硅藻土的火山灰活性研究

采用ICP-OES法,研究了煅烧条件对硅藻土火山灰活性的影响.运用XRD、FT-IR、SEM及EDS等表征方法,对煅烧过程中硅藻土的物相、结构、形貌变化及火山灰活性的作用机理进行了研究和探讨.结果表明:700～1100.℃,硅藻土可基本保持多孔结构,仍含有适当数量的活性Si-OH,800℃煅烧硅藻土的火山灰活性最高;粘土矿物在700℃时脱去羟基水,继续升温使层状结构破坏,火山灰活性降低.800℃时保温1 h,可使火山灰活性成分含最由未煅烧时的22.15%提高到37.21%.硅藻土的火山灰活性变化的主要原因是高温作用下宏观孔道结构、表面结构和晶体结构变化综合作用的结果.     

Leaching characteristics of boron and selenium for various coal fly ashes

The leaching characteristics of B and Se for coal fly ash (CFA) were examined. Twenty-one CFA samples were subjected to a leaching test, in which CFA was shaken with pure water in a liquid to solid ratio (L/S) of 100 for 24 h at room temperature. The correlation between the leaching amount and the concentration of element in CFA was investigated. The leaching amounts of B, Ca, S, and Se were essentially dependent upon their concentrations in CFA. As the degree of % leaching was higher, the leaching amount was more dependent upon the concentration. Also, the leaching test was performed under constant pH conditions. The leaching of Se tended to increase as the pH in the aqueous phase was raised. For CFA samples, which gave large degree of Ca leaching amount, the leaching of B and Se was decreased especially under high alkaline conditions. The effects of pH and the presence of leached Ca ion in the aqueous phase upon the leaching behavior were discussed.     

A simple LIBS method for fast quantitative analysis of fly ashes

An evaluation of quantitative analysis of major elements (Ca, Al, Mg, Si and Fe) present in fly ashes was made using a simple and cost effective LIBS system. LIBS parameters were optimized to obtain best sensitivity and repeatability. In this purpose different binders were compared, leading to best sensitivity and mechanical stability when a binder containing silver and cellulose was employed in a 1:1 mass ratio.In order to be able to determine major elements in different fly ashes, a multi-matrix calibration was employed. Four reference materials were employed for calibration and five other fly ashes were selected as sample. Concentrations obtained by LIBS were compared to wet acid digestion and alkali fusion followed by ICP-OES analysis. Ca, Mg, Fe, Si and Al concentrations found using the LIBS method developed were in a good agreement with the values obtained by classical methods.     

Phase-mineral and chemical composition of coal fly ashes as a basis for their multicomponent utilization. 1. Characterization of feed coals and fly ashes

The phase-mineral and chemical composition of feed coals and their fly ashes (FAs) produced in four large Spanish thermo-electric power stations was characterized as a basis for multicomponent FA utilization. The feed fuels used are bituminous coals, semi-anthracites and anthracites with high detrital mineral abundance and mixed carbonate and sulphide-sulphate authigenic mineral tendency. Their mineral composition includes quartz, kaolinite, illite-muscovite, pyrite, chlorite, plagioclase, K-feldspar, gypsum, siderite, calcite, dolomite, marcasite, montmorillonite, jarosite, and ankerite. The FAs studied have aluminosilicate composition with higher concentrations of alkaline and alkaline-earth oxides than Fe oxide. Elements such as Ag, As, Ba, Cr, Cs, Li, P, Sb, Sc, Sn, Sr, Ti, V, Zn, and Zr are relatively enriched in these FAs in comparison with the respective mean values for bituminous coal ashes worldwide. The FAs consist basically of aluminosilicate glass, to a lesser extent of mineral matter (with high silicate abundance and dominant oxide tendency) and moderate char occurrence. The phase-mineral composition (in decreasing order of significance) of these FAs is normally glass, mullite, quartz, char, kaolinite-metakaolinite, hematite, cristobalite, plagioclase, K-feldspar, melilite, anhydrite, wollastonite, magnetite and corundum plus 42 important accessory minerals or phases. A scheme of conventional separation procedures was applied to recover sequentially six initial and potentially useful and/or hazardous products from FAs, namely: (1) a ceramic cenosphere concentrate; (2) a water-soluble salt concentrate; (3) a magnetic concentrate; (4) a char concentrate; (5) a heavy concentrate; and finally (6) an improved FA residue.     

Physico-mechanical behavior of self-cementing class C fly ash-clay mixtures

Self-cementing class C fly ashes are being increasingly used for soil stabilization of road bases and in other civil constructions. Because of their self-cementing capability in the presence of water, they can be used for clay subgrade improvement as cement surrogates, or as road subgrade material. However, for efficient and economic utilization of self-cementing class C fly ash, the physico-mechanical characteristics of these ashes must be determined extensively. This paper focuses upon the laboratory evaluation of the (1) stabilization characteristics of clay soils blended with self-cementing class C fly ash, and (2) residual self-cementation capabilities of ponded class C fly ash. Testing carried out by the authors and other researchers have indicated that curing time, curing condition, clay mineralogy, amount of fly ash and swelling potential in the soil-fly ash mix are the important variables that control stabilization characteristics. In this paper, the stabilization characteristics were evaluated in terms of the gain in the uniaxial compressive strength and stiffness, and swelling potential. To examine these effects, 12 set of mixtures of ideal clay soils with known percentages of kaolinite and montmorillonite, self-cementing class C fly ash and appropriate amount of water were compacted and cured. In the mixed samples, amount of montmorillonite varied from 0, 2, 4 and 6%, and the amount of self-cementing class C fly ash varied from 5, 10 and 20%. To investigate the effect of curing condition, three curing environments were used. For swelling test, the cured samples were inundated and allowed to swell at the seating pressure of about 2 kPa applied by the weight of the top porous stone and load plate using the one dimensional oedometer apparatus. In addition to the stabilization characteristics of clay soils-fly ash blend, the residual self-cementation capabilities of ponded class C fly ash were also investigated in terms of unconfined compression and CBR tests performed at 7 and 14 days of curing. Results obtained from these test were encouraging and compared favorably with the typical subgrade materials.     

石灰乳投加的生产性试验

在水厂水处理生产期间,单独投加石灰乳或者生石灰药剂,然后收集生产试验过程中原水水质、出厂水和生产成本等生产数据,分析对比两种药剂在自来水工艺流程中的优点和不足之处。石灰乳投加和生石灰投加均能满足出厂水pH指标,生石灰原材料成本上占有优势,而石灰乳投加在工艺流程、工作环境卫生和工作强度方面占优。     

A stochastic simulation for the collection process of fly ashes in single-stage electrostatic precipitators

The dynamic evolution of particle size distribution (PSD) along the longitudinal length of electrostatic precipitator (ESP) quantitatively describes the collection process of ESP, and then is capable of estimating the performance of ESP. The details of the evolution of PSD are obtained by the solutions of population balance equation (PBE) for electrostatic collection. The paper promoted a stochastic method to solve the PBE. The method is based on event-driven technique and introduces the concept of weighted fictitious particles. The halving procedure of number weight of fictitious particle is adopted to restore the statistical samples of the stochastic approach and maintain the computational domain. The method, which is named event-driven constant volume (EDCV) method, is used to simulate the collection process of particles in a small-scale single-stage wire-plate ESP, considering simultaneously the electrostatic force, the convection force and the transverse particle diffusion in the model of collection kernel. The agreement among the results of the Monte Carlo method, the experimental data and the results of method of moments is good.     

Mineralogical Characterizations and Reaction Path Modeling of the Pozzolanic Reaction of Fly Ash–Lime Systems

Mineralogical studies show that fly ash–lime systems without NaOH produced Al-rich calcium silicate hydrates and a small amount of ettringite. The presence of NaOH accelerates the pozzolanic reaction of fly ash. Fly ash–lime systems with NaOH produced Al-rich calcium silicate hydrates, calcite, meixnerite, and NaX-type zeolite (or zeolite precursor) after 28 days of reaction time. Carbonation of alkali-activated fly ash–lime systems call for specific studies. The experimental work was supplemented with reaction path modeling, which provided a quantitative procedure to decipher the chemical nature of fly ash hydration and cementitious system formation.     

Application of zeolitised coal fly ashes to the depuration of liquid wastes

In this study, the application of some zeolitised fly ashes and synthetic zeolites to the decontamination of the leachate produced in a municipal solid waste (MSW) treatment plant and to the liquid waste from a pig farm was analyzed. Thus, the reduction of organic matter (BOD and COD), ammonium and total nitrogen, phosphorus and metals contents after a zeolite treatment was evaluated. Several synthetic zeolites were tested: some commercial zeolites and other synthetic zeolites and zeolitised ashes obtained after a coal fly ash alkaline hydrothermal process. Two forms of contact between the zeolitic material and the liquid waste were tested: in a stirred tank and in a column. In addition, other variables determined were the amount of zeolite and the residence time. The results showed that zeolites, especially zeolitised fly ash, clearly produced a strong reduction in the leachate nitrogen and phosphorus content.     

Determination of the reactive component of fly ashes for geopolymer production using XRF and XRD

Geopolymers are a class of versatile materials that have the potential for utilisation as a cement replacement, fireproof barriers, materials for high temperatures, and biological implant applications. This study investigated methods for determining the formulation for manufacturing geopolymers made with fly ash from coal-fired power stations. The accepted method of determining the formulation of geopolymers to get the desired matrix chemistry uses the bulk composition of the feedstock materials. This formulation method is widely used in investigations using feedstock materials that almost completely react during processing. It is widely considered that amorphous components of fly ash are the reactive components in the geopolymerisation reaction. However, quantification of the amorphous components is challenging and generally avoided with the concomitant problem that the formulation is far from optimum. For the work presented here, the composition of the amorphous part is determined accurately and this information utilised to synthesise geopolymers. The bulk composition is first determined using X-ray fluorescence spectroscopy (XRF) and then the amorphous composition determined using XRF and quantitative X-ray diffraction (QXRD). Formulating the mixture based on amorphous composition produced samples with a significantly higher compressive strength than those formulated using the bulk composition. Using the amorphous composition of fly ash produced geopolymers with similar physical properties to that of metakaolin geopolymers with the same targeted composition. We demonstrated a new quantitative formulation method that is superior to the accepted method.     

固硫灰渣的活性评定与现行标准的适应性研究

循环流化床固硫灰渣在矿物组成、化学成分等方面与煤粉炉粉煤灰存在显著区别,两者活性来源也不相同。现行标准中的火山灰活性评定方法主要针对的是低硫火山灰,而固硫灰渣中硫含量较高(以SO3计可高达10%以上),现行标准是否适合用来评价固硫灰渣活性存在疑问。对固硫灰渣与现行标准中的两种火山灰活性评定方法的适应性进行了研究,结果显示:"水泥胶砂28 d抗压强度比试验"不适合用来评定硫含量较高的火山灰质材料的活性;准确测定固硫灰渣的活性需改进现行试验方法。     

煅烧煤矸石活性测试方法的试验研究

分别采用Ca(OH)2吸收法、NaOH消耗法及比强度法测试了某煅烧煤矸石的活性.测试结果表明,28 d前煅烧煤矸石对碱吸收速度增加较快,其后变化平稳.Ca(OH)2吸收法早期样本中Ca(OH)2结晶相残留较多,28 d后该相消失;NaOH消耗法早期样本中无残留的NaOH结晶相,并且与比强度法的测定结果所反映的煅烧煤矸石活性变化规律更为一致,即随颗粒粒径的降低,煅烧煤矸石活性增加.NaOH消耗法能够更为准确且快速地反映煅烧煤矸石的活性.     

Characterisation of the glass fraction of a selection of European coal fly ashes

Fly ash largely consists of the inorganic content of coal that remains after combustion. The crystalline phases present in fly ash may form upon cooling of a molten alumino‐silicate glass. This view is supported by the spherical shape of many fly ash particles, inferring that they have gone through a viscous fluid state. The amorphous content in fly ash is believed to dominate reactivity behaviour, under both alkaline and acid conditions, because glasses have a higher potential energy than the equivalent crystal structure and the variation of bond angles and distances in a glass makes the bond breakage easier. It is the degradation behaviour under alkaline conditions, and the subsequent release of silica from the glass phase, that is important in the use of fly ash for conversion to zeolites and for pozzolanic applications in cement. This research comprehensively studies the composition, quantity and stability of the glass phase in a series of nine fly ashes sourced from Spanish and Italian power plants. The quantitative elemental composition of the glass phase in each fly ash was determined. Samples of the ashes then underwent a series of tests to determine the internal structure of the ash particles. Heat treatment of most of the ashes results in mullite crystallising from the glass phase; this is the crystalline phase that is predicated to form by both the relevant phase diagrams and also by NMR spectroscopy. In the ashes, mullite is present as a spherical shell, tracing the outline of the particle but in some specific cases the mullite skeleton is made up of coarse crystals reach also the internal parts of the particles. The morphology and density of the mullite crystals in these shells varies greatly. This work has supported the view that some crystalline phases present in fly ashes, such as mullite, form upon cooling of the amorphous glass melt as opposed to direct conversion from existing mineral phases in the coal during the combustion process. Copyright © 2004 Society of Chemical Industry     

宜春锂云母提锂渣的火山灰活性研究

采用强度指数法、选择性溶解法、结合水率法、TG-DTA同步热分析等检测手段,评价对比了锂渣与粉煤灰、煤矸石、花岗岩粉等几种常用硅铝质材料的火山灰活性.结果表明,锂渣在四种硅铝质材料中活性指数最高,对Ca(OH)2的消耗能力最强,显示锂渣具有优良的火山灰活性.     

Chemical fractionation for the characterisation of fly ashes from co-combustion of biofuels using different methods for alkali reduction

Chemical fractionation, SEM-EDX and XRD was used for characterisation of fly ashes from different co-combustion tests in a 12 MW circulating fluidized bed boiler. The fuels combusted were wood pellets as base fuel and straw pellets as co-fuel in order to reach a fuel blend with high alkali and chlorine concentrations. This fuel blend causes severe problems with both agglomeration of bed material if silica sand is used and with deposits in the convection section of the boiler. Counter measures to handle this situation and avoiding expensive shut downs, tests with alternative bed materials and additives were performed. Three different bed materials were used; silica sand, Olivine sand and blast furnace slag (BFS) and different additives were introduced to the furnace of the boiler; Kaolin, Zeolites and Sulphur with silica sand as bed material. The results of the study are that BFS gives the lowest alkali load in the convection pass compared with Silica and Olivine sand. In addition less alkali and chlorine was found in the fly ashes in the BFS case. The Olivine sand however gave a higher alkali load in the convection section and the chemical fractionation showed that the main part of the alkali in the fly ashes was soluble, thus found as KCl which was confirmed by the SEM-EDX and XRD.The comparison of the different additives gave that addition of Kaolin and Zeolites containing aluminium-silicates captured 80% of the alkali in the fly ash as insoluble alkali-aluminium-silikates and reduced the KCl load on the convection section. Addition of sulphur reduced the KCl load in the flue gas even more but the K₂SO₄ concentration was increased and KCl was found in the fly ashes anyhow. The chemical fractionation showed that 65% of the alkali in the fly ashes of the Sulphur case was soluble.     

Effects of three Turkish fly ashes on the heat of hydration of PC-FA pastes

Effects of the type and amount of fly ash substitution on the heat of hydration of portland cement-fly ash pastes were investigated. Three Turkish fly ashes were used. One of them was a high-calcium and the other two were low-calcium fly ashes. The specimens contained 0, 10, 20, and 40% fly ash by weight of portland cement. The tests were carried out as described in ASTM C 186 however one separate set of specimens were first subjected to an early external temperature of 67±2°C for six hours followed by the standard temperature until time of test. The results revealed that the low-calcium fly ashes, regardless of their type, reduce the heat evolution when used for partial cement replacement. The high-calcium fly ash, on the other hand, does not produce significant changes in the heat of hydration.     

Role of active sites in the steam activation of high unburned carbon fly ashes

Previous studies on carbon gasification have not included high unburned carbon content fly ashes, and therefore it remains unclear why not all fly ash carbon samples are equally suitable for activation. The concentration of active sites is well known to influence carbon gasification reactions. Therefore, the objective of this work was to investigate the effect of the concentration of active sites on the behavior of fly ash carbon samples upon steam activation. Six fly ash carbons were selected to produce activated carbons using steam at 850 °C. The concentration of active sites was determined by non-dispersive infrared analysis (NDIR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). XRD analyses were also conducted to determine the crystallite size. It was observed that the concentration of active sites played a more significant effect on the surface areas of activated carbons in the carbon burn-off zone of >60%. Statistical analysis was used to relate the surface areas of activated carbon variances with carbon burn-off levels.     

Effect of steam curing on class C high-volume fly ash concrete mixtures

The effect of steam curing on concrete incorporating ASTM Class C fly ash (FA), which is widely available in Turkey, was investigated. Cement was replaced with up to 70% fly ash, and concrete mixtures with 360 kg/m³ cementitious content and a constant water/binder ratio of 0.4 were made. Compressive strength of concrete, volume stability of mortar bar specimens, and setting times of pastes were investigated. Test results indicate that, under standard curing conditions, only 1-day strength of fly ash concrete was low. At later ages, the strength values of even 50% and 60% fly ash concretes were satisfactory. Steam curing accelerated the 1-day strength but the long-term strength was greatly reduced. Setting time of fly ash-cement pastes and volume stability of mortars with 50% or less fly ash content were found to be satisfactory for standard specimens. In addition, for steam curing, this properties were acceptable for all replacement ratios.     

不同激发剂对粉煤灰火山灰活性的影响

探讨不同激发剂对粉煤灰不同时期火山灰活性的影响。结果表明：单掺适量的不同激发剂可以不同程度地提高粉煤灰早期、中期与后期的火山灰活性，其中早期的激发作用最大，后期的激发作用最小。且不同时期激发作用效果从大到小的顺序依次为氯化物、硫酸盐、氢氧化物，其中当氯化钠掺量为2％时激发作用效果最大。当水灰比为0．48时激发剂对粉煤灰不同时期火山灰活性的激发效果均优于水灰比为0．46时的激发效果。且当水灰比从0．46增至0．48时,各水泥试样的3d抗压强度比值增幅最大，28d抗压强度比值增幅最小。     

Improving the performance of ternary blended cements by mixing different types of fly ashes

For overcoming certain drawbacks characterizing both basic types of fly ashes (of high and low calcium content), different ash intermixtures consisting of two types of fly ashes were prepared. The principal idea lying beneath the effort presented herein is that beneficial assets of the one type of ash could compensate for the shortcomings of the other. Compressive strength development, pozzolanic activity potential and nature of hydration products of all ternary cements were closely monitored and presented in comparison to the respective properties of the initial binary blends. Moreover, efficiency factors were calculated for all new systems and were further used to validate previously reported expressions describing Binary Fly ash-Cement (BFC) systems. In accordance with previous works, ternary fly ash systems examined here outperformed the respective binary systems almost throughout the curing period. Synergy between the different types of fly ashes was considered the main reason for the excellent performance of the ternary mixtures. Results obtained indicate that previously developed analytical expressions, correlating active silica of SCMs and k-values, can be applied in the case of multicomponent ash systems as well.