The determination of trace element concentrations in fly ash samples using ultrasound-assisted digestion followed with inductively coupled plasma optical emission spectrometry

A method of ultrasound-assisted digestion followed by inductively coupled plasma optical emission spectrometry (ICP-OES) used for the determination of trace element (chromium, copper, lead, nickel, vanadium and zinc) concentrations in fly ash samples was developed. All the measurements were performed in robust plasma conditions. Ultrasound-assisted digestion procedures using digestion solutions of aqua regia and hydrofluoric acid (HF) resulted in recovery rates of over 80% for all the analyte elements. Ultrasound-assisted two-step digestion with digestion solutions of 6 mL of HNO₃ (Step 1) and 3 mL of HNO₃ + 3 mL of HF (Step 2) resulted in recovery rates of over 92% for all the analyte elements with one exception, chromium, which had a recovery of about 85%. The analysis of SRM 1633b showed that the two-step ultrasound-assisted digestion method developed resulted in chromium, copper, nickel and zinc concentrations higher than the microwave digestion method standardized by the United States Environmental Protection Agency (USEPA method 3052). This is the very first time when a digestion method using ultrasound resulted in higher efficiency than microwave (USEPA method 3052) for chromium and nickel in very hard to dissolve samples. The major advantages of the ultrasound-assisted digestion over microwave digestion is the high treatment rate (about 30 samples simultaneously with a sonication time of 18 min) and the possibility to use new sample vessels without a significant increase in costs.     

An intrinsic kinetics model to predict complex ash effects (ash film,dilution, and vaporization) on pulverized coal char burnout in air (O2/N2) and oxy-fuel (O2/CO2) atmospheres

During coal combustion, char chemical reaction is the slowest step, particularly in the last burnout stage, where the char consists of small amounts of carbon in a predominant ash framework. Existing kinetics models tend to deviate from experimental measurements of late char burnout due to the incomplete treatment of ash effects. Ash can improve pore evolution through vaporization, hinder oxygen transport by forming an ash film, and reduce active carbon sites and available surface per unit volume by penetrating into the char matrix. In this work, a sophisticated kinetics model, focusing on these three ash evolution mechanisms (ash vaporization, ash film, and ash dilution) during pulverized coal (PC) char combustion, is developed by integrating them into a thorough mechanistic picture. Further, a detailed comparison of the three distinct ash effects on PC char conversion during air (O₂/N₂) and oxy-fuel (O₂/CO₂) combustion is performed. For the modeled coal, the mass of ash vaporization is approximate 3 orders less than the mass of ash remaining, which participates in ash dilution and ash film formation, both in O₂/N₂ and O₂/CO₂ atmospheres. The influence of these phenomena on burnout time follows the order: ash dilution > ash film > ash vaporization. The influence of ash vaporization on burnout time is minor, but through interactions with the ash dilution and ash film forming processes it can have an impact at high extents of burnout, particularly in O₂/CO₂ atmospheres. In O₂/N₂ atmospheres the residual ash predominately exists as an ash film, whereas it mainly exists as diluted ash in the char matrix in O₂/CO₂ atmospheres. The residual ash particle is encased by a thick film when the ash film forming fraction is high (low ash dilution fraction). These results provide in-depth insights into the conversion of PC char and further utilization of the residual ash.     

Simulation of the thermal degradation and curing kinetics of fly ash reinforced diglycidyl ether bisphenol A composite

Thermogravimetric Analysis (TGA) is concluding expanding applicability in determination of the thermal stability and degradation nature of materials. The present study investigates the thermal degradation behavior and the kinetics of degradation of epoxy mixed with varying percentages of 0, 2.5, 5, and 7.5 ​wt% fly ash. Thermal stability and degradation behavior of fly ash modified epoxy cast were determined by thermogravimetric analysis. The kinetic parameters of the EF composites were calculated by using Coats–Redfern, Broido and Horowitz–Metzger models under best-fit analysis and further proved by linear regression analysis. The kinetics of thermal degradation was calculated from data scanned at a heating rate of 10 ​°C/min. The obtained results reveal that kinetic parameters and thermal behavior of EF composites were improved with the reinforcement of fly ash. The cure kinetics of the varying content of fly ash reinforced epoxy cast were also studied by using a nonisothermal differential scanning calorimetric (DSC) technique at four different heating rates 5 ​°C/min, 10 ​°C/min, 15 ​°C/min and 20 ​°C/min. The curing kinetics of the EF composite was derived from the nonisothermal differential scanning calorimetry (DSC) data with the three Kissinger, Ozawa, and Flynn–Wall–Ozawa models, respectively.     

Relation between silico-aluminous fly ash and its coal of origin

Fly ashes are typical complex solids which incorporate at the same time intrinsic properties derived from the layers （various mineralogical and dimensional spectra） and major transformations generated during prior processing. To use fly ashes in various applications, it is necessary to characterise them completely. The first research to date carried out on silico-aluminous fly ashes in order to characterise them physically, morphologically, chemically and mineralogically, resulted in the recognition that they are relatively simple materials. In the present study, a silico-aluminous fly ash coming from the power station of Albi （France） was selected. Heat treatment at 450 and 1200℃ together with coal simulated the treatment undergone by coal in the power station in order to mimic real coal residue. In conclusion, the diversity of the particles contained in fly ash could only be exolained by the relation existing between the fly ash and its coal of origin.     

利用除尘灰制备活性炭的工艺研究

以除尘灰为原料，用物理活化法制备活性炭．研究了活化温度、活化时间、活化剂流量对活性炭性能的影响．实验结果表明，活化温度和活化时间对活性炭的BET比表面积和吸附性能有很大影响；该方法可制得1nm以下微孔和10nm以下中孔均比较发达的活性炭．     

Comparative Efficiencies of Trace Metal Extraction from Municipal Incinerator Ashes

Abstract

Five laboratory solvent extraction methods for the determination of leachable trace metals from municipal incinerator fly and bottom ashes are evaluated. The trace elements of interest were cadmium, chromium, copper, manganese and lead. Five different extractants, 0.1NHCl, 1.0 N ammonium acetate, methyl isobutyl ketone (MIBK), chloroform and hexane were used on each ash to determine comparative extraction efficiencies.

Extraction efficiencies of the five solvents were determined based on total metal concentration, and were found to rank in the following order: 0.1NHCl<1.0N ammonium acetate < MIBK < chloroform < hexane. No one solvent was optimal for obtaining environmentally available values for all five metals. The inorganic solvents, 0.1NHCl and 1.0N ammonium acetate, exhibited higher removal of trace metals from ash particles relative to the organic solvents. Manganese concentrations were removed more efficiently by 0.1NHCl, whereas 1.0 N ammonium acetate was more efficient for removing copper concentrations. Cadmium, Cr, and Pb could effectively be extracted by either of the two inorganic solvents. Concentrations of trace metals extracted from refuse ash appeared to be a function of the elemental boiling point and the species that exist on combustion. However, the classification of elements for refuse ash in this study strayed somewhat from the traditional geochemical classification scheme into which coal ash is placed.     

Horizontal attenuated total reflection applied to simultaneous determination of ash and protein contents in commercial wheat flour

Partial least-squares (PLS) regression was used to generate various models for the determination of both the protein and the ash contents of wheat flours by using spectroscopic data in the mid-infrared region obtained with a horizontal attenuated total reflectance (HATR) accessory. One hundred samples of wheat flour were used as purchased in the market: 55 for constructing the calibration model and 45 as external samples. The protein content varied between 8.85 and 13.23% and the ash content, between 0.330 and 1.287%, as determined by reference methods. Raw spectra and those corrected by multiplicative signal correction (MSC), first and second derivative spectra, were used as data for building the models. Different pre-treatments, such as mean centered and/or variance scaled (VS) methods, were tested and compared. Very good models were built as judged by the correlation coefficients (R²), root mean square error of calibration (RMSEC), root mean square error of validation (RMSEV) and root mean square error of prediction (RMSEP) that were obtained. Best results were achieved with MSC treated spectra.     

微波消解与ICP-OES/ICP-MS测定飞灰中的多种元素

研究了不同温度以及HNO3、HNO3/H2O2、HNO3/HF和HNO3/HF+H3BO34种酸对飞灰微波消解效果和元素分析的影响.以NIST-1633b为飞灰标准物质.建立了用HNO3/HF (9mL+ 1mL)分解0.05g飞灰,再加入10mL 4％(ρ)的H3BO3中和过量HF及氟化物沉淀的两步微波消解方法.并利用ICP-OES检测了Al、Ca、Fe、Mg、K、Na、S、Si和Ti等9种矿物元素,元素回收率在92％-105％之间;利用ICP-MS检测了V、Cr、Mn、Co、Ni、Cu、Zn、As、Se、Sr、Cs、Ba、Eu和Pb等14种重金属元素,元素回收率在83％-109％之间.各元素检测的RSD均小于3％.     

FTIR和XPS对沸石合成特性及Cr(Ⅲ)去除机制的谱学表征

以粉煤灰为原料,采用优化的水热晶化法合成沸石,使用XRD,SEM和ζ电位分析沸石产品的组成特性,借助FTIR和XPS等揭示废水中Cr(Ⅲ)的去除机制。合成产品主要为NaP1型沸石,在pH值8～12区间内,ζ电位由-8.72mV降到-24.46mV。准二级方程和Langmuir等温线对试验的拟合效果更好,理论饱和吸附量为33.557 0mg.g-1。FTIR图谱表明—OH和Si—O类官能团在反应过程中有重要贡献。XPS全谱发现:结合能576.45eV为Cr(2p3/2)的特征峰,揭示了吸附过程的有效性。吸附Cr(Ⅲ)后,沸石中Si—Si和Si—O对应的结合能增加了0.25和0.60eV,含Si官能团可能与Cr(Ⅲ)发生了配位反应。O(1s)的结合能在反应后变得更低。这些证据表明:沸石对Cr(Ⅲ)的去除过程是物理吸附和化学吸附共同作用的结果。     

A Sequential Extraction Method Measures the Toxic Metal Content in Fly Ash from a Municipal Solid Waste Incinerator

The purpose of this research was to develop an optimized pretreatment procedure for toxic metals (Pb, Cd, Zn and Cu) content in fly ash from a municipal waste incinerator. In addition, modified sequential extraction procedures were used to characterize the chemical composition of the fly ash samples. The sequential extraction resolved the fly ash elements into the following chemical forms: soluble, exchangeable, carbonate, oxide, organic, and silicate compounds. Certified reference city waste incineration ash (BCR.176) was used as target ash samples. A H₂O₂+HNO₃+HF mixed acid digestion solution with a low temperature evaporation procedure was selected as optimal for the fly ash digestion. The digested solution was analyzed by inductively coupled plasma mass spectrometry (ICP‐MS), which effectively determined the concentrations of the toxic metal elements in BCR.176. Except for Cd, the recovery of Pb, Zn, and Cu under H₂O₂+HNO₃+HF digestion and their sequential extraction procedures were higher than 95%. The relative standard deviations (RSD) for recoveries of the four elements were within 10%. Furthermore, the sequential extraction procedure's results provided information on the potential mobility of the studied elements. Most of the Cd was bound to water‐soluble and carbonate material in the fly ash samples. Most of the Pb, Zn, and Cu was released to carbonates and bound to organic matter in the fly ash samples.