Effect of curing conditions on the hydration and performance of CFBC ash cementitious system

Circulating fluidized bed combustion （CFBC） ash can be used as supplementary cementitious material for concrete production for its high pozzolanic activity. We investigated the effect of curing conditions on the hydration and performance of CFBC ash-Portland cement system （30： 70, by mass） including hydration products, paste microstructure, linear expansion ratio, chemically combined water content and compressive strength. The results show that tobermorite rather than ettringite is generated under the condition of autoclaved curing. The expansion and mortar strength of the system cured in water is higher than those cured in air at a given age, and the strength and bulk volume may retract under the condition of air curing. In addition, autoclaved curing facilitates the increase of strength gain at early curing ages （the increase rate lowers down in the following ages） and the improvement of system volume stability. It is suggested that sufficient water is necessary for the curing of CFBC ash cementitious system, and autoclaved curing may be considered where volume stability is a primary concern.     

Adsorption mechanism of polycarboxylate-based superplasticizer in CFBC ash-Portland cement paste

Circulating fluidized bed combustion （CFBC） ash exhibits the desirable pozzolanic activity which makes it a potential supplementary cementitious material to replace cement for concrete production. However, the high unburnt carbon content and porous surface structure of CFBC ash may adsorb water reducer and thereby significantly reduce the efficiency of water-reducing agents. The adsorption mechanism of polycarboxylate superplasticizer in CFBC ash-Portland cement paste was investigated by ultraviolet-visible spectrophotometer, and the conception of ＂invalid adsorption site＂ of CFBC ash was presented. The results show that the adsorption behavior of polycarboxylate superplasticizer in coal ash-Portland cement paste can be described by Langmuir isothermal adsorption equation. The adsorption capacity of CFBC ash-Portland cement paste is higher than that of pulverized coal combustion （PCC） fly ash-Portland cement paste. Moreover, the adsorption amount of polycarboxylate superplasticizer increases with the ratio of ash-to-cement in the paste. At last, the fluidity of CFBC ash-Portland cement paste is lower than that of the PCC fly ash paste. This work suggests that when CFBC ash is used as concrete admixture, the poor flowability of the cementitious system due to the high adsorption of water and water-reducing agent should be taken into consideration.     

Pozzolanic reaction kinetics of coal ashes

The pozzolanic reactivity was determined by the hydration kinetics of pozzolanic reaction based on the fact that the hydration products of active SiO₂ and Al₂O₃ with lime were soluble in dilute hydrochloric acid. The results show that the pozzolanic reaction of active SiO₂ and Al₂O₃ of coal ashes follows apparent first-order kinetics. The reaction rate constant of FBC ashes is greater than that of PC ashes, while the activation energy of the former is lower than that of the latter. It is confirmed that the pozzolanic activity of fluidized bed combustion(FBC) ashes is significantly higher than that of PC ashes, and the reaction barrier of the former is lower than that of the latter, because the microstructures of FBC ashes, such as mineralogical composition, morphology and polymerization degree of [SiO₄] and [AlO₆] are more favorable to the pozzolanic activity development than those of PC ashes. Funded by the National Natural Science Foundation of China (No. 50802080) and Shandong Provincial Scientific Research Foundation for Excellent Young Scientists (No.2008BS09005)     

电厂煤粉炉联产水泥熟料技术试验研究

以低硫兖州煤和高硫长广煤为试验煤种,在两段多相试验台开展了煤粉炉联产水泥熟料技术试验研究.试验结果表明:低硫兖州煤和高硫长广煤联产水泥熟料试验样品的固硫率均在50%左右,高于煤粉炉仅为30%的炉内喷钙脱硫效率,样品熟料矿物与普通水泥熟料矿物组成相似、性能相近.通过对样品熟料矿物的特征分析,提出了开展电厂煤粉炉联产水泥熟料技术研究的重点.     

Removal of Cr (VI) from aqueous solution using ultrafine coal fly ash

Coal fly ashes WSRA and BQRA were ball milled for 5 h to produce their ultrafine coal fly ashes WSUA and BQUA, respectively. Batch kinetic, isotherm and pH effect on adsorption were studied to evaluate removal of Cr (VI) from aqueous solutions by ultrafine coal fly ashes comparing with raw coal fly ashes. The kinetics of adsorption indicates the process to be intraparticle diffusion controlled and follows the Lagergren first-order kinetics for all coal fly ashes. The first-order rate constants (k ₁) of Cr (VI) adsorption onto WSRA, WSUA, BQRA and BQUA are 1.981, 1.497, 2.119 and 1.500 (×10⁻²) min⁻¹, respectively. The adsorption capacities of WSUA and BQUA are much better than those of WSRA and BQRA. Equilibrium adsorption data of all coal fly ashes well satisfy the Langmuir isotherm. The adsorbed amounts of Cr (VI) onto WSUA and BQUA decrease from pH 2 to pH 6 and then increase up to pH 12.     

细粒煤重介质离心分选脱硫试验研究

在重介质条件下利用Falcon离心重力分选系统,研究了-500μm不同窄粒级南桐细粒煤的脱硫降灰效果.采用可燃体回收率、脱灰率、脱硫率、脱硫效率4个指标,对比分析了Falcon重介离心分选和常规浮选对南桐细粒高硫煤各粒级的分选效果,结果表明:对于-500μm细粒级煤,脱灰率低于常规浮选,而其余3个指标均高于浮选.125μm是分选效果的显著分界粒度,500～125μm粒级煤的脱硫率、脱灰率高于浮选,而可燃体回收率低于浮选.-125μm粒级煤的脱硫率、脱灰率低于浮选,而可燃体回收率高于浮选.     

微细化煤粉灰中化学成分及其对燃煤NOx,SOx的影响

以混煤(神华烟煤和准格尔褐煤)、大同烟煤、邢台贫煤微细化煤粉为分析样品,采用标准方法对其灰分中的化学成分进行实验分析,研究微细化煤粉的种类、细度对灰分中化学成分的影响规律和影响机制。分析了煤灰分中的化学成分对煤粉燃烧过程中NOx,SOx等气态污染物产生的影响机理。     

Properties and mechanism of CFBC fly ash-cement based stabilizers for lake sludge

Circulating fluidized bed combustion(CFBC) fly ash was mixed with cement or lime at a different ratio as a stabilizer to stabilize lake sludge.In order to understand the influences of stabilizers on the lake sludge properties,tests unconfined compressive strength,water stability and SEM observation were performed.The experimental results show that with the increase of the curing time,the strength of all the stabilized specimens increase,especially the samples containing cement.The strength of the specimens is decreased with the increasing of the CFBC fly ash/cement ratio,the optimum ratio between CFBC fly ash and cement is 2:3.The water stability of CFBC fly ash-cement based stabilizers is higher than those of cement and lime.Moreover,the lake sludge stabilization mechanism of CFBC fly ash-cement based stabilizers includes gelation and filling of the hydration products,i e,C-S-H gel and the AFt crystal,which act as benders to solidify those particles together and fill in the packing void of the aggregates.     

Removal of Cr (VI) from Aqueous Solution Using Ultrafine Coal Fly Ash

Coal fly ashes WSRA and BQRA were ball milled for 5 h to produce their ultrafine coal fly ashes WSUA and BQUA, respectively. Batch kinetic, isotherm and pH effect on adsorption were studied to evaluate removal of Cr (VI) from aqueous solutions by ultrafine coal fly ashes comparing with raw coal fly ashes. The kinetics of adsorption indicates the process to be intraparticle diffusion controlled and follows the Lagergren first-order kinetics for all coal fly ashes. The first-order rate constants (k1) of Cr (V...     

Chemial Bond and Stability of Adsorption of [Au(AsS_3)]~(2-)on the Surface of Kaolinite

1　IntroductionKaoliniteisoneofthemostwide spreadphyllosili catesintheearthcrust.Thegoldiscloselyrelatedtoclayinmanysubmicrometergoldminerals .Itisimportanttostudytheinterrelationbetweengoldandclayforunder standingthecloseassociationofgoldandclaymineralsa…     

Quantum Chemistry Calculations on the Interaction Between Kaolinite and Gold

The density function and discrete variation method ( DFT - DVM) is used to study the interaction between kaolinite and gold. The correlation among the structure, chemical bond and stability is discussed. Several models are selected without gold and with gold in different directions and sites . The results show that the models with gold on the edge of kaolinite basal layer are more stable than those with gold above or under the layer, the models ivith gold near to [ A1O2 ( OH)4 ] octahedra are more stable than those with gold near to the vacancy without aluminium. The interaction between gold and the surface ions of kaolinite is strong enough to form the surface complexes.     

粉煤灰及其硬化体中六价铬离子的溶出现象

粉煤灰中含有一定数量的六价铬离子，鉴于粉煤灰使用的广泛性和六价铬离子对人体与生态的危害性，必须就粉煤灰中六价铬离子的溶出性能和溶出抑制方法进行研究，并制定相应的对策与措施以指导粉煤灰的合理与安全使用。探讨了粉煤灰和粉煤灰硬化体中六价铬离子的溶出性能。研究结果表明，无论是粉煤灰本身还是自干硬击实粉煤灰硬化体或粉煤灰泥浆硬化体，都有一定数量的六价铬离子溶出，其溶出量与粉煤灰的铬含量、比表面积及粒径、火山灰活性和试体成型方法等有关。一般来说，干硬击实粉煤灰硬化体中六价铬离子的溶出量较泥浆硬化体的高。     

生活垃圾焚烧飞灰重金属特性分析

对国内四个不同的垃圾焚烧厂产生的飞灰进行物理及化学特性分析.四种飞灰在颗粒尺寸分布上有相似的规律,飞灰中重金属的质量分数分析结果表明采用纯垃圾焚烧的炉排炉飞灰中的质量分数高于掺煤混烧的流化床焚烧飞灰中的质量分数.随着飞灰颗粒尺寸的减小,飞灰中重金属的浓度呈现增加的趋势.飞灰的渗滤特性表明,飞灰中Ca质量分数越高,飞灰的酸中合能力越强,且重金属的渗出率受飞灰渗滤液的pH影响大,而在碱性渗滤条件下受飞灰中重金属质量分数的影响小.     

CFBC锅炉安全经济运行中三大顽症的治理之一——CFBC锅炉入炉煤颗粒度优选及煤的制备

煤的制备系统能否提供符合要求的入炉煤是CFBC锅炉安全、经济运行的根本保证。通过对入炉煤颗粒度对CFBC锅炉的流化质量、燃烧效率与脱硫效率、传热系数以及对炉内受热面和炉壁磨损的影响的定性和定量的分析,并结合实验和实测的数据,指出对于入炉煤粒径范围的选择,不仅要限制其最大的颗粒直径,更重要的是选择合理的颗粒筛分分布,保证有足够的循环物料量。为CFBC锅炉的经济运行及其煤的制备系统的合理设计指明了方向。     

不同生物质活性炭脱除烟气中SO_2/NO_x的实验研究

利用锯末、麦秸、麦秸掺10%煤3种生物质颗粒制取的活性炭,根据比表面积、孔径分布、孔容、微孔结构、碱金属含量等特征参数讨论了活性炭品质。利用立式固定床管式炉系统进行了活性炭颗粒的烟气脱硫脱氮实验,研究了不同的活性炭原材料、工作温度对联合脱硫脱氮性能的影响,对脱除机理进行了分析。通过综合比较分析表明:秸秆加煤材料的活性炭在较长的时间里维持脱硫效率95%以上和脱氮效率85%以上;其在工作温度较低(70℃)时以物理吸附为主,在较高的工作温度(130℃)以化学吸附为主,均具有良好的吸附性能。     

弱还原气氛下淮南煤灰矿物质特性研究

对淮南煤在弱还原气氛下的矿物质特性进行实验研究,用X-射线衍射和红外光谱分析不同温度下煤灰矿物组成变化。结果表明：淮南煤中主要晶体矿物有高岭石、石英、方解石、黄铁矿等,高岭石类矿物含量越高,煤灰熔点越高;方解石和黄铁矿含量越高,煤灰熔点越低。煤灰中主要晶体矿物有石英、硬石膏、赤铁矿等,硬石膏和赤铁矿含量越高煤灰熔点越低。随着温度的升高,煤灰中石英、硬石膏、赤铁矿等结晶矿物含量逐渐减少,生成新的矿物质,莫来石的生成是导致淮南煤灰熔点高的主要原因,钙长石起到降低灰熔点的作用。     

淮南电厂粉煤灰的物质组成特征及其评价

利用XRF、XRD和ICP-MS等方法,对淮南电厂采集的20个粉煤灰样品的化学成分、矿物成分和微量元素的含量进行测试分析,并在分析的基础上,对淮南电厂粉煤灰中有害元素进行环境影响评价,并结合当前粉煤灰的利用情况,提出了合理的资源化利用途径。     

超声波处理对煤泥特性的影响研究

为了提高煤泥浮选的效率和选择性，提出了在浮选前对煤泥进行超声波预处理的方法．利用扫描电镜、激光粒度仪和图像识别软件等研究了超声处理对煤泥特性的影响．比较了超声波处理前后相同粒级煤泥的产率、硫分、灰分和圆形系数，分析了超声波处理前后煤泥颗粒的表面状态，并用真空浮选试验进行了验证．浮选速度试验结果表明，超声处理后精煤的硫分、灰分较超声波处理前分别降低了33．84％和32．09％，前2min的精煤产率平均提高了约10％．试验证明超声处理改变了煤泥颗粒的大小、形状以及煤粒表面的状态，促使煤粒与黄铁矿、矸石解离，因此超声波预处理是煤泥浮选脱硫降灰的一种有效方法．     

流化床燃煤固硫渣火山灰活性评定的探讨

流化床燃煤固硫渣是一种特殊的、具有火山灰活性的燃煤副产品,由于其f-CaO和SO3含量较普通煤粉锅炉灰渣高,具有一定的自硬性和膨胀性,目前尚无统一的方法或标准准确评定其火山灰活性,影响了该燃煤副产品的建材资源化利用。根据流化床燃煤固硫渣火山灰活性来源及其特点,参照《用于水泥中的火山灰质混合材料》GB2847和《用于水泥混合材料的工业废渣活性试验方法》GB12957-91,提出采用“水泥熟料胶砂28天抗压强度比”来评定流化床燃煤固流渣的火山灰活性。试验研究表明该方法测定的火山灰活性与其自硬性强度和活性率具有较好的一致性。     

新型固化剂GSC固化软土的力学性能试验研究

利用脱硫石膏及钢渣-矿渣复合胶凝材料(简称GSC)固化软土,既可以充分利用工业废渣,减少二次污染,又可以节约矿产资源,保护自然生态。通过研究在不同掺入比、不同水灰比和不同龄期时GSC固化土的无侧限抗压强度试验结果,分析了掺入比、水灰比、龄期对固化土强度的影响;同时引入似水灰比对GSC固化土后期强度进行预测。研究结果表明,GSC掺入比越大,对软土的固化效果越好,GSC固化土无侧限抗压强度随龄期的增长规律与水泥土一致但早期强度比水泥土低,当GSC掺入比高于水泥掺入比3%,在龄期达到28d后,如果GSC的水灰比小于水泥的水灰比时,GSC固化土的强度高于水泥土的强度,因此用GSC替代水泥作为软土固化剂可以满足固化土强度要求。