Showing papers on "Fly ash published in 1992"

Behavior of heavy metals in the combustion gases of urban waste incinerators

Abstract: The behavior of each of the principal heavy metals present in fly ash from urban waste incinerators is described on the basis of the standard free energies of formation of the oxide and the chloride from the metal, orygen, and hydrochloric acid, as well as the vapor pressure of the chlorides at working temperatures. The thermodynamic parameters are correlated with the three types of behavior in the volatilization process. The solubility in acid aqueous medium is also related to the oxide and chloride thermodynamic parameters

Zeolite Formation in Class F Fly Ash Blended Cement Pastes

Abstract: Zeolite formation in Class F fly ash blended cement pastes is under investigation. A Na–P type zeolite and Zeolite Y were synthesized from Class F fly ash and NaOH solution after 2 days of aging at room temperature and 6 days of curing at 80°C. However, no zeolites formed when KOH was used. In additional experiments, a Na–P type zeolite, Zeolite Y, and chabazite developed in cement pastes blended with Class F fly ash and NaOH solution which had been aged 2 days at room temperature and then cured 6 days at temperatures ranging from room temperature to 90°C. Seeding the pastes with natural zeolites was also investigated.

Extraction of uranium and molybdenum from aqueous solutions: a survey of industrial materials for use in chemical barriers for uranium mill tailings remediation

Abstract: Laboratory experiments were performed to simulate the interaction of contaminated pore fluids with a variety of industrial materials. The objective was to evaluate the materials for use in a chemical barrier under a repository containing uranium mill tailings. Pore water would pass through the barrier, but contaminants would remain fixed in the solid fraction. More than 99% of the dissolved uranium in a synthetic pore fluid (initial uranium concentration of 30.0 mg/L) was extracted by the addition of hydrated lime, fly ash, barium chloride, calcium phosphate, titanium oxide, peat, and lignite. More than 96% of the molybdenum (initial molybdenum concentration of 8.9 mg/L) was extracted by ferrous sulfate, ferric oxyhydroxide, titanium oxide, peat, hematite, calcium chloride, and barium chloride. Some materials were effective only for a limited range of pH values. Extraction was caused by both precipitation (as calcium uranate, calcium molybdate, ferrous molybdate, or barium molybdate) and sorption (on ferric oxyhydroxide, hematite, calcium phosphate, peat, or titanium oxide). Chemicals that precipitate contaminant-bearing minerals are able to control solution chemistry and, therefore, have an advantage over sorbents which are subject to externally determined solution variables such as pH. On the basis of the predicted flux of pore fluid from themore » Monticello (Utah) uranium mill tailings, some industrial materials may be suitable for a chemical barrier at that site. 37 refs., 6 figs., 6 tabs.« less

Ca(OH)2/fly ash sorbents for SO2 removal

Abstract: In this paper, the reactivity of Ca(OH)[sub 2]/fly ash sorbent with SO[sub 2] is studied by using a fixed-bed differential reactor under the conditions simulating the bag filters of the spray-drying flue gas desulfurization. The source of fly ash and the sorbent preparation conditions affect the reactivity of the sorbent. The reactivity of the sorbent was found to be closely related to the content of the calcium silicate hydrate formed in the sorbent preparation. The sorbent has a much higher utilization of Ca(OH)[sub 2] than that of pure Ca(OH)[sub 2] sorbent, and in some range of Ca(OH)[sub 2] content the sorbent also has a higher SO[sub 2] capture capacity per unit weight of sorbent than that of pure lime. The fly ash from the Shin-Da plant of the Taiwan Power Company produced the best sorbent of all fly ashes in this study. The higher ratio of fly ash/Ca(OH)[sub 2], the higher slurrying temperature, the longer slurrying time, and the smaller particles of fly ash enhance the utilization of Ca(OH)[sub 2], but the water/solid ratio has an optimal value. The relative humidity in the reactor has a significant effect on the reactivity of Ca(PH)[sub 2]/fly ash sorbents, but the effect ofmore » the sulfation temperature is subtle.« less

Interaction of inorganic leachate with compacted pozzolanic fly ash

Abstract: This paper presents results of a study on the feasibility of using pozzolanic western coal fly ash, either by itself or mixed with sand, as a construction material for waste‐containment liners and impermeable covers. Liners can be constructed from pozzolanic fly ash or fly ash‐sand mixtures to meet the usual requirement for the permeability to be 10-7cm/s or less. This paper reports an investigation of the effects of long‐term permeation of inorganic leachate solutions on such liner materials. The effluent leachate was tested to determine changes in chemical composition (in particular pH, boron, and heavy metals) due to leaching from the liner. The inorganic solution had no detrimental effect on liner permeability; in fact, the permeability decreased over time. The main chemical change in the permeate solution is an increase in pH, because the fly ash is highly alkaline. This had the beneficial effect of precipitating the heavy metals within the liner, so heavy metals in the effluent were minimal. Overall...

Hydrothermal processing of new fly ash cement

Abstract: The recent Mount Pinatubo volcanic eruption in the Philippines, in which at least 268 people died, shows that volcanic eruptions can be highly destructive. The eruption shot ash and debris over the countryside; six towns near the volcano faced a high risk of devastating mudslides, and nearly 2000 U.S. service members and their families were evacuated from two nearby military bases. However, this paper reports that not all the consequences of volcanic eruptions are bad. Under hydrothermal conditions, volcanic ash can be transformed into zeolitic tuff and, eventually, into clay minerals that constitute agricultural soils. The Materials Research Laboratory (MRL) has recently used some artificial pozzolanas (fly ash) that when mixed with lime, under hydrothermal conditions, also produced a new type of cementitious material. This was categorized as a new fly ash cement. The formation of a new hydrothermally treated wood-fiber-reinforced composite has also been demonstrated. It is apparent, however, that with respect to concerns about detailed knowledge of the reactivity of calcium silicate-based materials under hydrothermal conditions, the application of the technology far outweighs the understanding of the underlying principles of reactivity. It would seem that an understanding of reactions on the molecular level is just beginning, and that more » work on hydrothermal reactions is still a potentially lucrative area of research. « less

Sintering of ash during fluidized bed combustion

Abstract: Agglomeration of bed material and fuel ash may sometimes cause problems during fluidized bed combustion. In this paper a laboratory test method has been applied on different coal ashes to predict how they behave in temperatures typical for circulating fluidized bed boilers. The method is also useful when the influence of the different bed compounds on the sintering is studied or when the effect of the surrounding gas phase is investigated. The method is based on compression strength measurements of sintered cylindrical pellets and has been used earlier when slagging and fouling tendencies of different coal ashes in pulverized coal fired boilers have been studied. The results showed clear differences in sintering tendencies between the five different coal ashes studied. Temperatures where the sintering was initiated could vary between 500 and 900 [degrees]C, depending on the ash. The sintering tendency seemed also to correlate well with the experiences achieved from full-scale and pilot-scale operation. Addition of limestone decreased sintering of one coal ash when the amount exceeded the Ca/S ratio of 1.3. The decrease was even greater when an Al-Si-based clay mineral was used.

Carbonation of fly ash concrete

Abstract: The carbonation of fly ash concrete is reported, with particular emphasis on the role of curing. Concretes with nominal strength grades C25, C35 and C45 and a range of fly ash levels (0–50%) were e...

Class F. fly ash containing settable composition for general purpose concrete having high early strength and method of making same

Abstract: In general purpose concrete compositions, from about 10% but less than about 25% by wt of the usual amount of portland cement for such compositions is replaced with Class F fly ash and cement kiln dust, both abundant and inexpensive waste products, in the weight ratio of such fly ash to cement kiln dust of about 3:1-1:1 with a minimum of about 5% of the replaced portland cement being cement kiln dust. General purpose concrete prepared from these mix compositions exhibit early strength characteristics, especially from day 1 to day 3, generally equal to or better than those exhibited by comparable all portland cement mix compositions.

Concrete incorporating high volumes of astm class f fly ashes: mechanical properties and resistance to deicing salt scaling and to chloride-ion penetration

Abstract: This paper gives the results of an investigation of the performance of high-volume fly ash concrete made with ASTM Class F fly ashes from 3 different sources. High-volume fly ash concrete with adequate early age strengths and excellent late-age strengths can be produced with cement and total cementititous materials as low as 125 and 300 kg/ cu m, repectively. The Young's modulus of elasticity, creep, and drying shrinkage of high-volume fly ash concrete are comparable to those of the plain portland cement concrete. The high-volume fly ash concrete shows excellent resistance to chloride ion penetration and outperforms plain portland cement concrete.

Sorption of Low Molecular Weight Organic Contaminants by Fly Ash: Considerations for the Enhancement of Cutoff Barrier Performance

Abstract: Experimental measurements indicate that class F fly ashes have significant capacity for sorption of low molecular weight organic contaminants from aqueous solution, the capacity being related to the carbon content and to other properties specific to the fly ashes tested. Correlations of Freundlich sorption capacity parameters with the respective octanol-water partition coefficients and the aqueous solubilities of the organic contaminants were highly significant.

Fixation and utilization of ash residue from the incineration of municipal solid waste

Abstract: Municipal solid waste ash is utilized in the manufacture of an aggregate and is processed to form a cold bonded pellet which, when tested by means of TCLP leaching extraction tests using TCLP No. 2 extraction fluid, does not exceed the 1990 limits for the RCRA priority heavy metals. The pellets may be surface coated with defined agents to seal the pellet or to provide properties which enhance the use of the pellet in either asphaltic or cement concrete mixes. A method of utilizing MSW ash includes the steps of collecting the bottom ash and fly ash components, processing the bottom ash component to remove unprocessible material and crushing the crushable component to a desired size, magnetically separating the magnetic material from at least the processed bottom ash component, treating at least the fly ash component of the ash with alkali silicate to fix the heavy metals, and utilizing the processed ash such as by adding cement or other binders in a mix to form pellets having an early strength sufficient to permit handling after 24 hours. Pellets may be treated with selective components and coatings to enhance the pellet's use as an aggregate in asphaltic or cement concrete mixes.

Fouling of convection heat exchangers by lignitic coal ash

Abstract: Ash deposits formed at moderate temperatures (1100-1300 K) in the convective sections of utility boilers firing coals containing lignitic ash are associated with the formation of sticky particles following condensation of sodium sulfate from the vapor phase at 1200-1300 K The deposits are enriched in calcium, due to the abundance of calcium among the particles impacting and sticking and the low melting temperature of mixtures of calcium, magnesium, and sodium sulfates Because the formation of these deposits occurs only in a limited range of gas temperatures, approximately from the dew point to the melting temperature of sodium sulfate, they are not observed during experiments in which deposition is accelerated by increasing the temperature to values typical of furnace exit gas or higher

Fixant for mixed organic and inorganic contaminated materials and method for using same

Abstract: A toxic waste fixant for detoxification of a contaminated material includes a mixture of ferric sulfate, manganese sulfate, organophilic clays, an oxidizer and aluminium sulfate. The respective amounts are preferably about 15-19% b.w. of ferric sulfate, about 15-19% b.w. of manganese sulfate, about 37-46% b.w. of organophilic clay, about 16-19% b.w. of an oxidizer and about 0-12,5% b.w. of alumimium sulfate. All or part of the ingredients in said fixant may be added as a pretreatment into contaminated materials such as soils, sediments, or sludges. This pretreatment can range from 0 to 100% b.w. to said material. The fixant is blended with various amounts of Portland cement, and/or blast furnace slag, or lime, or gypsum, or coal fly ash, or cement kiln dust as a means to derive a chemical fixation treatment for contaminated soils, sediments, and sludges to prevent the leaching of organic and inorganic compounds and elements.

Utilization of coal-ash minerals for technological ceramics

Abstract: Glasses synthesized from Utah bituminous coal-ash melts were crystallized to form glass ceramics to determine the feasibility of coal-ash utilization. The use of additives to promote glass formation and catalysts to serve as nucleation sites for crystallization was studied. The microstructure of the crystalline phase was investigated using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The bulk glasses and glass-ceramics were evaluated by Knoop microhardness and density measurements. The crystalline phase formed has been identified as anorthite, CaAl2Si2O8. Crystallization of the ash was possible up to a maximum of approximately 40%. The use of TiO2 as a nucleation catalyst did little to improve the degree of crystallinity; however, the crystal phase became better defined when this catalyst was used, even in small amounts.

Palladium nitrate—magnesium nitrate modifier for electrothermal atomic absorption spectrometry. Part 3. Determination of mercury in environmental standard reference materials

Abstract: A single addition of 15 µg of palladium is sufficient for 40–60 determinations of mercury if the graphite tube is not heated to temperatures higher than 1500 °C in the cleaning step. A pyrolysis temperature of 400 °C can be used without any loss of mercury, and a characteristic mass of 0.1 ng of mercury was obtained for an atomization temperature of 1000 °C. Interferences caused by high sodium chloride concentrations could be eliminated by using a mixture of 95% argon and 5% hydrogen as the purge gas. Mercury could be determined accurately in Aquatic Plant, Albacore Tuna, River Sediment and Coal Fly Ash reference materials.

Fly ash design manual for road and site applications. Volume 2: Slurried placement: Final report

Abstract: This design manual is the second of two volumes pertaining to the use of fly ash as a construction material in road and site development applications. Volume 1 describes the use of fly ash conditioned with small amounts of water to produce a solid, soil-like material. Volume 2 describes the use of fly ash mixed with sufficient water to create a fluid or semi-fluid material. In most applications, Portland cement is added to the mixture to provide the desired level of strength. In some applications, aggregate filler is also added to the mixture to improve the durability of the mix. The flowable nature of these materials determines the manner in which they are handled, placed, and used in construction. The following uses are discussed: Slurry Backfills; Grouting; and Hydraulic Fills. Miscellaneous uses are also discussed, including the use of fly ash in high fly ash content concrete, unsintered synthetic aggregate, and slurry walls. Also included are three appendices containing additional information of interest to the designer: Mix Design; Laboratory Test Procedures; and a Bibliography.

Plant and animal species composition and heavy metal content in fly ash ecosystems

Abstract: Plant and animal species present on a coal fly ash slurry pond site and a dry deposit site were surveyed and sampled during a two-day period in October. Elemental analyses were determined for most of the species encountered. A total of 48 plant species were observed on the two sites, with 35 species on the wet site, and 20 on the dry site. Eighteen terrestrial and 7 aquatic animal species were found on the wet site, exclusive of vertebrates which were not studied with the exception of a carp (Cyprinus carpio). Eleven terrestrial invertebrates and one aquatic species were observed on the dry site. Neutron activation analysis was carried out for: Se, Hg, Cr, Ni, Zn, Co, Sb, Cd, and As. Using literature values for phytotoxicity, we conclude that, in general, plants did not accumulate toxic levels of metals. Only one plant (Impatiens biflora Willd.) showed a significant level of Cd. Of 20 plants analyzed on the wet site, 10 had excessive Se concentrations (>5 ppm); on the dry site 6 out of 18 had high Se values. In animals (Gryllus sp.; Melanoplus sp.; Trachelipus sp.; Lumbricus terrestris; Physa integra; Cyprinus carpio) the trace metal concentration was generally in between that of control animals and that of the fly ash itself. One exception included Zn, which, although the most variable element examined, was concentrated in all the terrestrial animals to levels higher than in fly ash. Crickets are the most consistent bioconcentrators with Cr, Se, and Zn at higher levels than for control animals. All animal species studied accumulated Se compared to controls.

MSW Incinerator Ash as Aggregate in Concrete and Masonry

Abstract: The properties of concrete and concrete masonry using municipal solid waste (MSW) ash as fine aggregate were studied. Mass-burn combined ash and refuse-derived-fuel (RDF) bottom ash were studied. The properties included compressive strength, expansion, time of set, unit weight, leaching characteristics, and gas generation by the mixtures. These ashes were not suitable for use in concrete because of low strength and cracking caused by gas generation. Some concrete-masonry specimens containing ash had adequate strength but had bad smell and cracking and spalling problems. Mass-burn ash produced higher concrete and concrete-masonry strengths than RDF ash. EPTOX tests showed that leachate from the MSW concrete or concrete masonry did not exceed toxicity limits.

Pumpable backfill grout

Abstract: A pumpable backfill grout which hardens into a controlled low strength material and an additive for making up such a backfill grout. The grout consists essentially of portland cement, a smooth surfaced vesicular expanded perlite, fly ash, fine aggregate, water, an air entraining agent, a quick dispersing thixiotropic suspending agent and a bentonite thickening agent.