医疗垃圾焚烧飞灰重金属形态分析

利用原子吸收光谱仪分别对医疗垃圾焚烧飞灰重金属含量和重金属形态及其随颗粒度分布特性进行了分析,结果表明,飞灰中Cd、Zn、Pb等的浸出浓度远超标与这些重金属的可交换态和碳酸盐态含量较高有关;飞灰颗粒度主要在96 μm以下,96～150 μm的颗粒中Cd、Pb含量最高,且Zn、Cd的形态以可交换态为主.     

不同粒度飞灰中16种微量元素的含量分布

研究了不同粒级的燃煤飞灰中的Ｂａ、Ｂｅ、Ｃｄ、Ｃｒ、Ｃｕ、Ｈｇ、Ｌｉ、Ｍｎ、Ｎｉ、Ｐｂ、Ｓｒ、Ｔｉ、Ｖ、Ｚｎ、Ｚｒ元素的含量分布,煤中元素的含量比及富集因子。     

Dechlorination and destruction of PCDD,PCDF and PCB on selected fly ash from municipal waste incineration

The potential of fly ash to dechlorinate and destroy PCDD, PCDF and PCB was tested under oxygen deficient conditions in the laboratory. Specifically, two types of fly ash were compared, originating either from a fluidized bed incinerator using Ca(OH)₂ spray (FA1), or a stoker incinerator without Ca(OH)₂ impact (FA2).

Results from the present study indicate that on FA2 type fly ash, the degradation processes of OCDD, OCDF and D₁₀CB occurred primarily via dechlorination/hydrogenation up to temperature settings of 340 °C. In contrast, FA1 type fly ash was found to effect both dechlorination and destruction of these compounds already at temperature settings of 260 °C.

The dechlorination velocity of PCDD and PCDF did not differ significantly. However, the first dechlorination step of OCDF in the 1,9-position occurred faster compared to the first dechlorination step of OCDD.

The isomer pattern resulting from the dechlorination processes was quite similar on both FA1 and FA2, indicating that differences in alkalinity or elemental composition of the two types of fly ashes do not have a significant influence on the position of dechlorination. PCDD and PCDF dechlorination of the 2,3,7,8-positions was not favoured over dechlorination of the 1,4,6,9-positions on either type of fly ash. In contrast, dechlorination of PCB occurred predominantly on the toxicological relevant 3- and 4-positions.

The dechlorination/destruction processes were completed on both types of fly ash at 380 °C within one hour, which correlates well with results obtained from actual plant operation practices.     

垃圾焚烧飞灰的资源化处置前景

对大量数据进行统计分析,得出垃圾焚烧飞灰中主要重金属元素和二噁英类物质的含量分布特征,并根据垃圾焚烧飞灰的综合特点,结合其他领域现有技术,初步提出了3个垃圾焚烧飞灰的资源化处置方案:①烧制陶粒;②作为凝石成岩剂的原料;③作为上流式厌氧污泥床(UASB)或膨胀式颗粒污泥床(EGSB)废水处理装置的生化反应促进剂.同时回收重金属,并对其前景进行了初步分析.若将上述3个方案逐步完善,不但能节约1000～2000元/t的垃圾焚烧飞灰处置费用,还能够产生很大的附加经济效益.     

Differential pulmonary inflammation and in vitro cytotoxicity of size-fractionated fly ash particles from pulverized coal combustion

Exposure to airborne particulate matter (PM) has been associated with adverse health effects in humans. Pulmonary inflammatory responses were examined in CD1 mice after intratracheal instillation of 25 or 100 microg of ultrafine (< 0.2 microm), fine (< 2.5 microm), and coarse (> 2.5 microm) coal fly ash from a combusted Montana subbituminous coal, and of fine and coarse fractions from a combusted western Kentucky bituminous coal. After 18 hr, the lungs were lavaged and the bronchoalveolar fluid was assessed for cellular influx, biochemical markers, and pro-inflammatory cytokines. The responses were compared with saline and endotoxin as negative and positive controls, respectively. On an equal-mass basis, the ultrafine particles from combusted Montana coal induced a higher degree of neutrophil inflammation and cytokine levels than did the fine or coarse PM. The western Kentucky fine PM caused a moderate degree of inflammation and protein levels in bronchoalveolar fluid that were higher than the Montana fine PM. Coarse PM did not produce any significant effects. In vitro experiments with rat alveolar macrophages showed that of the particles tested, only the Montana ultrafine displayed significant cytotoxicity. It is concluded that fly ash toxicity is inversely related with particle size and is associated with increased sulfur and trace element content.     

The leachability of carbon-14-labelled 3,4-benzopyrene from coal ash into aqueous systems

The leachability of polycyclic aromatic hydrocarbons from coal ash into aqueous systems was studied. Carbon-14-labeled 3,4-Benzopyrene (BaP) was deposited on coal fly ash by adsorption from the liquid phase in quantities of about 10 μg/g ash. After a thermal treatment in air at 120 °C for 2 hours the desorption of BaP was measured using aqueous solutions of acetone and methanol as extractants and liquid scintillation counting as detection method. In all cases the ¹⁴C-recovery was incomplete. Using water as extractant, ¹⁴C-recoveries of about 1 % were found. In the presence of a non-ionic surface active agent (Tween 80) the ¹⁴C-recovery was enhanced significantly. For these reasons further experiments under realistic waste disposal conditions are necessary.     

Dioxins not detected in effluents from coal/refuse combustion

No 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin was detected in effluents from a power plant burning coal supplemented with processed municipal wastes. These negative findings, in contrast with the many reports of the presence of dioxins from waste incineration, are proposed to be due to the high temperature of 1200°C for the combustion of small pieces of refuse with adequate oxygen for times sufficient to insure complete oxidation.     

Release of mercury vapor from coal combustion ash

The long-term stability of Hg in coal combustion by-products (CCBs) was evaluated at ambient and near-ambient temperatures. Six CCB samples with atypically high levels of total Hg were selected for study assuming a greater potential for release of measurable amounts of Hg vapor. The samples selected included two fly ash samples from U.S. eastern bituminous coal, two fly ash samples from South African low-rank coal, one fly ash from Powder River Basin (PRB) subbituminous coal blended with petroleum coke, and one PRB subbituminous coal fly ash incorporated with flue gas desulfurization material. Air scrubbed of Hg was passed through compacted 100-g aliquots of each sample at 1 mL/min and vented to a gold-coated quartz trap to collect released Hg vapor. The samples were maintained at ambient and near-ambient (37 degrees C) temperatures. All samples released low-picogram levels of Hg after 90 days. No pattern was evident to link the total Hg content to the rate of release of Hg vapor. An average of 0.030 pg Hg/g CCB/day was released from the samples, which equates to 2.2 x 10(-8) lb Hg/ton CCB/year. If this were applied to a coal-fired power plant production of 200,000 tons of fly ash per year, there would be a maximum potential release of 0.0044 lb, or 2.00 g, of Hg per year. Experiments are continuing to determine long-term vapor release of Hg from CCBs. All samples have been set up in duplicate at ambient temperature with an improved apparatus to reevaluate results reported in this article.     

The role of ammonia on mercury leaching from coal fly ash

The Federal Clean Air Interstate Rule issued in March 2005 will result in many power plants employing ammonia-based technologies to control NO(x) emission. The Clean Air Mercury Rule, issued at the same time, will encourage many power plants to use various technologies to remove mercury from flue gas, generating fly ashes that contain elevated concentrations of mercury. Ammonia forms relatively strong complexes with mercury compared to most other cationic elements and, therefore, may change the leaching characteristics of mercury. Understanding the impact of ammonia on the leaching of mercury from fly ash is critical in predicting the potential environmental impact of future fly ash. Batch methods were used to investigate the ammonia impact on mercury leaching from fly ash under different pH conditions. The results indicated that mercury leaching without external ammonia addition is not significant. However, ammonia addition increased mercury leaching in the alkaline pH range, due to the formation of less adsorbable mercury-ammonia complexes. Washed ash released more mercury than the raw ash if the ammonia concentration is the same, mainly due to the dissolution of some ash components during washing which exposed more mercury on ash surface. Mercury adsorption data indicated that more than 90% of available mercury was adsorbed by fly ash even in the presence of 1000 mg l(-1) ammonia addition.     

Synthesis of high-purity Na-A and Na-X zeolite from coal fly ash

Coal fly ash (CFA) was used as a raw material for the synthesis of zeolite molecular sieve. The synthesis began with the pretreatment of CFA to remove impurities (e.g., Fe₂O₃, CaO, etc.) under various acid types (HCl, H₂SO₄, and HNO₃) and acid/CFA ratios (5–25 mL_acid/g_CFA). High product purity (up to 97%) was achieved with HCl (20%wt), and acid/CFA ratio of 20 mL_HCl/g_CFA. The treated CFA was then converted to zeolite by the fusion reaction under various Si/Al molar ratios (0.54–1.84). Zeolite type A was synthesized when the Si/Al molar ratios were lower than 1, whereas sodium aluminum silicate hydrate was formed when the Si/Al molar ratio were higher than 1. The highest water adsorption performance of the zeolite product, i.e., the outlet ethanol concentration of 99.9%wt and the specific adsorption capacity of 2.31 × 10^?2 g_water/g_zeolite, was observed with the Si/Al molar ratio of 0.82. The zeolite was tested for its water adsorption capacity repeatedly 10 times without deactivation.

Implications: This work evaluated the technical feasibility in the conversion of CFA to zeolite, which would help reduce the quantity of waste needed to be landfilled. This adds value to the unwanted material by converting it into something that can be further used. The synthesized products were shown to be quite stable as water adsorbent for the dehydration of ethanol solution.     

Determination of trace rare earth elements in coal fly ash and atmospheric particulates by electrothermal vaporization inductively coupled plasma mass spectrometry with slurry sampling

A method of fluorination assisted electrothermal vaporization (FETV)-ICP-MS with polytetrafluoroethylene as fluorinating reagent was developed for the direct determination of trace rare earth elements (REEs) in coal fly ash and atmospheric particulates. Under the optimal conditions, the detection limits for REEs were 0.1 pg m(-3)(Eu) to 6.7 pg m(-3)(Nd) with the precisions of 4.1%(Yb) to 10%(La) (c=1 microg L(-1), n=9). The proposed method was applied to determine trace REEs in coal fly ash, airborne particulates and NIES SRM No. 8 Vehicle Exhaust Particulates. It was found that the determined values for Y, La, Pr and Nd obtained by slurry sampling FETV-ICP-MS with external calibration coincided with that obtained by pneumatic nebulization (PN)-ICP-MS and slurry sampling FETV-ICP-MS with standard addition. However, the determined values for Ce and Sm obtained by slurry sampling FETV-ICP-MS with external calibration were lower than that obtained by PN-ICP-MS and slurry sampling FETV-ICP-MS with standard addition.     

Influence of coexisting surface-active agents on leachability of dioxins in raw and treated fly ash from an MSW incinerator

The leaching behavior of dioxins from raw and treated fly ash (FA) under the coexistence of several types of surface-active agents (SAAs) was examined by batch leaching tests to obtain significant information not only for evaluating leachability of dioxins as hydrophobic organic pollutants (HOPs) under the severe environment in which SAAs coexist, but also for evaluating the reduction efficiency of dioxin-leachability from the treated FA. Enhancement of dioxin-leachability by sufficient addition of SAAs was observed in the leaching test, whereas addition of a smaller quantity depressed the leachability. The higher the degree of chlorination in PCDDs/PCDFs homologues, the more effectively the SAAs enhanced the leachability. Moreover, there was a large difference in the potential for leachability enhancement due to each surface activity, based on critical micelle concentration (CMC) of the SAAs although Aldrich humic acid enhanced the leachability at a much lower concentration than CMC. A comparison of the leachability in FA treated by several methods showed a difference in the reduction efficiency of leachability, depending on the adsorption of SAAs by each treated FA.     

The dissolution kinetics of major elements in municipal solid waste incineration bottom ash particles

Leaching and tracer experiments in batches at L/S 20 were performed with 3-month-old MSWI bottom ash separated into eight different particle sizes. The time-dependent leaching of major elements (Ca(2+), K(+), Na(+), Cl(-) and SO(4)(-2)) was monitored for up to 747 h. Physical properties of the particles, the specific surface (BET), pore volume and pore volume distribution over pore sizes (BJH) were determined for all particle classes by N(2) adsorption/desorption experiments. Some common features of physical pore structure for all particles were revealed. The specific surface and the particle pore volume were found to be negatively correlated with particle size, ranging from 3.2 m(2)/g to 25.7 m(2)/g for the surface area and from 0.0086 cm(3)/g to 0.091 cm(3)/g for the pore volume. Not surprisingly, the specific surface area was found to be the major material parameter that governed the leaching behavior for all elements (Ca(2+), K(+), Na(+), Cl(-) and SO(4)(-2)) and particle sizes. The diffusion resistance was determined independently by separate tracer (tritium) experiments. Diffusion gave a significant contribution to the apparent leaching kinetics for all elements during the first 10-40 h (depending on the particle size) of leaching and surface reaction was the overall rate controlling mechanism at late times for all particle sizes. For Ca(2+) and SO(4)(-2), the coupled effect of diffusion resistance and the degree of under-saturation in the intra particle pore volume was found to be a major rate limiting dissolution mechanism for both early and late times. The solubility control in the intra particulate porosity may undermine any attempt to treat bottom ash by washing out the sulfate. Even for high liquid/solid ratios, the solubility in the intra-particular porosity will limit the release rate.     

Speciation and mobility of cadmium in straw and wood combustion fly ash

Two fly ashes from biomass combustion have been analysed regarding cadmium speciation and mobility. A fly ash from straw combustion contained 10 mg Cd/kg dry matter, and around 50% of the cadmium was leachable in water. The possible main speciation of cadmium in this fly ash was CdCl2. When adding this fly ash to agricultural soil a threat for groundwater contamination and plant uptake is existing. A fly ash from wood chip combustion had 28.6 mg Cd/kg dry matter. In this fly ash, the cadmium was bound more heavily, with only small amounts of cadmium leached in mild extractants. A possible speciation of cadmium in this fly ash was as oxide or as CdSiO3. Long-term effects and accumulation of cadmium could be a problem when adding this fly ash to agricultural or forest soils.     

An assessment of the significance of mercury release from coal fly ash

Some mercury (Hg) naturally present in coal is retained in the fly ash remaining after combustion. Concern has been raised regarding the potential for release of this Hg to the environment. The exchange of Hg between fly ash and the atmosphere was measured in the laboratory and in situ at a fly ash landfill. All samples of fly ash used in the laboratory study, with the exception of that derived from lignite-type coal, acted as a sink for atmospheric Hg. Deposition rates were found to increase as air Hg concentrations increased and to decrease with incident light and increased temperature. Addition of water to fly ash samples resulted in re-emission of deposited atmospheric Hg. Deposition was the dominant flux measured in situ at a fly ash landfill. Atmospheric Hg was deposited to all samples collected as part of two demonstration projects using carbon injection for enhanced Hg capture. Hg concentrations of extracts derived using U.S. Environmental Protection Agency Method 1312 (Synthetic Precipitation Leaching Procedure) were < or = 14.4 ng/L. Data developed demonstrate that fly ash, including that collected from Hg removal projects, will release little Hg to the air or water, and under certain conditions, absorbs Hg from the air.     

Bioleaching of metal from municipal waste incineration fly ash using a mixed culture of sulfur-oxidizing and iron-oxidizing bacteria

We investigated the behavior and characteristics of metal leaching from municipal solid waste incineration (MSWI) fly ash among pure cultures of a sulfur-oxidizing bacterium (SOB) and an iron-oxidizing bacterium (IOB) and a mixed culture. The IOB has a high metal-leaching ability, though its tolerability against the ash addition is low. The SOB might better tolerate an increase in ash addition than the IOB, though metal leaching ability of the SOB is limited. Mixed culture could compensate for these deficiencies, and high metal leachability was exhibited in the 1% ash culture, i.e., 67% and 78% of leachabilities for Cu and Zn, respectively, and 100% for Cr and Cd. Furthermore, comparably high leachabilities such as 42% and 78% for Cu and Zn were observed even in the 3% ash cultures. Characterization of metal leaching by the mixed culture revealed that the acidic and oxidizing condition had remained stable thorough the experimental period. Ferric iron remained in the mixed culture, and the metal leaching was enhanced by redox mechanisms coupling with the leaching by sulfate. An increase of ferrous iron enhanced the Cr, Cu, and As leaching. The optimum concentration of sulfur existed for As and Cr (5 gl(-1)) and Cu (2 gl(-1)). The presence of the degradable and non-degradable organic compound that must be existed in the natural environment or waste landfills made no significant change in the leachability of metals other than Zn. These results suggested that bioleaching using a mixed culture of SOB and IOB is a promising technology for recovering the valuable metals from MSWI fly ash.     

用于粉煤灰排放的加湿卸灰设备

针对粉煤灰排放产生二次污染问题，经过分析比较，选用了科学的加湿排放工作原理，设计了用于粉煤灰排放的新型灰料加湿卸灰机。     

粉煤灰和电石渣对聚丙烯塑举裂解的影响研究

研究了粉煤灰和电石渣对聚丙烯塑料裂解的影响，讨论了加入量对裂解速度和裂解产物的影响。结果表明：粉煤灰和电石渣都使裂解产物中的轻质部分（汽油和裂解气）增加、重油降低；粉煤灰比电石渣更能加快反应的进行，而且加入量越多，反应越快，需时越短；粉煤灰比电石渣对聚丙烯塑料的裂解具有明显的催化促进效果。     

垃圾焚烧飞灰有毒重金属固化稳定技术研究综述

采用焚烧法处理生活垃圾正呈快速增长的趋势,焚烧过程产生的飞灰中所含有的大量有毒重金属对自然环境和人类生存都造成极大影响。阐述了目前常用的几种固化稳定垃圾焚烧飞灰有毒重金属的方法,综合分析了其固化特点和优缺点,并初步探索了一种低能耗环境下实现高温熔融处置技术的有效途径,从而为垃圾焚烧飞灰高温固化稳定有毒重金属的实施提供一定的理论基础和技术支持。