非饱和压实膨胀土掺煤矸石的特性研究

研究了掺煤矸石的非饱和压实膨胀土的工程性质。通过击实实验确定混合料的最佳含水率和最大干容重;在最佳含水率、不同的煤矸石掺量和控制压实度条件下,通过加州承载比实验测得CBR值和膨胀率;由直剪实验测定混合料的黏聚力(c)和内摩擦角(φ);利用滤纸法在3种控制压实度、5种控制含水率、不同煤矸石掺量组合条件下测定混合料的吸力。实验结果表明:随着煤矸石掺量的增加,膨胀土的最佳含水率随之降低,最大干容重逐渐增大;当煤矸石掺量在25%~35%之间,混合料的c、φ值得到明显提高;当煤矸石掺量大于35%时可较大地提高CBR值和降低膨胀率,可取得较好的压实效果,满足各级公路全厚式填筑路堤的强度要求;掺入煤矸石后,同一压实度条件下,随着煤矸石掺量的增加,混合料的吸力随之降低,利于降低膨胀土的膨胀率,减少吸水膨胀变形破坏。     

控制酸性矿山废水的污泥屏障压缩特性

污泥屏障通过物理拦截以及化学作用可以有效控制重金属离子迁移,采用污泥屏障处理酸性矿山废水(AMD)已被证明具有可行性.作为尾矿渣处置场屏障的主体材料,研究污泥压缩特性很有必要.实验结果表明,对于含水率相同的压实污泥试样,孔隙比随干密度增大而减小,最终趋于1;干密度相同的试样,最优含水率的孔隙比随应力增大减小最快.试样压缩系数随干密度增大而减小,随含水率增大先增大后减小,最优含水率的压缩系数为0.8 MPa-1.AMD溶液作孔隙液能提高试样压缩系数.通过对比分析有机质土的压缩特性,为以后的深化研究提供相关参数支持.     

消化污泥作为垃圾填埋场覆盖材料的研究

为解决城市污染,实现污泥"减量化、无害化、稳定化、资源化"的目标,有必要寻求更多技术上可行、低成本的污泥综合利用新技术.测定了消化污泥本底的含水率、有机质含量以及经过预处理后不同含水率的消化污泥模拟降雨实验的渗透系数,浸出液的COD、氨氮、pH等.选择渗透系数低、污染负荷小的含水率为50%和60%的消化污泥,分别与石灰、炉渣以不同比例混合改性后,再测定模拟降雨实验浸出液的各个指标.实验结果表明,含水率为60%的消化污泥与炉渣以2∶1(质量比)混合时,渗透系数达到10-6数量级,已接近垃圾填埋场对防渗层的要求.因此,消化污泥改性后可作为垃圾填埋场覆盖材料.     

改性土-膨润土阻隔墙阻控离子型稀土矿氨氮污染

以土-膨润土为阻隔材料,使用硅灰及水泥对其进行固化改性,研究改性后阻隔墙对离子型稀土矿原地浸矿氨氮污染的阻控效果。通过了解阻隔墙材料的渗透性能、力学性能,并结合阻隔材料对氨氮的吸附效果、穿透效果和数值模拟结果,探讨改性土-膨润土阻隔材料对氨氮污染的阻控性能。结果表明:硅灰改性土-膨润土阻隔材料,最佳质量配比为硅灰∶土=1∶10,最佳含水率为67.80%;改性阻隔材料生成的铝硅酸盐提高了阻隔墙防渗性能,渗透系数为2.36×10~(-9) m·s~(-1);CaCO_3提高了材料的力学性能,使抗压强度达到0.896 MPa;改性阻隔材料对氨氮的吸附过程符合准二级动力学模型及Langmuir等温模型。这说明该吸附过程以化学吸附为主,并且该吸附是放热过程。在不同氨氮浓度的穿透下,渗透系数呈逐渐减小的趋势,实验期间并未达到穿透浓度。利用Visual MODFLOW数值模型对阻隔墙的阻控效果进行模拟发现,7 300 d后NH_4~+扩散范围小,未穿透阻隔墙。硅灰改性土-膨润土阻隔墙用于对离子型稀土矿氨氮污染阻控的效果较好。     

矿区炼金废渣的固化/稳定化处理

通过对金矿矿区炼金废渣的酸中和能力、净产酸量及浸出毒性实验，测定了废渣的产酸潜力及重金属砷、镉、铅、锌的总量和它们的浸出量。为了合理处置矿区炼金废渣，并为矿区重金属污染土壤的修复提供技术支持，采用石灰、粉煤灰、堆肥化污泥作为添加剂对废渣进行固化/稳定化处理；通过浸出毒性实验对固化/稳定化处理效果进行综合分析，试图寻求一种最佳的稳定剂。结果表明，无论是单独添加石灰、粉煤灰或者堆肥化污泥还是两两组合混合添加，样品浸出液的pH都有升高，As、Cd的浸出浓度都有明显下降，而且两两组合添加比单独添加的固化/稳定化处理效果更好。在两两组合添加中，粉煤灰混合堆肥化污泥的处理效果最好，浸出液的pH值达到7.82，As、Cd的浸出率分别下降72.0%和72.2%。说明粉煤灰混合堆肥化污泥处理炼金废渣效果最佳，同时具有以废治污的资源化生态效能。     

垃圾堆体固有渗透与孔隙度协同演化特征实验研究

为探讨上覆载荷作用下垃圾堆体渗透特性的变化规律,采用自制的生活垃圾渗透率/孔隙度测试实验装置,研究了不同载荷、不同压实密度及不同含水率对垃圾堆体固有渗透率和孔隙度变化规律的影响,并构建了固有渗透率与孔隙度之间的协同表征模型。结果表明,压实密度与上覆载荷呈指数递增的变化形式;随着含水率的增大,垃圾固有渗透率显著降低;垃圾固有渗透率随孔隙度的减小呈现指数递减,传统K-C模型无法描述这一变化规律,而幂函数形式(κ=AnB)和线性形式(lg(κ)=a+blg(n))2种协同表征模型均与实验结果达到了良好的拟合效果,验证了2种模型的可靠性;随着模型尺度的增大,固有渗透率从10-15m2量级增加至10-12m2量级,孔隙度从0.378增加至0.685。     

响应曲面法优化微波修复二甲苯污染土壤工艺参数

目前土壤污染问题得到越来越多的关注,污染土壤修复技术的研究更加受到重视。通过单因素和响应曲面法优化实验,研究了含水率、处理量、辐照时间和微波功率对二甲苯去除效果的影响,并且对不同敏化剂的作用进行了实验研究。结果表明,微波功率、辐照时间和含水率对二甲苯的去除率均有显著影响。模型优化结果显示,微波修复二甲苯污染土壤的最佳工艺参数为:微波功率530W,辐照时间3.4min,含水率32%,去除率可达到79.75%,实验验证结果与预测值之间相对误差为1.89%。活性炭在反应过程中主要起吸附作用,粉煤灰的添加对二甲苯的去除有非常显著的作用,去除率最高可达到98.42%。     

垃圾填埋场生物覆盖材料筛选及甲烷减排

通过模拟柱实验研究了消化污泥、矿化垃圾和黏土作为垃圾填埋场生物覆盖材料的甲烷氧化能力。3种材料的甲烷日氧化率平均值、总氧化率和氧化速率V(CH4)分别是:消化污泥10.27%、75.82%、1.76 mmol/(kg·d);矿化垃圾11.05%、75.61%、2.04 mmol/(kg·d);黏土9.05%、68.15%、1.33 mmol/(kg·d),消化污泥和矿化垃圾对甲烷的氧化能力均大于黏土。进一步探讨了消化污泥中添加粉煤灰、建筑垃圾和黏土进行改性后对甲烷的氧化能力,考察了改性污泥的渗透系数和抗压强度。结果表明:粉煤灰对消化污泥的改性效果最好,其日氧化率平均值、总氧化率和V(CH4)分别达到17.27%、92.37%和2.35 mmol/(kg·d),粉煤灰与消化污泥以1∶1～1.5∶1混配后可满足填埋场对覆盖材料渗透系数和抗压强度的要求。     

电渗透脱水污泥干燥特性曲线及干燥模型

通过电渗透脱水技术及自然风干技术两种预处理方式降低污泥含水率，当污泥初始含水率相近时，研究经两种方式处理后污泥的干燥特性曲线，并对电渗透脱水污泥干燥特性曲线的优势情况进行探讨。在40—120℃的低温条件下，研究电渗透脱水污泥（泥饼厚度为3．5mm）的干燥特性曲线并分析其干燥特性。通过所得电渗透脱水污泥的干燥特性曲线，引人薄层污泥干燥模型进行数值分析。结果表明，在实验条件下，电渗透脱水污泥的干燥速率要优于自然风干污泥的干燥速率。随着温度的升高，电渗透脱水污泥的干燥速率随之升高，干燥到所需含水率的时间则随之减少。Logarithmic模型比其他模型更适合描述薄层电渗透脱水污泥在低温条件下的干燥特性。     

粉煤灰的改性及其在垃圾渗滤液深度处理中的应用研究

实验采用物理方法和化学方法对粉煤灰进行改性,并用改性粉煤灰深度处理垃圾渗滤液。通过扫描电镜和X-射线衍射对改性前后粉煤灰的表面结构和主要晶相组成进行分析,同时考察其在垃圾渗滤液深度处理中的吸附效果。结果表明,改性后粉煤灰的比表面积和孔隙度增大,吸附能力增强。通过比较,吸附能力最强的改性粉煤灰是将引发剂A与粉煤灰以质量比为1∶9的比例混合,在800℃下恒温焙烧2 h所制得的改性粉煤灰,该改性粉煤灰对垃圾渗滤液中COD和色度的去除率可达到67.3%和87.3%,相对于改性前去除率提高了96.0%和57.8%。     

A pilot study of mercury liberation and capture from coal-fired power plant fly ash

The coal-fired electric utility generation industry has been identified as the largest anthropogenic source of mercury (Hg) emissions in the United States. One of the promising techniques for Hg removal from flue gas is activated carbon injection (ACI). The aim of this project was to liberate Hg bound to fly ash and activated carbon after ACI and provide high-quality coal combustion products for use in construction materials. Both bench- and pilot-scale tests were conducted to liberate Hg using a thermal desorption process. The results indicated that up to 90% of the Hg could be liberated from the fly ash or fly-ash-and-activated-carbon mixture using a pilot-scale apparatus (air slide) at 538 degrees C with a very short retention time (less than 1 min). Scanning electron microscope (SEM) evaluation indicated no significant change in fly ash carbon particle morphology following the thermal treatment. Fly ash particles collected in the baghouse of the pilot-scale apparatus were smaller in size than those collected at the exit of the air slide. A similar trend was observed in carbon particles separated from the fly ash using froth flotation. The results of this study suggest a means for power plants to reduce the level of Hg in coal-combustion products and potentially recycle activated carbon while maintaining the resale value of fly ash. This technology is in the process of being patented.     

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.     

Joint US/USSR Test Program for Reducing Fly Ash Resistivity

An electrostatic precipitator preceded by a wet scrubber was tested at the Reftinskaya Power Station. The unit collects a high resistivity fly ash from the combustion of low sulfur Ekibastuz coal. The operating parameters of the precipitator were measured as well as the mass emissions and the in-situ electrical resistivity of the fly ash. Density, particle size distribution, electrical resistivity, and chemical composition were determined for collected samples of the fly ash. The fly ash was also characterized by x-ray diffraction and scanning electron microscopy. When a centrifugal wet wall scrubber was installed ahead of the electrostatic precipitator, the temperature of the flue gas entering the precipitator was decreased and the moisture content increased. The electrical resistivity of the fly ash was attenuated a decade, but not enough to overcome the adverse effects of back corona in the precipitator. Lowering the flue gas temperature to about 85°C by the addition of a venturi scrubber ahead of the centrifugal scrubber reduced the electrical resistivity of the fly ash another decade and allowed the operation of the precipitator without back corona.     

An Assessment of the Significance of Mercury Release from Coal Fly Ash

Abstract

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 ≤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.     

The leachability and chemical speciation of selected trace elements in fly ash from coal combustion and refuse incineration

A laboratory leaching test has been used to predict the potential mobility of As, Se, Pb and Cd in landfilled fly ash produced by coal combustion and refuse incineration. These waste residues also formed the basis of a speciation study in which the valency states of As and Se and the chemical forms of Pb and Cd have been determined. Selenium displayed the greatest leachability in each ash type, despite being present at relatively low concentrations in both materials. Substantial amounts of other trace elements were also leached, particularly Pb and Cd from refuse ash and As from coal ash. Chemical associations of Pb and Cd were examined by a sequential extraction procedure. In coal fly ash, both elements were mostly present in the residual fraction, while in refuse ash these elements were mainly associated with the exchangeable fraction. Water-soluble extracts of coal fly ash contained As exclusively as As(V); high background interference prevented the detection of water-soluble As in refuse ash. Selenium was present largely as Se(IV) in aqueous extracts of both ash types. The value of speciation techniques and leaching tests as predictors of environmental behaviour is discussed in conjunction with results of routine trace element determinations and plant uptake studies.     

Formation of Oxides of Nitrogen in Pulverized Coal Combustion

Nitrogen oxides are a potential atmospheric pollutant. Their formation and decomposition were studied in an experimental pulverized-coal-fired furnace. The concentration of nitrogen oxides (NO_x) was a maximum in the combustion zone and decreased as the combustion gas cooled. At a coal burning rate of 2 Ib/hr and 22% excess air, reduction of nitrogen oxides was obtained by selective secondary-air distribution. With 105% cf the stoichiometric air fed to the coal-combustion zone and 17% additional air fed just beyond the flame front, 62% reduction of NO_x occurred with good combustion efficiency. Lowering the quantity of excess air lowered the NO_x concentration, but at the expense of combustion efficiency. When 22% excess air was fed to the primary combustion zone, NO_x concentration in the effluent was 550 ppm and carbon in the fly ash 2.0%. With 5% excess air, the NO_x concentration fell to 210 ppm and carbon in the fly ash rose to 13.8%. With stoichiometric combustion the NO_x was 105 ppm a reduction of 81 %, and the carbon was 42.3%. Recirculation of combustion gas was not an effective means of lowering NO_x formation.     

Reduction of combustion by-products in WTE plants: O2 enrichment of underfire air in the MARTIN SYNCOM process

The SYNCOM process involves oxygen enrichment of underfire air, recirculation of flue gas and a combustion control system using infrared thermography of the waste layer on the grate. At the demonstration plant in Coburg, operational reliability and plant availability using SYNCOM could be proven under real disposal conditions with a waste throughput of 7 t/h. Oxygen enrichment of the underfire air promotes the destruction of pollutants due to the high oxygen partial pressures and temperatures. This is then reflected in very low residual amounts of organic combustion by-products in the bottom ash and flue gas from the SYNCOM unit. The flue gas concentrations of organic pollutants are reduced, as compared with conventional operation, by over 35% (for CO, total hydrocarbons and PCDD/F) at the boiler outlet. As the flue gas flow is reduced by oxygen enrichment and flue gas recirculation, the resulting reduction in terms of kg of pollutant per Mg of waste is even higher. In the bottom ash, the level of organic residues is reduced, by 45% in the case of loss on ignition and by 55% in the case of TOC and dioxins (I-TE of PCDD/F). This is due to the higher oxygen partial pressures and the fuel bed temperature which is increased by 135 to 1200 degrees C. Other important features of the process include more intense sintering and thus improved immobilization of the bottom ash, as well as reduced flue gas and fly ash flows.     

Arsenic and copper stabilisation in a contaminated soil by coal fly ash and green waste compost

In situ metal stabilisation by amendments has been demonstrated as an appealing low-cost remediation strategy for contaminated soil. This study investigated the short-term leaching behaviour and long-term stability of As and Cu in soil amended with coal fly ash and/or green waste compost. Locally abundant inorganic (limestone and bentonite) and carbonaceous (lignite) resources were also studied for comparison. Column leaching experiments revealed that coal fly ash outperformed limestone and bentonite amendments for As stabilisation. It also maintained the As stability under continuous leaching of acidic solution, which was potentially attributed to high-affinity adsorption, co-precipitation, and pozzolanic reaction of coal fly ash. However, Cu leaching in the column experiments could not be mitigated by any of these inorganic amendments, suggesting the need for co-addition of carbonaceous materials that provides strong chelation with oxygen-containing functional groups for Cu stabilisation. Green waste compost suppressed the Cu leaching more effectively than lignite due to the difference in chemical composition and dissolved organic matter. After 9-month soil incubation, coal fly ash was able to minimise the concentrations of As and Cu in the soil solution without the addition of carbonaceous materials. Nevertheless, leachability tests suggested that the provision of green waste compost and lignite augmented the simultaneous reduction of As and Cu leachability in a fairly aggressive leaching environment. These results highlight the importance of assessing stability and remobilisation of sequestered metals under varying environmental conditions for ensuring a plausible and enduring soil stabilisation.     

Batch test assessment of waste-to-energy combustion residues impacts on precipitate formation in landfill leachate collection systems

Disposal practices for bottom ash and fly ash from waste-to-energy (WTE) facilities include emplacement in ash monofills or co-disposal with municipal solid waste (MSW) and residues from water and wastewater treatment facilities. In some cases, WTE residues are used as daily cover in landfills that receive MSW. A recurring problem in many landfills is the development of calcium-based precipitates in leachate collection systems. Although MSW contains varying levels of calcium, WTE residues and treatment plant sludges have the potential to contribute concentrated sources of leachable minerals into landfill leachates. This study was conducted to evaluate the leachability of calcium and other minerals from residues generated by WTE combustion using residues obtained from three WTE facilities in Florida (two mass-burn and one refuse-derived fuel). Leaching potential was quantified as a function of contact time and liquid-to-solid ratios with batch tests and longer-term leaching tests using laboratory lysimeters to simulate an ash monofill containing fly ash and bottom ash. The leachate generated as a result of these tests had total dissolved solid (TDS) levels ranging from 5 to 320 mg TDS/g ash. Calcium was a major contributor to the TDS values, contributing from 20 to 105 g calcium/kg ash. Fly ash was a major contributor of leachable calcium. Precipitate formation in leachates from WTE combustion residues could be induced by adding mineral acids or through gas dissolution (carbon dioxide or air). Stabilization of residual calcium in fly ashes that are landfilled and/or the use of less leachable neutralization reagents during processing of acidic gases from WTE facilities could help to decrease the calcium levels in leachates and help to prevent precipitate formation in leachate collection systems.     

掺固硫灰AC-13型沥青混合料配合比设计

固硫灰是循环流化床锅炉燃煤固硫产生的废弃物,具有自硬性、火山灰活性和膨胀性等特性,若以其替代矿粉制备沥青混合料并用于道路工程建设中,将有望为固硫灰处理处置提供新途径。选用固硫灰做填料等量替代普通矿粉,通过马歇尔实验研究固硫灰不同替代量(0%、25%、50%、75%、100%)对AC-13型沥青混合料性能的影响,并对机理进行了分析。结果表明,掺固硫灰沥青混合料在一定油石比范围内均能满足现行规范要求,与普通矿粉沥青混合料相比,掺固硫灰沥青混合料水稳定性良好,压实度相同时,掺固硫灰沥青混合料具有更好的抗车辙性。