Preparation Of Glass-ceramics Via Co-sintering Of Coal Fly Ash And Metastable Slag

China is a country that riched coal resources.The energy structure with rich coal,lean oil,and low gas determines that the main position of coal is the most important resource in China and will not change for a long time.At the same time,with the rapid development of China's economy and energy demand,the accumulation and genaration of coal fly ash(CFA)is increasing every year.At present,coal fly ash is used as an admixture to produce cement,concrete,and sintered bricks as a building material,,reducing its accumulation and environmental impact.However,the added-value of these traditional building materials and utilization rate of CFA is relatively low.Therefore,based on the analysis of crystallization ability and sintering activity of metastable slag(MS),the mixtures of CFA and MS were used as raw materials to prepare high-value glass-ceramics.Meanwhile,the solidification mechanism and potential ecological risk evaluation of heavy metals in the products were also studied.The main conclusions are as follows:(1)Metastable slag obtained by melting-quenching technology was used to prepare glass-ceramics.The effects of C:M and sinter temperature on the glass-ceramics was studied.The results showed that the compressive strength,chemical corrosion resistance and density of glass-ceramics increased with the increase of MS and sintering temperature,however the water absorption showed the opposite tendency.The compressive strength of glass-ceramic with 10-40%CFA at 850-1085^oC could meet the requirements of GB/T 19766-2016"Natural Marble Building Board"(?50MPa).In addition,when the CFA is 10-30%and the sintering temperature is 940^oC,the chemical corrosion resistance of glass-ceramic meets industrial requirements(acid loss rate?96%,alkali loss rate?98%).Compared with the traditional melting method,the energy consumption of glass-ceramics prepared by this method can be reduced by 11.67-27%.(2)The leaching toxicity results show that the leaching concentrations of the heavy metals(Cu,Zn,Cr,Cd,Pb,Ni)in glass-ceramics are far below the threshold limit value when the amount of coal fly ash is not more than 40%and the sintering temperature is 850-1085^oC.The values of Cf,Er,and RI of typical heavy metals(Cu,Zn,Cr,Cd,Pb,Ni)decreased with the increase of MS and sintering temperature.The results indicated that the glass-ceramics showed a low degree comprehensive potential ecological risks to the environment.(3)To investigate stabilization mechanism of heavy metals in glass-ceramics,the metallic oxides(Cr₂O₃ and Zn O)were added into the raw materials to prepare glass-ceramics.The results showed that glass phase and crystal phase in glass-ceramics play a double barrier protection role for the stabilization of heavy metals.Ca₂Zn Si₂O₇ and Cr₂O₃ were the forms of Zn and Cr is in heavy metal-doped crystals.