Study On The Technology And Properties Of Multi-phase Porous Ceramics Prepared By Various Solid Wastes

High titanium slag is a kind of industrial aluminosilicate solid waste produced in the smelting process of vanadium titanium magnetite in Panxi area.Massive accumulation has caused land pollution and waste of resource.Silica fume is a by-product produced in the melting process of silicon and ferrosilicon factory with more than 85%amorphous silicon.Granite tailings are a large number of tailings,scraps and chips produced in the production process of granite.Granite tailings have a high content of aluminosilicate,which can be used to prepare porous cordierite ceramics.Cordierite porous ceramics have the advantages of low thermal expansion coefficient and high temperature resistance.The preparation of cordierite ceramics from industrial solid waste can reduce the synthesis temperature and cost,but it also introduces unnecessary impurities in the synthesis of cordierite.Cation with smaller radius will enter the lattice of cordierite,result in higher coefficient of expansion.These impurities may also generate other phase resulting in the cordierite decreases or even disappears,and the mixed quantity of industrial solid waste exist for synthesis of cordierite threshold.In order to acquire the influence of solid waste on the synthesizes of cordierite,thermodynamic simulation software was employed to simulate the optimal dosage in advance.Result shows that industrial solid waste could be guided by the simulation value for the synthesis of cordierite.Due to the complex chemical composition of high titanium slag,the multiphase porous ceramics consisting of cordierite-anorthite-spinel were prepared.In this study,high titanium slag,silica fume and granite tailings as the main raw materials,while magnesium oxide/magnesia and alumina as supplementary materials,cordierite-anorthite-spinel multiphase porous ceramics were prepared by high temperature solid-state method.The effects of high titanium slag content,calcination temperature,holding time and replacement ratio of granite tailings to silica fume on the phase,pore structure and mechanical properties of porous ceramics were investigated.Testing and analysis methods such as XRD,SEM,XRF and image analysis software were used to explore the variation of phase composition and microstructure evolution process of porous ceramic matrix.Finally,mechanical properties of multiphase porous ceramics were characterized by apparent density,water absorption and specific strength.The main results are as follows:（1）Cordierite was synthesized by high titanium slag,silica fume,industrial magnesium oxide and alumina at 1250℃for 2h.The high titanium slag threshold for synthesis of cordierite was 25wt.%.The oxide needed for cordierite synthesis range is MgO（7.96～19.32wt.%）,Al₂O₃（20.08～43.50wt.%）,SiO₂（44.54～71.96wt.%）,CaO（0～7.5wt.%）.The maximum proportion of replacing silica fume with granite tailings is50wt.%,at the same time,the threshold of CaO is 7wt.%,which is close to 7.5wt.%,the threshold of CaO for high titanium slag.In addition,the threshold of CaO for synthesize of cordierite by high titanium slag is 10wt.%and 7.5wt.%respectively by simulation and experiment.Therefore,the simulation method has guiding significance for the synthesis of cordierite from solid wastes with complex composition.On the basis of previous studies on the synthesis of cordierite from ferrochrome slag and fly ash,and the study on the synthesis of cordierite from high titanium slag in this paper,the equilibrium phase diagrams of MgO-Al₂O₃-SiO₂、MgO-Al₂O₃-SiO₂-CaO and MgO-Al₂O₃-SiO₂-CaO-TiO₂systems at different temperatures were simulated.The results show that the phases and their contents by simulated and experimental are almost the same,which has enlightenment significance for the future use of thermodynamic simulation software,especially for the guidance of the high temperature phase reconstruction by aluminosilicate solid waste.（2）When using high titanium slag and silica fume to prepare porous ceramics,the content of high titanium slag increases from 20wt.%to 40wt.%,at the same time,the content of silica fume decreases from 41.0wt.%to 30.5wt.%,and the porosity decreases from 78.6%to 33.2%.With the increase of calcination temperature from 1200℃to 1310℃,the porosity of porous ceramics increased from 5.0%to 62.3%,while holding time increased from 0.5h to 8h,the porosity of porous ceramics remained around 60%.The sample with high titanium slag content of 25wt.%has the most uniform distribution of pores held at 1250℃for 2h.Its highest porosity is 72.6%,the median diameter is 1.3mm,the probability of pores ranges 0.5～1.0mm,1.0～2.0mm 2.0～3.0mm 40%,57%and 3%,respectively.After the type of industrial solid waste used to prepare porous ceramics is increased,the porosity decreases from 72.7%to 27%when the replaced proportion of silica fume by granite tailings increases from 25wt.%to100wt.%.When the granite tailings replacement ratio is 50wt.%,the porosity of porous ceramics,the probability of 0.5～1mm pore,the probability of 1.0～2.0mm pore,the probability of 2.0～3.0mm pore and the median diameter is 61.0%,85%,15%,0%and 1.3mm,respectively.When the granite tailings replacement ratio is 100wt.%,the porosity of porous ceramics,the probability of 0.5～1mm pore,the probability of 1.0～2.0mm pore,the probability of2.0～3.0mm pore and the median diameter is 27%,50%,15%,35%and 1.6mm,respectively.（3）With the increase of the content of high titanium slag from 10wt.%to 80wt.%,the specific strength of porous ceramics reaches a maximum of 4.92MPa·cm~3/g when the content of high titanium slag is 25wt.%.At this time,the porous ceramic matrix contains three crystal phases of of cordierite,anorthite and spinel,which are interwoven and stacked together,resulting in high strength of matrix.The maximum specific strength is 6.4MPa·cm~3/g when the content of high titanium slag increases to 80wt.%,because the specific strength is enhanced by more glass phases in the matrix.When the replacement ratio of granite tailings reaches50wt.%,the utilization rate of solid waste reaches 67.2wt.%,and the matrix phase consists of cordierite-anorthite-spinel.At this time,the specific strength,porosity,apparent density and water absorption of porous ceramics are 4.9MPa·cm~3/g,62%,1.92g/cm~3 and 1.52%,respectively.When the replacement ratio of granite tailings is 100wt.%,the utilization rate of industrial solid waste reaches the maximum value of 77.9wt.%,and the phase composition of the matrix is anorthite-spinel.The specific strength,porosity,apparent density and water absorption of porous ceramics are 10.14MPa·cm~3/g,27%,2.65g/cm~3and 1.5%,respectively.