Reusing Fly Ash Research Articles

A magnetic recyclable MCM-48/ZnFe2O4/BiOBr heterojunction with improved RhB visible light degradation efficiency

The MCM-48/ZnFe2O4/BiOBr (MZBB) heterojunction photocatalyst was constructed and applied to decompose rhodamine B (RhB) under the influence of visible light to investigate its photocatalytic effect. The outcomes revealed that 0.75 MZBB compound semiconductor degraded RhB dye at a concentration of 40 mg/L, pH 6.0, by 99.03% after 60 min, and the total organic carbon (TOC) mineralization rate was 0.0631. The combination of n-type ZnFe2O4 and BiOBr is responsible for the increased photocatalytic performance of the MCM-48/ZnFe2O4/BiOBr composite, and the presence of n-n junctions promotes the separation of photogenerated carriers and prolonged reorganization time. In addition, MCM-48 has good absorption properties and effective specific surface area. The present work accomplished the dual challenges of constructing MCM-48 and ZnFe2O4 on flower-like BiOBr and reusing fly ash. The material shows an excellent ability to decompose organic pollutants and magnetically recoverable.

Re-using of coal-fired fly ash for arsenic vapors in-situ retention before SCR catalyst: Experiments and mechanisms

Arsenic is easily evaporated with coal combustion, which not only causes serious environmental issues but also leads to the deactivation of selective catalytic reduction (SCR) catalyst. This study focused on the re-using of coal-fired fly ash for arsenic vapors in-situ retention before SCR catalyst in the furnace. Experiments were carried out to estimate the effects of typical fly ash compounds (Ca-, Fe-, and Al-bearing components) as well as acid gases (SO2/NO) on arsenic capture at temperatures of high-temperature furnace stage (900 °C) or SCR system entry stage (450 °C). The results demonstrated that, regardless of collection plants, all the ash samples showed certain capacity in arsenic vapors retention and the capture performance was enhanced at 900 °C than at 450 °C. Both physical and chemical adsorptions occurred for arsenic capture at low temperature, while chemical adsorption by effective mineral components dominated at high temperature. The role of Ca-compounds was more remarkable than Fe/Al-compounds and CaSO4/calcium silicates were identified as the key calcium compounds that acted on arsenic adsorption by fly ash. Insignificant effects were found regarding the acid gases (SO2 and NO) on arsenic retention by fly ash owing to the high resistance of CaSO4 and calcium silicates to acid gases. These findings provided reference for the in-situ retention of arsenic by reusing fly ash that enriched in specific compositions.

Synthesis and characterization of single-phase submicron zeolite Y from coal fly ash and its potential application for acetone adsorption

Abstract The large emission of coal fly ash (CFA) brings a series of environmental and health problems. Therefore, it is extremely necessary and significant to explore efficient ways to reuse fly ash. Zeolitization of CFA provides a potential alternative for creating high-added-value products from this hazardous solid waste. But the synthesis of zeolite from CFA is still a long way from industrialization. In this paper, a single-phase submicron zeolite Y (FAZ-Y3) was successfully synthesized from CFA via the alkali fusion hydrothermal method without the use of any organic structure guide agents. Results indicated that the type and purity of zeolite greatly depended on the preparation parameters and zeolite P was the major competitive phase. With an average size of approximately 250 nm, FAZ-Y3 possessing a specific surface area of 386.9 m2 g−1 and crystallinity of 92.73% was prepared at 80 °C for 12 h by adding the inorganic liquid-phase directing agent and exhibited excellent thermal stability. The product was then applied to acetone adsorption. It was found that Langmuir and Bangham model could better describe the experimental data and internal diffusion was the main resistance of mass transfer. The adsorption capacity of FAZ-Y3 could reach approximately 82% of that for the commercial zeolite Y (CZ-Y) and it also possessed considerable regenerability property. The results of this study provided a foundation for the synthesis of a low-cost adsorbent for controlling the emission of volatile organic compounds.

Solidification/stabilization of stainless steel pickling residue with aluminum potassium sulfate amended fly ash

This article presents an original study on the feasibility of reuse fly ash (FA) solidified/stabilized stainless steel pickling residue (SSPR). SSPR was characterized using different leaching procedure and solidified/stabilized using aluminum potassium sulfate dodecahydrate (KAl(SO4)2.12H2O) amended fly ash. A modified four-step Community Bureau of Reference (BCR) sequential leaching test and risk assessment code (RAC) was employed to evaluate the potential hazards of metals in SSPR. Results show that SSPR mainly consists of sulfates and heavy metals. The major elements are Ca and Fe, with the total amount of 191,600 and 122,400 mg/kg. Cr is the most notable metal with a total amount of 22,500 mg/kg. Its concentrations in HJ/T 299 and HJ/T 300 extracts are 28.6 and 285 mg/L respectively. Another metal that is of some concern is Ni, its concentration in HJ/T 300 extract is 229 mg/L and total content in the residues is 10,690 mg/kg. The RAC of four list heavy metals are: Ni (61.36%) > Zn (43.48%) > Cr (20.64%) > Cu (19.83%). Therefore, SSPR has a higher potential to be hazardous to the environment. After treatment by 10% of KAl(SO4)2.12H2O with 40% of FA2 (10KA40FA2), the concentration of Cr is 7.9 mg/L in HJ/T 299 extract and 12.68 mg/L in HJ/T 300 extract. While these two values for Ni is 0 and 14.34 mg/L. The RAC of the metals after treatment by 10KA40FA2 followed the order of Ni (20.38%) > Zn (10.59%) > Cu (8.54%) > Cr (7.71%). The unconfined compression strength (UCS) tests showed that the 7-d UCS of the 10KA40FA2 remolded sample achieved 3556.2 kPa which was much higher than that of raw SSPR remolded sample of 1746.7 kPa.

Utilization of coal fly and bottom ash pellet for phosphorus adsorption: Sustainable management and evaluation

Recycling of coal combustion solids can have several environmental benefits. The objective of this study was to evaluate a sustainable approach to recycle coal fly ash and bottom ash as pelletized-adsorbents for dissolved phosphorus (P). Sodium Dodecyl Sulfate (SDS), a foaming agent, was added to enhance the phosphorus adsorption capacity of fly ash pellets (FAP) and bottom ash pellets (BAP) during the pellet fabrication. Ten types of fly ash pellets and bottom ash pellets with varying Sodium Dodecyl Sulfate proportions (FAP-0/BAP-0: 0% SDS; FAP-1/BAP-1: 2% SDS; FAP-2/BAP-2: 4% SDS; FAP-3/BAP-3: 6% SDS; FAP-4/BAP-4: 8% SDS by weight) were manufactured with a high temperature (700℃) modification process. The results indicated that the bottom ash pellet was more suitable adsorbent than fly ash pellet due to the better phosphorus adsorption capacity and lower heavy metal leaching. After the addition of Sodium Dodecyl Sulfate, the volumetric porosity of fly ash pellets and bottom ash pellets increased by 45.5%–163.6%, 52.9%–76.5%, respectively. However, higher Sodium Dodecyl Sulfate fraction did not result in better pellet phosphorus removal, since FAP-2 and BAP-3 resulted in the highest phosphorus removal among the pellets tested in this study. The results from X-ray diffraction demonstrated that Calcium and Silica were the major phases in the pellets. This study provides a feasible approach to reuse fly ash and bottom ash as effective pelletized-adsorbents for water quality improvement. These pellets can be applied in edge-of-field and in-stream treatment to control P loss from the agricultural area.

An Assessment of Reuse of Light Ash from Bayer Process Fluidized Bed Boilers in Geopolymer Synthesis at Ambient Temperature

Sustainable civil construction in the future, besides having low energy consumption and greenhouse gas emissions, must also adopt the principle of reusing wastes generated in the production chain that impact the environment. The aluminum production chain includes refining using the Bayer process. One of the main wastes produced by the Bayer process that has an impact on the environment is fly ash. Geopolymers are cementitious materials with a three‐dimensional structure formed by the chemical activation of aluminosilicates. According to studies, some are proving to be appropriate sources of Al and Si in the geopolymerization reaction. The research reported here sought to assess the possibility of reusing fly ash characteristic of the operational temperature and pressure conditions of Bayer process boilers in geopolymer synthesis. Geopolymerization reaction was conducted at an ambient temperature of 30°C, and the activator used was sodium hydroxide (NaOH) 15 molar and sodium silicate (Na2SiO3) alkaline 10 molar. Fly ash and metakaolin were used as sources of Al and Si. XRD, XRF, and SEM Techniques were used for characterizing the raw materials and geopolymers. As a study parameter, the mole ratios utilized followed data from the literature described by Davidovits (year), so that the best results of the geopolymer samples were obtained in the 2.5 to 3.23 range. Resistance to mechanical compression reached 25 MPa in 24 hours of curing and 44 MPa after 28 days of curing at ambient temperature.

Development of Nano-Sulfide Sorbent for Efficient Removal of Elemental Mercury from Coal Combustion Fuel Gas.

The surface area of zinc sulfide (ZnS) was successfully enlarged using nanostructure particles synthesized by a liquid-phase precipitation method. The ZnS with the highest surface area (named Nano-ZnS) of 196.1 m(2)·g(-1) was then used to remove gas-phase elemental mercury (Hg(0)) from simulated coal combustion fuel gas at relatively high temperatures (140 to 260 °C). The Nano-ZnS exhibited far greater Hg(0) adsorption capacity than the conventional bulk ZnS sorbent due to the abundance of surface sulfur sites, which have a high binding affinity for Hg(0). Hg(0) was first physically adsorbed on the sorbent surface and then reacted with the adjacent surface sulfur to form the most stable mercury compound, HgS, which was confirmed by X-ray photoelectron spectroscopy analysis and a temperature-programmed desorption test. At the optimal temperature of 180 °C, the equilibrium Hg(0) adsorption capacity of the Nano-ZnS (inlet Hg(0) concentration of 65.0 μg·m(-3)) was greater than 497.84 μg·g(-1). Compared with several commercial activated carbons used exclusively for gas-phase mercury removal, the Nano-ZnS was superior in both Hg(0) adsorption capacity and adsorption rate. With this excellent Hg(0) removal performance, noncarbon Nano-ZnS may prove to be an advantageous alternative to activated carbon for Hg(0) removal in power plants equipped with particulate matter control devices, while also offering a means of reusing fly ash as a valuable resource, for example as a concrete additive.

Life-cycle environmental and cost impacts of reusing fly ash

Municipal solid waste incinerator (MSWI) fly ash, which includes residues collected from semidry scrubbers and bag filters, is a common hazardous waste that is difficult to recycle. We evaluate a novel application of the reuse of MSWI fly ash as a substitute alkali reagent in the Waelz process at an electric arc furnace (EAF) ash recycling plant because of its economical and environmental benefits. Life-cycle assessment and cost-benefit analysis were used to compare the application with other alternatives, namely, disposal in landfill after stabilization/solidification, reuse as part of raw material in a cement kiln, and reuse as part of aggregates in brick. Data from field experiments which were performed at a commercial EAF ash recycling plant in Taiwan were used for the evaluation. Our results show that the proposed application has the lowest environmental impact because the ZnO recycling of EAF ash is environmental friendly for reducing the excavation of zinc ore. In terms of economy, the higher sale price of the resulting cement product offers the best benefit among different applications in this research. After integration of environmental and economic effects, the application was still superior to the three alternatives. Although stabilization/solidification and subsequent disposal of MSWI fly ash is common practice, the scarcity of landfill sites and its volume leads to risks associated with operation of incinerators. Thus, finding multiple approaches to recycling of MSWI fly ash is necessary. This study provides a potential option for the recycling of MSWI fly ash and presents its environmental and economic benefits in management of fly ash from MSWIs.

Life Cycle Assessment of Reusing Fly Ash from Municipal Solid Waste Incineration

Many countries consider the fly ash produced from the incineration of municipal solid waste (MSW) as hazardous waste. In Taiwan, 24.5 thousand tons of MSW is incinerated and 554.7 tons of fly ash is produced daily. As landfill capacity in the country is limited, this vast amount of fly ash should ideally be reused. However, some treatment methods to enable the reuse of fly ash can have a worse impact on the environment than was previously believed. The aim of this research was therefore to compare the different processes for the reuse of fly ash by employing data collected from the incineration process in Taiwan in order to establish a life-cycle assessment (LCA) database. The database, containing information on the assessment of reuse treatments, is intended to inform decision making on the best practices for the reuse of fly ash. The study poses four scenarios for reuse treatment and disposal of one ton of fly ash: 1) landfilling after solidification, 2) reuse as cement after a washing process, 3) reuse as bricks after a washing process, 4) reuse as an alkali in the waelz process of steelmaking. The results from the LCA showed that the washing processes consumed more water but less electricity; however, more electricity was consumed and higher toxicity was caused in scenario 4, the reuse as an alkali in the waelz process. More water and chemical additives were used in scenario 2 because of the higher limits of chloride compounds and heavy metals used in construction materials. To conclude, the comprehensive LCA inventory database established by this study could assist in reducing the environmental impacts of reuse treatments for fly ash, and consequently could contribute to the safer management of fly ash worldwide.

Chloride Behavior in Washing Experiments of Two Kinds of Municipal Solid Waste Incinerator Fly Ash with Different Alkaline Reagents

To efficiently reduce and reuse fly ash from incinerators, we suggest trying a new alkaline reagent to neutralize the acid compounds in discharged gas from incinerators and reuse fly ash as the raw material in the cement industry. Normally the washing process includes a pretreatment method to remove chlorides to comply with the strict standards for cement. We examined chloride behavior in washing experiments by X-ray absorption near edge structure (XANES) and X-ray diffraction (XRD) for two kinds of fly ash: (1) fly ash collected in a bag filter with the injection of calcium hydroxide (Ca(OH)2) for acid gas removal (CaFA), and (2) fly ash collected in a bag filter with the injection of sodium bicarbonate (NaHCO3) for acid gas removal (NaFA). We found that the insoluble chlorides in both CaFA and NaFA combined calcium chloride (CaCl2), with some sodium chloride (NaCl) also possibly combined. Under some conditions, the combined CaCl2 and NaCl were released. In particular, when the liquid/solid ratio was greater than 3 or the washing frequency was doubled, less chlorine, insoluble chlorine, and CaCl2 were left in the residues of NaFA than in the residues of CaFA. As a result, it is desirable to use NaHCO3 as the alkaline reagent instead of Ca(OH)2 in the air pollution control system of incinerators for recycling fly ash as a raw material in the cement industry.

Reusing fly ash in glass fibre reinforced cement: A new generation of high-quality GRC composites

New composite materials based on an alkali-resistant glass-fibre reinforced cement (AR-GRC) system are being developed by using fly ash (FA) produced at coal thermoelectric power plants, and fluid catalytic cracking catalyst residue (FC3R) from the petrol industry as cement replacement materials. These wastes are reactive from the pozzolanic viewpoint, and modify the nature and the microstructure of the cement matrix when a part of the Portland cement is replaced in the formulation of GRC. Several microstructural and mechanical aspects are being studied for AR-GRC systems. The behaviour of composites exposed to ageing shows that the pozzolanic activity of the ground FA added in high amounts and its mixture with the FC3R increase the flexural strength and no evidences of strength decay are observed. Additionally, the fibres due to the high alkalinity of the cementing matrix can be deteriorated. Fibres in the control (only Portland cement) and FC3R containing composites were attacked, whereas composites with FA and their mixture with FC3R show that the fibres have not been attacked, due to the pozzolanic activity of replacing materials that reduce the calcium hydroxide content in the cementing matrix.

A case study on stabilization and reuse of geopolymer-encapsulated brown coal fly ash

Fly ash disposal for coal power stations is an ongoing problem. This paper explores the use of a geopolymeric material to stabilize fly ash and reduce the leach rates of metals, and at the same time determine whether the stabilized material can be reused and recycled as value-added products. Fly ash from the Latrobe Valley, Victoria, Australia, was collected and stabilized in a geopolymer with a molar silica to alumina ratio of 3. Fly ash was collected from electrostatic precipitators [precipitator fly ash (PFA)] and ash disposal ponds [leached fly ash (LFA)] so that a comparison in results between the two types could be made. In terms of stabilization of selected heavy metals, PFA showed better trends towards reduction in leach rates, although for this fly ash the initial concentration of heavy metals is low. LFA showed better trends towards reduction in major elemental leach rates. Compressive strength tests were carried out to determine the potential of the material to be used as recycled products. A maximum compressive strength of 32 MPa was achieved with a PFA‐geopolymer combination, which shows that these materials can be recycled and reused. However, more research is still required to achieve greater compressive strengths. Scanning electron microscopy linked the leaching behaviour and compressive strength values with images that showed the fly ash particle‐geopolymer interaction. Materials cost estimation was conducted to determine the cost of materials required to stabilize and reuse fly ash geopolymers.

マイクロ波加熱水熱処理を利用したフライアッシュからのゼオライト合成

The synthesis of phillipsite from fly ash, which can be used as adsorbents, catalysts etc., was proposed as a new way to reuse fly ash. The effects of morphology of fly ash and the synthesis conditions on the generated zeolite are studied. We proposed a method for selective synthesis of phillipsite improving the purity and yield by introducing microwave heating. The microwave heating enhanced the growth rate of zeolite and improved the crystalline state. The synsethis process which is affected by the microwave irradiation is also clarified.

98/02942 Upgrading and reusing fly ash from coal-fired thermal power plants after heat treatment

98/02942 Upgrading and reusing fly ash from coal-fired thermal power plants after heat treatment