Experimental study on the activation of coal gasification fly ash from industrial CFB gasifiers

Coal gasification fly ash(CGFA)is an industrial solid waste from the coal circulating fluidized bed(CFB)gasification process,and it needs to be effectively disposed to achieve sustainable development of the environment.To realize the application of CGFA as a precursor of porous carbon materials,the physicochemical properties of three kinds of CGFA from industrial CFB gasifiers are analyzed.Then,the activation potential of CGFA is acquired via steam activation experiments in a tube furnace reactor.Finally,the fluidization activation technology of CGFA is practiced in a bench-scale CFB test rig,and its advantages are highlighted.The results show that CGFA is characterized by a high carbon content in the range of 54.06%–74.09%,an ultrafine particle size(d50:16.3–26.1 μm),and a relatively developed pore structure(specific surface area SSA:139.29–551.97 m^(2)·g^(-1)).The proportion of micropores in CGFA increases gradually with the coal rank.Steam activation experiments show that the pore development of CGFA mainly includes three stages:initial pore development,dynamic equilibrium between micropores and mesopores and pore collapse.The SSA of lignite fly ash(LFA),subbituminous fly ash(SBFA)and anthracite fly ash(AFA)is maximally increased by 105%,13%and 72%after steam activation;the order of the largest carbon reaction rate and decomposition ratio of steam among the three kinds of CGFA is SBFA>LFA>AFA.As the ratio of oxygen to carbon during the fluidization activation of LFA is from 0.09 to 0.19,the carbon conversion ratio increases from 14.4%to 26.8%and the cold gas efficiency increases from 6.8%to 10.2%.The SSA of LFA increases by up to 53.9%during the fluidization activation process,which is mainly due to the mesoporous development.Relative to steam activation in a tube furnace reactor,fluidization activation takes an extremely short time(seconds)to achieve the same activation effect.It is expected to further improve the activation effect of LFA by regulating the carbon conversion ratio range of 27%–35%to create pores in the initial development stage.

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%.

Hydrothermal synthesis of zeolites-calcium silicate hydrate composite from coal fly ash with co-activation of Ca(OH)_(2)-NaOH for aqueous heavy metals removal

Coal fly ash is a typical secondary aluminum/silicon resource.The preparation of zeolite-type absorbent is a potential way for its value-added utilization,while the purity and adsorption property of zeolite are limited due to the occurrence of side reactions in the synthesis process.In this study,a designated composite consisted of crystalline zeolites and amorphous calcium silicate hydrate was selected,which was direct synthesized from fly ash under conditions of a Ca/Si molar ratio of 0.8,an initial NaOH concentration of 0.5 mol/L,a hydrothermal temperature of 170℃and a liquid–solid ratio of 15 mL/g.The results indicated that this composite had superior adsorption property for a variety of heavy metals,which was based on the exchange of calcium and sodium ions in zeolites and calcium silicate hydrate.Its adsorption capacities for Pb^(2+),Ni^(2+),Cd^(2+),Zn^(2+),Cu^(2+)and Cr^(3+)attained 409.4,222.4,147.5,93.2,101.1 and 157.0 mg/g,respectively,in single solution with a pH of 4.5.After regulating the synthesis conditions,the transformation of amorphous calcium silicate hydrate into crystallized tobermorite weakened the adsorption capacity of the composite.Besides,due to the competitive adsorption in a multiple ions solution,the adsorption capacities for these heavy metals had a reduction.

Catalytic spectrophotometric determination of trace vanadium in fly ash and coal gangue by Triton X-100 enhancing effect

Trace Ⅴ(Ⅴ) catalyzes mightily the decolorization reaction of arsenazo Ⅲ(AsA Ⅲ) by oxidizing with H_2O_2 in a pH 4.0 HAc-NaAc buffer solution, and the addition of TritonX-100 can further increase the sensitivity of the reaction and its catalytic extent is linear withthe content of Ⅴ(Ⅴ). A catalytic spectrophotometric procedure for determining trace Ⅴ(Ⅴ)wasdeveloped. The results show that the maximun absorption of the color solution is at 560 nm and thedetection limit of the method for Ⅴ(Ⅴ) is 0.014 mg·L^(-1). Beer's law is obeyed for Ⅴ(Ⅴ) in therange of 0.00-0.20 mg·L^(-1). The recoveries are 99.0%-104.6%, and the relative standarddeviations (RSD) are 2.7%-3.7%. Combined with ion-exchange resin, the method has been applied to thedetermination of trace vanadium in fly ash and coal gangue with satisfactory results.

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.

Synthesis of Mullite from High-alumina Fly Ash:a Case from the Jungar Power Plant in Inner Mongolia, Northern China

In this paper, an experimental study was conducted in order to test the feasibility of sintering mullite directly from the high-alumina fly ash, without adding any extra material. The results show that the mullite contents in most sintered samples are over 70%. The samples sintered from the beneficiated fly ash have a higher content of mullite than those from the as-received fly ash under the same synthetic conditions. To obtain an equal amount of mullite, a higher sintering temperature is needed for the beneficiated fly ash than for the as-received fly ash. Considering the physical properties of sintered mullite, the favorable sintering temperature is 1400℃ for the as-received fly ash and 1500℃ for the beneficiated fly ash. A higher sintering temperature and a shorter holding time are profitable to sintering mullite. The orthogonal test confirmed that the dominant factor affecting mullite synthesis is sintering temperature, and that the most profitable matching conditions are 200 MPa-1500℃-3 h for the as-received fly ash and 200 MPa-1500 ℃-4 h for the beneficiated fly ash.

Bioleaching of trace elements and rare earth elements from coal fly ash

Coal fly ash originated from coal combustion has high concentrations of metals. If suitable leaching techniques are identified, then coal fly ash could serve as a useful source of valuable minerals including rare earth elements (REEs). In this study, three microbial strains, Candida bombicola, Phanerochaete chrysosporium and Cryptococcus curvatus were tested on their performance of leaching trace elements and REEs from fly ash. Through comparing mineral loss and leaching efficiencies resulting from indirect leaching or use of the culture supernatant, C. bombicola was identified to be the best leading to the highest mineral loss and extracting efficiencies of trace elements and REEs among the three strains. The highest mineral loss observed from using the supernatant of this yeast strain was 59.7%. Among all trace elements, As and Mo had the highest leaching efficiency of 80.9% and 79.5%. respectively. The same leaching test led to 67.7% of Yb and 64.6% of Er dissolved from the ash. This study, thus, demonstrated that bioleaching is feasible for leaching metals out of fly ash. The C. bombicola strain deserves further investigation due to its robust actions on metal leaching.

Removal of lead(Pb(Ⅱ))and zinc(Zn(Ⅱ))from aqueous solution using coal fly ash(CFA)as a dual-sites adsorbent

Coal fly ash(CFA)is composed of minerals containing some oxides in crystalline phase(i.e.,quartz and mullite),as well as unburned carbon as mesoporous material,thus enabling CFA to act as a dual-sites adsorbent with unique properties.This work focused on the adsorption of Pb(Ⅱ)and Zn(Ⅱ)from binary system,a mixture containing two metal ion solutions present simultaneously,onto NaOH-modified CFA(MCFA).Several adsorption tests were conducted to evaluate the effect of several parameters,including pH and contact times.The experiment results indicated that chemical treatment of CFA with NaOH increased pore volume from 0.021 to 0.223 cm^3·g^(-1).In addition,it could also enhance the availability of functional groups on both minerals and unburned carbon,resulting in almost 100%Pb(Ⅱ)and 97%Zn(Ⅱ)adsorbed.The optimum pH for adsorption system was pH=3 and quasi-equilibrium occurred in 240 minutes.Equilibrium data from the experimental results were analyzed using Modified Extended Langmuir(MEL)and Competitive Adsorption Langmuir-Langmuir(CALL)isotherm models.The analysis results showed that the CALL isotherm model could better describe the Pb(Ⅱ)and Zn(Ⅱ)adsorption process onto MCFA in binary system compared with MEL isotherm model.

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.

Dissolution of Rare Earth Elements from Coal Fly Ash Particles in a Dilute H₂SO₄Solvent

Recently, the worldwide supply of rare earth element (REE) resources will be severely restricted. On the other hand, coal fly ash particles emitted from coal-fired electric power plants contain relatively high concentrations of REEs. The contents of REEs in coal fly ash are regularly several hundreds of ppmw. In order to extract and recover REEs from coal fly ash particles, as a first step, we have investigated their dissolution behavior in a dilute H2SO4 solvent. The REE content of coal fly ash specimens has been precisely determined, and their presence in the ash component of the original coal and their enrichment in coal fly ash particles during coal combustion have been suggested. REEs in coal fly ash dissolve gradually in H2SO4 over time, and this implies two types of occurrences of the REEs in coal fly ash particles. By applying the unreacted core model to the dissolution behavior of REEs in a H2SO4 solvent, we can explain both types of occurrences.

Removal of Cr (VI) from Aqueous Solution Using Ultrafine Coal Fly Ash

Coal fly ashes WSRA and BQRA were ball milled for 5 h to produce their ultrafine coal fly ashes WSUA and BQUA, respectively. Batch kinetic, isotherm and pH effect on adsorption were studied to evaluate removal of Cr （VI） from aqueous solutions by ultrafine coal fly ashes comparing with raw coal fly ashes. The kinetics of adsorption indicates the process to be intraparticle diffusion controlled and follows the Lagergren first-order kinetics for all coal fly ashes. The first-order rate constants （k1） of Cr （VI） adsorption onto WSRA, WSUA, BQRA and BQUA are 1.981, 1.497, 2.119 and 1.500 （×10^-2） min^-1, respectively. The adsorption capacities of WSUA and BQUA are much better than those of WSRA and BQRA. Equilibrium adsorption data of all coal fly ashes well satisfy the Langmuir isotherm. The adsorbed amounts of Cr （VI） onto WSUA and BQUA decrease from pH 2 to pH 6 and then increase up to pH 12.

Influence of Coal Fly Ash Particle Size on Structure and Adsorption Properties of Forming Adsorbents for Cr^6＋

Forming adsorbents FFA-R,FFA-A and FFA-B were prepared from different particle size coal fly ashes FA-R,FA-A and FA-B,their average particle sizes（d_（50）） were 15.75,3.61 and 1.73 μm respectively.The structure and adsorption properties for Cr^（6＋） of forming adsorbents from aqueous solution were studied.The results show that forming adsorbent prepared from the coal fly ash with smaller particle size exhibits higher specific surface area,higher pore volume and better adsorption properties for Cr^（6＋）.The adsorption kinetics of Cr^（6＋） on FFA-R,FFA-A and FFA-B fitts the second order kinetic model and the second adsorption rate constants are 7.523,3.197 and 2.187 mg·g^（-1）·min^（-1/2）,respectively.The adsorption of Cr^（6＋） on FFA-R,FFA-A and FFA-B can be described in terms of Langmuir isotherms better,and the adsorption processes are spontaneous and exothermic.

Trends and advances in the development of coal fly ash-based materials for application in hydrogen-rich gas production:A review

Coal fly ash(FA),a valuable industrial solid residue generated from coal combustion,is composed of various metal oxides and has a high thermal stability.Given that the coal-based energy will continue to account for a significant portion of global electricity generation in the coming years,the lack of effective management strategies exacerbates the threat of FA wastes to the surrounding environment and human health.For a sustainable development,green and renewable hydrogen economy and CO_(2)capture efforts provide appealing opportunities to valorize FA as catalysts and/or sorbents due to their appealing physicochemical properties.Hydrogen applications along with carbon neutrality are potential strategies to mitigate climate change crisis,but high processing costs(catalysts/sorbents)are challenging to realize this purpose.In this context,the utilization of FA not only enhances industrial competitiveness(by reducing manufacturing costs),but also provides ecologically friendly approaches to minimizing this solid waste.This state-of-the-art review highlights a wide-ranging outlook on the valorization of FA as catalysts and sorbents for hydrogen-rich gas production via conventional/intensified processes(CO_(2)/H_(2)O reforming,ammonia decomposition,hydride hydrolysis).The fundamental physicochemical characterizations and hazards/utilization of FA,which significantly affect the FA's utilization in various fields,are first introduced.The influence of several factors(like FA types and catalysis/sorption operation conditions)on the activity performance of FA-based materials is then discussed in detail.This critical review aims to open the window to further innovative ideas regarding the application of different FA residues in other catalytic and sorption processes.

Technological and Environmental Behavior of Coal Fly Ash in Lime-Based Materials

Coal fly ash is considered an industrial by-product derived from coal combustion in thermal power plant. It is one of the most complex anthropogenic materials. Its improper disposal has become an environmental concern and resulted in a waste of recoverable resources. The aim of this paper is to study the physico-chemical characteristics of binders based on coal fly ash and lime in order to develop an eco-cement. The various characterization tests carried out are X-ray fluorescence, X-ray diffraction, compressive strengths, thermophysical properties and setting time. X-ray fluorescence and X-ray diffraction were used to determine the chemical composition and phases of fly ash, lime and binders. This allowed us to see that the chemical composition of fly ash is similar to that of cement. Compressive strengths of mortars containing 20%, 40%, 60% and 80% of fly ash have shown that fly ash has a long-term positive effect which might be related to a pozzolanic activity. The L3 binder consisting of 60% of coal fly ash and 40% lime has a higher compressive strength than the others. The binder setting start time is greater than that of cement but shorter than that of lime. The study of the thermophysical properties of the L3 binder shows that it has a higher thermal resistance than cement mortar. Moreover, it heats up less quickly because of its low effusivity compared to that of the latter. This analysis highlighted the principal characteristics that must be taken into account to use coal fly correctly in lime-based materials.

Study of Remediation of Soil Contamined with Heavy Metals by Coal Fly Ash

The labile fraction of heavy metals in soils is the most important for toxicity for plants. Thus it is crucial to reduce this fraction in contamined soils to decrease the negative effect of heavy metals. In an experiment, the effects of two additives on the labile fractions of Cu, Mn and Zn were investigated in a soil contamined during long-term application. The additive used was the coal fly ash. The treated soil was further enriched with heavy metals and allowed to age at room temperature for 30 days. After this period, they were extracted plant-available (EDTA;HNO3;CH3COOH) metal species. The addition of fly ash strongly reduced the plant-available of Mn for plants but to a lesser extent this applies to the plant-available of Cu and Zn for plants. By addition of 1% of fly ash as well as 2% of fly ash, the labile fraction of Cu, Mn and Zn were lowered by 6.3, 145.0 and 29.7 mg?kg-1, respectively. Moreover essential correlation between total Cu and Zn contents was stated in the soil with plant-available content of metals, with reference to both metals. Value of coefficients of correlation is attesting to it between the total and plant-available Cu and Zn contents which are respectively equal: R(Cu) = 0.845, R(Mn) = 0.864 and R(Zn) = 0.872 for p = 99.5%. The results suggested that leading into the soil of the additional amount of fly ash can be an effective way of chemical remediation with reference to soils contaminated by Cu or Mn or Zn. Because he causes immobilization of examined heavy metals in the soil and in the process in the arrangement a—soil is limiting the availability of these metals plant and more distant bonds of the food chain.

THE EXPERIMENTAL INVESTIGATION OF COAL COMBUSTION CHARACTERISTICS IN A FBC WITH FLY ASH RECYCLE

In order to seek the effective method of increasing the coal combustion effi-ciency and to obtain the dcsign data for a certain kind of coal in fluidized bed combustors(FBCs),the experiments of coal combustion characteristics were conducted in a FBC facil-ity with the cross-section of 0.3m×0.3m and 6m in height.The variations of carbon con-tent of particles with recycle ratio,particle diameter,sample location and flow direction,the effects of bed temperature and fluidizing velocity on combustion efficiency and the va-riations of the temperature characteristic and combustion fraction in freeboard were inves-tigated.The experimental results indicate that using fly ash recycle not only can increasethe combustion efficiency,but also can improve the operation performances obviously.

Effects of Sintering Temperature on Crystallization Behavior and Performance of Glass-Ceramics From Coal Fly Ash

The glass-ceramics was prepared from coal fly ash, limestone and Na2CO3 by sintering processes. Effects of the crystallization temperature (850–1100 ℃) on crystallization behavior, microstructure, sintering character and chemical stability of the glass-ceramics samples were analyzed by means of DTA, XRD, SEM and other analytical methods. The results show that the main crystalline phase of as-prepared glass-ceramics after crystallization treatment is gehlenite (Ca2Al2SiO7). The species of crystalline phases keep the same, however, the main crystalline intensity, line shrinkage rate and bulk density increase first then decrease with the increasing of heat treatment temperature. Water absorption of the samples was reduced as the heat treatment temperature rising. The glass-ceramics display high performance crystallization properties and chemical stability. The optimized glass-ceramics with desired sintering character and chemical stability was obtained by crystallized at 1050 ℃.

New Process for Preparation Alumina and Silica White from Coal Fly Ash

Fly ash was used to prepare alumina and silica white, The 3 stages of the process are as follows: ammonium sulfate calcining, acid leaching and alkali dissolution. The optimum conditions for the experiments to determine are as follows: molar ratio of (NH4)2SO4/Al2O3 is 6, the calcining time is 2h, he H2SO4 concentration is 20%, the leaching temperature is 80℃ and dissolution duration is 2h, the ratio of solution and solid reaction material is 6 for ammonium sulfate calcining and acid leaching stage, reaction time 30min, ratio of liquid to ore 5∶1, alkali concentration 45% and reaction temperature 95 ℃for the alkali dissolution stage. Under these conditions, the total leaching efficiencies of Al2O3 and SiO2 are 78.86% and 95%, respectively. The quality of the main products alumina and silica white can meet the national standards of GB/T24487-2009 and GB10517-89, respectively.

Leaching Kinetics of As, Mo, and Se from Acidic Coal Fly Ash Samples

Annually, coal-fired electric power plants produce large volumes of potentially hazardous coal combustion products (CCPs) including fly ash. Since majority of the coal fly ash and other CCPs deposited in dry land fills or wet lagoons, they pose risk of contamination to local environment. In this study, we present results of leaching kinetics for As, Mo, and Se from three acidic fly ash samples collected from coal-fired power plants in the southeastern United States. This study shows that the leachate concentrations of As, Mo, and Se increase over time. Three kinetics equations, pseudo-second order, Elovich, and power-function, are able to adequately describe the experimental leaching kinetics data. Experimental leaching data and modeling results indicate that the rate limiting leaching of As, Mo, and Se is controlled by the diffusional process responsible for transferring these elements from interior to the surface of the particles as well as the dissolution of the fly ash particles. Therefore, it is important to adopt effective containment/treatment schemes to avoid potential and persistent dispersion of trace elements from ash disposal facilities to surrounding environment for a long time.

Preparation of biological aerated filter media with coal fly ash and coal gangues

A novel kind of filter media has been studied using in biological aerated filter process which is produced by waste coal fly ash and coal gangues.The specific surface area and sum of braking and ware rate are viewed as the main factor for determining preparation conditions,including calcination temperature (in the range of 900 ℃ to 1250 ℃),proportion of coal gangue (in the range of 0 to 25%) and soaking time (in the range of 0 to 40 min).The effects of sintering conditions on the main property parameters are researched and the reasons have been analyzed.Considered with all factors,the optimum technological conditions are chosen as follows:the calcination temperature is 1050 ℃ ;the soaking time is 10 min and the proportion of coal gangue is 5%.When at these condition,the main property parameters of the filter media in the technological conditions are 1.6 m 2 /g for the specific surface area and 2.96 % for sum of braking and are rate respectively.Finally,a scanning electron microscope is used for analyzing the microstructure of the filter media.