Manufacture Of Glass-ceramic Made From Municipal Solid Waste Incineration Fly Ash And The Solidification Mechanism Of Cr

Municipal solid waste incineration is one of the main treatment ways for municipal solid waste in China,of which environmental problems have attracted much attention.The municipal solid waste incineration fly ash(MSWI fly ash)has been included in the National Hazardous Wastes Catalogue(2016)for being rich in Pb,Zn,Cr,Cu and other heavy metals and belongs to HW772-002-18 Hazardous Solid Wastes.The general disposal ways for MSWI fly ash as landfill,cement solidification,melting and solidificationv have leaching risk of toxic heavy metals.Harmless treatment and resource utilization of MSWI fly ash has been an important topic to be studyed.In this study,the fly ash from municipal solid waste incineration was used as raw material,and the waste glass,coal ash,steel slag,acid pickling sludge and volatile kiln slag were used as additives to prepare multiple microcrystal products.The effect of alkalinity on crystallization behavior of glass ceramics was studyed,glass ceramics rapid crystallization model was built,and the solidification mechanism of Cr in glass-ceramics was demonstrated.It's mainly concluded as following:The MSWI fly ash,stainless steel slag and coal ash were used as raw materials to investigate the effects of alkalinity on diopside-based glass ceramics.Based on the chemical composition of high Ca and low Si in incineration fly ash,the CaO-MgO-Al2O3-SiO2 glass ceramic was prepared through adjustment of ratio of(Ca+Mg)and(Si+Al)in this mixture by high temperature melting and heat treatment technology.The effects of alkalinity(Ca+Mg)/(Si+Al)change on the crystallization kinetics,bridging oxygen content,crystal phase composition,microstructures,mechanical and physical properties,and chemical resistance of glass-ceramics was systematically studied.The results showed,when the alkalinity decreased from 1.2 to 0.9,the bridging oxygen content increased from 1.18×1021/cm3 to 1.34×1021/cm3,and the polymerization degree of the glass network also increased.The increase in content of structural units which connected the silica tetrahedron to the three bridging oxygens can lead to an increase in polymerization degree and the crystallization activation energy rise from 336.0 kJ/mol to 360.7 kJ/mol.The hardness and bending strength of glassceramics reduced with decreasing alkalinity.When the alkalinity was 1.2,the bending strength,acid resistance.and alkali resistance of glass-ceramics were 120.4 MPa,?99%and ?99%,respectively.All of them were above than the requirements for bending strength ?70 MPa,acid resistance ? 96%,and alkali resistance ? 98%,as specified in Industrial Microcrystalline Plate Material(JC/T 2097-2011).The MSWI fly ash and bottom ash were used as raw materials,volatile Pb kiln slag was used as foamer and Na3PO4 as foam stabilizer to prepare foam glass ceramics.The experimental results showed,the raw materials of 68 wt%incineration fly ash,17 wt.%bottom ash,10 wt.%Pb fumed slag and 5wt.%Na3PO3 were mixed after ball milling and subsequently incubated for 1 hour at 11-50?.The prepared sample was provided with better overall performance with pore diameter of 0.3?1.2 mm,apparent density of 0.92 g/cm3,porosity of 76.03%,water absorption rate of 4.21%,and compressive strength of 12.33 MPa.This study provided a new solution for the co-processing and high-value utilization of incineration ash and volatile Pb kiln slag.A "rapid crystallization" model was established to clarify the phase separation-nucleation-crystal growth mechanism of rapid crystallization.In the phase separation process of base glass,Na+ and K+ can reduce the polymerization degree of the glass network,accelerate the phase separation of base glass,and enhance the nucleation driving force of the main crystal phase of diopside,resulting in formation of Na+ and K+-rich diffusion layer on the interface between the main crystal phase and the glass phase.This narrowed the difference between the nucleation temperature and the crystallization temperature so that nucleation and crystal growth can run continuously at the same temperature.To increase the Na2O content in diffusion layer could promote further polymerization of the glass network.With Na+ increasing from 0.10 mol to 0.14 mol,the amount of crystals in the base glass increased by 3.5 times,but the content of Si-O-Na bonds in the fast diffusion layer around crystals was relatively reduced,and the crystal growth was suppressed instead.The solidification mechanism of Cr in glass ceramics was studied.Cr formed a substitution solid solution in the pyroxene phase and was solidified in the glass ceramics.The excess Cr was solidified in the crystal phase in the form of magnesia-chrome oxide spinel MgCr2O4.The above two crystal phases were not easily leached by the H+ replacement in the environment.When the Cr2O3 content in glass ceramics reached 16.6wt%,the leaching rate of Cr was 0.72 mg/L,which is lower than the standard limited value of TCLP(5 mg/L).