Experimental Study On Glass-ceramic Prepared From Sewage Sludge Ash By Microwave Melting Method

The quantity of sewage sludge is being generated in an ever increasing amountdue to rapid urbanization and higher effluent criteria implemented in recent decades.As a new sludge treatment and disposal technology, pyrolysis brings a lot of by-products(sewage sludge ash), when widely used. The ultimate way for future sludgedisposal is how to effectively utilize the component of the ash, to achieve theenvironmental and economic benefit. The advantages of glass-ceramic, such as highadded values, abundant batch composition and satisfactory effect of solidifyingharmful ingredients, makes glass-ceramic the focus of solid waste utilization.Microwave heat source posses unique heating principles and characteristics. Thereexists the main composition of preparing glass-ceramic in ash pyrolyzed bymicrowave(APM), but also shows a similar microstructure of vitreous, which makesthe glass-ceramic preparation become possible. Microwave heat resource requireslower power consumption than traditional energy sources, therefore the introducingmicrowave fabrication process has the significance of application and research.In this paper, we initially carried on the test to prepare glass-ceramic by fusionmethod with high dosage of APM as main composition, where the heat treatingregime was determined by DSC. Microwave heat source was initially used in thepreparation process of base glass, to reduce energy consumption during traditionalheating treatment. Then the influences of heat treatments on the phase compositions,the microstructure and crystal composition of glass-ceramics were investigatedaccording to the results of the XRD, SEM and FTIR. Physical and chemicalproperties were tested to compare the mechanical properties of glass-ceramics bytraditional method and microwave method. Leaching test of typical heavy metals wasmade using TCLP method to investigate the solidify effectiveness of heavy metals byglass-ceramic.The result indicated that the glass-ceramics contain main crystal phase anorthitewere successfully prepared, which had excellent microstructure and properties. Thesample was melted at 1450℃for 2h, with the optimal nucleation at 700℃for 90min,crystallization at 900℃for 120min, where the velocity of increasing temperaturebetween 20℃~700℃was 5℃/min, the velocity of increasing temperature between700℃~900℃was 3℃/min. Base glass with specular gloss was made with the2+2mm powder bed of different properties activated carbon(doping ratio is activatedcarbon: Al2O3=5:5, activated carbon:Al2O3=9:1)under microwave irradiation(2000 W)for 10min. This method could save about 50% of energy consumption comparisonwith traditional heat source. Crystallization of the parent glass occurred above 900℃,crystallization of the nucleated specimen in the region of 950~1000℃resulted in theformation of two crystalline phases, i.e. wollastonite with cylindrical interlockStructure and tabular anorthite. And with increase of crystallization temperature,wollastonite gradually transformed to anorthite. Higher nucleation temperature wasbeneficial to crystallization, but not obvious. The comparison between traditionalmethods and microwave method found that the abundant crystal in the glass-ceramicsmade by microwave radiation method microwave method were more homogeneous,compact; the physical chemical properties were more excellent. TCLP test indicatedthe leaching efficiency of heavy metals was lower in glass-ceramic than in AMP,which also noticed that the process of producing glass-ceramic could solidify heavymetals very well.