Study On Preparation And Crystallization Properties Of Building Glass-ceramics From Iron Tailings

Glass-ceramics is a kind of composite materials,which is prepared by adding specific composition of nucleating agent or without nucleating agent into the glasses,through the method of crystallization heat treatment in controlled conditions,making the original single glass phase become into a composite material which is uniformly distributed by the micro crystalline phase and the glass phase.With its excellent properties,such as mechanical,electrical,optical,thermal,biological and so on,glass-ceramics has been widely used in building materials,optics,medicine and electromagnetic fields.The tailings is one of the products of the separation operation in mineral processing,and it’s target component is the lowest.In the past five years,China’s annual emissions of tailings were more than 15 billion tons,but the rate of tailings comprehensive utilization was only 18.9%,most of that were directly wasted,not only causing the pollution of the ecological environment,but also causing a huge waste of resources.After the analysis,as the main types of tailings,the composition of iron tailings contains SiO2,and it’s content are majority more than 60%,while SiO2 is the key to form the basic framework structure of the glass,in addition,other chemical components in iron tailings can be adjusted by adding auxiliary materials to form a glass composition for the iron tailings used for preparation of glass-ceramics is feasible.In the use of iron tailings to prepare building glass-ceramics,previous research focusing on nucleating agent,alkaline earth metal oxides,single flux effect on crystallization,less studying tailings content change on glass ceramics crystallization performance and color.In addition,the crystallization behavior of the glass-ceramics is characterized by crystallization activation energy and volume density,and the results are verified by the actual crystallization effect.In this paper,we use iron tailings and auxiliary materials,prepared by sintering to get CaO-MgO-Al2O3-SiO2 glass-ceramics,and by differential thermal analysis(DSC),X ray diffraction(XRD)and scanning electron microscopy(SEM)analysis methods,to study the effects of basic composition of oxide,dosage of iron tailings,SiO2/CaO and heat treatment system on the glass-ceramics crystallization property,and then optimize the composition and heat treatment system,the results of the studies show that:(1)the effect of four kinds of oxides on the crystallization activation energy E is:CaO>Al2O3>MgO>SiO2.The best scheme is A3B3C2D2,that is:SiO2:60%,CaO:18%,Al2O3:7%,MgO:8%.The results of the variance analysis shows that SiO2 has a significant affection on the crystallization activation energy E of the glass-ceramics,and the effects of CaO,MgO and Al2O3 on the crystallization activation energy E are not significant.(2)When the iron tailings changes from 5%to 40%,with the increase of iron tailings content,the color of glass-ceramics samples gradually increased,the bulk volume density of glass ceramics gradually increased,the acid resistance of glass ceramics is getting better and better.When the dosages of iron tailings are in the range of 5%～20%,we can prepare light-color glass-ceramics;when the dosages of iron tailings are more than 20%,the color of the glass-ceramics are dark.(3)With the decrease of SiO2/CaO ratio,the stability of the glass decreases at first and then increases.When SiO2/CaO=4,the stability is the worst,when SiO2/CaO=6,the stability is the best.The internal structure of the crystal is gradually compact from loose to dense,and the crystal form is from coarse to fine columnar to thin column,and then it is gradually refined.The volume density increases first and then decreases,while the volume density of SiO2/CaO=6 is the smallest,which is 2.39g/cm3;the volume density of SiO2/CaO=4 is the biggest,which is 2.70g/cm3.Acid resistance first decreased and then increased,When SiO2/CaO=6,the quality loss rate was the largest,was 0.21%;When SiO2/CaO=4,the quality loss rate was 0.13%.(4)The influence of the four factors on the volume density of the glass ceramics is that:nucleation time>nucleation temperature>crystallization temperature>crystallization time.The best heat treatment process system is:A2B2C2D2,that is:the nucleation temperature is 827 ℃,nuclear time is 90min,crystallization temperature is 896 ℃,crystallization time is 90min.The results of variance analysis showed that the influence of factors on nucleation time was very significant;the influence of crystallization temperature and crystallization temperature was significant;the effect of crystallization time was not significant.Besides,in this paper,the main crystalline phases of all the glass-ceramics are diopside,and the sub-phases are anorthite.