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.     

Extraction of heavy metals from MSW incinerator fly ash using saponins

An extraction process with saponins was evaluated for removing heavy metals from MSW (municipal solid waste) incinerator fly ashes. Two different fly ashes, A and B, were treated on a laboratory scale with three triterpene-glycoside type of saponins, M, Q, and T, in the pH range 4-9. The results were compared with those of the HCI and EDTA treatment. The treatment with saponins extracted 20-45% of Cr from the fly ashes. Saponins were also effective in extracting Cu from fly ash A attaining 50-60% extraction. Saponin T extracted 100% of Pb from fly ash A at pH around 4. The extraction of Zn with the saponin treatment was similar to that of the HCl treatment. Further, Cr, Cu, Pb, and Zn were fractionated by sequential extraction to investigate the effect of saponins on each fraction. Extraction behavior of other elements during the saponin treatment was also studied. The leaching test on the residues received after the saponin treatment showed that the fly ashes were successfully detoxified to meet the landfilling guideline.     

粉煤灰免烧陶粒制备及其重金属废水净化性能

摘要重金属废水对环境的污染已经引起科研人员的广泛关注。以粉煤灰和水泥为原料、添加活性成分FeS,制备一种免烧陶粒用于含重金属Cu2＋、Zn2＋、Pb2＋的废水处理。探讨了物料配比及蒸养时间对陶粒筒压强度及其比表面积的影响;研究了固液比、接触时间、pH、温度及初始溶液浓度等因素对Cu2＋、Zn2＋、Pb2＋离子净化效果的影响规律,并对实验结果进行了等温线拟合。XRD分析显示,免烧陶粒中存在Ca（OH）2、C—D—H、FeS等矿物相,对重金属离子具有非常好的固定化作用。该免烧陶粒对重金属离子具有很好的去除效果,具备较好的应用前景。     

水泥对垃圾焚烧飞灰中重金属的固化研究

采用水泥固化法处理垃圾焚烧飞灰,研究了飞灰与水泥质量比、养护时间、添加剂和化学预处理对垃圾焚烧飞灰固化块中重金属Zn、Pb、Cu、Cd、Cr浸出的影响.结果表明,当飞灰与水泥质量比为3:4,养护时间为11d的条件下,以砂浆塑化剂为添加剂,固化块Pb、Cu、Cd和Cr的浸出浓度分别降低了72.4％、70.6％、60.0％...     

流化床飞灰固化焚烧飞灰效果及微观分析

以深圳某垃圾焚烧厂焚烧飞灰为例分析了焚烧飞灰的性质和重金属毒性.结果表明,飞灰中 Pb 和 Cr 超出TCLP 阈值,必须进行稳定化处理.以流化床飞灰为主要成分配制固化材料,按不同比例掺人焚烧l￡灰进行固化实验,结果表明,实验范围内重金属固定效果良好.微观测试显示,固化过程主要产物有水化硅酸钙凝胶、钙矾石等,通过物理包胶、物理吸附、复分解沉淀反应和同晶替代等作用抑制重金属浸出.     

Immobilization of heavy metals in polluted soils by the addition of zeolitic material synthesized from coal fly ash

The use of zeolitic material synthesized from coal fly ash for the immobilization of pollutants in contaminated soils was investigated in experimental plots in the Guadiamar Valley (SW Spain). This area was affected by a pyrite slurry spill in April 1998. Although reclamation activities were completed in a few months, residual pyrite slurry mixed with soil accounted for relatively high leachable levels of trace elements such as Zn, Pb, As, Cu, Sb, Co, Tl and Cd. Phytoremediation strategies were adopted for the final recovery of the polluted soils. The immobilization of metals had previously been undertaken to avoid leaching processes and the consequent groundwater pollution. To this end, 1100 kg of high NaP1 (Na6[(AlO2)6(SiO2)10] .15H2O) zeolitic material was synthesized using fly ash from the Teruel power plant (NE Spain), in a 10 m3 reactor. This zeolitic material was manually applied using different doses (10000-25000 kg per hectare), into the 25 cm topsoil. Another plot (control) was maintained without zeolite. Sampling was carried out 1 and 2 years after the zeolite addition. The results show that the zeolitic material considerably decreases the leaching of Cd, Co, Cu, Ni, and Zn. The sorption of metals in soil clay minerals (illite) proved to be the main cause contributing to the immobilization of these pollutants. This sorption could be a consequence of the rise in pH from 3.3 to 7.6 owing to the alkalinity of the zeolitic material added (caused by traces of free lime in the fly ash, or residual NaOH from synthesis).     

粉煤灰提取液的絮凝效应

为了回收利用粉煤灰,采用盐酸浸提法制备粉煤灰提取液（CFAL）用作絮凝剂。通过单因素实验优化CFAL的制备条件,并在高岭土模拟体系内研究CFAL的絮凝效应。研究在不同CFAL投加量下浊度的去除率,确定最佳的投加剂量及在此剂量下絮体的大小与沉降性能。对原浊度为100 NTU的高岭土悬浊液,当CFAL为0.44 mg·L-1（以Al的含量计）时,浊度去除率达到90%以上。在同等剂量下,聚合氯化铝（PAC）和氯化铝（AlCl3）的浊度去除率均低于CFAL,分别为78.7%和79.2%。CFAL的絮体大小约为400 μm,沉降较快,在20 min后,去除率达到90%以上;PAC和AlCl3的絮体分别为260和330 μm,分别沉降60和40 min后,去除率稳定在80%左右。在实验剂量范围内,CFAL絮凝后对高岭土悬浊液的pH不会造成明显影响,且余铝满足《生活饮用水卫生标准》（GB 5749-2006）,CFAL是一种廉价、高效、安全的混凝剂。     

Removal of PCBs from wastewater using fly ash

Liquids and sludges containing polychlorinated biphenyls (PCBs) can be treated to concentrate the PCBs in a solid residue. The latter can then be handled to destroy the PCBs. A study on sorption kinetics of PCBs on fly ash was conducted in controlled batch systems. TCB and HeCB are removed at 25 degrees C by adsorption on fly ash up to 97% at pH 7, with an adsorbent dose of 5 g/l. An examination of the thermodynamic parameters shows that the adsorption of TCB and HeCB by fly ash is a process occurring spontaneously at ambient conditions. Activation energies for the sorption process ranged between 5.6 and 49.1 kJ/mol. It was observed that the rate at which TCB and HeCB are adsorbed onto fly ash showed a diffusion limitation. The uptake rate of TCB and HeCB increases with increasing initial concentration and gradually tends to a constant value. A decrease in the adsorption of TCB and HeCB was observed when interfering ions and other PCB congeners were present. Changing the pH in the aqueous solution from 2 to 10 had no effect on the adsorption process. Overall, fly ash can be used for an efficient removal of PCBs from several aqueous solutions.     

Stabilization of Pb- and Cu-contaminated soil using coal fly ash and peat

The stabilization of metal contaminated soil is being tested as an alternative remediation method to landfilling. An evaluation of the changes in Cu and Pb mobility and bioavailability in soil induced by the addition of coal fly ash and natural organic matter (peat) revealed that the amount of leached Cu decreased by 98.2% and Pb by 99.9%, as assessed by a batch test. Metal leaching from the treated soil was lower by two orders of magnitude compared to the untreated soil in the field lysimeters. A possible formation of mineral Cu- and Pb-bearing phases and active surface with oxides were identified by chemical equilibrium calculations. Low metal leaching during a two-year observation period, increased seed germination rate, reduced metal accumulation in plant shoots, and decreased toxicity to plants and bacteria, thereby demonstrating this stabilization method to be a promising technique for in situ remediation of Cu and Pb contaminated soil.     

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.     

粉煤灰制备高纯分子筛及对氨氮的去除

结合碱熔处理和引入晶种的方法,用粉煤灰制备出高纯的分子筛。运用XRD,SEM和BET等技术手段对制备的纯分子筛的晶体类型,形貌结构和物理参数等进行表征。通过续批实验,研究了pH值,投加量和初始氨氮浓度对氨氮去除的影响。实验结果表明,这些实验参数对于制备的分子筛去除氨氮有着重要的影响。其动力学行为非常符合准二级动力学方程。Langmuir方程能较好描述分子筛对氨氮的等温吸附过程,相关系数为0.9919。因此,利用粉煤灰制备高纯分子筛可以高效去除氨氮并达到"以废治废"的价值。     

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.     

烧结活化-酸浸法浸出粉煤灰中铝元素

为实现粉煤灰的高效资源化,并控制资源化过程中的能耗,采用NaOH为烧结助剂,利用烧结活化-酸浸法浸出粉煤灰中的铝元素;在探究最佳工艺条件的同时,通过分析烧结产物矿物组成及官能团的变化来探究粉煤灰烧结活化的机理。结果表明,当烧结温度为550 °C、NaOH/CFA 质量比=1.40、硫酸浓度为30%、烧结时间为10 min的条件下,铝元素浸出率可达95.00%以上。在粉煤灰烧结活化过程中,莫来石及非晶态硅铝化合物与NaOH反应,其中的铝氧八面体结构转变为铝氧四面体结构,铝氧四面体与硅氧四面体结构相结合形成以四元环和六元环为基本结构的铝硅酸盐,即八面沸石和霞石。在酸浸过程中,八面沸石和霞石与硫酸发生反应使铝元素以离子形式存在于酸浸液中,其中霞石相更有利于烧结产物的酸浸过程。该研究结果可为烧结活化-酸浸法浸出粉煤灰中铝元素提供参考。     

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.     

Process optimization for enhanced carbon capture and cyclic stability using adsorbents derived from coal fly ash

Environmental Science and Pollution Research - Zeolites and metal–organic frameworks (MOFs) are popular adsorbents when it comes to capturing CO2 from the gaseous feed stream. In this study,...     

生活垃圾焚烧飞灰重金属的受热特性

研究了飞灰重金属在不同煅烧温度下的挥发情况及其存在形态.结果表明:重金属挥发能力由强到弱依次为Hg＞Pb＞As、Cd＞Zn＞Cr、Ni、Cu;其中Hg、Pb、As和Cd属易挥发重金属,在1 150 ℃时几乎全部挥发;Zn属较易挥发重金属,1 150 ℃时的挥发率在40%～50%;Cr、Ni和Cu属难挥发重金属,在1 150 ℃的挥发率不超过10%;在400～1 150 ℃,随温度的升高,部分Zn、Hg、Cu、Pb、Cd、Ni和As由可溶态向残渣态、铁锰氧化态转化;在400～900 ℃,随温度的升高Cr可溶态比例减少,而在900～1 150 ℃,随温度的升高其可溶态比例增加.     

螯合剂与水泥协同稳定垃圾焚烧飞灰中的重金属

开展了水泥和螯合剂协同处置全烧垃圾循环流化床炉飞灰的研究,并对经济性进行了分析.实验结果表明,当水泥添加比例为30%时,重金属的浸出毒性均低于生活垃圾填埋污染物控制标准的规定.有机硫螯合剂TMT(三巯基均三嗪三钠盐类)对Cu、Pb、Cd的稳定效果最好,有机硫螯合剂DTCR(二硫代氨基甲酸盐衍生物)以Cu、Pb最佳,同等有效添加量时TMT的稳定效果优于DTCR,完全达标时二者所需的添加量分别为2%和3%.水泥和螯合剂协同处置时,满足生活垃圾填埋标准的水泥和螯合剂之间的用量关系并非为线性.螯合剂在实现减容化的同时,存在成本提高的问题,以DTCR为例,在兼顾经济性和增容性时水泥用量可以控制在20%,稳定剂为1.75%.     

粉煤灰吸附除磷的改性研究

研究了粉煤灰的最佳改性条件及其吸附理论模型.获得了粉煤灰用于吸附含磷量为5 mg P/L的模拟二级出水的3种改性的最佳条件(21℃):(1)0.25 mol/L盐酸改性的粉煤灰对磷的去除率为76.0%,出水含1.20 mg P/L;(2)300℃下煅烧的粉煤灰对磷的去除率为93.8%,出水中磷含量达到了0.31 mg P/L;(3)低火(119 W)改性的粉煤灰的磷去除率达95.4%,出水含0.23 mg P/L.试验结果表明:Langmuir方程能很好地解释两种改性粉煤灰的吸附动力学(R2=0.9188,S.E=0.0032),而Simple Elovieh方程在描述两者的吸附动力学试验数据上显示出优越性(R2=0.9427,S.E=0.029).     

Application of surface-deposition models to size-fractionated coal fly ash

Stack fly ash emitted from a large, coal-fired power plant was separated in situ into 8 or 12 discrete fractions with inertial cascade impactors. The fractions, ranging in size from 0.1 to 50 μm and including three fractions with aerodynamic mass dia. ≥ 1 μm, were previously analyzed for up to 43 elements by instrumental neutron-activation analysis. In this report geometric and theoretical surface deposition models are used to estimate the depth of the surface layer as well as the concentrations of enriched elements in the surface layer. The results indicate that the thickness of the surface layer is small, even at particle sizes of 0.1 μm where it is estimated to be about 20% of the particle diameter. The behavior of the relative concentrations of surface-enriched elements as a function of particle size was consistent with the slip-flow regime of aerosol mechanics.     

不同释钾菌对粉煤灰的生态效应

粉煤灰治理难度大,但它含有植物生长必需的营养元素钾,将其就地资源化生物利用是一条较好的途径。释钾菌是一种能把矿物中的难溶性钾转化为有效钾的细菌,从土壤中筛选出2种释钾菌,经过在粉煤灰基质中的驯化培养,通过盆栽试验种植紫花苜蓿,比较不同菌株对粉煤灰的改良作用及其对植物生长的影响。结果表明,筛选出的菌株C6对粉煤灰中速效钾的释放效果明显,降低了基质pH,显著地促进了植物的生长,对粉煤灰生态修复具有重要意义。