Showing papers on "Fly ash published in 1996"

Industrial Ecology: Towards Closing the Materials Cycle

Abstract: Introduction - material perspective resource perspective alumina, aluminium and gallium copper, cobalt, silver and arsenic chromium sources, uses and losses zinc and cadmium sulfur and sulfuric acid phosphorus, flourine and gypsum nitrogen-based chemicals the chlor-alkali sector electronic grade silicon (EGS) for semiconductors post-consumer packaging wastes scrap tires coal ash - sources and possible uses on industrial ecosystems. Appendices: Production and consumption data data sources for the study.

Metal Leaching of Fly Ash from Municipal Waste Incineration by Aspergillus niger

Abstract: Biological leaching of fly ash from municipal waste incineration by Aspergillus niger was examined in batch cultures and compared with chemical leaching. A. niger grew in the presence of up to 10% (w/v) of fly ash in the medium. In the presence of fly ash A. niger produced gluconate, whereas in its absence citrate was produced. Variation of the fly ash concentration in the growth medium (one-step process) resulted in different amounts of solubilized metals. A total of 3% (w/v) fly ash generally gave maximum extraction yields (in percent of the amount applied). In a two-step process A. niger first was cultivated in the growth medium, and subsequently the microbiologically produced citric acid was used as the leaching agent. At 6% (w/v) fly ash, the amounts of leached metals (leaching for 1 day) were 81% of Cd, 66% of Zn, 57% of Cu, 52% of Pb, 32% of Mn, 27% of Al, and less than 10% of Cr, Fe, and Ni, respectively. Chemical leaching with commercial citric acid of equal molarity was only slightly higher than...

Synthesis and Properties of Zeolites from Coal Fly Ash

Abstract: Previous attempts to use fly ash as a soil amendment have had limited success because of its low nutrient value, low cation exchange capacity (CEC), and elevated levels of toxic trace elements. However, treating fly ash with NaOH or KOH at an elevated temperature converts the ash into zeolite minerals and solubilizes the toxic trace elements, which are removed in the base solution. The CEC of the untreated fly ash was <100 mmolC kg-1 but increased to over 3000 mmolC kg-1 when heated for 3 days at 100 °C in 3 M NaOH. The dominant zeolites formed at 100 °C in NaOH were zeolite Na-Pl and zeolite P-C, and at temperatures of 150−250 °C, the mineralogy changed to zeolite X and pectolite. In KOH at 100 °C, zeolite K-G (potassium chabazite) was formed. The fly ash zeolites had a high affinity for K+, Ca2+, and NH4+, although attempts to use the treated ash to remove NH4+ and heavy metals from wastewater and electroplating wastes were only partially successful. Potential uses of the treated ash were limited due to...

Complete heavy metal removal from fly ash by heat treatment : Influence of chlorides on evaporation rates

Abstract: Thermal treatment is a promising way for the decontamination and inertization of residues from waste incineration. The evaporation of heavy metal compounds thereby is of great significance. It is the goal of this work to identify, by analyzing evaporation rates, the predominant thermochemical reactions of the heavy metals with other constituents of fly ash, with respect to volatilization. To this end, experiments were performed with fly ash from a municipal solid waste (MSW) incineration plant as well as with synthetic powder mixtures in the temperature range of 670−1000 °C. The rates of Cd, Cu, Pb, and Zn evaporation can be described accurately by a simple first-order rate law and a rate coefficient which itself follows an exponential temperature dependence analogous to the Arrhenius equation. The degrees (completeness) as well as the rates of evaporation of the heavy metals are markedly influenced by chlorides contained in the fly ash, largely as NaCl. Experiments with model substrates indicate that the...

Role of Sulfur in Reducing PCDD and PCDF Formation

Abstract: Past research has suggested that the presence of sulfur (S) in municipal waste combustors (MWCs) can decrease the downstream formation of chlorinated organic compounds, particularly polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Thus, co-firing a MWC with coal, because of the S species from coal, may reduce PCDD and PCDF emissions. Experiments were carried out to test this hypothesis and to determine the role of S. A field-sampled MWC fly ash was injected into the EPA's pilot-scale reactor, doped with hydrogen chloride (HCl). The tests involved either natural gas or coal combustion. Besides the combustion environment, MWC fly ash injection temperature and sulfur-to-chlorine ratio (S/CI) were varied. Flue gas was sampled and analyzed for PCDD and PCDF to determine in-flight formation. In the natural-gas-fired reactor, when S was added (as sulfur dioxide, SO 2 ), the PCDD and PCDF formation decreased dramatically at S/Cl ratios as low as 0.64, and with varying furnace conditions, the inhibitory effect was consistent for S/Cl ratios of about 1. In tests with the coal-fired furnace, the S inhibitory effect was again observed at S/Cl values of 0.8 and 1.2, respectively, for the two coals tested. S inhibition mechanisms were studied in a bench-scale reactor. Results show that the depletion of molecular chlorine (Cl 2 ), an active chlorinating agent, by SO 2 through a gas-phase reaction appears to be a significant inhibition mechanism in addition to previously reported SO 2 deactivation of copper catalysts.

Wood and combination wood-fired boiler ash characterization

Abstract: Ashes resulting from the combustion of wood residues in industrial boilers are characterized relative to (i) macroelement compositions, (ii) trace and heavy metal microelement compositions, (iii) organics, and (iv) polychlorinated dibenzo-dioxins and -furans (PCDD/Fs). Ash compositions, both macro and microelements, are compared with coal ash and limestone. Microelements in wood ashes are also compared with other potential soil amendments such as pulp mill sludges. The impact of burning sludge and combinations of coal and wood residue on ash metal concentrations is presented. Levels of PCDD/Fs in ash resulting from combustion of 100% inland wood residue, salty wood, or bleached mill sludge with wood residue are reviewed, as are the levels of PCDD/Fs in ashes and soot resulting from residential wood combustion. The concentrations of metals in wood ash are comparable to other potential soil amendments. The concentration in wood ash of common organics of environmental concern appears to be negligible. The levels of PCDD/Fs in the ash appear to have a direct correlation with extraneous sources of chloride in the wood fuel.

Cementitious gypsum-containing compositions and materials made therefrom

Abstract: A cementitious composition useful for water-resistant construction materials, including floor underlayments, backing boards, self-leveling floor materials, road patching materials, fiberboard, fire-proofing sprays, and fire-stopping materials includes about 20 wt. % to about 75 wt. % calcium sulfate beta-hemihydrate, about 10 wt. % to about 50 wt. % Portland cement, about 4 wt. % to about 20 wt. % silica fume and about 1 wt. % to about 50 wt. % pozzolanic aggregate. The Portland cement component may also be a blend of Portland cement with fly ash and/or ground blast slag.

Adsorption of Phenolic Compounds on Fly Ash

Abstract: Adsorption isotherms for adsorption of phenol, 3-chlorophenol, and 2,4-dichlorophenol from water onto fly ash were determined. These isotherms were modeled by the Freundlich isotherm. The fly ash adsorbed 67, 20, and 22 mg/g for phenol, chlorophenol, and 2,4-dichlorophenol, respectively, for the highest water phase concentrations used. The affinity of phenolic compounds for fly ash is above the expected amount corresponding to a monolayer coverage considering that the surface area of fly ash is only 1.87 m2/g. The isotherms for contaminants studied were unfavorable, indicating that adsorption becomes progressively easier as more solutes are taken up. Phenol displayed a much higher affinity for fly ash than 3-chlorophenol and 2,4-dichlorophenol.

Investigation of lignite-based bottom ash for structural concrete

Abstract: A pilot study was undertaken on the use of lignite-based bottom ash as a fine aggregate in structural grade concrete. Bottom ash is combined with portland cement, crushed limestone coarse aggregate, and water to produce concretes with a uniform slump of 100 mm (4±¼ in.). Four different mixes with cement contents ranging from 297 to 475 kg/m³ (500 to 800 lb/yd³) are utilized. The bottom ash concretes are studied for fresh properties, hardened characteristics, and long-term durability. The engineering characteristics of mixtures made with bottom ash are compared with those of conventional concretes in order to evaluate the effectiveness and suitability of bottom ash as a viable fine aggregate in portland cement-based mixtures. Laboratory test results conclude that the inclusion of bottom ash increases the demand for mixing water in obtaining the required workability. As a consequence, both fresh and hardened properties are impacted, particularly for mixtures of low cement content. When a water-reducing admixture is used, the engineering properties of bottom ash concretes are similar, and in most cases superior, to those of control concretes.

Chlorophenol Reactions on Fly Ash. 1. Adsorption/Desorption Equilibria and Conversion to Polychlorinated Dibenzo-p-dioxins

Abstract: Tetrachlorophenol (T 4 CP) reactions to PCDD products in the presence of MSWI fly ash were measured as a function of gas-phase precursor concentration, reaction time, and reaction temperature. Tetrachlorophenol concentrations ranged from 150 to 700 ng/mL in 10% O 2 , and temperatures ranged from 250 to 400 °C, which resulted in PCDD formation rates from about 0 to 35 μg of PCDD (g-fly ash) -1 min -1 . Reaction conditions were found such that the reactor approached differential behavior, which led to the breakthrough of the T4CP and the desorption of adsorbed PCDD products into the gas-phase. At constant temperature, the surface coverage of chlorophenols on fly ash was found to be constant for reaction times between 2 and 120 min, suggesting that the system had quickly reached adsorption/desorption equilibrium. Yields of PCDD were observed to increase with increasing precursor concentration but either peaked, leveled off, or increased as the temperature was raised. Studies of T4CP reactions on different fly ashes showed a correlation between total conversion of T 4 CP-to unknown products-and total yield of the trace reaction forming PCDD.