, hazardous waste types and additive proportion, with correlation coefficients of 0.79, 0.83, and 0.89, respectively. This study provides a basis for exploring the high environmental benefits of disposing of hazardous solid waste by co-processing in cement kilns.

Study of Extraction of Rare Earth Elements from Hard Coal Fly Ash

Rare earth elements (REEs) extraction from wastes and/or by-products is alternative possibility of their winning. The occurrence ofREEs, namely 50.1 ppm of La, 100.1 ppm of Ce and 44.3 ppm of Nd was confirmed in solid fly ash samples from the coal fired heatingplant (TEKO, Inc. Košice, eastern Slovakia). The submitted contribution presents laboratory results of REEs leaching from coal fly ashusing 3M HCl, HNO3, H2SO4 and H3PO4 at 80°C during 120 min.It was found, that recoveries 65.5% of La, 64.4% Ce and 64.3% of Nd into liquor may be attained after grain size reduction to below5 μm.

Compressive Strength of Coal Fly-ash Based Geopolymer with Integration of Graphene Nanosheets (GNs)

The compressive strength of coal fly ash-based geopolymers has been improved by integrating the graphene nanosheets (GNs) as additive. Proximate analysis and crystal structure were also investigated using atomic absorption spectroscopy (AAS) and X-ray diffractometer. The geopolymer composites were created by mixing the solid fly ash and sand (weight ratio of 1:3) with 10 M NaOH and sodium silicate (Na2SiO3) solutions (weight ratio of 1: 2.5), where the liquid to solid weight ratio reached an economical composition of 1: 4. Low-cost GNs with various concentrations of 5 – 20 mg/ml was then added to the mixtures. The prepared mixtures were poured into mortar molds and allowed to stand for few hours at room temperature before heat treatment (curing) in the oven at various temperatures of 40°C, 60°C, and 80°C for 24 hours. Investigation results showed that the average compressive strength of geopolymer increased about 113.8 % or more than double compared to geopolymer without the addition of GNs. The highest compressive strength (29.5 MPa) was shown by a sample with GNs of 20 mg/mL and a curing temperature of 8°C. Meanwhile, geopolymer without GNs showed the lowest compressive strength in all curing temperatures. Proximate analysis showed that fly ash used in this work was the high calcium of type-C fly ash with the CaO content of 11.18%. XRD analysis results indicated that the GNs had integrated well in the geopolymer matrix. The presence of graphene-like structure was also detected, but it was not agglomerated with GNs. Good compressive strength and inexpensive production processes make this geopolymer very prospective for further development.

Stablization of medical waste incineration fly ash in cement mortar matrix

Laboratory experiments were performed to assess the suitability of using medical waste incineration fly ash in cement as a construction material based on the engineering properties of fly ash-cement matrix and the leaching potential of toxic heavy metals from the stabilized mix. Fly ash-cement samples were prepared with different proportions of fly ash (0%, 5%, 10%, 15% and 20% by weight) in the laboratory under controlled conditions. The solidified matrix exhibited a compressive strength from 3950 to 4980 psi when fly ash is mixed in varying proportions. The 28-day compressive strength has been found to decrease with the increase in fly ash content but it meets the minimum requirement of compressive strength for cement-mortar. Soundness test exhibited acceptable results for cement-mortar mixes having up to 15% fly ash. Final and initial setting times of cement have been found to generally increase with fly ash content. Water requirement (for normal consistency) also increased with the increase in fly ash content in cement. Based on physical properties of the cement-mortar matrix it is recommended that up to 10% (by weight) medical waste incineration fly ash can be incorporated for producing cement-mortar of optimum quality. Leaching behaviors of several targeted heavy metals (As, Cu, Ni, Cd, Pb, Hg and Zn) were analyzed using Toxicity Characteristics Leaching Procedure (TCLP) of fly ash and solidified fly ash-cement matrix which shows that the leached concentrations of As, Cu, Cd, Pb and Zn were reduced by 80.13%, 89.47%, 33.33%, 23.9% and 100% respectively for 10% fly ash incorporated cement-mortar matrix compared to that of original fly ash. The leached concentrations of heavy metals from the matrix were far below the EPA land disposal limits. These results suggest that the solidified fly ash incorporated cement-mortar matrix can effectively confine and immobilize the heavy metals contained in the fly ash without significantly diminishing the engineering properties of cement-mortar.
 Bangladesh J. Sci. Ind. Res.55(2), 131-138, 2020

Comparison between geopolymer reaction and cement hydration in solidification of fly ash generated in municipal solid waste incineration

Comparison between geopolymer reaction and cement hydration in solidification of fly ash generated in municipal solid waste incineration

Pengaruh Variasi Temperatur Terhadap Kinetika Reaksi Solidifikasi Fly Ash Paving Blok Geopolimer

This paper reported about the investigated of fly ash solidification with geopolymer process that studied temperature variation on the rate of solidification using Vicat Nidle apparatus and leaching tests on the content of heavy metals Cu, Pb, Cr and Cd in paving blocks after solidification. The transformation process of geopolymer crystalline formation was analyzed by Avrami’s kinetics theory (Avrami’s kinetica theory). From the results of the study obtained the optimum temperature of 80 oC, the highest rate of crystal growth solidification (K) value of 0.0475 and the Avrami exponent value (n) of 2.310 in this geopolymerization process shows a two-dimensional structure. From the results of leaching levels of heavy metals Cu, Pb, Cr and Cd in fly ash paving blocks are very small degraded in water and still below the environmental threshold.

Influence of graphene oxide in a chemically activated fly ash

To divert fly ash from hazardous waste stream to beneficial uses, this work aims to improve the solidification of fly ash as a geopolymer material by using graphene oxide (GO). The hydration precursors, morphology, elemental composition, mineralogy, chemical structure and ordering of GO-modified fly ash geopolymer were investigated by means of Raman spectroscopy, SEM/BSE, EMPA, XRD/TGA and 29Si/27Al MAS-NMR, respectively, to unravel the role of GO. The experimental results suggest that GO regulated the Ca/Si, Si/Al and Ca/(Si + Al) mole ratios to facilitate the formation of fly ash hydrates with improved mechanical strength, as GO showed the ability to selectively affect the distribution of different hydration precursors. GO also promoted the formation of low quartz and jennite-like hydrates. Overall, the 28-day compressive strength of fly ash geopolymer (w/b = 0.35) in this study was improved by 23% (from 33.6 MPa to 41.4 MPa) with GO admixed at 0.02% by mass of fly ash. The NMR study showed that GO improved the polymerization degree of fly ash geopolymer by increasing the total Q3 and Q4 Si-tetrahedrons, which suggests potential for improving the immobilization of heavy metals in fly ash.

Use of cement-chelated, solidified, municipal solid waste incinerator (MSWI) fly ash for pavement material: mechanical and environmental evaluations

As a by-product from the incineration of municipal solid waste (MSW), fly ash usually contains mobile heavy metals that may engender severe pollution when reused. In this study, fly ash was solidified with cement and a chelating agent to immobilize these polluting elements. The possibility of using the solidified fly ash for pavement materials was also assessed through mechanical and environmental perspectives. According to the results, the strength of solidified fly ash was found proportional to both the cement/fly ash ratio and curing time. This indicated that the increase of fly ash loading reduced the concentration of products from cement hydration, and thus destroyed the structure of the products of hydration. With the increase of freeze–thaw cycles, the compressive strength of cement-stabilized fly ash decreased between days 7 and 14, and then increased between days 14 and 28. Subsequently, the finite element analysis showed that placing the solidified fly ash layer as a pavement material between an unbound base course and subgrade was beneficial to prolong fatigue life and reduce rutting distress of asphalt pavements. Finally, leachability of metals from the mixtures was tested, which showed that leaching concentration decreased as the cement/ash ratio, curing time, and chelating agent content increased.

Fabrication and photocatalytic activity of floating type Ag3PO4/ZnFe2O4/FACs photocatalyst

We used floating solid fly ash cenospheres (FACs) as the carrier to prepare Ag3PO4/ZnFe2O4/FACs composite materials using sol-gel and liquid phase deposition methods We studied the material photocatalytic activity in visible light and used methylene blue as the goal pollutant. Compared with single powder catalysts, Ag3PO4/ZnFe2O4/FACs composites have the highest photocatalytic efficiency and could float in water because FACs are lightweight and hollow. Moreover, the composite materials can absorb high amounts of light energy and are conducive for catalyst recycling and reuse. Recycling experiments showed that the Ag3PO4/ZnFe2O4/FACs catalyst retained high photocatalytic activity after five times of recovery.

形状差のある原料を用いた土木資材用途フライアッシュ固化物の開発

形状差のある原料を用いた土木資材用途フライアッシュ固化物の開発

Mercury Retention by Fly Ashes from Oxy-fuel Processes

The objective of this study is to determine the mechanism of mercury retention in fly ashes, the main solid waste from coal combustion power plants, and to evaluate the interactions between the type of mercury and fly ashes. The work was based on the results of mercury speciation in the gas and the solid fly ash before and after mercury retention. The identification of the mercury species in the gas was performed using previously validated methods, but the speciation of the mercury retained in the fly ashes was carried out using a mercury temperature-programmed desorption technique (HgTPD) still under development. The fly ashes were sampled from conventional coal combustion in air and oxy-combustion power plants. The main mercury species identified in the raw fly ashes and after they were subjected to an oxy-combustion atmosphere were mercury bound to organic matter and HgS, the ratio of these species depending on the characteristics of the ashes. The results obtained indicate that fly ashes are the route of mercury oxidation in an oxy-combustion atmosphere, although they hardly retain any mercury unless the unburned carbon content is high. HgTPD analysis shows that the main mechanism for mercury retention in the fly ashes is via the carbon matter.

Improvement of peaty soils with municipal solid waste fly ash

Municipal solid waste fly ash is one of the products in the incineration process of solid waste and is usually disposed of in a landfill. The high lime content present in municipal solid waste fly ash indicates a possibility of using it to improve poor quality soils. Peaty soils are found at shallow depths in Singapore. These soils are generally excavated and disposed of in a landfill. This paper investigates the possibility of improving the peaty soil using municipal solid waste fly ash and also evaluates the environmental impact of the use of the latter. Test results showed that the shear strength of peaty soil can be improved by a few times by mixing with municipal solid waste fly ash. Leaching tests conducted on peaty soil–municipal solid fly ash mixes showed that the effluent element concentrations are below the limits set for trade effluent discharged into an uncontrolled watercourse but are generally above the limits set for drinking water and trade effluent discharged into a controlled watercourse. Therefore, peaty soil–municipal solid waste fly ash mixes should not be used at sites where there is a possibility for the effluent to discharge into controlled watercourses.

The effect of particle size and metal contents on arsenic distribution in coal-fired fly ash

Fly ash samples were collected from a Chinese power station and divided according to particle size. The solid fly ash samples were digested according to ASTM methods. The arsenic contents of samples with different particle sizes were analyzed using atomic fluorescence spectroscopy after digestion. Other metals were analyzed using inductively coupled plasma-atomic emission spectrometer after digestion, and the carbon content was analyzed by a CHN elemental analyzer. The results show that the arsenic components are enriched in smaller fly ash particles. The arsenic contents have a positive relationship with calcium, magnesium, and iron contents, which indicate that stable compounds are formed between these components. Thermogravimetric experiments of fly ash samples with different particle sizes were conducted, and the results indicate the combination of calcium hydroxide with arsenic form stable compounds.

Mass Deposition, Etching and Sputtering Effects of Low-Energy N+ Ion Irradiation on Solid Fly Ash

Fly ash is an industrial waste created when coal is burned to generate electrical power. In the present study, we used low-energy nitrogen ion implantation on fly ash to improve its surface properties. Scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) were used to study the changes of physical and chemical properties of fly ash after N+ ion implantation, and the mechanism of fly ash modified by ion implantation. In the optimal implantation with energy of 5 keV and dose of 15D0, the ion beam could effectively increase the specific surface area (approximately 150% increase) of the fly ash. Lots of scratches were generated in the surface of the fly ash after N+ ion implantation, therefore it is good for enhancing the specific surface area. Experimental results show that the ion implantation could open the chemical bonds of Si-O, Si-Al and Al-O, and deposit nitrogen ions on the surface of fly ash.

Experimental Study on the Solidification of MSWI Fly Ash

This paper studied the characteristics of MSWI fly ash. Using cement and lime as a binder for the fly ash treatment effect has carried out in the experimental research. This study analyzed the fly ash solidification process and the best process parameters by using cement and lime and discussed the binder curing fly ash and its mechanism in the fly ash behavior. This paper provides a valuable reference for the further study on the harmless treatment of MSWI fly ash.

Mechanical and Fractographic Studies of Surface-Treated Fly Ash Reinforced Polyester Composites

In this study, the surface-treated fly ash particles, ranging from 0 to 50 percent of weight were used as fillers added to the unsaturated polyester (UP). The fly ash (FA) particles were characterized using Mastersizer 2000 particle size analyzer, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicated that the effective reinforcing particles had a mean diameter of 60 μm and were both the glass and crystalline phases of the solid FA. The mechanical properties of the composites were evaluated by conducting the hardness and tensile tests. The Charpy impact test was used to determine the amount of energy absorbed during break, and the fractography was observed by SEM. The micro-hardness was found to increase with the increasing amounts of FA particles. The 20-40 wt.% of the particles showed the best results of both impact strength and Modulus of elasticity . Also, high strength was obtained indicating that the FA can be a good filler to improve the mechanical properties of the UP matrix. The fractographic studies of the chosen compositions confirmed that the particles had strongly bonded with the UP matrix.

Characterization of metals released from coal fly ash during dredging at the Kingston ash recovery project

A storage-pond dike failure occurred on December 22, 2008 at the Tennessee Valley Authority Kingston Fossil Plant resulting in the release of over 4million cubic meters (5million cubic yards) of fly ash. Approximately half of the released ash was deposited in the main channel of the Emory River, Tennessee, USA. Remediation efforts of the Emory River focused on hydraulic dredging, as well as mechanical excavation in targeted areas. However, agitation of the submerged fly ash during hydraulic dredging introduces river water into the fly ash material, which could promote dissolution and desorption of metals from the solid fly ash material. Furthermore, aeration of the dredge slurry could alter the redox state of metals in the fly ash material and thereby change their sorption, mobility, and toxicity properties. The research presented here focuses on the concentrations and speciation of metals during the fly ash recovery from the Emory River. Our results indicate that arsenite [As(III)] released from the fly ash material during dredging was slowly oxidized to arsenate [As(V)] in the slurry recovery system with subsequent removal through precipitation or sorption reactions with suspended fly ash material. Concentrations of other dissolved metals, including iron and manganese, also generally decreased in the ash recovery system prior to water discharge back to the river.

Coal Fly Ash Solidification by Calcination Products of CaCO<sub>3</sub>–Al(OH)<sub>3</sub> Mixtures Accompanied by Prevention of Oxoanion Leaching

Coal Fly Ash Solidification by Calcination Products of CaCO<sub>3</sub>–Al(OH)<sub>3</sub> Mixtures Accompanied by Prevention of Oxoanion Leaching

Enhanced properties of fly ash-reinforced unsaturated polyester composites

Polyester, which is often fibre reinforced, can make a potent combination when reinforced with fly ash particles. In this study, both the as-received and surface-treated fly ash particles, ranging from 0% to 50% of weight, were used as fillers added to the unsaturated polyester utilising the route of curing. The mechanical properties of the composites were evaluated by conducting the hardness and tensile tests. The Charpy impact test was used to determine the amount of energy absorbed during fracture. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS) were used to identify the fly ash particles and to observe the fractographs of the composites. Through the density and SEM-EDS analyses, the type of solid fly ash was identified. For the surface-treated fly ash-reinforced polyester (TFAP), micro-hardness and tensile properties were improved with the addition of fly ash particles. Many improvements were also achieved in the as-received fly ash-reinforced (AFAP) composite. In terms of impact strength analysis, an excellent achievement was obtained in both composites. The fractograph, tribological and surface analyses confirmed the uniform distribution and consequently the effectiveness of the bonding.