Novel synthesis of fly-ash-derived Cu-loaded SAPO-34 catalysts and their use in selective catalytic reduction of NO with NH3

A combined acid–alkali hydrothermal method was used to prepare fly ash–derived SAPO-34 molecular sieves from a thermal power plant in Inner Mongolia(China).The specific surface area of the prepared fly-ash-derived SAPO-34 molecular sieves was 579 m^2 g^-1,the total pore volume was about 0.27 cm^3 g^-1,and the pore size was 0.56 nm;the molar ratios of Al2O3:P2O5:SiO2 were 1:0.86:0.45.Cu/SAPO-34 catalysts were prepared by impregnation of low-cost fly-ash-derived SAPO-34 molecular sieves as a support and tested in selective catalytic reduction with NH3(NH3-SCR).Powder X-ray diffraction(XRD),N2 adsorption–desorption,X-ray photoelectron spectroscopy(XPS),H2 temperatureprogrammed reduction(H2-TPR),NH3 temperature-programmed desorption(NH3-TPD),electron paramagnetic resonance(EPR),nuclear magnetic resonance(NMR),X-ray fluorescence analysis(XRF)and scanning electron microscopy(SEM)were used for catalyst characterization and investigation of the relationships between the catalyst structure and the catalytic activity.The actual silica:alumina ratio of the molecular sieves did not increase with increasing Cu loading,indicating that increasing the Cu loading does not change the original structure of the SAPO-34 molecular sieves.The XRF and NMR results showed that replacement by Cu results in more Si islands.The molecular sieve acidity decreased because of the increased number of Si islands.The NH3-TPD results showed that for the Cu/SAPO-34 catalysts there was a low correlation between the low-temperature activity and the amount of acidic sites.SCR activity is closely related to the location of Cu.The 4.47 Cu/SAPO-34 catalyst has the highest isolated Cu2+showed the highest NH3-SCR activities(>90%)at 250–350℃.This work opens up new avenues for recycling fly ash formed in coal-fired power plants(reducing environmental pollution)and developing low-cost SCR catalysts for NOx pollution control.

Dry Mix Slag—High-Calcium Fly Ash Binder. Part Two: Durability

This work investigates durability of cement-free mortars with a binder comprised of ground granulated blast furnace slag (GGBFS) activated by high-calcium fly ash (HCFA) and sodium carbonate (Na2CO3): the soundness, sulfate resistance, alkali-silica reactivity and efflorescence factors are considered. Results of tests show that such mortars are resistant to alkali-silica expansion. Mortars are also sulfate-resistant when the amount of HCFA in the complex binder is within a limit of 10 wt%. The fineness of fly ash determines its’ ability to activate GGBFS hydration, and influence soundness of the binder, early strength development, sulfate resistance and efflorescence behavior. The present article is a continuation of authors’ work, previously published in MSA, Vol. 14, 240-254.

LOW TEMPERATURE SINTERING OF FLY-ASH CERAMICS AND ITS MICROSTRUCTURE

In this paper, the fly-ash ceramics with prior physical propertieswas fabricated in a low sintering temperature range. XRD, SEM wereused to study the microstructure and sintering mechanism. The resultsshow that in this fly-ash ceramics, three kinds of matter form itsstructure frame such as the glass pearls from the fly-ash rawmaterials, quartz and mullite in which glass liquid phase wasproduced during sintering. And the sintering mechanism is that ofliquid sintering.

Simultaneous removal of ammonium and phosphate by zeolite synthesized from coal fly ash as influenced by acid treatment

Zeolite synthesized from fly ash （ZFA） without modification is not efficient for the purification of NH4＋ and phosphate at low concentrations that occur in real effluents, despite the high potential removal capacity. To develop an effective technique to enhance the removal efficiency of ammonium and phosphate at low concentrations, ZFA was modified with acid treatment and the simultaneous removal of ammonium and phosphate in a wide range of concentration was investigated. It was seen that when compared with untreated ZFA, only the treatment by 0.01 mol/L of H2SO4 significantly improved the removal efficiency of ammonium at low initial concentrations. The behavior was well explained by the pH effect. Treatment by more concentrated H2SO4 led to the deterioration of the ZFA structure and a decrease in the cation exchange capacity. Treatment by 0.01 mol/L H2SO4 improved the removal efficiency of phosphate by ZFA at all initial P concentrations, while the treatment by concentrated H2SO4 （≥0.9 mol/L） resulted in a limited maximum phosphate immobilization capacity （PIC）. It was concluded that through a previous mild acid treatment （e.g. 0.01 mol/L of H2SO4）, ZFA can be used in the simultaneous removal of NH4＋ and P at low concentrations simulating real effluent.

Microstructure and properties of mullite-based porous ceramics produced from coal fly ash with added Al_2O_3

Using coal fly ash slurry samples supplemented with different amounts of Al2O3, we fabricated mullite-based porous ceramics via a dipping-polymer-replica approach, which is a popular method suitable for industrial application. The microstructure, phase composition, and compressive strength of the sintered samples were investigated. Mullite was identified in all of the prepared materials by X-ray diffraction analysis. The microstructure and compressive strength were strongly influenced by the content of Al2O3. As the Al/Si mole ratio in the starting materials was increased from 0.84 to 2.40, the amount of amorphous phases in the sintered microstructure decreased and the compressive strength of the sintered samples increased. A further increase in the Al2O3content resulted in a decrease in the compressive strength of the sintered samples. The mullite-based porous ceramic with an Al/Si molar ratio of 2.40 exhibited the highest compressive strength and the greatest shrinkage among the investigated samples prepared using coal fly ash as the main starting material. © 2017, University of Science and Technology Beijing and Springer-Verlag Berlin Heidelberg.

Evaluation of zeolites synthesized from fly ash as potential adsorbents for wastewater containing heavy metals

The pure-form zeolites （A and X） were synthesized by applying a two-stage method during hydrothermal treatment of fly ash prepared initial Cu and Zn gel. The difference of adsorption capacity of both synthesized zeolits was assessed using Cu and Zn as target heavy metal ions. It was found that adsorption capacity of zeolite A showed much higher value than that of zeolite X. Thus, attention was focused on investigating the removal performance of heavy metal ions in aqueous solution on zeolite A, comparing with zeolite HS （hydroxyl-solidate） prepared from the residual fly ash （after synthesis of pure-form zeolite A from fly ash） and a commercial grade zeolite A. Batch method was used to study the influential parameters of the adsorption process. The equilibrium data were well fitted by the Langmuir model. The removal mechanism of metal ions followed adsorption and ion exchange processes. Attempts were also made to recover heavy metal ions and regenerate adsorbents.

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.

Fabrication and properties of foam geopolymer using circulating fluidized bed combustion fly ash

In recent years, circulating fluidized bed combustion fly ash （CFA） is used as a raw material for geopolymer synthesis. Hydrogen peroxide was employed as a foaming agent to prepare CFA-based foam geopolymer. The particle distribution, mineral composition, and chemical composition of CFA were examined firstly. Geopolymerization products were characterized by mechanical testing, scanning elec- tron microscopy （SEM）, X-ray diffraction （XRD）, and X-ray fluorescence （XRF）. The CFA-based foam geopolymer was successfully fabri- cated with different contents of hydrogen peroxide and exhibited uncompleted alkali reaction and reasonable strength with relative low atomic ratios of Si/Al and Si/Na. Type-C CFA in this research could be recycled as an akernative source material for geopolymer production.

Thermodynamics and kinetics of alumina extraction from fly ash using an ammonium hydrogen sulfate roasting method

A novel method was developed for extracting alumina （Al2O3） from fly ash using an ammonium hydrogen sulfate （NH4HSO4） roasting process, and the thermodynamics and kinetics of this method were investigated. The thermodynamic results were verified experi-mentally. Thermodynamic calculations show that mullite present in the fly ash can react with NH4HSO4 in the 298-723 K range. Process op-timization reveals that the extraction rate can reach up to 90.95% when the fly ash reacts with NH4HSO4 at a 1：8 mole ratio of Al2O3/NH4HSO4 at 673 K for 60 min. Kinetic analysis indicates that the NH4HSO4 roasting process follows the shrinking unreacted core model, and inner diffusion through the product layer is the rate-controlling step. The activation energy is calculated to be 16.627 kJ/mol;and the kinetic equation can be expressed as 1-（2/3）α-（1-α）2/3=0.0374t exp[-16627/（RT）], whereαis the extraction rate and t is the roasting temperature.

Alkali desilicated coal fly ash as substitute of bauxite in lime-soda sintering process for aluminum production

By desilication treatment,the Al2O3/SiO2 molar ratio of coal fly ash could be improved to the range of 1.63-2.0.The desilicated coal fly ash(DSCFA)was enriched in alumina extraction.A processing technology was developed for alumina extraction from the DSCFA with the lime sintering process.Ca/(SiO2+TiO2)molar ratio,and NaO/Al2O3 molar ratio,sintering time,and temperature were the most significant parameters impacting on the aluminum extraction efficiency.The optima aluminum extraction efficiency was obtained under conditions of Ca/(SiO2+TiO2)molar ratio of 2.0,NaO/Al2O3 molar ratio of 0.98,and sintering at 1 200 ℃for 60 min.Astandard industrial dissolution method was used under conditions of caustic ratio(αk=n(NaO)/n(Al2O3)of 2.0,Al2O3 concentration of 50 g/L,sodium hydroxide concentration(Nk)of 60.78 g/L,Na2CO3 concentration of 10 g/L,temperature of 85℃, and dissolution duration of 10 min.The final aluminum extraction efficiency was 90%.

Investigation of the medium calcium based non-burnt brick made by red mud and fly ash: durability and hydration characteristics

Red mud is a type of highly alkaline waste residue produced in the process of alumina smelting by the Bayer process.Based on the idea of medium calcium content,solid wastes such as red mud and fly ash were used to prepare non-burnt bricks;and the mass ratio of CaO/SiO2 was selected in the range of 0.88–1.42.Mechanical properties and durability were investigated with a compressive strength test.X-ray diffractometry(XRD),scanning electron microscope(SEM),and Fourier transform infrared spectroscopy(FTIR)techniques were used to characterize the hydration characteristic.The environmental performance was analyzed by Inductively Coupled Plasma Mass Spectrometry(ICP).The results indicated that the mechanical properties and the durability were optimal when the mass ratio of CaO/SiO2 was 1.23.The hydration products were mostly C–S–H gel,ettringite,Na4Ca(Si10All6)O32·12H2O and Ca3Al2(SiO4)(OH)8.They were responsible for the strength development,and the CaO/SiO2 mass ratio of 1.23 had the best polymerized structure.The results of an environmental performance test showed that the heavy metals in the raw materials were well-solidified in the brick.Therefore,this paper provides an effective solution for use of solid wastes in building material.

Effects of key factors of rotary triboelectrostatic separator on efficiency of fly ash decarbonization

On the basis of understanding the principle of rotary triboelectrostatic separation, dynamic analysis of charged fly ash particles aimed at determining the key factors and separation experiments to improve decarbonization efficiency had been carried out Variables of electrode plate voltage and corrected wind speed are the key factors which affect the decarbonization efficiency on the separation of fly ash, The results of separation experiments show that:(1) With the plate voltage increasing, the efficiency of decarbonization continuously rises and in its selected range, the optimal voltage level is 45 KV;(2) The corrected wind speed can impact the efficiency of decarbonization significantly: with the speed increasing, the efficiency of decarbonization shows a trend of first decline, then increase and decrease again, and in its selected range, the optimal speed is 2.0 m/s. This study is of significance for the improvement of rotary triboelectrostatic separation performance and its decarbonization separation efficiency.

Surface Modification of Fly Ashes with Carbide Slag and Its Effect on Compressive Strength and Autogenous Shrinkage of Blended Cement Pastes

Surfaces of grade III fly ashes were modified through mixing with carbide slag and calcining at 850 ℃ for 1 h. Mineralogical compositions and surface morphology of fly ashes before and after modification were characterized by X-ray diffraction （XRD） and scanning electron microscopy （SEM）, respectively. Effect of surface-modified fly ashes on compressive strength and autogenous shrinkage of blended cement pastes was investigated. Microstructures of cement pastes were examined by backscattered electron （BSE） imaging and mercury intrusion porosimetry （MIP）. The experimental results showed that β-C2S was formed on the surfaces of fly ashes after modification. Hydration ofβ-C2S on the surface-modified fly ashes densified interface zone and enhanced bond strength between particles of fly ashes and hydrated clinkers. In addition, surface modification of fly ashes tended to decrease total porosity and 10-50 nm pores of cement pastes. Surface modification of fly ashes increased compressive strength and reduced autogenous shrinkage of cement pastes.

Properties of high calcium fly ash geopolymer pastes with Portland cement as an additive

The effect of Portland cement （OPC） addition on the properties of high calcium fly ash geopolymer pastes was investigated in the paper. OPC partially replaced fly ash （FA） at the dosages of 0, 5%, 10%, and 15% by mass of binder. Sodium silicate （Na2SiO3） and sodium hydroxide （NaOH） solutions were used as the liquid portion in the mixture： NaOH 10 mol/L, Na2SiO3/NaOH with a mass ratio of 2.0, and alkaline liquid/binder （L/B） with a mass ratio of 0.6. The curing at 60℃ for 24 h was used to accelerate the geopolymerization. The setting time of all fresh pastes, porosity, and compressive strength of the pastes at the stages of 1, 7, 28, and 90 d were tested. The elastic modulus and strain capacity of the pastes at the stage of 7 d were determined. It is revealed that the use of OPC as an additive to replace part of FA results-in the decreases in the setting time, porosity, and strain capacity of the paste specimens, while the compressive strength and elastic modulus seem to increase.

Effect of SiO_2/Na_2O mole ratio on the properties of foam geopolymers fabricated from circulating fluidized bed fly ash

Geopolymers are three-dimensional aluminosilicates formed in a short time at low temperature by geopolymerization. In this pa-per, alkali-activated foam geopolymers were fabricated from circulating fluidized bed fly ash （CFA）, and the effect of SiO2/Na2O mole ratio （0.91-1.68） on their properties was studied. Geopolymerization products were characterized by mechanical testing, scanning electron mi-croscopy （SEM）, energy-dispersive X-ray spectroscopy （EDX）, and X-ray diffraction （XRD）. The results show that SiO2/Na2O mole ratio plays an important role in the mechanical and morphological characteristics of geopolymers. Foam samples prepared in 28 d with a SiO2/Na2O mole ratio of 1.42 exhibit the greatest compressive strength of 2.52 MPa. Morphological analysis reveals that these foam geo-polymers appear the relatively optimized pore structure and distribution, which are beneficial to the structure stability. Moreover, a combina-tion of the Si/Al atomic ratio ranging between 1.47 and 1.94 with the Na/Al atomic ratio of about 1 produces the samples with high strength.

MINTEQ modeling for evaluating the leaching behavior of heavy metals in MSWI fly ash

At present,all kinds of municipal solid waste incineration (MSWI) fly ash stabilization technology has been reported and successfully applied in many countries.However,leaching procedures are very different that the technologies lack uniform standard,and it is even impossible to predict the long-term stabilization.Geochemical model can explain the environmental stabilization based on chemical phase and thermodynamic crystal structure,and it is also able to guide the development of environment-friendly stabi...

Influence of fly ash fineness and shape on the porosity and permeability of blended cement pastes

The effects of the fineness and shape of fly ash on the porosity and air permeability of cement pastes were investigated. Pulverized coal combustion （PCC） fly ash and fluidized bed coal combustion （FBC） fly ash classified into three different finenesses were used. River sand with particle size distribution similar to that of fly ash was also used for comparison. Portland cement was replaced with fly ash and ground sand at the dosages of 0, 20wt%, and 40wt%. A water-to-binder ratio （w/b） of 0.35 was used throughout the experiment. The results show that the porosity and air permeability of the pastes are influenced by the shape, fineness, and replacement level of fly ash. The porosity and air permeability of FBC fly ash pastes are higher than those of PCC fly ash pastes. This is due to the higher irregular shape and surface of FBC fly ash compared to the spherical shape and relatively smooth surface of PCC fly ash. The porosity increases with the increase in fly ash replacement level and decreases with the increase in its fineness. The permeability of PCC fly ash pastes decreases with the increase in replacement level and fineness, while for FBC fly ash, the permeability increases with the increase in replacement level. Decreases in porosity and permeability are due to a combined effect of the packing of fine particles and the reaction of fly ash.

Zeolite P synthesis based on fly ash and its removal of Cu(Ⅱ) and Ni(Ⅱ) ions

Zeolite P was synthesized through hydrothermal method based on a kind of Class C fly ash(FA). X-ray diffraction(XRD), scanning electron microscopy(SEM), and Brunauer–Emmett–Teller(BET) were used to analyze and characterize the synthetic sample. The kinetics and thermodynamics of copper and nickel ions removed by the zeolite samples were experimentally explored in detail. The results of kinetic treatment showed the second-order exchange second-order saturation model(SESSM) can well describe the removal process of copper ions, while the first-order empirical kinetic model(FEKM) is the best kinetic model for nickel ions. Langmuir and Freundlich isotherms were used to fit the equilibrium concentration of Cu(Ⅱ) or Ni(Ⅱ) under certain conditions. Whether for copper or nickel ion, the Langmuir model is in good agreement with the experimental equilibrium concentration.The apparent theoretical removal capacities for Cu(Ⅱ) and Ni(Ⅱ) can reach to 138.1 mg·g^(-1) and 77.0 mg·g^(-1),respectively.

Compressive Strength, Pore Size Distribution and Chloride-ion Penetration of Recycled Aggregate Concrete Incorporating Class-F Fly Ash

The effects of fly ash on the compressive strength, pore size distribution and chloride-ion penetration of recycled aggregate concrete were investigated. Two series of concrete mb：tures were prepared. The concrete mixtures in series I had a water-to-binder ratio and a cement content of 0.55 and 410 kg/ m^3 , respectively. The concrete rnixtures in series II had a water-to-binder ratio and a cement content of 0.45 and 400 kg/ ml respectively. Recycled aggregate was ased as 20% , 50% , and 100% replacements of natural coarse aggregate in the concrete mixtures in both series. In cutdition, fly ash was used as 0% , 25% and 35% by weight replacements of cement. The results show that the compressive strengths of the concrete decreased as the recycled aggregate and the fly ash contents increased. The total porosity and average porosity diameter of the concrete increased us the recycled aggregate content increased. Furtherrruore , an increase in the recycled aggregate content decreased the resistance to chloride ion penetration. Nevertheless, the replacement of cement by 25% fly ush improved the resistance to chloride ion penetration and pore diameters and reduced the total porosity of the recycled aggregate concrete.

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.