Leaching behavior of heavy metals with hydrochloric acid fromfly ash generated in municipal waste incineration plants

The extraction behavior of heavy metals from municipal waste incineration （MWI） fly ash was investigated systematically. The extraction process includes two steps, namely, fly ash was firstly washed with water, and then subjected to hydrochloric acid leaching. The main parameters for water washing process were tested, and under the optimal conditions, about 86% Na, 70% K and 12% Ca were removed from fly ash, respectively. Hydrochloric acid was used for the extraction of valuable elements from the water-washed fly ash, and the optimal extraction was achieved for each heavy metal as follows： 86% for Pb, 98% for Zn, 82% for Fe, 96% for Cd, 62% for Cu, 80% for Al, respectively. And the main compositions of the finally obtained solid residue are Ca2PbO4, CaSi2Os, PbsSiO7, Ca3A12Si3012 and SiO2.

A mini review on the separation of Al,Fe and Ti elements from coal fly ash leachate

The electricity demand is increasing rapidly with the development of society and technology.Coal-fired thermal power plants have become one of the primary sources of electricity generation for urbanization.However,coal-fired thermal power plants produce a great amount of by-product coal fly ash every year.Coal fly ash disposal in landfills requires a sizable space and has negative environmental impacts.Therefore,it is crucial to develop new technologies and methods to utilize this enormous volume of solid waste in order to protect the environment.In this review,the fundamental physical and chemical character-istics of coal fly ash are introduced,and afterward the disposal policies and utilization ways of coal fly ash are discussed to gain a comprehensive understanding of the various ways this waste.The leaching of valuable metals in coal fly ash and the extraction of metal elements in leachate under different conditions are also summarized.Furthermore,the possibility of coal fly ash to serve as a supplementary source for mineral resources is analyzed,providing a basis for its extensive use as a raw material in the metal industry in China and worldwide.

Investigation of basic properties of fly ash from urban waste incinerators in China

Basic properties of fly ash samples from different urban waste combustion facilities in China were analyzed using as X-ray fluorescence （XRF）, scanning electron microscopy （SEM）, X-ray diffraction （XRD）. The leaching toxicity procedure and some factors influencing heavy metals distribution in fly ash were further investigated. Experimental results indicate that the fly ash structures are complex and its properties are variable. The results of XRF and SEM revealed that the major elements （〉10000 mg/kg, listed in decreasing order of abundance） in fly ash are O, Ca, Cl, Si, S, K, Na, Al, Fe and Zn. These elements account for 93% to 97%, and the content of Cl ranges from 6.93% to 29.18 %, while that of SiO2 does from 4.48% to 24.84%. The minor elements （1000 to 10000 mg/kg） include Cr, Cu and Pb. Primary heavy metals in fly ash include Zn, Pb, Cr, Cu etc. According to standard leaching test, heavy metal leaching levels vary from 0 to 163.10 mg/L （Pb） and from 0.049 to 164.90 mg/L （Zn）, mostly exceeding the Chinese Identification Standard for hazardous wastes. Morphology of fly ash is irregular, with both amorphous structures and polycrystalline aggregates. Further research showed that heavy metals were volatilized at a high furnace temperature, condensed when cooling down during the post-furnace system and captured at air pollution control systems. Generally, heavy metals are mainly present in the forms of aerosol particulates or tiny particulates enriched on surfaces of fly ash particles. The properties of fly ash are greatly influenced by the treatment capacities of incinerators or the variation of waste retention time in chamber. Fly ash from combustors of larger capacities generally has higher contents of volatile component and higher leaching toxicity, while those of smaller capacities often produce fly ash containing higher levels of nonvolatile components and has lower toxicity. The content of heavy metals and leaching toxicity maybe have no convincing correlation, and high alkali content of CaO greatly contribute to leaching toxicity of heavy metal and acid neutralization capacity against acid rain.

Solidification of Municipal Solid Waste Incineration FlyAsh with Cement and Its Leaching Behaviors of Heavy Metals

The solidifying effect of cement addition on municipal solid waste incineration fly ash (MSWFA for short,collected from the gas exhaust system of MSW incinerator),the interaction of MSWFA with cement and water and the leaching of heavy metals from cement solidified MSWFA are investigated.The main results show that:(1) when MSWFA is mixed with cement and water,H 2 evolution,the formation and volume expansion of AFt will take place,the volume expansion can be reduced by ground rice husk ash addition;(2) heavy metals do leach from cement solidified MSWFA and at lower pH more leaching will occur;(3) compared with cement-solidified fly ash,the leachate of solidified MSWFA is with higher heavy metal contents;(4) with the increment of cement addition leached heavy metals are decreased;and (5) concentrations of Zn,Mn,Cu and Cd in all the leachates can meet the relevant Standards of Japan,but as the regulations for soil and groundwater protection of Japan are concerned,precautions against the leaching of Pb,Cl - and Cr 6+ and so on are needed.

Chemical speciation and mobility of heavy metals in municipal solid waste incinerator fly ash

Chemical speciation is a significant factor that governs the toxicity and mobility of heavy metals in municipal solid waste incinerator fly ash. Sequential extraction procedure is applied to fractionate heavy metals(Pb, Zn, Cd, Cu, and Cr) into five defined groups: exchangeable, carbonate, Fe-Mn oxide, organic, and residual fractions. The mobility of heavy metals is also investigated with the aid of toxicity characteristic leaching procedure. In the fly ash sample, Pb is primarily presented in the carbonate(51%) and exchangeable(20%) fractions; Cd and Zn mainly exist as the exchangeable(83% and 49% respectively); Cu is mostly contained in the last three fractions(totally 87%); and Cr is mainly contained in the residual fraction(62%). Pb, Zn and Cd showed the high mobility in the investigation, thus might be of risk to the natural environment when municipal solid waste incinerator fly ash is landfilled or reutilized.

Glass-ceramics made from arc-melting slag of waste incineration fly ash

Grate fly ash and fluidized bed fly ash mixed with glass cullet additive respectively were melted in the electronic arc-furnace. The product, arc-melting slag, was further treated by crushing, pressing and heat treatment in order to make the glass-ceramics. The crystallization behaviors of the produced glass-ceramics were examined by differential thermal analysis （DTA）, X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. Results show that main crystalline phase of the glass-ceramics fi＇om grate fly ash is wollastonite （CaSiO3） with small amount of diopside （Ca（Mg,Al）（Si,Al）206）, and that from fluidized bed fly ash is diopside （Ca（Mg,Al）（Si,Al）206）. It is found that the glass-ceramics sintered at 850 ℃and 1 000℃ from grate fly ash and fluidized bed fly ash respectively have the optimal physical, mechanical and chemical characteristics. Glass-ceramics samples, produced from incinerator fly ash with desirable properties and the low leaching concentration of heavy metals, can be the substitute of nature materials such as marble, granite and porcelain tiles.

Microstructures and thermal properties of municipal solid waste incineration fly ash

To analyze the feasibility of utilization of thermal technology in fly ash treatment, thermal properties and microstructures of municipal solid waste incineration （MSW1） fly ash were studied by measuring the chemical element composition, specific surface area, pore sizes, functional groups, TEM image, mineralogy and DSC-TG curves of raw and sintered fly ash specimens. The results show that MSWI fly ash particles mostly have irregular shapes and non-typical pore structure, and the supersonic treatment improves the pore structure; MSWI fly ash consists of Such crystals as SiO2, CaSO4 and silica-aluminates, and some soluble salts like KCl and NaCl. During the sintering process, mineralogy changes largely and novel solid solutions are produced gradually with the rise of temperature. Therefore, the utilization of a proper thermal technology not only destructs those persistent organic toxicants but also stabilizes hazardous heavy metals in MSWI fly ash.

The Future Resources for Eco-building Materials:Ⅱ. Fly Ash and Coal Waste

To use fly ash and coal waste effectively, the current technologies for reprocessing and recycling these wastes into eco-building materials were reviewed, such as utilizing fly ash as the component of fly ash cement and low heat cement after the processes of separation, removal of carbon remains and fine comminution, calcining coal waste into kaolin and meta-kaolin with suspension technology, and preparing clinkerless alkali-activated geopolymer materials with fly ash and meta-kaolin.

Mechanism of high concentration phosphorus wastewater treated by municipal solid waste incineration fly ash

The mechanism of removing phosphate by MSWI(municipal solid waste incineration)fly ash was investigated by SEM(scanning electron microscopy)with EDS(energy dispersion spectrum),XRD(X-ray diffraction),FT-IR(Fourier transform infrared spectroscopy),BET(specific surface area),and BJH(pore size distribution).The results indicate that the removal rate of phosphate(100 mg/L)in 50 mL phosphorus wastewater reaches at 99.9% as the dosage of MSWI fly ash being 0.9000 g under room temperature.The specific surface area of MSWI fly ash is less than 6.1 m2/g and the total pore volume is below 0.021 cm3/g,suggesting that the absorption capacity of calcite is too weak to play an important role in phosphate removal.SEM images show that drastic changes had taken place on its specific surface shape after reaction,and EDS tests indicate that some phosphate precipitates are formed and attached onto MSWI fly ash particles.Chemical precipitation is the main manner of phosphate removal and the main reaction is: 3Ca2++2 PO4 3-+xH2O→Ca3(PO4)2↓·xH2O.Besides,XRD tests show that the composition of MSWI fly ash is complex,but CaSO4 is likely to be the main source of Ca2+.The soluble heavy metals in MSWI fly ash are stabilized by phosphate.

Reusing oxide-based pulverised fly ash and medical waste particles to develop electroless nickel composite coatings(Ni–P/fly ash and Ni–P/SiO2–Al2O3)

Recycling and reusing materials from waste have become a nexus in the development of sustainable materials,leading to more balanced technologies.In this study,we developed a composite coating by co-depositing recycled ceramic particles,pulverised fly ash(PFA)and medical ceramics(MC),into a nickel–phosphorus matrix using a typical electroless plating process.Scanning electron microscopy(SEM)images indicated well-dispersed particles in the Ni–P matrix.However,compared with the MC particles,the PFA particles were distributed scantily with a lower content in the matrix,which could be due to the less impingement effect during the co-deposition.A modified microstructure with refined grains was obtained for the PFA-incorporated composite coating,as seen in the SEM micrograph.The X-ray diffraction result of the MC-incorporated composite coating showed the formation of Nix Siy phases in addition to the typical Ni3 P phases for the heattreated electroless Ni–P coatings.Upon heat treatment,the PFA-reinforced composite coating,due to a modified microstructure,exhibited a higher microhardness up to HK0.05818,which is comparable to that of the traditional SiC particle-embedded composite coating(HK0.05825).The findings can potentially open up a new strategy to further advance the green approach for industrial surface engineering.

Thermal treatment and utilization of Al-rich waste in high calcium fly ash geopolymeric materials

The Al-rich waste with aluminium and hydrocarbon as the major contaminant is generated at the wastewater treatment unit of a polymer processing plant. In this research, the heat treatment of this Al-rich waste and its use to adjust the silica/alumina ratio of the high calcium fly ash geopolymer were studied. To recycle the raw Al-rich waste, the waste was dried at 110℃ and calcined at 400 to 1000℃. Mineralogical analyses were conducted using X-ray diffraction （XRD） to study the phase change. The increase in calcination temperature to 600, 800, and 1000℃ resulted in the phase transformation. The more active alumina phase of active θ-Al2O3 was obtained with the increase in calcination temperature. The calcined Al-rich waste was then used as an additive to the fly ash geopolymer by mixing with high calcium fly ash, water glass, 10 M sodium hydroxide （NaOH）, and sand. Test results indicated that the calcined Al-rich waste could be used as an aluminium source to adjust the silica/alumina ratio and the strength of geopolymeric materials. The fly ash geopolymer mortar with 2.5wt% of the Al-rich waste calcined at 1000℃ possessed the 7-d compressive strength of 34.2 MPa.

Hydration Kinetics of Municipal Solid Wastes Incineration(MSWI) Fly Ash-Cement

Hydration heat behavior and kinetics of blended cement containing up to 20% MSWI fly ash were investigated based on its hydration heat evolution rate measured by isothermal calorimeter. Kinetics parameters, N and K, and hydration degree, Ca(OH)2 content, were also calculated and analyzed. According to the experimental results, the induction period was elongated, the second heat evolution peak was in advance, and the third hydration heat peak could be detected due to MSWI fly ash pozzolanic reaction. The hydration reaction rate was controlled by nucleation kinetics in the acceleration period and then by diffusion in the decay period, but in the deceleration period, the hydration experienced a dual controlling reaction of autocatalytic chemical reaction and diffusion. The hydration rate of blended cement was faster. Ca(OH)2 content increased before 14 days.

Parametric optimization of packed bed for activated coal fly ash waste heat recovery using CFD techniques

Coal fly ash is an industrial solid waste generated from coal preparation during the processing and cleaning of coal for electric power generation.Comprehensive investigation on the reutilization of waste heat of activated coal fly ash is of great economic significance.The method of recovering the waste heat,proposed in this study,is the transfer of heat from activated coal fly ash to gas with the movement of air using the packed bed,providing valuable energy sources for preheating the raw coal fly ash to reduce the overall energy consumption.The investigation is carried on the heat transfer characteristics of gas–solid(activated coal fly ash)phases and air temperature fields of the packed bed under some key conditions via computational fluid dynamics.A two dimensional geometry is utilized to represent key parts of packed bed.The distribution mechanism of the temperature field for gas phase is analyzed based on the transient temperature contours at different times.The results show that the obtained rule of gas–solid heat transfer can effectively evaluate the influences of operating parameters on the air temperature in the packed bed.Simultaneously,it is found that no temperature differences exist in the hot air at the outlet of the packed bed.The investigation provides guidance for the design and optimization of other similar energy recovery apparatuses in industries.

Comparative evaluation of processes for heavy metal removal from municipal solid waste incineration fly ash

Hydrochloric acid leaching, chloride evaporation, acetic acid leaching, and biological leaching were evaluated and compared as processes of heavy metal removal for municipal solid waste incineration fly ash(MSWFA). Six factors, namely, energy consumption, process efficiency, process handling, process cost estimation, cost reduction potential, and study progress, were used in order to find out their advantages and disadvantages and to help develop a better recovery process of heavy metals from MSWFA in terms of treatment of the waste material. Hydrochloric acid leaching process was found to be most balanced among the evaluated processes. It showed superiority on energy consumption, process cost estimation, and study progress. On the other hand, despite of its excellency in process efficiency, chloride evaporation process was most unfavorable mainly due to heavy energy dependence. Biological process, with huge potential of cost reduction, was concluded to be the second best process.

Sustainable Fly Ash Based Roof Tiles with Waste Polythene Fibre: An Experimental Study

The compressive stress-strain behavior and other characteristics of treated fly ash based roof tiles have been studied by several experimental tests. This paper attempts to presents the results and observations of a study and comparison based on the past reported experimental data. Based on the results and observations of the comprehensive experimental study, five “control points” have been identified. The new sets of experiment have been carried out to investigate whether it might be possible the use of fly ash in fly ash based roof tiles for residential construction. In the present study, treated fly ash (TFA) of C category was used with different materials as a replacement of clay for making treated fly ash stone dust roof tiles (TFASDRT). Treated fly ash stone dust roof tiles (TFASDRT) were studied at varying percentages of cement, coarse sand, and radish stone dust (RSD) along with the constant percentage of waste polythene fibre (WPF). A research program was undertaken to evaluate the suitability of such test for assessing the properties of treated fly ash stone dust roof tiles (TFASDRT). The result of this study recommends that the fly ash based roof tiles provides a sustainable supplement to the traditional clay roof tiles, they increase the efficiency of traditional roof tiles and significantly help to reduce the environmental issues associated with the disposal of these waste materials.

Mechanical and environmental properties of geopolymer-stabilized domestic waste incineration slag in an asphalt pavement base

Domestic waste incineration slag(WIS)includes fly ash and slag.Fly ash is classified as hazardous waste because it contains heavy metals.Most of slag are directly stacked or landfilled due to problems such as large output and low utilization rate.Harmless treatment is imminent.If WIS is used effectively in the road engineering,which can realize the high-quality and high-efficiency recycling of WIS,and it is of great significance to save resources and protect the environment.This study applies a geopolymer prepared from WIS fly ash as a stabilizing agent in WIS blending macadam for use as a pavement base mixture,and reports the mechanical properties(unconfined compressive strength,splitting strength,and resilience modulus)of the geopolymer-stabilized WIS blending macadam(GeoWIS).The leaching concentrations of harmful heavy metals of GeoWIS soaked in water were also investigated.Finally,the strength formation and heavy metal stability mechanisms were explored.The unconfined compressive strength,splitting strength,and compressive resilient modulus of GeoWIS all increased with increasing geopolymer content and decreasing WIS content.The strength of GeoWIS was derived from its geopolymerization and hydration products(C-S-H gel,N-A-S-H gel,and AFt).When the geopolymer content reached 12%–14%,the GeoWIS without natural macadam met the strength criterion of the asphalt pavement base.Through physical adsorption and chemical bonding,the geopolymer significantly reduced the leaching of harmful heavy metals.In GeoWIS with 50%WIS and stabilized with 10%geopolymer,the Cr,Ni,Cd,and Pb concentrations met the grade III groundwater standard.Concentrations of heavy metals leached from GeoWIS are low and exert little impact on environment.

Effects of Wood Ash and Waste Glass Powder on Properties of Concrete in Terms of Workability and Compressive Strength in Jaresh City

The potential for using fly ash as a supplementary cementing material in concrete has been known almost since the beginning of the previous century. Fly ash was used as a supplementary cementing material (SCM) in the production of Portland cement concrete. A supplementary cementing material, when used in conjunction with Portland cement, contributes to the properties of the hardened concrete through hydraulic or pozzolanic activity, or both. In this study, the fly ash and waste glass powder were used in concrete blocks to study the improvement of concrete in terms of workability and strength. Therefore, an experimental study will be conducted to measure the engineering properties of cured concrete. In this research, local raw material from Jaresh area was used.

A review of the synthesis and application of zeolites from coal-based solid wastes

Zeolite derived from coal-based solid wastes(coal gangue and coal fly ash)can overcome the environmental problems caused by coal-based solid wastes and achieve valuable utilization.In this paper,the physicochemical properties of coal gangue and coal fly ash are introduced.The mechanism and application characteristics of the pretreatment processes for zeolite synthesis from coal-based solid wastes are also introduced.The synthesis processes of coal-based solid waste zeolite and their advantages and disadvantages are summarized.Furthermore,the application characteristics of various coal-based solid waste zeolites and their common application fields are illustrated.Finally,we propose an alkaline fusion-assisted supercritical hydrothermal crystallization as an efficient method for synthesizing coal-based solid waste zeolites.In addition,more attention should be given to the recycling of alkaline waste liquid and the application of coal-based solid waste zeolites in the field of volatile organic compound adsorption removal.

Dry coal fly ash cleaning using rotary triboelectrostatic separator

More than 80 million metric tons of fly ash is produced annually in the U.S. as coal combustion by-product. Coal fly ash can be converted to value-added products if unburned carbon is reduced to less than 2.5%. However, most of fly ash is currently landfilled as waste due to lack of efficient purification technologies to separate unburned carbon from fly ash. A rotary triboelectrostatic separator has been developed and patented recently at the University of Kentucky with unique features. Several fly ash samples have been used to understand the effects of major process parameters on the separation performance. The results show that compared to existing triboelectrostatic separators, the rotary triboelectrostatic separator has significant advantages in particle charging efficiency, solids throughput, separation efficiency, applicable particle size range.

Effect of Water Washing Pre-treatment on the Properties of Glass-ceramics from Incinerator Fly Ash Using Electronic Arc Furnace

Production of glass-ceramics by sintering the molten slag obtained from electric arc furnace treatment of fly ash was investigated. The effect of washing pretreatment prior to melting the fly ash on the microstructure and properties of the glass-ceramics was examined. The results show that washing pretreatment of fly ash can decrease alkali metal chloride and increase network former in fly ash, which results in the increase of peak crystallization temperature of parent glass and strengthening of properties of bending strength and chemical stability of the glass-ceramics. The optimal heat treatment temperature for parent glass of washed fly ash is 1 173 K, at which the crystalline phase of glass-ceramics is composed of gelignite （Ca2A12SiO7） and akermanite （Ca2MgSi207）. Glass-ceramics produced at optimal heat treatment temperature are excellent in term of the physical and chemical properties and leaching characteristics, indicating attractive potential as substitute of nature materials.