Distinguishing respirable quartz in coal fly ash using computer-controlled scanning electron microscopy

Determination and classification of quartz in coal fly ash (CFA) is a subject of interest because of the adverse health effects caused by inhalation of crystalline silica. Workers with prolonged exposure to this carcinogen can develop respiratory diseases over time. This obviously may include utility plant workers involved in the handling, loading, and hauling of CFA. In this investigation, computer-controlled scanning electron microscopy (CCSEM) and X-ray diffraction (XRD) were used to investigate Si-rich phases in CFA to develop a better approach for the determination of respirable quartz. Three CFA samples from utility boilers and a NIST standard CFA sample were investigated. The XRD measurements indicated that the four samples contained from 7.0 to 16.0 wt.% of quartz. The CCSEM measurements utilized both particle size distributions and a particle shape parameter, circularity, to classify the Si-rich phases in these ashes as either crystalline or amorphous (glass). The results indicated that the amount of free, respirable, quartz in these CFA samples ranged from only 0.1-1.0 vol % and showed little correlation with the XRD results for the bulk ash. These results are significant in view of the factthat XRD is the traditional method of measuring crystalline silica in dust collected from workplace atmospheres.     

Investigation of the microcharacteristics of PM2.5 in residual oil fly ash by analytical transmission electron microscopy

Atmospheric emissions from combustion of residual oils often consist of carbonaceous material and metal compounds, both of which are of concern for health and environmental issues. In this study, particulate matter fractions with aerodynamic diameters nominally less than 2.5 microm (PM2.5) in two residual oil fly ash (ROFA) samples generated from combustion experiments were investigated by analytical transmission electron microscopy (TEM) techniques, including energy-dispersive X-ray spectroscopy, selected area electron diffraction (SAED), high-resolution TEM, and electron energy loss spectroscopy (EELS). Carbonaceous particles, which dominate both samples, exist in two distinctive forms: as soot aggregates with spherical primary particles of size 10-80 nm that exhibit a concentric arrangement of graphitic layers around the particle center and as larger spherical or irregular-shaped porous residual char particles of size 1-20 microm that usually have anisotropic microtextures and contain organic sulfur species. Such carbon-rich particles were often observed to be coated with inorganic species, notably transition metals (V, Ni, Fe, Zn) in the form of sulfates, oxides, vanadates, and phosphates. In this respect, they therefore differ from similar carbonaceous particles generated in combustion of diesel fuels that lack significant inorganic species. Crystalline phases of vanadium, nickel, and iron oxides and multi-element oxides were identified by the SAED technique. The valence state of V in some V-rich oxide particles probed by EELS was found to vary from +2 to +5. Individual transition metal sulfate, oxide, and phosphate particles are typically compositionally complex, containing multiple metallic elements. These microcharacteristics of individual PM2.5 particles revealed by electron microscopy techniques should be important parameters to include in future toxicological investigations of ROFA PM.     

Continuous fractionation of fly ash particles by SPUTT for the investigation of PCDD/Fs levels in different sizes of insoluble particles

A combined analytical method has been developed to characterize the size dependent levels of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) contained in fly ash particles from a municipal solid waste incinerator (MSWI). Gravitational SPLITT fractionation (GSF), a relatively new technique for the fast and continuous separation of micron sized particles, was used to fractionate a fly ash sample, directly collected from a bag-filter house of MSWI in Korea, into six different size groups (<1.0, 1.0-2.5, 2.5-5.0, 5.0-10, 10-20, and 20-53 microm in diameter) in water solution, and the resulting fractions are examined by high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) in order to determine the concentration of PCDD/Fs according to these particle sizes. The results from SPLITT fractionation show that approximately 54% of the fly ash particles (sieved fraction <53 microm) by weight have been found to be smaller than 5.0 microm excluding the water soluble matter in the sample. From the HRGC/HRMS measurements, particle fractions in the size range of PM 1.0-2.5 and 2.5-5.0 appear to carry about 76 and 79 ng/g of PCDD/Fs which are relatively larger than those found in other diameter ranges. Principal component analysis (PCA) shows that particles larger than 5.0 microm are clustered into a group predominantly containing low chlorinated dioxins and fractions smaller than 5.0 microm into another group with lower chlorinated furans. This study demonstrated that the combining GSF with a secondary analytical method such as HRGC/HRMS has the potential to obtain size dependent information of particulate materials in relation to their production processes, chemical compositions, environmental fates, and other factors.     

还原性气氛下煤灰颗粒的熔融特性

利用SEM-EDX和XRD分析了神华煤煤灰颗粒的熔融特性,结果表明在还原性气氛下,在1000°C之前煤灰熔融相的份额比较少,但在900°C富Na-K铝硅酸盐颗粒已经熔融,在1000°C出现富Fe-Ca铝硅酸盐熔融相,从1000°C到1100°C产生大量的熔融相。大部分的Fe和Ca元素存在于铝硅酸盐颗粒内。虽然富Fe-Ca铝硅酸盐颗粒含量比较少,但是这些小颗粒在低温下容易发生熔融。温度对碳酸钙的破碎影响比较大。     

Characterizing the metal adsorption capability of a class F coal fly ash

The surface physical-chemical characteristics of a class F coal fly ash were studied in an effort to establish a quantitative understanding of metal adsorption. The ash surface acidity (acid site density and acidity constant), surface electrical characteristics, and adsorption constants for selected heavy metal ions were determined using a batch titration method, an electrophoretic method, and a batch equilibrium metal adsorption method, respectively. Results showed that the fly ash has a pHzpc value of 6.2. Its surface contains three types of acid sites. The densities of these acid sites are 2.1 x 10(-4), 1.8 x 10(-5), and 5.3 x 10(-5) mol/g, with acidity constants (pK(H)) of 2.7, 7.8, and 11.0, respectively. Metal adsorption results indicated that, of the three types of acid sites on surface, only the acid site with 7.8 pK(H) is responsible for metal adsorption. The adsorption constants (log K(S)) of Cd(II), Cr(III), Cu(II), Ni(II), and Pb(II) are 4.8, 7.0, 6.4, 4.9, and 8.6, respectively. Adsorption results indicated that the metal adsorption is in the linear range of the Langmuir isotherm if the total metal in the system is less than 10% of the total metal binding site. Results also showed that the presence of anionic metal ions does not affect the adsorption of cationic metal ions by the fly ash.     

Nitration of benzo[a]pyrene adsorbed on coal fly ash particles by nitrogen dioxide: role of thermal activation

Nitration of benzo[a]pyrene (BaP) by nitrogen dioxide (NO2) adsorbed on the surface of thermally activated coal fly ash and model aluminosilicate particles led to the formation of nitrobenzo[a]pyrenes as verified by extraction and gas chromatography/mass spectrometry (GC/MS). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was utilized to follow the nitration reaction on the surface of zeolite Y. Nitrobenzo[a]pyrene formation was observed along with the formation of nitrous acid and nitrate species. The formation of the BaP radical cation was also observed on thermally activated aluminosilicate particles by electron spin resonance (ESR) spectroscopy. On the basis of GC/MS, DRIFTS, and ESR spectroscopy results, a mechanism of nitration involving intermediate BaP radical cations generated on thermally activated aluminosilicate particles is proposed. These observations have led to the hypothesis that nitration of adsorbed polyaromatic hydrocarbons on coal fly ash by reaction with nitrogen oxides can occur in the smokestack, but with the aging of the fly ash particles, the extent of the nitration reaction will be diminished.     

改性粉煤灰微粉高填料纸的增强技术研究

探讨了对改性粉煤灰高填料纸的增强技术。研究结果表明:改性的粉煤灰微粉适合于作为造纸填料,不仅留着率可以达到50%以上,而且不会引起严重的掉毛掉粉现象,纸张的白度和不透明度分别可以达到83%ISO以上和93%以上。实验试用了5种增干强剂,自制的一种增干强剂效果较好,其他几种增干强剂作用效果都不太显著。添加聚乙烯醇合成纤维对于提高高填料纸的强度作用明显。添加量为5%时抗张强度明显改善,添加量为10%时耐破强度明显改善。PVA合成纤维与增干强剂混合使用对高填料纸各项性能改善良好,PVA用量为10%,N64170增干强剂用量为2%时,高填料纸各项性能最好。     

粉煤灰在印染废水处理中的应用

介绍了粉煤灰在印染、染料废水处理方面的研究现状及应用情况,分析讨论了粉煤灰处理废水的机理,指出了应用中存在的问题并对今后的研究方向进行了展望。     

MSWI fly ash particle analysis by scanning electron microscopy-energy dispersive X-ray spectroscopy

Municipal solid waste incinerator (MSWI) fly ash was investigated to study metal distribution on the particle surface. A detailed investigation into the distribution of chlorine, copper, iron, and zinc was carried out by electron microscopy coupled with X-ray fluorescence spectroscopy. Compositional and leaching test data were used to identify the correlation of significant variables and to formulate a hypothesis about metals speciation. The presence of copper chloride, iron, and zinc oxides was inferred. The iron and zinc accumulation in the submicron nuclei indicates that these metals came from the condensation of volatile species. As far as concerns copper, morphological data together with the element correlation study suggest that this element accumulates on particles involved in heterogeneous condensation processes. Furthermore, during such processes, particles of small size containing copper are formed.     

Copper stabilization by zeolite synthesis in polluted soils treated with coal fly ash

This study deals with the process of zeolite formation in an agricultural soil artificially polluted by high amounts of Cu (15 mg of Cu/g of soil dry weight) and treated with fused coal fly ash at 30 and 60 degrees C and how this process affects the mobility and availability of the metal. As a consequence of the treatment, the amount of dissolved Cu, and thus its mobility, was strongly reduced, and the percentage of the metal stabilized in the solid phase increased over time, reaching values of 30% at 30 degrees C and 40% at 60 degrees C. The physicochemical phenomena responsible for Cu stabilization in the solid phase have been evaluated by EDTA sequential extractions and synchrotron radiation based X-ray microanalytical techniques. These techniques were used for the visualization of the spatial distribution and the speciation of Cu in and/or on the neo-formed zeolite particles. In particular, micro XRF (X-ray fluorescence) tomography showed direct evidence that Cu can be entrapped as clusters inside the porous zeolitic structures while mu-XANES (X-ray absorption near edge structure) spectroscopy determinations revealed Cu to be present mainly as Cu(ll) hydroxide and Cu(ll) oxide. The reported results could be useful as a basic knowledge for planning new technologies for the on site physicochemical stabilization of heavy metals in heavily polluted soils.     

Utilization of zeolites synthesized from coal fly ash for the purification of acid mine waters

Two pilot plant products containing 65 and 45% NaP1 zeolite were obtained from two Spanish coal fly ashes (Narcea and Teruel Power Station, respectively). The zeolitic product obtained showed a cation exchange capacity (CEC) of 2.7 and 2.0 mequiv/g, respectively. Decontamination tests of three acid mine waters from southwestern Spain were carried out using the zeolite derived from fly ash and commercial synthetic zeolite. The results demonstrate that the zeolitic material could be employed for heavy metal uptake in the water purification process. Doses of 5-30 g of zeolite/L have been applied according on the zeolite species and the heavy metal levels. Moreover, the application of zeolites increases the pH. This causes metal-bearing solid phases to precipitate and enhances the efficiency of the decontamination process.     

Low temperature catalytic oxidation of hydrogen sulfide and methanethiol using wood and coal fly ash

The feasibility of reusing waste material as an inexpensive catalyst to remove sulfur compounds from gaseous waste streams has been demonstrated. Wood and coal fly ash were demonstrated to catalytically oxidize H2S and methanethiol (CH3SH) at low temperatures (23-25 degrees C). Wood ash had a significantly higher surface area compared to coal ash (44.9 vs 7.7 m2/g), resulting in a higher initial H2S removal rate (0.16 vs 0.018 mg/g/min) under similar conditions. Elemental sulfur was determined to be the end product of H2S oxidation, since X-ray diffraction analysis indicated the presence of crystalline sulfur. Catalytic decay occurred apparently due to surface deposition of sulfur and a subsequent decline in surface area (44.9-1.4 m2/g) during the reaction of H2S with the ash. Methanethiol was stoichiometrically converted to dimethyl disulfide ((CH3)2S2) without significant catalytic decay. Catalytic decay was reduced and H2S conversion increased (10% at 1.8 days vs 94% at 4.2 days) when H2S loading was decreased to levels typical of many environmental applications (500 ppmv inlet and 1.43 mg/min vs 60 ppmv, 0.09 mg/ min). Catalyst regeneration using hot water (85 degrees C) washing was possible, but only increased fractional conversion from 0.2 to 0.6 and the initial reaction rate to 50% of the original H2S oxidation activity.