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Query: UMLS:C0205700 (ash)
 15,125 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In this study, a melting process with addition of SiO2 was applied to treat incinerator fly ash. To describe the encapsulation behaviors of metals quantitatively, the amorphous volume fraction (AVF) of slags was initially determined. Vitrification appeared to reduce the mobility of Cr, Cu, Mn, and Ni instead of significantly immobilizing Cd, Pb, and Zn. It was verified that SiO2 enhanced the formation of an amorphous glassy structure. With the increase of SiO2, the crystalline phases would gradually diminish and transform into a higher silica-connected species. During the formation of slag matrix, Al, Ca, and Mg could modify the glass network, and consequently the encapsulation behaviors of these species would noticeably affect the chemical stability of slags. Significant immobilization of crust metals could be achieved only when a more compact and interconnected amorphous glass network was formed. Hence, it indicated that a higher AVF silica-based slag had a better potential to resist acid attack. In conclusion, for environmental protection, it is important to investigate the correlation between the encapsulation behaviors of metals and the crystalline characteristics of slag structure.
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PMID:Encapsulation behaviors of metals in slags containing various amorphous volume fractions. 1768 97

Manufacturing the glass-ceramic has been proposed as a useful choice to recycle coal fly ash from power plants. In this work, a glass-ceramic of SiO2-Al2O3-Fe2O3-CaO family was synthesized by mixing 90 wt% of coal fly ash, from a power plant in west of China, with Na2O, and then melted at 1350 degrees C. The ceramization of the obtained glass was carried out at 770 degrees C for 2h. Esseneite and nepheline were found present as major crystal phases. The produced glass-ceramic exhibited good chemical durability as well as good mechanical properties. The toxicity characteristic leaching procedure (TCLP) method found that the glass-ceramic was non-hazardous.
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PMID:Utilization of coal fly ash in the glass-ceramic production. 1776 38

The objective of this study is to investigate how cooling rate and basicity in a vitrification process govern the crystalline characteristics of slags. In this experiment, the incineration fly ash mixtures with various SiO2 addition ratios were vitrified at 1450 degrees C and cooled down separately by air or water. Different thermal analysis, scanning electron microscopy and X-ray diffraction analysis with an internal standard addition were applied to investigate the crystalline characteristics of slags. The microanalytical mapping images showed that water quenching and the addition of SiO2, both enhanced the glassy amorphous phase to distribute more uniformly in slags. Addition of SiO2 would lower the melting temperature of fly ash mixtures and retard the formation of crystalline phases in slags. When the basicity (mass ratio of CaO to SiO2 before vitrification) was >0.990, the profiles of crystalline phases in slags with equal basicity were similar no matter how they were cooled. However, when the basicity <0.674, water quenching greatly enhanced the formation of the glassy amorphous phase in slags. For air cooled slags, an even lower basicity (<0.511) is required to vitrify fly ash well.
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PMID:Effect of water quenching and SiO2 addition during vitrification of fly ash Part 1: on the crystalline characteristics of slags. 1776 40

Basic properties of fly ash samples from different urban waste combustion facilities in China were analyzed using as X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD). The leaching toxicity procedure and some factors influencing heavy metals distribution in fly ash were further investigated. Experimental results indicate that the fly ash structures are complex and its properties are variable. The results of XRF and SEM revealed that the major elements (>10000 mg/kg, listed in decreasing order of abundance) in fly ash are O, Ca, Cl, Si, S, K, Na, Al, Fe and Zn. These elements account for 93% to 97%, and the content of Cl ranges from 6.93% to 29.18 %, while that of SiO2 does from 4.48% to 24.84%. The minor elements (1000 to 10000 mg/kg) include Cr, Cu and Pb. Primary heavy metals in fly ash include Zn, Pb, Cr, Cu etc. According to standard leaching test, heavy metal leaching levels vary from 0 to 163.10 mg/L (Pb) and from 0.049 to 164.90 mg/L (Zn), mostly exceeding the Chinese Identification Standard for hazardous wastes. Morphology of fly ash is irregular, with both amorphous structures and polycrystalline aggregates. Further research showed that heavy metals were volatilized at a high furnace temperature, condensed when cooling down during the post-furnace system and captured at air pollution control systems. Generally, heavy metals are mainly present in the forms of aerosol particulates or tiny particulates enriched on surfaces of fly ash particles. The properties of fly ash are greatly influenced by the treatment capacities of incinerators or the variation of waste retention time in chamber. Fly ash from combustors of larger capacities generally has higher contents of volatile component and higher leaching toxicity, while those of smaller capacities often produce fly ash containing higher levels of nonvolatile components and has lower toxicity. The content of heavy metals and leaching toxicity maybe have no convincing correlation, and high alkali content of CaO greatly contribute to leaching toxicity of heavy metal and acid neutralization capacity against acid rain.
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PMID:Investigation of basic properties of fly ash from urban waste incinerators in China. 1791 10

In order to extend the recycling of waterworks sludge to engineering applications, this paper addresses the influence of nano-SiO2 on incinerated waterworks sludge ash (IWSA) cement paste attacked by sulfate. Tests were performed such as length measurement for volume change, compressive strength, weight loss, and micro-structural testing using scanning electron microscopy (SEM). The results indicate that when a portion of the cement in the paste was replaced by IWSA, the IWSA diluted the cementitious material C3A, and filled the capillary pores in the hardened paste. Moreover, since IWSA has potential pozzolanic activity, it can chemically react with Ca(OH)2 crystals in the paste and can consequently improve the resistance of the paste to sulfate attack. Test results also show that due to the fully developed pozzolanic effect of IWSA, the major reaction products of sulfate attack, gypsum and ettringite, were clearly reduced. Hence, the expansion rate in length decreased with the increase of IWSA replacement. Furthermore, the addition of nano-SiO2 to IWSA cement paste can also reduce the length expansion rate.
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PMID:The application of waterworks sludge ash to stabilize the volume of cement paste. 1823 78

Treatment of municipal solid waste incineration (MSWI) fly ash is becoming an important issue in China. A pilot-scale experiment was carried out to treat MSWI fly ash by using a diesel oil furnace (DOF) for more than 6 months. The effects of melting temperature on volume reduction, weight loss, compositional changes, and toxicity of leach water for molten slag have been investigated and reported. Results indicated that the volume reduction fraction of raw fly ash (RFA) and washed-fly ash (WFA) was 75-80% and the weight loss fraction was 23.8-30% at 1260-1350 degrees C. During the vitrification, CaO, A12O3, and SiO2 percentages in fly ash increased as the temperature increased, especially for SiO2, which was caused by both the decomposition of carbonates or sulfates and the volatilization of metal chlorides because the main components in secondary fly ash collected from fabric filter bags were NaCl and KCl. The leaching concentrations of heavy metals in molten slag were lower than the standard values of TCLP. The releasing levels of dioxin and other pollutants (such as SO2, HCl, CO, NOx, etc.) in flue gas were all lower than the Chinese standard.
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PMID:Melting characteristics during the vitrification of MSWI fly ash with a pilot-scale diesel oil furnace. 1843 55

TCLP analysis (USEPA method 1311) was employed on fly ash in order to analyze the metals leachability and the concentration of cadmium was 0.3225 mg/L which exceeded state TCLP standard(0.3 mg/L). According to USEPA method 1613, I-TEQ of PCDD/Fs in fly ash was 0.45 ng/g. Then a double arcs DC plasma torch was developed to vitrified fly ash. And the results showed that heavy metals were mostly immobilized in the vitrified slag and also I-TEQ of PCDD/Fs in fly ash was destroyed near 91.6%. The morphology of vitrified slag was amorphous state which showed the glassy slag of SiO2 and the microstructure of slag was very compact.
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PMID:[Study on vitrification of fly ashes from municipal wastes incinerator with a plasma torch]. 1863 71

A method for the determination of SiO2, Al2O3, Fe2O3, CaO, SO3, TiO2, K2O, Na2O, P2O5, MgO, MnO and BaO in coal ash by X-ray fluorescence spectrometry with melt sample preparation was developed. This method solved the problems of determination accuracy of S by using the 12:22 mix flux and oxide to lower the melt temperature. Using the soil standard sample and mixing the soil standard sample and coal ash standard sample solved the problem that there are not enough standard samples for coal ash analysis by XRF. The accuracy and precision of this method are acceptable, and the results are comparable to the those obtained by wet chemical method.
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PMID:[Determination of 12 elements in coal ash by x-ray fluorescence spectrometry]. 1880 Jul 42

To improve the drawbacks caused by the sludge ash replacement in mortar, the previous studies have shown that the early strength and durability of sludge ash/cement mortar are improved by adding nano-silicon dioxide (nano-SiO2) to mortar. In this article, three types of nano-SiO2--SS, HS, and SP (manufacturer code names)--were applied to sludge ash/cement mixture to make paste or mortar specimens. The object is to further extend the recycle of the sludge ash by determining the better type of nano-SiO2 additive to improve properties of sludge ash/ cement paste or mortar. The cement was replaced by 0, 10, 20, and 30% of sludge ash, and 0 and 2% of nano-SiO2 additives were added to the sludge ash paste or mortar specimens. Tests such as setting time, compressive strength, scanning electron microscopy, X-ray diffraction, nuclear magnetic resonance, and thermogravimetric analysis/differential thermal analysis were performed in this study. Test results show that nano-SiO2 additives can not only effectively increase the hydration product (calcium silicate hydrate [C-S-H] gel), but also make the crystal structure denser. Among the three types of nano-SiO2 additive, the SS type can best improve the properties of sludge ash/cement paste or mortar, followed by the SP and HS types.
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PMID:The effects of different types of nano-silicon dioxide additives on the properties of sludge ash mortar. 1941 18

The rice hull ash is composed by 94% of SiO2, an agricultural waste that can be recovered and purified by a depolymerization reaction yielding an organo-silicic gel. The purpose of this paper is to show that this silica can be used to fix Cd2+ from aqueous solution. The pH of hydrolysis of the organo-silicic gel is the main factor modifying the distribution between the solid and the solution. The contact time between the Cd2+ solution and the solid was studied to optimize the sorption conditions. The equilibrium measurements were performed after 40 hours at room temperature. The competition with Ca2+ ions in the solutions was also studied in order to evaluate the selectivity of the Cd2+ fixation. It was found that the rice hull ash has a higher capacity to fix Cd2+ than the rice hull derivatives.
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PMID:Selectivity of the Cd2+/Ca2+ exchange on modified rice hull silica. 1943 59


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