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

The surface-mediated reactions of 2-chlorophenol, 1,2-dichlorobenzene, and chlorobenzene were studied using CuO/ SiO2 as a fly ash surrogate. These compounds served as model precursors that have been implicated in the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). With FTIR, we determined that reactions of the model precursors with a substrate composed of CuO dispersed on silica result in the formation of a mixture of surface-bound phenolate and carboxylate partial oxidation products from 200 to 500 degrees C. Chemisorption of 2-chlorophenol and 1,2-dichlorobenzene resulted in the formation of identical surface-bound species. Using X-ray absorption near-edge structure spectroscopy, we measured the time- and temperature-dependent reduction of Cu(II) in a fly ash surrogate during reaction with each precursor. It was demonstrated that CuI2O is the major reduction product in each case. The rate of Cu(II) reduction could be described using pseudo-first-order reaction kinetics with Arrhenius activation energies for reduction of Cu(II) of 112, 101, and 88 kJ mol(-1) for 2-chlorophenol, 1,2-dichlorobenzene, and chlorobenzene, respectively. We demonstrate that chlorinated phenol and chlorinated benzene both chemisorb to form chlorophenolate. Although chlorinated phenols chemisorb at a faster rate, chlorinated benzenes are found at much higher concentrations in incinerator effluents. The implication is that chlorinated benzenes may form 10 times more chlorophenolate precursors to PCDD/Fs than chlorinated phenols in combustion systems.
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PMID:An infrared and X-ray spectroscopic study of the reactions of 2-chlorophenol, 1,2-dichlorobenzene, and chlorobenzene with model cuO/silica fly ash surfaces. 1624 7

Waste incineration is still an essential technology in the concept of integrated waste management. Most of the combustion residues are incinerator bottom ash. It has been discovered that incinerator bottom ash from the incineration of separated waste in the primary chamber of the modular two-stage incinerator mainly consists of metal oxides, especially SiO2 and CaO, in proportions that are quite similar to those in cement and so the feasibility of its application as a substitute for cement in concrete was investigated. It was found that after 28 days, the flexural and compressive strengths of the binder using bottom ash were practically comparable with those of a pure cement mixture. The results show that it is reasonable to use a binder containing incinerator bottom ash for applications in which an early-stage lower strength of concrete element is acceptable.
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PMID:Utilization of bottom ash from the incineration of separated wastes as a cement substitute. 1627 55

Sludge incinerated ash has been fired at different temperatures. This material was fired at 1050 degrees C for 3 h and until a peak of 1010 degrees C. After thermal treatment the ash was screened at 200 mesh.The ash was characterized by X-ray fluorescence and trace elements like Cr, Pb, Zn, Cu, and some oxides like quartz(SiO2), Al2O3, P2O5, Fe2O3 were found. Scanning electron microscopy(SEM) has shown one change of particle between 2 microm at 90 microm and apparent porosity, thermal analysis has shown loss of mass and residual decomposition in the TG, DTG and DTA curves.
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PMID:An experimental study of sewage sludge incineration. 1706 31

The possibility of using incinerator bottom ash as a substitute for natural aggregates was investigated. Rough, porous surface of bottom ash, which diminishes the strength of solidified products, was improved by colloidal silica solution. As a result, a significant increase of mechanical strength was accomplished by a slight amount of silica (<1 wt% to total). Moreover, pozzolanic reaction was induced in initial cement hydration due to the nano-particle size of about 20 nm in colloidal silica solution. Cylindrical specimens and bricks were prepared from bottom ash added to a colloidal silica (SiO2) solution and cement, and then their compressive strengths were evaluated. Cylindrical specimens showed an increase of approximately 60% in compressive strength when colloidal solution containing 4 wt% silica particles was sprayed onto the bottom ash. The strength of bricks containing colloidal silica was in excess of 20 MPa, which meets the requirement of construction materials. Results of leaching tests based on Toxicity Characteristic Leaching Procedure (TCLP) proved that the solidified bottom ash possessed good chemical stability.
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PMID:Solidification and recycling of incinerator bottom ash through the addition of colloidal silica (SiO2) solution. 1708 41

Chemical composition and toxicity leaching characteristics of fly ash was analyzed. The experiment results show that many heavy metals were contained; leaching concentration of Pb is 67.03 mg/L, which exceeds the limit of identification standard for hazardous wastes. Effect of input mass of H3PO4 on immobilization of heavy metals and its long-term environmental stability was studied. The results show that when input 8% - 14% (H3PO4 mass/ fly ash mass) of H3PO4 sound immobilization effect can be achieved; 8% and 12% of H3PO4 will bring a satisfactory environmental stability of heavy metals, while more H3PO4 led to less buffer capacity to acid conditions. In fly ash treated by 12% H3PO4, a small quantity of crystal Cr2P2O7, ZnP2, Pb3P4O13, Pb3P2O7, NaZnPO4, NaPbP3O9, Ca2ZnSi2O7 can be detected by XRD; many independent fly ash particles and bar-shaped Pb5 (PO4)3Cl with a diameter of 0.3 - 0.5 microm were observed by SEM; concentrated heavy metal materials were not obtained by CHBr3 floatation. Conclusions can be drawn that, through neutralization reaction of H3PO4 with strongly alkaline fly ash, stabilization reaction conditions were improved, entrapped heavy metals were chemically activated and PO4(3-) needed in stabilization was produced. Activated heavy metals combined with PO4(3-) on surface of fly ash,generated phosphates existing as forms of solid solution in SiO2, CaCO3, CaSO4, KCl, NaCl.
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PMID:[Immobilization technology and mechanism of fly ash using H3PO4]. 1711 36

In this study, the effects of the basicity on the pouring point of the municipal solid waste incinerator fly ash-sewage sludge ash mixture is investigated. Four kinds of sewage sludge ash, which were collected from several primary and secondary sewage treatment plants and were produced by different processes and sludge conditioning alternatives, were used as modifiers. The results indicate that the pouring point of the mixture increased with increasing basicity, within the range of 0.65-1.90. The pouring point is affected by the contents of the mixtures (CaO, SiO2, Al2O3, and the flux). It is suggested that an increase in the CaO content tends to raise the pouring point, whereas an increase in the SiO2 and/or the Al2O3 contents cause as adverse reaction. The prediction equation, obtained by multilinear regression (significant level is 0.05), is as follows: pouring temperature = 1189.6 + 4.19 CaO - 0.96 SiO2 - 4.33 Al2O3 (R2 = 0.91). In general, the pouring point decreased when the basicity was < 1. The pouring point apparently increased when the basicity was > 1.2. The regression squares for the different basicities were between 0.84 and 0.91. From these relationships, we note that a basicity index of 5 gave the best R2 (0.91). From the results of this study, it can be concluded that the modification of the basicity of the fly ash by the addition of sewage sludge ash to lower the pouring point is feasible and leads to a more energy-efficient melting process. In addition, these synthetic slags have a good pozzolanic reactive activity.
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PMID:Effects of the basicity on the comelting conditions of municipal solid waste incinerator fly ash and sewage sludge ash. 1719 93

Fundamental properties and the factors that influence the distribution of heavy metals of several fly ashes are analyzed. Experiments indicate that the structures are complex and the properties are changeable. The study results show that the chemical composition is Cl, Ca, K, Na, Si, Al, O, etc, and heavy metals are Zn, Pb, Cr, Cu etc. The main structures of fly ash are irregularly amorphous forms and polycrystalline aggregates. Generally, the ieaching toxicity exceeds the identification standard for hazardous wastes. Heavy metals are chiefly in the forms of tiny aerosol particles and aggregates on the surface of fly ash. The properties of fly ash are greatly influenced by the change of incinerators or the variation of incinerating time. The content of Cl ranges from 6.93% to 29.18%, while that of SiO2 does from 4.48% to 24.84%. The leaching toxicity varies between 0 and 163.10 mg x L(-1) (Pb) and between 0.049 and 164.90 mg x L(-1) (Zn).
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PMID:[Fundamental properties of fly ash from municipal solid waste incineration]. 1732 41

In this work coal fly ash has been employed for the synthesis of geopolymers. Two different systems with silica/alumina ratios stoichiometric for the formation of polysialatesiloxo (PSS, SiO2/Al2O3=4) and polysialatedisiloxo (PSDS, SiO2/Al2O3=6) have been prepared. The alkali metal hydroxide (NaOH or KOH) necessary to start polycondensation has been added in the right amount as concentrated aqueous solution to each of the two systems. The concentration of each alkali metal solution has been adjusted in order to have the right liquid volume to ensure constant workability. The systems have been cured at four different temperatures (25, 40, 60, and 85 degrees C) for several different times depending on the temperature (16-672 h at 25 degrees C; 72-336 h at 40 degrees C; 16-120 h at 60 degrees C and 1-6h at 85 degrees C). The products obtained in the different experimental conditions have been submitted to the quantitative determination of the extent of polycondensation through mass increase and loss on ignition, as well as to qualitative characterization by means of FT-IR spectroscopy. Furthermore, physico-structural and mechanical characterization has been carried out through microscopic observations and the determination of unconfined compressive strength, elasticity modulus, apparent density, porosity and specific surface area. The results have indicated that the systems under investigation are suited for the manufacture of pre-formed building blocks at room temperature.
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PMID:Coal fly ash as raw material for the manufacture of geopolymer-based products. 1738 28

This work investigated the vitrification of hazardous electroplating sludge containing 140 mg/g Cr with/without bottom ash or cullet conditioning to lower specimens' basicities to 0.97-1.17 or 0.18-0.23, respectively. The conditioning was found to enhance the smooth/glassy appearance of slags but no ingot was obtained. Cr was >98% retained in the vitrified slags. Cr2O3 dominated in crystalline structure for the slag vitrified from the sludge, but this domination gradually shifted to Fe2SiO4/Fe3O4/SiO2 or SiO2 crystalline with increasing addition of bottom ash or cullet into the sludge, respectively. Compared to the raw sludge, the sludge-vitrified slag displayed lower leaching concentrations for most metals (particularly Cr (2.54 mg/L)), and smaller leaching ratios for Ag, Cr, and Cu (1.35, 0.02, and <0.01%, respectively) but greater ones for Cd, Pb, and Zn (3.83, 2.46, and 0.36%, respectively). The Cr leaching ratios were approximately 0.01% for the slags vitrified from the conditioned sludge. Independent of the slag basicity and crystalline structure, metal leaching quantity increased but leaching ratio decreased with increasing slag metal content. The slag compressive strengths were improved to >14.7 MPa at the mixing ratios > or = 2/1 and 1/1 for bottom ash/sludge and cullet/sludge, respectively. Fulfilling the criteria of Toxicity Characteristic Leaching Procedure (TCLP), all the slags were recyclable.
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PMID:Vitrification of chromium electroplating sludge. 1753 63

Structural changes in fly ash geopolymers activated with different sodium hydroxide and silicate concentrations are investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy over a period of 200 days. A strong correlation is found between the concentration of silicate monomer in the activating solution and the position of the main Si-O-T stretching band in the FTIR spectrum, which gives an indication of the relative changes in the gel Si/Al ratio. The FTIR spectra of geopolymer samples with activating solution concentrations of up to 1.2 M SiO2 indicate that an Al-rich gel forms before the final gel composition is reached. The time required for the system to reach a steady gel composition depends on the silicate activating solution concentration and speciation. Geopolymers activated with solutions containing predominantly high-order silicate species rapidly reach a steady gel composition without first forming an Al-rich gel. A minimum silicate monomer concentration of approximately 0.6 M is required to shift the geopolymer synthesis mechanism from hydroxide activation to silicate activation. Silicate speciation in the activating solutions also affects zeolite formation and geopolymer microstructures, with a more homogeneous microstructure and less zeolite formation observed at a higher SiO2 content.
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PMID:Attenuated total reflectance fourier transform infrared analysis of fly ash geopolymer gel aging. 1759 27


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