Showing papers on "Fly ash published in 1997"

A Fast Method for Recycling Fly Ash: Microwave-Assisted Zeolite Synthesis

Abstract: Zeolitic material was synthesized from fly ash by conventional and microwave-assisted hydrothermal alkaline activation experiments. The zeolite synthesis was studied as a function of temperature, time, and activation solution concentration. K+-Na+/NH4+ exchange properties of the zeolitic material synthesized were studied as a function of time and zeolite type. The zeolitic material synthesized from the same fly ash by changing the synthesis parameters contained: NaP1, hydroxysodalite, hydroxycancrinite, analcime, tobermorite, and nepheline hydrate using NaOH as an activation agent and F linde zeolite, kalsilite, and phil lipsite-KM zeolite from KOH activation. Synthesis yields and zeolite types obtained from the microwave and conventional experiments were very similar, but the activation time needed was drastically reduced by using microwaves (from 24−48 h to 30 min). Consequently, the industrial application of the synthesis process is enhanced by the microwave-assisted method. From this point of view, t...

Geochemical modeling of weathering reactions in municipal solid waste incinerator bottom ash

Abstract: The leaching of municipal solid waste incinerator (MSWI) bottom ash has been studied at different stages of natural weathering Bottom ash samples, originating from a single incinerator, included grate siftings, unquenched, quenched, 6-week-old, 15-year-old and 12-year-old bottom ash Leaching experiments were performed at various pH levels and liquid/solid ratios The speciation code MINTEQA2 was used to evaluate whether the leachates are in equilibrium with minerals that are expected to form in MSWI bottom ash environments Three major stages in weathering are identified, each stage having a characteristic pH that is controlled largely by Ca minerals and pCO2, but also by soluble Al and SO4: (1) unweathered bottom ash, with pH > 12 (grate siftings and unquenched samples); (2) quenched/non-carbonated bottom ash, with pH 10−105 (freshly quenched and 6-week-old samples); and (3) carbonated bottom ash with pH 8−85 (15- and 12-year-old samples) A comparison of the leaching mechanisms identified for the

Stabilisation of biofuel ashes for recycling to forest soil.

Abstract: A Swedish research program concerning the technical and ecological effects of wood fuel ash recycling to forest biotopes has been on-going for several years. Within this program, a study of the stabilisation of ash by the so-called self-hardening process was carried out. Chemical reactions occurring in the ash materials on water addition and during solidification were identified based on results from chemical analysis, X-ray diffraction, FTIR spectroscopic and scanning electron microscopy analysis. The stability and importance of the individual reaction products are discussed. Some results of practical importance are: alkali metals are to a large extent present as salts dissolved in the pore solution, i.e. the hardened ash should be stored in a way that protects it from rainfall; the dominant wood ash element calcium forms Ca(OH) 2 and subsequently CaCO 3 during hardening and storage; ettringite formation binds sulphur and aluminium and contributes to the stability of the ash structure; and phosphorous is bound in apatite and other compounds with low solubilities.

Fly Ash in Concrete: Production, Properties and Uses

Abstract: 1. Uses of Fly Ash in Cement and Concrete 2. Effect of Fly Ash on the Properties of Fresh Concrete 3. Effect of Fly Ash on the Structural Properties of Hardened Concrete 4. Admixtures in Fly Ash Concrete 5. Miscellaneous Opportunities for Fly Ash Use 6. Fly Ash Usage in Waste Management 7. Special Problems Including Use Constraints 8. Types and Properties of Fly Ash 9. Effect of Fly Ash on the Durability of Concrete 10. Applications of Fly Ash in Special Concretes

In Vivo Evidence of Free Radical Formation in the Rat Lung after Exposure to an Emission Source Air Pollution Particle

Abstract: Exposure to air pollution particles can be associated with increased human morbidity and mortality. The mechanism(s) of lung injury remains unknown. We tested the hypothesis that lung exposure to oil fly ash (an emission source air pollution particle) causes in vivo free radical production. Electron spin resonance (ESR) in conjunction with the spin trap alpha-(4-pyridyl 1-oxide)-N-tert-butylnitrone (4-POBN) was used to detect radical adducts. Rats were instilled with 500 micrograms of either oil fly ash or saline. Twenty-four hours later, ESR spectroscopy of the chloroform extract from lungs of animals exposed to the oil fly ash gave a spectrum consistent with a carbon-centered radical adduct (hyperfine coupling constants alpha N = 15.0 G and alpha H beta = 2.5 G), while those spectra from lungs instilled with saline revealed a much weaker signal. This signal was reproduced by instilling animals with the soluble fraction of the oil fly ash, which contains soluble metal compounds. The same signal was observed after instillation of either a mixture of vanadium, nickel, and iron sulfates or VOSO4 alone. We conclude that, after instillation of an air pollution particle in the rat, ESR analysis of lung tissue demonstrates in vivo free radical production. This generation of free radicals appears to be associated with soluble metals in the oil fly ash.

The effectiveness of palm oil fuel ash in preventing expansion due to alkali-silica reaction

Abstract: Laboratory tests were conducted to evaluate the performance of palm oil fuel ash (POFA), a recently identified pozzolanic material, in reducing the expansion of mortar bars containing Tuff as a reactive aggregate where ordinary Portland cement (OPC) was replaced, mass for mass, by 0, 10, 30 and 50% POFA. The South African NBRI Accelerated Test method was used in the experimental investigation, which revealed that palm oil fuel ash has a good potential in suppressing expansion due to alkali-silica reaction.

Toxicity and occupational health hazards of coal fly ash (cfa). a review of data and comparison to coal mine dust

Abstract: Coal fly ashes (CFA) are complex particles of a variable composition, which is mainly dependent on the combustion process, the source of coal and the precipitation technique. Toxic constituents in these particles are considered to be metals, polycyclic aromatic hydrocarbons and silica. The purpose of this review was to study the in vitro and in vivo data on coal fly ash and relate the studied endpoints to the role of (crystalline) silica, considering its recent classification as a human carcinogen. For most of the effects coal mine dust was chosen as a reference, since it contains up to 10% of crystalline silica (alpha-quartz) and is well studied both in vivo and in vitro. Most studies on fly ash toxicity were not designed to elucidate the effect of its silica-content nor did they include coal mine dust as a reference. Taking this into account, both in vitro and in vivo experimental studies show lower toxicity, inflammatory potential and fibrogenicity of CFA compared to silica and coal mine dust. Although in vitro and in vivo studies suggest genotoxic effects of fly ash, the data are limited and do not clarify the role of silica. Epidemiological studies in fly ash exposed working populations have found no evidence for effects commonly seen in coal workers (pneumoconiosis, emphysema) with the exception of airway obstruction at high exposure. In conclusion, the available data suggest that the hazard of coal fly ash is not to be assessed by merely adding the hazards of individual components. A closer investigation of 'matrix' effects on silica's toxicity in general seems an obligatory step in future risk assessment on fly ashes and other particles that incorporate silica as a component.

Mechanism of Arsenic Sorption by Hydrated Lime

Abstract: Arsenic, along with mercury and selenium, represents one of the trace metallic emissions from fossil fuel-fired power plants that exhibit a tendency to remain in the gas phase. In this study, the effectiveness of some commonly used mineral sorbents is tested for the removal of arsenic from flue gas. Investigations are conducted with hydrated lime sorbent to identify the mechanism of As/Ca interaction and the chemical state and characteristics of captured species. Arsenic oxide (As2O3) is used as the representative arsenic species, and investigations are conducted in a differential fixed bed reactor at medium (400−600 °C) and high (1000−800 °C) temperature conditions. Comparison of Ca(OH)2 with three other mineral sorbents (kaolinite, alumina, and silica) reveals that calcium hydroxide is the most effective in capturing arsenic. The capture mechanism of Ca(OH)2 does not involve a simple physical adsorption but proceeds by means of an irreversible chemical reaction leading to a solid product. X-ray diffract...

The effect of cement composition and ph of environment on sulfate resistance of portland cements and blended cements

Abstract: This paper presents an investigation into the sulfate resistance of Portland cements and blended cements. Four Portland cements of different characteristics and blended cements containing fly ash, ground granulated blast furnace slag and silica fume were used in this work. The performances of binders were evaluated in sulfate solutions maintained at different pH levels ranging from 3 to 12 using expansion of mortar prisms (ASTM C 1012) and strength development of mortar cubes. The results indicate that sulfate resistance of cementitious materials is dependent on its composition and on the pH of the environment. Portland cement with low C3A and low C3S performed well in all sulfate solutions. Blended cements containing silica fume and fly ash (particularly at 40% replacement) showed a more superior performance than any of the Portland cements used. For slag blended cement, this can be achieved when the replacement percentage is higher than 60%.

Preparation of aluminium-fly ash particulate composite by powder metallurgy technique

Abstract: Aluminium-fly ash mixtures containing different weight percentages of fly ash were prepared and compacted at pressures from 138–414 MPa. The compacts prepared at 414 MPa were sintered in nitrogen atmosphere at 600, 625 and 645°C, respectively. The time of sintering ranged from 0.5–6 h. The densification parameter and the green densities of the compacts were determined as a function of compacting pressure and fly ash weight per cent. Density, hardness and strength of the sintered compacts were determined as a function of weight per cent of fly ash particles. Volume changes during sintering of green compacts were also evaluated as a function of increasing fly ash weight per cent. Microscopic studies of green and sintered compacts were done to study the effectiveness of sintering. Green and sintered density of the compacts were found to decrease with increasing weight per cents of fly ash. Sintering results in slight decrease in density and increase in volume of green compacts within the range investigated. Strength of the sintered compacts decreased with increasing weight per cent of fly ash under the present experimental conditions; however, the hardness was found to increase slightly up to 10 wt% fly ash, beyond which it decreased.

Friction and abrasion resistance of cast aluminum alloy-fly ash composites

Abstract: The abrasive wear properties of stir-cast A356 aluminum alloy-5 vol pct fly ash composite were tested against hard SiC p abrasive paper and compared to those of the A356 base alloy. The results indicate that the abrasive wear resistance of aluminum-fly ash composite is similar to that of aluminum-alumina fiber composite and is superior to that of the matrix alloy for low loads up to 8 N (transition load) on a pin. At loads greater than 8 N, the wear resistance of aluminum-fly ash composite is reduced by debonding and fracture of fly ash particles. Microscopic examination of the worn surfaces, wear debris, and subsurface shows that the base alloy wears primarily by microcutting, but the composite wears by microcutting and delamination caused by crack propagation below the rubbing surface through interfaces between fly ash and silicon particles and the matrix. The decreasing specific wear rates and friction during abrasion wear with increasing load have been attributed to the accumulation of wear debris in the spaces between the abrading particles, resulting in reduced effective depth of penetration and eventually changing the mechanism from two-body to three-body wear, which is further indicated by the magnitude of wear coefficient.

Polychlorinated Dibenzo-p-dioxins and Dibenzofurans Formation in Incineration: Effects of Fly Ash and Carbon Source

Abstract: Research aimed at understanding polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) formation in combustion and incineration processes constitutes an important component in developing s...

Feasibility of Using Coal Ash Residues as CO-Composting Materials for Sewage Sludge

Abstract: Alkaline coal ash residues produced from a coal-fired power plant were co-composted with sewage sludge to evaluate it's effect on heavy metal availability and the biological process of composting. Coal fly ash (FA) and lagoon ash (LA) were mixed with dewatered sludge at 0, 10 and 25% w/w, and the mixtures were composted for 100 days in laboratory batch reactors. The changes in pH, electrical conductivity (EC), CO2 production, microbial population, soluble and extractable heavy metal contents were measured during the composting period. Following an initial increase, pH started to decrease from day 7 onward till the end of the composting period for all treatments. Sludge with coal fly ash amendment had a higher pH and EC than those of the control and LA-sludge composts. Increasing fly ash amendment levels resulted in a significant reduction in DTPA-extractable Cd, Cu, Zn, Mn and Pb contents of the FA-sludge composts while the reduction was less obvious in the LA-sludge composts. No significant difference in...