Self-cementing Mechanism of CFBC Coal Ashes at Early Ages

The self-cementing mechanism at early ages of circulating fluidized bed combustion （CFBC） coal ashes was studied by X-ray diffraction （XRD）, infrared （IR） spectroscopy and chemical method. The results indicate that the amorphous phase is predominant in CFBC coal ashes. The polymerization degree of [SiO4] and [AlO6] of CFBC desulphurization coal ashes is lower than that of those without desulphurization. The contents of the components with fast hydration rate of CFBC desulphurization coal ashes are significantly greater than those of the ashes without desulphurization. This work confirms that the amorphous minerals with high chemical activity are the main causes of the self-cementing property of CFBC desulphurization coal ashes at early ages.

Leaching Behavior of Fly Ashes from Power Plants

The Yanzhou mine district, located in southwestern Shandong Province, is about 1300 km2 with more than 8×109tons of proved coal reserves and there are 10 big power plants in this area. A large amount of coal ashes, which are regarded as waste materials, have been stockpiled in the area and have influenced the environment of the mine district. In this paper, analysis of fly ash samples from three power plants is carried out, the enrichment and concentration of trace elements, Pb, Zn, Cu and As, in coal ashes are analyzed, and petrological and mineralogical characteristics and chemical compositions of coal ashes are studied. The aim of this work is to provide basic scientific data for utilization of ashes and reduction of environmental pollutions.

Effects of NaOH Concentrations on Properties of the Thermal Power Plant Ashes-Bricks by Alkaline Activation

The use of the thermal power plant ashes including fly ash(FA) and bottom ash(BA) for producing unfired building bricks(UBB) using sodium hydroxide(NaOH) solution as an alkaline activator was investigated. A low applied forming pressure of 0.5 MPa and various NaOH concentrations of 5, 8, 10, and 12 M were used for the preparation of brick samples with different solution-to-binder(S/B) ratios of 0.35 and 0.40. The bricks were subjected to various test programs with reflecting the effect of both NaOH concentrations and S/B ratios on the brick’s properties. The compressive strength, unit weight, ultrasonic pulse velocity, and thermal conductivity of bricks increased with increasing NaOH concentration, whereas the contrary trend was found with increasing S/B ratio. Also, the water absorption of bricks was observed to reduce with increasing NaOH concentration and decreasing S/B ratio. As the results, the combined utilization of both low forming pressure and coal power plant ashes can produce the UBBs with low unit weight, low heat conductivity, and acceptable strength and water absorption rate as stipulated by TCVN 6477-2016. Furthermore, the outcomes of chemical analysis and microstructure observation also demonstrate that a high concentration of the Na OH promoted the geopolymerization process. Notably, the use of NaOH solution of either 10 M or above is recommended for the production of UBBs, which are classified as grade M5.0 or higher.

Validation for the Determination of Extractable Metals in Ashes from Biomass Incinerators by ICP-OES

Biomass ashes contain valuable elements for plant growth, but also often high amounts of harmful heavy metals which limit their reuse in forests and on grassland. For monitoring metal concentrations, a fast and reliable method allowing the quantitative determination even at trace levels is mandatory. Therefore an analytical method consisting of an acidic microwave assisted digestion prior to ICP-OES measurement was optimized. The elements of interest were AI, As, B, Ba, Cd, Co, Cr, Cu, Fe, Mg, Mn, Na, Ni, Pb, Sb, St, Ti, V, and Zn. A validation including the following parameters was performed for each analyte： limit of detection, limit of quantification, recovery by spiking experiments, accuracy by analyzing a certified reference material, reproducibility （wihtin-24 hours, 4 and 7 days）, linearity, and uncertainty of measurement. Two standards series were used for calibration - one with 1 M HNO3 and one with additionally 2 g/L Mg（NOD2 to investigate the elimination or decrease of possible matrix effects. Both calibration methods showed very good recoveries. The method optimized allows the determination of the relevant elements covered by the recommendation of the Austrian ministry for agriculture and represents thus an appropriate tool for monitoring the metal contents in biomass ashes.

Study on Inorganic Flocculant Prepared from Powdered Coal Ashes

The feasibility of preparing flocculant from powdered coal ashes is studied in detail. By means of orthogonal tests, the influence of various factors, such as the activation temperature, the activation time, the ratio of CaO to Al2O3, the hydrochloric acid concentration, the reaction time and the reaction temperature, on preparation is investigated, and the hest operating condition is determined.

Pozzolanic Reaction Kinetics of Coal Ashes

The pozzolanic reactivity was determined by the hydration kinetics of pozzolanic reaction based on the fact that the hydration products of active SiO2 and Al2O3 with lime were soluble in dilute hydrochloric acid. The results show that the pozzolanic reaction of active SiO2 and Al2O3 of coal ashes follows apparent first-order kinetics. The reaction rate constant of FBC ashes is greater than that of PC ashes, while the activation energy of the former is lower than that of the latter. It is confirmed that the pozzolanic activity of fluidized bed combustion（FBC） ashes is significantly higher than that of PC ashes, and the reaction barrier of the former is lower than that of the latter, because the microstructures of FBC ashes, such as mineralogical composition, morphology and polymerization degree of [SiO4] and [AlO6] are more favorable to the pozzolanic activity development than those of PC ashes.

Comparison of Ashes Produced in a Biomass Moving Grate Boiler by Wood Chips and Sewage Sludge

One option to fight global warming is to convert our use of fossil energy into renewables such as biomass energy.However,the forest preservation and the quality of the ambient air are also two major issues.Therefore,the use of biomass waste without any supplementary emissions could represent a part of the solution.In this study,two fuels were considered for a 200 kW moving grate boiler.A multicyclone and a bag filter were fitted on the boiler.The first fuel consisted of classical wood chips whereas the second was a mixture of wood chips with sewage sludge.This second fuel presented a high ashes mass ratio compared to wood chips.The aim was to verify the possibility to burn this kind of fuel without any modification of the installation.The first relevant result is that the conventional pollutants,i.e.,CO and NOx,remained under the emissions limits even with the sewage sludge combustion.The Total Suspended Particles emissions at the exhaust were always under 5.4 mg·Nm-3 dry based corrected at 6%of O_(2),which is low with respect to the standard limitation.The majority of the ashes remained on the combustion room.However,with both fuels,about 5%of ashes mass remained in the heat exchanger.Nevertheless,the heat exchanger was more clogged with the second fuel,which produced five time more ashes.This may lead to a yield loss.Thus,sewage sludge can be used in a wood boiler without any issue if an automatic exchanger sweep is fitted on the installation.

Research and Application of Pollution Control in the Middle Reach of Ashe River by Multi-Objective Optimization

Based on one-dimensional water quality model and nonlinear programming, the point source pollution reduction model with multi-objective optimization has been established. To achieve cost effective and best water quality, for us to optimize the process, we set pollutant concentration and total amount control as constraints and put forward the optimal pollution reduction control strategy by simulating and optimizing water quality monitoring data from the target section. Integrated with scenario analysis, COD and ammonia nitrogen pollution optimization wasstudiedin objective function area from Mountain Maan of Acheng to Fuerjia Bridge along Ashe River. The results showed that COD and NH3-N contribution has been greatly reduced to AsheRiverby 49.6% and 32.7% respectively. Therefore, multi-objective optimization by nonlinear programming for water pollution control can make source sewage optimization fairly and reasonably, and the optimal strategies of pollution emission are presented.

Effect of Varying Corn Cob and Rice Husk Ashes on Properties of Moulding Sand

The use of rice husk and corn cob ashes as aggregates for foundry moulding sand has been studied. 5-12.5 weight percent of rice husk and corn cob ashes were added to the sand mixture and the sand properties determined. A mixture of equal proportion of rice husk and corn cob ashes was also used. In each case, four weight percent water and clay were added to the sand mixture. Some of the properties of the sand tested are: permeability, green compression strength, dry compression strength, green shear strength, dry shear strength, moisture content and permeability. The results showed that the green compression strength, green shear strength, moisture content and permeability decrease with increase in the additives (rice husk ash, corn cob ash, and (50% rice husk and 50% corn cob ashes). While dry compression strength and dry shear strength increase with increase in weight percent of the additives.

Assessment of the Radiological Impact on the Environment near a Storage Site of Coal Ashes in a Thermal Power Plant

The radiological impact of coal ashes, with enhanced natural radioactivity in the storage site, is due to the presence of naturally occurring radionuclides. Some of these radionuclides have a radioactive period of several million years and will, therefore, have time to migrate to the soil, atmospheric air, surface water, and groundwater. This impact depends mainly on the activity of these coal ashes, the duration of exposure to such waste, transfers to the air, and the leaching phenomenon by rainwater. In this study, and so as to assess the radiological impact of coal ashes of the storage site of the JLEC-Morocco thermal power plant on environment, some analyses are performed by alpha dosimetry and a digital dosimeter on samples of coal ashes, soil, atmospheric air, surface water and groundwater belonging to a perimeter of 10 km around that site. The obtained results show that, within the studied area, the radiological impact on the soil of the coal ashes of the storage site is insignificant even though the concentrations of radon in the near vicinity (1 to 2 km) are moderately important, and remain below 200 Bq/m3. In the atmospheric air, this impact remains medium for the neighborhoods of the storage site (2 to 3 km) with radon activities superior to 10 Bq/m3. These results also show that there may be a water contamination of wells located at the storage site without any transfer of radioactivity into the groundwater of the area studied where the concentrations of radon are less than 11.1 Bq/l.

Rwanda Rises From the Ashes

International shameWhen the Rwandan Genocide took place two decades ago, approxi-mately 1 million people were killed during the 100-day conflict between the Hutu and Tutsi ethnic groups. More than 2 million refugees fled the country, with a further 2 million people left homeless.

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.

Extraction of aluminium as aluminium sulphate from thermal power plant fly ashes

Valuable metal extraction technology from thermal power plant fly ash is limited.In the present study,aluminium is extracted from fly ash as highly pure aluminium sulphate(>99.0%)by leaching with sulphuric acid,followed by pre-concentration and successive crystallization.Two types of fly ashes from different sources,i.e.,Talcher Thermal Power Station(TTPS)and Vedanta Aluminium Company Limited(VAL)were chosen for comparative study on the extraction of aluminium as aluminium sulphate.The product is characterized by powder X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR)and thermogravimetric analysis(TGA).Purity of aluminium sulphate was also investigated by inductively coupled plasma?optical emission spectrometry(ICP?OES).The extraction efficiency of aluminium depends on the varied solid-to-liquid ratio(fly ash:18mol/L H2SO4,g/mL)and particle size of fly ashes.Physico-chemical analysis indicates that the obtained product is Al2(SO4)3·18H2O,having low iron content(0.08%).

Microstructure of ferrospheres in fly ashes: SEM, EDX and ESEM analysis

Ferrospheres in fly ashes from a coal-fired power plant were extracted by a magnetic separation technique and their microstructure was studied by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and environmental scanning electron microscopy (ESEM). Ferrospheres in fly ashes show significant iron enrichment compared to their respective fly ashes. Iron oxides in ferrospheres mainly occur as minerals magnetite (Fe3O4) and hematite (α-Fe2O3), which are derived mainly from the decomposition and oxidation of iron-bearing minerals in coal during combustion. EDX data indicate that ferrospheres also contain Si, S, Al and Ca resulting from quartz, mullite, anhydrite and amorphous materials. A large percentage of ferrospheres are commonly 5～50 μm in size. The microstructure of ferrospheres includes smooth, polygonal, dendritic, granular and molten drop characteristics. SEM coupled with EDX provided fast and accurate results of the microstructure and chemical composition of ferrospheres, and helped us to assess environmental issues related to the disposal and utilization of fly ashes.

The Mineral Transformation of Huainan Coal Ashes in Reducing Atmospheres

By using the advanced instrumentation of a Computer Controlled Scanning Electron Microscope （CCSEM）, X-ray diffraction （XRD） and X-ray fluorescence （XRF）, the ash composition and the mineral components of six typical Huainan coals of different origins were studied. The transformation of mineral matter at high temperatures was tracked by XRD in reducing conditions. The quartz phase decreased sharply and the anorthite content tended to increase at first and then decreased with increasing temperatures. The formed mullite phase reached a maximum at 1250 ℃ but showed a tendency of slow decline when the temperature was over 1250 ℃. The mullite formed in the heating process was the main reason of the high ash melting temperature of Huainan coals. Differences in peak intensity of mullite and anorthite reflected differences in phase concentration of the quenched slag fractions, which contributed to the differences in ash melting temperatures. The differences in the location of an mnorphous hump maximum indicated differences of glass types which may affect ash melting temperatures. For Huainan coal samples with relatively high ash melting tempera- tures, the intensity of the diffraction lines for mullite under reducing condition is high while for the samples with relatively low ash melting temperature the intensity for anorthite is high.

Optimizing Non-Ferrous Metal Value from MSWI Bottom Ashes

The bottom ashes resulted annually from the incineration of municipal solid waste in Europe contain about 400,000 tonnes of metallic aluminium and 200,000 tonnes of heavy non-ferrous metals, such as copper and zinc. Efficient recovery of this non-ferrous metal resource requires state-of-the-art separation technologies and a continuous feedback of laboratory analyses of the metal products and the depleted bottom ash to the operators of the bottom ash treatment plants. A methodology is presented for the optimization of the production of non-ferrous metal value from Municipal Solid Waste Incinerator bottom ash. Results for an incineration plant in the Netherlands show that efficient recycling can have a significant impact on value recovery as well as on non-ferrous metal recycling rates, producing up to 8% more revenue and 25% more metals from the ash.

Flotation performance analysis on coal washery rejects

The coal washery rejects cause major environmental problems in various parts of the globe.Nearly 1 Mt of coal rejects discarded as waste,is accumulated per annum in India,during washing or cleaning of raw coal.Cleaning coal,especially washery rejects,has posed a major challenge to the recovery of fine coal.Froth flotation is a better choice for processing coal washery rejects.In this study,flotation studies are attempted on the coal slurry received from Sudamdih coal washery,Jharkhand,India.A statistical design package(Minitab V17)was used to study the effect of process variables like collector and frother dosages on the responses.Regression equations for froth height,froth density,recovery and ash content of clean coal were developed.The coefficient of correlation(R2)values between the experimental and the predicted values of the flotation responses was found to be greater than 0.98 for all the models.Clean coal product was analyzed for recovery,froth height,and ash content by varying pulp densities.Results show that the coal slurry sample could be evaluated with acceptable recovery via flotation.Clean coal with an ash content of 17.2%is obtained with a 70%recovery from 35.5%ash.The cleaned coal can be used in powder coal-consuming industries.

Use of fly and bottom ashes from a thermoelectrical plant in the synthesis of geopolymers:Evaluation of reaction efficiency

The use of by-products as raw materials in the manufacturing of industrial products has risen in the last years because of environmental considerations.One example is the use of coal ashes from thermalelectrical plants in the production of geopolymer–a green cement made by mixing aluminosilicate with alkaline activator.In this study,fly and bottom ashes from a thermal-electrical unit were used as sources of aluminosilicate in the synthesis of geopolymers.A mixture of sodium hydroxide(10 mol/L)and sodium silicate(SiO_(2)/Na_(2)O ratio of 2.2)was used as the alkaline activator.The type(fly or bottom ash)and content of the ash were the variables in the synthesis.The ashes were characterized by X-ray fluorescence(XRF),X-ray diffraction(DRX),particle size distribution(PSD),specific surface area(BET),and thermal analysis(DTA/TGA).The ash-based geopolymer samples were measured to obtain their compressive strength after curing.The evolution of the geopolymerization process was also assessed based on final alkali concentration measurements.The results show that it is possible to obtain geopolymers using coal ashes as raw materials with high solid content.The compressive strength for the bottom ash geopolymer after 90 days of curing is 35 MPa.The low concentration of unreacted alkalis after curing(1.5×10^(-3)e 3.5×10^(-3)M)corresponds to high efficiency of the geopolymerization reaction.

Using zircon saturation thermometry of source magma in strongly altered volcanic ashes

The present study deals with the possibilities of applying the zircon saturation thermometry, which is based on the equilibrium between the zircon crystals and the melt, to strongly altered volcanic ashes—bentonites. It proposes an alternative to a widely used method of calculating magma temperature from Zr content and major component composition(Boehnke in Chem Geol351:324–333, 2013), that is not suitable for bentonites, as most of the major components have been largely altered in these rocks. For calculating source magma temperatures in strongly altered volcanic ashes, the exponential function from the Zr(ppm)/Al_(2)O_(3)(%) ratio with compositional corrections from the TiO_(2)/Al_(2)O_(3) ratio was found applicable. The idea to use the ratios of these elements is based on the low mobility of these elements in the earth’s surface conditions. Temperatures of magma, forming in the partial melting process, are assessed from the bulk rock composition. Pre-eruption temperatures were estimated from the composition of fine fractions of bentonites. The accuracy of the new method was established from comparison with the method by Boehnke et al.(Chem Geol 351:324–333,2013). The difference between the two methods was mostly less than ± 30° to ± 50°. The comparison with the magma temperature, estimated from the sanidine composition,revealed 13° lower values on average. Although the proposed method for estimating the source magma temperatures is less precise than the method of accounting for detailed rock compositions, it can be used in strongly altered rocks, where other methods are not usable. The new method still enables differentiation between felsic source magmas originating at low or high temperatures. Early Palaeozoic bentonites in the Baltic Basin can be divided,according to the source magma temperatures, into two types:(1) Low temperature(650–790 ℃), containing potassium-rich sanidine and abundant biotite(S type),(2)high temperature(770–850 ℃) with sodium-rich sanidine and scarce biotite(I type).

Mechanical Properties of Cement Mortar Containing Fine-Grained Fraction of Fly Ashes

This paper presents the effect of fly ash grain-size fractions on Portland-fly ash cement hydration and its properties. Siliceous fly ashes of size fraction of 0 - 16 and 16 - 32 μm, separated from initial fly ash samples from 1st, 2nd and 3rd hopper in ESP system, were analysed. Cement hydration was investigated by determination of hydration heat and content of Ca(OH)2 and C3S in cement samples. Water to cement ratio and initial setting time of cement pastes as well as compressive strength and microstructure of cement mortars were also analyzed. Results showed that the same amount of the same size ash fraction can give cement of lower or higher early strength and its lower or higher increase with time. Incorporation of 20 wt% of ash fraction of 0 - 16 μm can produce Portland-fly ash cement CEM II/A-V of strength class 42.5R (from 2nd hopper) or 52.5N (from 3rd hopper). Cement containing 40 wt% of ash fraction of 0 - 16 μm from 2nd and 3rd hopper can be classified as pozzolanic cements CEM IV/A-V of strength class 42.5 and normal or rapid early strength, respectively. Different development of strength of cement with addition of the same size ash fraction separated from the initial ash sample from the next hopper in ESP system is connected with higher depolymerization degree of SiO4 units in ash glass, resulting from the greater amount of AlO4 units replacing SiO4 units. Ash fraction of 16 - 32 μm shows lower depolymerisation of glass network and as a consequence lower hydration degree of C3S to portlandite and calcium silicate hydrates (C-S-H).