| Oil shale fly ash (OSFA) was used as the main raw material to prepare glass-cermaics in this study, and the effects of basicity on the product performances were studied. Based on the analysis of chemical compositions and mineral phases of different kinds of solid wastes, oil shale fly ash and municipal solid waste incineration bottom ash were firstly used as raw materials to prepare oil shale fly ash-based composite ashes. The compositions of composite ashes meet the requirements of CaO-Al2O3-SiO2 system glass-ceramics. Then, oil shale fly ash-based composite vitrified slag was mixed with oil shale fly ash to prepare glass-ceramics from the point of improving utilization rate of solid wastes and reducing energy consumption. Meanwhile, the stabilization/solidification of municipal solid waste incineration fly ash was achieved via co-sintering the composite vitrified slag and FA, depending on higher sintering activity and greater crystallization ability of composite vitrified slag. The following works are carried out and the main conclusions are as follows in this dissertation:(1) Glass raw materials with different basicity (CaO/SiO2) were obtained by adjusting the proportion of CaO and Al2O3 in OSFA. Then they were used as raw materials to prepare CaO-Al2O3-SiO2 system glass-ceramics by melting/queching and single sintering technique. Effect of basicity on crystallization kinetics of glass-ceramics was studied by using Kissinger and Augis-Benne equations. In addition, some analytical methods, including the differential scanning calorimetry (DSC), X-ray powder diffraction (XRD), and toxicity characteristic leaching procedure (TCLP), were used to analyze the effects of basicity on crystalline phase compositions, microstructure, mechanical, physical and chemical properties, and heavy metal toxicity leaching of glass-ceramics. The results indicated that the crystallization mechanism of glass-ceramics was surface crystallization mechanism. The value of crystallization activation energy was decreased from 231.61 kJ/mol to 196.84 kJ/mol when increasing the basicity from 0.2 to 0.5. The main crystalline phase of glass-ceramics changed from anorthite (CaAl2Si2O8) to the coexisting of anorthite & gehlenite (Ca2Al2SiO7), and the properties of glass-ceramics were improved with the increase of basicity. The compressive strength and bending strength of glass-ceramics with the basicity of 0.5 attained their maximum values of 186 MPa and 78 MPa at 1050 ?, respectively. The chemical resistances of glass-ceramics in acid and alkali solutions decreased as follows:NaOH> HAc> H2SO4. Toxicity characteristic leaching procedure results indicated that the leaching concentrations of heavy metals in glass-ceramics were much lower than the threshold limit values of US EPA. Heavy metals were immobilized into the crystal structures and were stable and harmless to surroundings.(2) OSFA and municipal solid waste incineration bottom ash were used as raw materials to synthesize the composite vitrified slag. Then it was mixed oil shale fly ash to synthesize glass-ceramics via single sintering method. Effects of composite vitrified slag addition and sintering temperatures on the crystalline phase compositions, sintering shrinkage, weight loss on ignitions, product density, compressive strength, and chemical resistances of glass-ceramics were studied. The results indicated that anorthite and quartz were identified as the main crystalline phases of glass-ceramics. The values of sintering shrinkage, density, and compressive strength of glass-ceramics increased with the increase of composite vitrified slag addition and sintering temperatures, however the values of weight loss on ignitions showed the opposite tendency. With the increase of OSFA addition from 10%to 30%, the sintering shrinkage, product density, and compressive strength of the 1000 ? sintered glass-ceramics decreased from 29.62% to 17.2%, from 2.13 g/cm3 to 1.73 g/cm3, and from 139.63 MPa to 35.69 MPa, respectively, and the weight loss on ignition increased from 4.28%to 8.12%. Slow cooling slag was selected as the contrast additive, and the results indicated that the sintering shrinkage, product density, and compressive strength of slow cooling slag-based products decreased from 12.43% to 10.28%, from 1.66 g/cm3 to 1.55 g/cm3, from 23.08 MPa to 16.76 MPa, respectively, and the weight loss on ignition increased from 10.35% to 13.91%. In addition, the composite vitrified slag-based products showed better chemical resistances than that of slow cooling slag-based products. The metastable state composite vitrified slag showed higher sintering activity and greater crystallization ability, and is easier to achieve an amorphous-crystallization transition by crystallization at the same sintering temperature, which result in larger crystal volume, denser crystal microstructure and better product properties of glass-ceramics. The energy consumption of the proposed method can be reduced by 5.91%?12.53% when the compressive strength of glass-ceramics was up to the standard of natural marble.(3) The higher sintering activity and greater crystallization ability of composite vitrified slag make it easier to achieve sintering densification and crystallization by viscious flow and mass transfer process. Based on this, the composite vitrified slag was used as curing agent to co-sintering with municipal solid waste incineration fly ash at low temperatures (<1000?). The stabilization/solidification of fly ash was achieved by the phase transition reactions between various substances during phase transformation processes. The results indicated that the crystal diffraction peaks in fly ash gradually decreased with the increase of composite vitrified slag and sintering temperatures. Anorthite (CaAl2Si2O8), yoshiokaite (Ca(Al,Si)2O4), chlorellestadite (Ca10(SiO4)3(SO)3Cl2), wadalite (Ca6Al5SiO16Cl13), and some heavy metals-containing phases were detected in the sintered products. With the increase of composite vitrified slag addition, the residual rates of heavy metals increased and the leaching concentrations of heavy metals were much lower than the threshold limits of USA, Europe, and China. The phase transformation of Cl from the soluble chlorides into the chemically stable Cl-containing phases should be responsible for the low leaching values, and the leaching ratio and leaching potential of Cl decreased with the increase of composite vitrified slag. The values of Cf, Er, and RI of typical heavy metals (Pb, Cu, Zn, Cr) decreased with the increase of composite vitrified slag and sintering temperature, but the results indicated that the sintered products showed a low degree of potential risk to the environment. The obtained products can be either used as safe and harmless inert material or as second raw material for further material utilization. |
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