Carbonthermal Reduction Reaction Mechanism And Preparation Process Of Iron Tailings Porous Ceramics With High Thermal Conductivity

Iron tailings is solid waste discharged from iron ore after dressing.The main hazards include occupying land,causing geological disasters and contaminating soil and so on.At present,in addition to the application of coarse iron tailings in building materials and recovery elements,the muddy fine iron tailings containing a lot of clay minerals are still unable to be utilized.In this paper,the porous ceramics of iron tailings with high thermal conductivity were prepared by carbothermal reduction reaction sintering process.The raw materials are fine muddy iron tailing powder and graphite powder.The effects of sintering temperature,holding time and graphite content on its composition,structure and properties were systematically studied.When it is used as composite phase change material carriers,the heat transfer efficiency of the phase change materials can be effectively improved.Therefore,the solid waste harmful to the environment can be transformed into new energy saving and environmental protection materials.In the process of high temperature reactive sintering,graphite will react with each oxide in iron tailings in a complex way.The thermodynamic and kinetic analysis of the carbothermal reduction reaction process of iron tailings was carried out.The results indicate that the carbothermal reduction reaction of high silicon iron tailings is mainly the reduction of SiO₂ and Fe₂O₃.Among them,the reduction temperature of SiO₂ is relatively high,starting at about 1300°C,and it mainly generates high thermal conductivity phase SiC.After sintering at 1500°C for 2 h,the reaction product SiC becomes the absolute main crystal phase in the sintered samples.Based on the analysis of sintering mechanism of carbon thermal reduction reaction of iron tailings,the effects of technological parameters,reaction process and sample morphology on porous ceramics of iron tailings were investigated.The results show that the structure and properties of iron tailings porous ceramics are greatly affected by graphite content and sintering temperature,but less by holding time.The effect of porosity on thermal conductivity of porous ceramics is much greater than that of SiC production.And by changing the experimental conditions,the performance of porous ceramics can be adjusted and controlled.After sintering at 1600°C for 2 h,the apparent porosity and thermal conductivity of the sintered samples are 81.10%and 0.58W/(m·K).Under the same porosity,the thermal conductivity of the sintered samples is increased by 6.6 times,which compared with the porous ceramics with iron tailings without graphite powder.Adding a certain amount of SiC powder to the raw materials can effectively reduce the defects such as deformation,cracking and collapse of iron tailings porous ceramics in the sintering process.The performance improvement technology of porous ceramics for iron tailings was studied by the control variable method.Under the same process conditions,the mechanical properties of SiC/iron tailings porous ceramics are significantly better than those of iron tailings porous ceramics without adding SiC.When SiC content is 5 wt%,graphite content is 25 wt%,sintering temperature is1700°C,and holding time is 2 h,the SiC/iron tailings porous ceramics own the best comprehensive properties.In this paper,the oxide and mineral phases with low thermal conductivity in iron tailings are transformed into metal phases and carbides with high thermal conductivity by carbothermal reduction reaction sintering,which break through the limitation of poor thermal conductivity of porous ceramics with high porosity.The apparent porosity,thermal conductivity and compressive strength of SiC/iron tailings are 80.4%,1.19W/(m·K)and 1.01 MPa,respectively.Compared with the porous ceramics without SiC,the thermal conductivity is doubled and the compressive strength is increased by 20%.The study in this paper can improve the utilization rate of iron tailings and reduce environmental pollution.