Showing papers on "Fly ash published in 1993"

Selective formation of Na-X zeolite from coal fly ash by fusion with sodium hydroxide prior to hydrothermal reaction

Abstract: Hydrothermal treatment of fly ash with alkali gives various types of zeolites such as Na-Pl, Na-A and hydroxysodalite, where the zeolite zone was formed like an egg white, covering the central core of fly ash particles, as evinced in the previous paper. By fusion with sodium hydroxide, most of the fly ash particles were converted into sodium salts such as silicate and aluminate, from which hydrothermal reaction without stirring favourably resulted in the formation of Na-X zeolite. Crystallinity of Na-X zeolite as high as 62% was attained at the optimum condition of NaOH/fly ash = 1.2 and a fusion temperature of 823 K. Fly ash contains 14 wt% mullite (3Al2O3·2SiO2), which was revealed to be a less-active crystalline component for zeolite formation. Aluminium-enriched fly ash gave Na-A in place of Na-X zeolite. Scanning electron microscope images of cubic and octahedral crystals characteristic of Na-A and Na-X zeolite, respectively, obtained from fly ash, are given.

Mineralogy and Surface Properties of Municipal Solid Waste Ash

Abstract: Bulk chemical analysis shows most elements enriched over average soil abundances except for Si, which is 60% of the concentration in soils. Eleven minerals were identified using pownder X-ray diffraction (XRD). Standard additions using XRD gave the following weight percent of minerals (±2σ) in combined bottom and fly ash: gypsum, 1.8±1.9; hematite, 3.7±1.7; quart, 2.3±1.0; spinel,∼3-5; halite, 0.5±0.4; calcite 3.5±1.9; rutile, 1.1±1.3 Mullite, sylvite, anhydrite, and wustite were also identified. The ash contains 18% minerals, 9% structural and adsorbed water, and 72% glass. An estimated composite glass composition is reported.

The relationship between de novo synthesis of polychlorinated dibenzo-p-dioxins and dibenzofurans and low-temperature carbon gasification in fly ash

Abstract: Four fly ashes, three from municipal solid waste incinerators (MSWI) and one from a coal-fired power plant, were studied for their potential to promote carbon gasification and de novo synthesis of PCDD/F, chlorobenzenes, and chlorophenols from native carbon precursors in the temperature range 275-350 o C. A fixed-bed tubular reactor employing mixtures of oxygen and nitrogen was used in this laboratory study. The incinerator fly ashes showed steadily increasing yields of chlorobenzenes with temperature and an optimum temperature window for PCDD/F formation in the range 300-325 o C. The rate of PCDD/F formation for one of the fly ashes, found to be 2×10 -2 μg (PCDD/F) g -1 min -1 , was constant for reaction times from 5 to 30 min

Fly ash cementing compositions and methods

Abstract: The present invention provides fly ash cementing compositions and methods which are useful in any cementing application, and are particularly suitable for cementing in subterranean zones penetrated by well bores. The cementing compositions can include a portion of the drilling fluid used to drill a well bore as a component thereof. Also, drilling fluid can be disposed of by combining it with the fly ash cementing composition whereby it solidifies in a disposal location.

Fly ash mediated reactions of phenol and monochlorophenols: oxychlorination, deep oxidation, and condensation

Abstract: Monochlorophenols are smoothly oxidized to carbon dioxide and carbon monoxide when vapors in air are passed over fixed beds of municipal waste incinerator fly ash at 625-725 K. Simultaneously polychlorinated benzenes, monobenzofurans, and dibenzo-p-dioxins are formed with a large fraction of the original chlorine concentrated in these products. Fly ash catalyzed oxychlorination of phenol in the presence of HCl at 425-725 K resulted in the formation of chlorinated phenols which, in turn, were converted above 625 K into mainly CO 2 and the (poly)chloroarenes mentioned above. In contrast, under similar conditions, (chlorinated) benzenes are inert

Fly Ash, Slag, Silica Fume, and Rice Husk Ash in Concrete: A Review

Abstract: Environmental problems associated with waste product disposal, resource conservation considerations, and the cost of portland cement will demand the increasing use of of fly ash, slag, condensed silica fume and rice-husk ash in the production of cement and ready-mixed and precast concretes. This article discusses this issue, the properties and limitations of these materials, and the effects that this will have on concrete properties. It is noted that North American trends indicate preference for the separate batching of these materials at concrete-batching plants rather than the intergrinding with portland cement clinker at a cement plant. This, however, is not advised in developing countries. It is also noted that recent developments in chemical admixtures, especially the introduction of superplasticizers, will increasingly facilitate the incorporation of supplementary cementing materials in concrete. Technology transfer needs are also noted.

Application of Boron Isotopes for Identifying Contaminants such as Fly Ash Leachate in Groundwater

Abstract: The B isotopic ratio of a fly ash leachate can be very different from the B isotopic ratio of a natural groundwater. Mixtures of leachate and groundwater typically result in nonlinear B isotope mixing curves that enable identification and quantification of leachate contamination in a groundwater at much lower levels than possible using concentration analyses alone. Limits on B isotope use for contaminant quantification will exist for some environments such as landfills with multiple ash types, but B isotopic analysis may often remain the preferred method for qualitative identification. 20 refs., 4 figs., 3 tabs.

Simulation of ash deposit growth in a pulverized coal-fired pilot scale reactor

Abstract: A model has been developed to relate the deposition behavior of ash under slagging conditions to boiler operating conditions and coal composition data. This model has been incorporated into a comprehensive combustion code and used to investigate the effects of ash deposition rate, thermal conditions, and ash chemistry on slag growth in a pilot-scale combustor. Results for simulated deposits from a coal blend fired at 3.7 MBtu/h showed a relatively high liquid fraction corresponding to denser and presumably stronger deposits. The same coal blend fired at a lower rate produced deposits which were less dense because of the lower temperatures and heat flux levels in the combustor, as well as the lower ash deposition rates

Mechanical properties of concrete incorporating high volumes of fly ash from sources in the u.s.

Abstract: This paper presents the results of studies to determine the properties of fresh and hardened high volume fly ash concretes using 8 fly ashes and 2 portland cements from the U.S. The details of the studies are described. The anslysis of the test results lead to the conclusion that high performance air entrained high volume fly ash concrete can be produced with the fly ashes and cements used in this investigation. The concretes so produced have low bleeding, satisfactory slump and setting characteristics and low autogenous temperature rise. These concretes also have excellent mechanical properties at both early and late ages with compressive strengths reaching as high as 50 MPa at 91 days. The creep and drying shrinkage of the concretes investigated are relatively low.

Nondestructive determination of trace element speciation in coal and coal ash by XAFS spectroscopy

Abstract: The environmental impact of specific trace element species in coal utilization and waste disposal depends not only on the abundance but also on the form(s) of occurrence of the element present in coal and coal ash. While there are a number of analytical methods for determining the abundance of trace elements in coal and ash, there are very few methods available for determining the form of occurrence (speciation) of a trace element in such materials at abundances as low as 10 ppm. In this report, the potential of XAFS spectroscopy for trace element speciation is demonstrated by means of measurements on two environmentally important trace elements, arsenic and chromium, in coal and ash

Magnetic Susceptibility of Soils in the Areas Influenced by Industrial Emissions

Abstract: The magnetic susceptibility in forest soils of Katowice province is largest in the litter layer, mainly in the Of and Oh horizons In the arable soil near steel plants the magnetic susceptibility was greatest in the ploughed layer (20–25 cm) The magnetic susceptibility is due largely to industrial emissions of metallurgical dust, cement dust and fly ash from combustion of pulverized hard coal The large magnetic susceptibility is accompanied by substantial contents of heavy metals Measurements of the magnetic susceptibility of forest soil litter may be used in soil monitoring to ascertain the presence of ferromagnetics of anthropogenic origin

Use of Self-Cementing Fly Ashes as a Soil Stabilization Agent

Abstract: Fly ash produced in the combustion of sub-bituminous coals exhibits self-cementing characteristics that can be adapted to a wide range of stabilization applications. Ash treatment can effectively reduce the swell potential of fat clay soils and increase subgrade support capacity of pavement subgrades. Ash hydration occurs rapidly and must be addressed by the construction procedures to obtain maximum potential benefit from the ash treatment. This can be accomplished by limiting the delay between incorporation of the ash and final compaction to less than 2 hours. Hydration chemistry can differ significantly between specific sources and design mixes must be based on the specific ash to be used. Compressive strengths of ash treated materials are dependent upon moisture content at time of compaction and strict moisture control is required during construction. For the covering abstract see IRRD 863991.

Efficiency of fly ash in concrete

Abstract: Earlier efforts towards an understanding of the efficiency of fly ash in concrete has led to the introduction of rational methods. Based on the results available on some of the more recent pulverised fuel ashes, the authors evaluated the efficiency of fly ash in concrete over a wide range of percentage replacements (15–75%). It was clearly shown that the overall efficiency of fly ash cannot be adequately predicted using a single efficiency factor at all percentages of replacements. The overall efficiency factor (k) has been evaluated at all percentages of replacements considering the general efficiency factor (ke) and the percentage efficiency factor (kp). This study resulted in a quantitative assessment of the behaviour of fly ash in concrete, especially for the 28 day compressive strength at different percentages of replacement.

Settable composition for general purpose concrete and method of making same

Abstract: From about 25% to about 50% but not more than about 200 lbs of the Portland cement of a general purpose concrete mix which contains for each cubic yard of the concrete to be produced in generally homogeneous admixture about 400-750 lbs. portland cement, about 1600-2000 lbs. coarse aggregate of a size of at least about 3/8 inch, and sufficient fine aggregate of a size less than 3/8 inch and up to minor amounts of conventional additives to yield one cubic yard when the admixture is combined with water in an amount equal to about 40-70% by weight of said portland cement, is replaced with a) Class F fly ash having a calcium oxide content up to about 6% and b) cement kiln dust (CKD) in a weight ratio of fly ash to CKD of about 2:3-3:2. Preferably, 30% or more of the Portland cement is replaced.

Immobilization Science of Cement Systems

Abstract: Portland cement and Ca(OH)2, “slaked lime,” are representative of a family of materials that have conceptual and practical advantages as matrices for the immobilization of wastes. These are relatively proven construction materials with an extensive history of use in various ground-water regimes, and in various climates. The raw materials are widely available and they exhibit a reasonable amount of resistance to physical damage and attrition. They are also durable. Although modern Portland cements are only about 150 years old, numerous examples of Roman concrete made from slaked lime and volcanic pozzolanic ash survive; the Pantheon in Rome (circa A.D. 300) continues in regular use.Satisfactory immobilization matrices can also be formed by incorporating other artificial waste materials, e.g. coal combustion fly ash, blast furnace slag, and natural materials such as calcined kaolin or siliceous volcanic ashes containing glass and zeolites. These materials react with Ca(OH)2 and cement to become an integral part of a cement matrix. Thus one waste (ash, slag) can be used to help immobilize another, and may actually improve the retentive capacity of a cementitious matrix.Since cements require water to harden, they are tolerant of wet wastes and are especially useful for many effluents. In addition, they are low-cost, nonflammable materials with the potential to provide chemical and physical immobilization of wastes, but their set characteristics can be affected by certain material additions. Table I balances some advantages against disadvantages of the use of cement systems for waste immobilization.

Removal of phenols from effluents by fly ash

Abstract: Removal of phenol and chlorophenols from effluents by fly ash has been investigated. The effects of contact time, concentration of solute, pH and temperature have been studied. Langmuir's model is used for the equilibrium modelling, and the constants are calculated at 30, 40 and 50°C. Thermodynamic constant AH has also been calculated. The Lagergren equation has been used for dynamic modelling of the process and rate constants for phenol, 4‐chlorophenol and 2,4‐dichlorophenol are found to be 7.68 × 10‐2, 7.24 × 10‐2 and 6.45 × 10‐2 min‐1 at 30°C. It has been observed that low pH as well as higher temperature favours greater removal of 2,4‐dichlorophenol than of phenol and 4‐chlorophenol.

Predicting ash behavior in utility boilers

Abstract: In recent years, significant advances have been made in the development of methods to predict ash behavior in utility boilers. This paper provides an overview of methods used to assess and predict ash formation and deposition. These prediction methods are based on a detailed knowledge of ash formation and deposition mechanisms that has been obtained through bench, pilot, and field testing and detailed coal and ash characterization. The paper describes advanced methods of coal and ash analyses and the advantages of these methods over conventional methods. The advanced coal characterization methods provide sufficient data to predict size and composition distribution of fly ash

Blended hydraulic cement for both general and special applications

Abstract: A blended, hydraulic cement binder, is disclosed, consisting of water, fly ash, Type III portland cement, Type I portland cement, slag cement, ground silica, boric acid, borax, citric acid and an alkali metal activator. The cement binder and sequences for mixing the composition, is particularly useful because it provides: time to mix all components adequately, unrestricted transporting time that can be terminated, at will, followed by alterable placement and finishing times. The cement binder can be used as a neat cement or it can be extended with fillers, such as sand and gravel, to make mortar or concrete, that rapidly gains very high structural strengths.

Study of the pre-crystallization stage of hydrothermally treated amorphous aluminosilicates through the composition of the aqueous phase

Abstract: A detailed study of the parameters and phases involved in the pre-crystallization of the hydrothermal conversion of coal fly ash to zeolites has been performed. The study has also been extended to pumice, a natural glassy aluminosilicate.Dissolution of the main components, their concentration ratio in the solution phase, the re-precipitation in the form of an amorphous gel from which evolves zeolite crystals, and the compositions, occurrence times and degrees of completeness of the gel and zeolite crystals have been found to be strongly interrelated and all influenced by the temperature and alkali–metal content of the treatment.In the case of coal fly ashes, the halt occurring in the conversion to zeolites some time after its beginning has been shown to be due to the mullitic phase located inside the ash particles and containing most of the total aluminium content of the ashes. In contrast to the external amorphous phase, this phase is insoluble at the experimental conditions suitable for the conversion treatment.

Trace Elements in Coal and Coal Combustion Residues

Abstract: Introduction: Coal Ashes--Industrial Wastes or Beneficial By-Products? (R.F. Keefer). An Overview of Electric Power Research Institute (EPRI) Related to Effective Management of Coal Combustion Residues (I.P. Murarka, S.V. Mattigod, and R.F. Keefer). Environmental Effects from Power Plants: Coal-Based Environmental Problems in a Low-Rainfall Tropical Region (M. Agrawal, J. Singh, A.K. Jha, and J.S. Singh). Trace Element Concentrations in the Soft Tissue of Transplanted Freshwater Mussels Near a Coal-Fired Power Plant (C.S. Klusek, M. Heit, and S. Hodgkiss). Tests for and Monitoring of Fossil Fuel Dispersion and Ash Disposal: Strontium and Lead Isotopes as Monitors of Fossil Fuel Dispersion (R.W. Hurst, T.E. Davis, A.A. Elseewi, and A.L. Page). Baker Soil Test Applications for Land Reclamation, Animal Health, and Food Chain Protection (D.E. Baker, F.G. Pannebaker, J.P. Senft, and J.P. Coetzee). Transport and Leachability of Metals from Coal and Ash Piles: Multicomponent Transport Through Soil Subjected to Coal Pile Runoff Under Steady Saturated Flow (M.A. Anderson, P.M. Bertsch, and L.W. Zelazny). Leachability of Ni, Cd, Cr, and As from Coal Ash Impoundments of Different Ages on the Savannah River Site (S.S. Sandhu, G.L. Mills, and K.S. Sajwan). Use of Coal Ash for Plant Growth: Extractable and Plant Concentrations of Metals in Amended Coal Ash (A.P. Schwab). Uptake of Chemical Elements by Terrestrial Plants Growing on a Coal Fly Ash Landfill (L.H. Weinstein, M.A. Arthur, R.E. Schneider, P.B. Woodbury, J.A. Laurence, A.O. Beers, and G. Rubin). Accumulation of Mo in Wheat and Alfalfa Grown on Fly Ash-Amended Acid Mine Spoils (R.F. Keefer, D.K. Bhumbla, and R.N. Singh). Elements in Coal and Coal Ash Residues and Their Potential for Agricultural Crops (M.P. Menon, K.S. Sajwan, G.S. Ghuman, J. James, and K. Chandra).

Alkali activated class C fly ash cement

Abstract: Class C fly ash may be activated with strong alkali to yield a novel, dense, quick-setting cement having unexpected properties. The setting time of the cement decreased as the pH of the activating solution increased. The microstructure and phase assemblage of the novel cement depended on the pH. Ettringite was absent beyond pH 14.30 (2.0N); a hexagonal plate-like crystalline form (stratlingite (gehlenite hydrate, C 2 ASH 8 ) and other compounds) became more abundant at higher pH. At higher pH the microstructure was characterized by high amounts of the plate-like crystalline phase and a dense matrix, due to higher reactivity of the glassy phase in fly ash. The novel cement will have uses in a number of areas, including fixation of hazardous wastes such as radioactive wastes, applications where rapid setting is desired, and formation of concrete in hot environments where ordinary Portland cements may tend to crack due to their heat of hydration.