Extractability of metals in municipal solid wastes fly ash using supercritical CO(2) containing Cyanex 302.

The extraction of lead from fly ash produced during the thermal treatment of municipal solid wastes was studied using supercritical carbon dioxide (SC-CO(2)) and Cyanex 302 (bis(2,4,4-trimethylpentyl)monophosphinic acid). The extraction of lead from the fly ash was carried out in a 5 cm(3) internal volume reaction vessel under static extraction conditions at 323 K, and 24 MPa for 1 h. The extraction efficiencies of lead ranged from 4% to the total extraction under the conditions of 0.05 g fly ash with 2 cm(3) Cyanex 302. There was a linear relationship between the extraction efficiencies of lead using the SC-CO(2) + Cyanex 302 and using a water-based method described by JLT13.     

医疗垃圾焚烧飞灰中OCDD/OCDF的球磨机械化学法降解试验研究

利用机械化学法进行含二噁英废弃物的无害化处置,是一个值得关注的研究领域.本研究以去除大部分二噁英及其它有机成分的医疗垃圾焚烧飞灰作为反应基质,添加了八氯代二噁英和呋喃(OCDD/OCDF)后,在自行研制的行星式球磨试验装置上进行了球磨机械化学法降解试验研究.实验球磨两种飞灰分别采自某回转窑热解流化多段焚烧系统和某简易固定床焚烧系统的医疗垃圾焚烧炉布袋除尘器,其中对于简易固定床焚烧处置的飞灰,OCDD和OCDF分别减少了64.7%和63.6%,氯化度由6.86降至5.53.两种飞灰处理后,平均粒径大幅缩小,比表面积、孔容积显著增加,CaCO3强度显著减弱.实验证实飞灰本身的某些组分(CaCO3等)在球磨机械化学处理过程中起到类似氧化钙(CaO)的脱氯还原剂作用,且机械化学法降解二噁英的效果显著.研究结果对实际医疗垃圾焚烧飞灰中二噁英类污染物的脱除具有指导意义.     

垃圾焚烧飞灰理化特性研究

应用能谱分析、灰熔点炉、XRD、压汞仪等仪器手段对国内外8种垃圾焚烧飞灰的成分、熔点、晶相结构、颗粒特性等物理化学性质进行了系统研究。研究表明,飞灰成分因为受原料、炉型、取样位置等因素影响而差异很大。由于飞灰的成分差异导致垃圾焚烧飞灰比煤灰更易于熔融,对熔融处理有利,这主要归因于飞灰中SiO2含量以及SiO2/Al2O3差异,熔点与SiO2含量存在正比关系；添加CaO实现助熔是有条件的,不同飞灰由于焚烧条件和飞灰成分不同导致晶相组成有一定差异；飞灰内部孔径主要分布于0.3 μm～1.5 μm范围内,飞灰的比表面积为20.5 m2/g。     

Supercritical fluid extraction of polychlorinated dibenzo-p-dioxins from municipal incinerator fly ash

The supercritical fluid extraction of polychlorinated dibenzo-p-dioxins from an incinerator fly ash sample has been investigated; supercritical nitrous oxide and its mixtures with methanol and toluene were employed as mobile phases. Recoveries of individual polychlorinated dibenzo-p-dioxins congeners were calculated from results of analysis of ¹³C-labeled dioxins by high resolution GC-MS employing selected ion monitoring. The extraction procedure was compared with extraction in a Soxhlet apparatus, which is currently used as a standard method for removing chlorinated dibenzo-p-dioxins from fly ash samples: the results indicated that the time required for the extraction and clean-up can be reduced from 24 to 2.5 hours/sample. Quantitative recovery of the chlorinated dibenzo-p-dioxins was achieved at μg/kg levels, the relative standard deviation was between 1.8 and 5.8%. The use of a virtually inert fluid such as pure nitrous oxide provides significant improvement over conventional extraction procedures because no solvent residue is left in the processed extract.     

Rapid and cost-effective analysis of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in soil, fly ash and sediment certified reference materials using pressurized liquid extraction with an integrated carbon trap

Pressurized liquid extraction with an integrated carbon trap (PLE-C) has recently been developed for fast and efficient analysis of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in food and feed. The method has also been tested, but not verified, for use on more complex soil samples, such as soil, sediment and fly ash. Hence, the primary aim of this study was to verify that PLE-C can produce reliable data for PCDDs/PCDFs in various abiotic matrixes. A second aim was to find a replacement for the previously used AX21 active carbon that is currently not commercially available. The performance of the PLE-C was evaluated using both single congener concentrations and toxic equivalency potentials (TEQ-pot) of three (soil, sediment and fly ash) certified reference materials. The results clearly show that PLE-C can be used for abiotic samples and that a commercially available carbon (Norit SA 4PAH HF) can replace the AX-21 carbon in the carbon trap. The TEQ-pot values obtained for the soil and sediment samples were within the uncertainty limits of the corresponding certified values, as were the determinations of single congener concentrations. PLE-C therefore has great potential for determination of PCDDs/PCDFs in soil and sediment samples. The TEQ-pot result for the fly ash was slightly lower than the certified TEQ-pot value, but it is still within the uncertainty limits of the certified value. Out of the single congener concentrations all but four (out of 17) agreed well with the values. Hence, PLE-C may potentially be used also for fly ash—after slight modifications. The integrated PLE-C and cleanup procedure is less labour-intensive than traditional methods such as Soxhlet extraction followed by a multistep cleanup, and consumes smaller quantities of ultrapure solvents than the commonly used Power-Prep system. In addition, PLE-C is capable of larger sample throughputs than the conventional methods. Thus, PLE-C is a promising alternative to the currently used sample preparation procedures for dioxins in abiotic samples. Figure PLE with integraded carbon trap for rapid PCDD/Fs analysis Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Determination of polar nitroaromatic compounds in soils and the impact of the soil properties on the extraction results

An HPLC compatible method based on pressurized solvent extraction (PSE) for the determination of fifteen polar nitroaromatic compounds (pNC) in soil is described. The PSE method was compared with ultrasonic activated extraction. Thereby, analyzing sandy, clayey, and organic rich spiked soil samples, the influence of soil texture on the extraction yield was examined. Considering different soil properties recovery rates of investigated pNC and limiting extraction parameters were determined for both techniques. The extraction recovery of some pNC was found to show dependence on the clay content and correlation with the organic carbon amount of the soil.     

Extractability of dioxins from soil: I. Extractability of dioxins from airborne particulates and humic acid fraction in soil

The extractability of dioxins (polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and coplanar polychlorinated biphenyls) from airborne particulates (APs) and humic acid (HA) in soil was evaluated. APs collected from ambient atmosphere and dioxins-associated precipitated HA fraction (PHA) were extracted by pressurized liquid extraction with either toluene or acetone. Native dioxins were equivalently extracted from APs with both solvents, whereas only acetone could satisfactorily recover the ¹³C-labelled compounds from metal-free PHA. The recovery rates of dioxins by toluene extraction from metal-free PHA varied with the organic carbon content of the PHA. However, even with acetone, the recovery of dioxins from metal-bound HA was poor (11–40%). These results suggest that PHA prevented the solvents from accessing sequestered dioxins. This characteristic of solid HA may influence the extractability of dioxins from humus-rich soil.     

Extraction of cloransulam-methyl from soil with subcritical water and supercritical CO2

Cloransulam-methyl was extracted from soil samples with supercritical CO2, subcritical water and conventional organic solvents. Supercritical CO2 was less efficient than conventional organic solvents; polarity modifiers had no impact on extraction efficiency. Extraction with supercritical CO2 exhibited a strong temperature dependence. Water was as effective as strong organic solvents for the extraction of cloransulam-methyl; however cloransulam-methyl hydrolyzed when extracted at 150 degrees C. Extraction temperature was the most important variable in increasing the efficiency and rate of extraction, while extraction pressure was not a significant variable.     

垃圾焚烧炉飞灰中二噁英的分布特性

采用高分辨色谱/低分辨质谱联机分析了不同炉型垃圾焚烧炉布袋除尘器飞灰中的二噁英分布特性。结果表明，燃料组成及飞灰中氯含量对飞灰中二噁英的浓度均有影响。飞灰中氯含量与灰中的二噁英含量成正比关系。尽管飞灰中含有大量重金属，但与飞灰中二噁英的含量并不存在显著的关系。流化床炉与炉排炉布袋除尘器飞灰中二噁英同系物分布特性不同。飞灰中二噁英的主要同系物是1,2,3,4,6,7,8-HpCDD(heptachlorinated dibenzo-p-dioxin)，1,2,3,4,6,7,8-HpCDF(heptachlorinated dibenzofuran)和OCDD(octachlorinated dibenzo-p-dioxin)，PCDFs(polychlorinated dibenzofurans)，TEQ (toxic equivalence quantity)高于PCDDs含量。初步研究表明，炉排炉飞灰中二噁英总量及毒性当量（TEQ）大于流化床炉飞灰。     

Supercritical fluid extraction of polycyclic aromatic hydrocarbons (PAH) from native soil and fly ash with pure and modified carbon dioxide and dimethylether

Polycyclic aromatic hydrocarbons (PAH) and alkyl-PAH in the lower mg/kg range were extracted from soil and fly ash. Extraction yields were measured for toluene Soxhlet, supercritical carbon dioxide, toluene modified carbon dioxide, and toluene modified dimethylether (DME) extractions. Pure DME similarly to toluene Soxhlet extraction enhances extraction yields (32 mg/kg) as compared to pure carbon dioxide (21 mg/kg). In particular, higher molecular weight PAH are extracted with pure DME. 5% Toluene modified carbon dioxide (43 mg/kg) and toluene modified DME (50 mg/kg) yield much better extraction yields than Soxhlet (32 mg/kg) or pure supercritical fluid extractions. Received: 19 July 1996 / Revised: 23 September 1996 / Accepted: 22 October 1996     

Method development of combining pressurized liquid extraction and off-line HPLC fractionation with a porous graphite carbon column for the analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in environmental samples

A method was developed for analysis of PCDD/Fs in fly ash and soil samples by using the combination of pressurized liquid extraction (PLE) and off-line HPLC fractionation with a porous graphite carbon (PGC) column, followed by analysis using HRGC/HRMS. The samples were automatically extracted by PLE. A multi-layer silica column was used for the preliminary cleanup. Then off-line fractionation was applied for the separation of PCDD/Fs and the collected PCDD/Fs fraction was analyzed by HRGC/HRMS. The use of solvent back-flushing at 70°C successfully solved the carry-over problem of PGC column. The procedure of single extraction and cleanup provided advantages of high automation and significant reduction of solvent and time compared to conventional methods. The method was validated by certified materials of fly ash and industrial sandy soil, and applied for the analysis of fly ash samples collected from three two-ton medical waste incinerators in Beijing and one farm soil sample collected in the vicinity of the incinerators.     

Study of mercury adsorption by selected Chinese coal fly ashes

Recent research has shown that fly ash produced in coal-fired power plants can play an important role in mercury removal. The aim of this study was to establish the relationships between fly ashes produced from different coals and boiler types and their mercury adsorption capacity. In order to achieve this objective, Brunauer–Emmett–Teller surface area, scanning electron microscopy, thermogravimetric analysis, and a mercury measurement system were employed to characterize the samples. The results show that the average pore size of fly ash is the single most important factor with residual carbon content fulfilling a secondary role in the capture of elemental mercury. The addition of HBr with fly ash can remarkably enhance the mercury adsorption performance of fly ash.     

Humic acid adsorption on fly ash and its derived unburned carbon

Fly ash is solid waste from combustion process, containing oxide minerals and unburned carbon. In this investigation, fly ash has been separated into metal oxide mineral section and unburned carbon. The fly ash with different contents of unburned carbon was employed for humic acid adsorption to investigate the influence of unburned carbon on adsorption. It is found that metal oxides and unburned carbon in fly ash exhibit significant difference in humic acid adsorption. The unburned carbon plays the major role in adsorption. Higher content of unburned carbon in fly ash results in higher surface area and thus higher humic acid adsorption. Fly ash and unburned carbon exhibit adsorption capacity of humic acid of 11 and 72 mg/g, respectively, at 30 degrees C, pH 7. Humic acid adsorption is also affected by ion strength, pH, and temperature. The thermodynamic calculations indicate that the adsorption is endothermic nature with DeltaH(0) and DeltaS(0) as 5.79 kJ/mol and 16.0 J/K mol, respectively.     

Development of porosity in carbons from yeast grains by activation with alkali metal carbonates

Cellular structured activated carbon samples were prepared with the aid of alkali carbonates X2CO3 (X = Li, Na, K, Rb, or Cs) from dry bread yeast with a milling procedure. The resultant carbon possesses a very large adsorption amount even for supercritical methane. The activation with Cs2CO3 gave the greatest surface area of 2420 m2 g(-1) from the subtracting pore effect method. The activation efficiency of X2CO3 (X = Li, Na, K, Rb, and Cs) was associated with the order of Gibbs free energy of X2O (X = Li, Na, K, Rb, and Cs) which should play an important role in the gasification. The carbon activated with Rb2CO3 gave the greatest adsorption amount of supercritical methane of 90 mg g(-1) at 0.9 MPa at 303 K.     

Supercritical fluid extraction of 2,3,7,8-tetrachlorodibenzo-p-dioxin from sediment samples

Supercritical fluid extraction (SFE) is a promising technique for the extraction of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) from environmental matrices such as contaminated sediments. The ability of SFE to solubilize many organic contaminants is well documented in industrial processes but its analytical applications were exploited just recently. In this study supercritical carbon dioxide and nitrous oxide and their mixtures with 2% methanol were used to extract 2,3,7,8-TCDD from aquatic sediments. An attractive feature of this process is that the carbon dioxide, being a virtually inert fluid, leaves no solvent residue on the processed sediment. Almost 100% of the 2,3,7,8-TCDD can be extracted from a sediment spiked with 200 μg/kg 2,3,7,8-TCDD in 30 minutes by using supercritical carbon dioxide + 2% methanol. Cleanup procedure is compared with the Soxhlet extraction procedure currently used as a standard method for extracting dioxins from sediment samples.     

Adsorption of Carbon Dioxide on Activated Carbon

The adsorption of CO2 on a raw activated carbon A and three modified activated carbon samples B, C, and D at temperatures ranging from 303 to 333 K and the thermodynamics of adsorption have been investigated using a vacuum adsorption apparatus in order to obtain more information about the effect of CO2 on removal of organic sulfur-containing compounds in industrial gases. The active ingredients impregnated in the carbon samples show significant influence on the adsorption for CO2 and its volumes adsorbed on modified carbon samples B, C, and D are all larger than that on the raw carbon sample A. On the other hand, the physical parameters such as surface area, pore volume, and micropore volume of carbon samples show no influence on the adsorbed amount of CO2. The Dubinin-Radushkevich (D-R) equation was the best model for fitting the adsorption data on carbon samples A and B, while the Preundlich equation was the best fit for the adsorption on carbon samples C and D. The isosteric heats of adsorption on carbon samples A, B, C, and D derived from the adsorption isotherms using the Clapeyron equation decreased slightly increasing surface loading. The heat of adsorption lay between 10.5 and 28.4 kJ/mol, with the carbon sample D having the highest value at all surface coverages that were studied. The observed entropy change associated with the adsorption for the carbon samples A, B, and C (above the surface coverage of 7 ml/g) was lower than the theoretical value for mobile adsorption. However, it was higher than the theoretical value for mobile adsorption but lower than the theoretical value for localized adsorption for carbon sample D.     

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．     

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.     

A detection method for unified chromatography: Ion mobility monitoring

Ion mobility monitoring has been used for detection in gas, supercritical fluid, and liquid chromatography, illustrating its potential as a method of detection for unified chromatography. Applications presented include GC-IMD of dioxins in fly ash, SFC-IMD of vitamin E, and HPLC-IMD of alkylamines. Ion mobility spectra of several mixed supercritical fluid mobile phases are also presented. Use of methanol, acetonitrile, and dichloromethane as modifiers of supercritical carbon dioxide, and use of supercritical dichlorodifluoromethane and chlorodifluoromethane as mobile phases had little effect on the reactant ion pattern at the flow rates and concentrations used in this study. Only when acetone was used as a modifier of carbon dioxide did the positive reactant ions change significantly. No effect of modifiers or mobile phase was observed for the negative reactant ions.     

Storage stability of ketones on carbon adsorbents

Activated coconut carbon constitutes the more widely used sorbent for preconcentration of volatile organic compounds in sampling workplace air. Water vapour is always present in the air and its adsorption on the activated carbon surface is a serious drawback, mainly when sampling polar organic compounds, such as ketones. In this case, the recovery of the compounds diminishes; moreover, ketones can be decomposed during storage. Synthetic carbons contain less inorganic impurities and have a lower capacity for water adsorption than coconut charcoal. The aim of this work was to evaluate the storage stability of various ketones (acetone, 2-butanone, 4-methyl-2-pentanone and cyclohexanone) on different activated carbons and to study the effect of adsorbed water vapour under different storage conditions. The effect of storage temperature on extraction efficiencies was significant for each ketone in all the studied sorbents. Recovery was higher when samples were stored at 4 degrees C. The results obtained for storage stability of the studied ketones showed that the performance of synthetic carbons was better than for the coconut charcoals. The water adsorption and the ash content of the carbons can be a measure of the reactive sites that may chemisorb ketones or catalize their decomposition. Anasorb 747 showed good ketone stability at least for 7 days, except for cyclohexanone. After 30-days storage, the stability of the studied ketones was excellent on Carboxen 564. This sorbent had a nearly negligible ash content and the adsorbed water was much lower than for the other sorbents tested.