Research On The Technology Of Liquid-solid Separation In Liquid-solid Mixed Melts By Pressure Filtration

The liquid-solid mixed melts are common in the metallurgy field,but the technologies for their liquid-solid separation are lack of attention.As one of the most frequently used technologies for the liquid-solid separation under ambient temperature,pressure filtration is believed to be potential and valuable for the separation of liquid-solid mixed melts.In this work,pressure filtration was applied in solvent refining for the silicon purification and in hot galvanizing dross for the zinc recovery,respectively.As pressure filtration being combined with solvent refining,the refining process with precipitation of high purity silicon and segregation of impurity elements was the first step,and silicon grains were then separated from melts by pressure filtration.The separation of silicon from Al-Si melts and Sn-Si melts were studied,and the effects of pressure differential,filtration temperature and melt composition were evaluated.At the conditions of filtering media of 80-mesh sieve,pressure differential of 0.25 MPa and filtration temperature of 600?,the separated silicon was obtained from Al-45%Si melt,with a silicon content of 92.4 wt%.At the conditions of filtering media of carbon fiber felt,pressure differential of 0.30 MPa and filtration temperature of 250?,the separated silicon was obtained from Sn-20%Si melt,with a silicon content of 80.0 wt%.The porosity and specific surface area of filtering cakes formed in the filtration process of Al-Si melts and Sn-Si melts were measured,respectively.Based on the fact that silicon was enriched at the bottom of melt by alternating electromagnetic field during solvent refining process,the filtration equation could be established as q=(KA/V)t.When the best separation results were achieved,the filtration constant K in Al-Si melt and Sn-Si melt were 0.0426 m2/s and 0.0137 m2/s,respectively.The existing forms of metal impurities in the process of pressure filtration were studied,which were dissolved in the liquid phase of Al-Si melt and existed as the solid particles in Sn-Si melt,respectively.As impurity removal being analyzed,90%of phosphorus and over 95%of metal impurities were removed in Al-Si refining process,while more than 80%of boron were removed in Sn-Si refining process.After combining Al-Si and Sn-Si refining processes,which contained twice solvent refining and twice filtration,the contents of boron and phosphorus in silicon decreased to less than 1 ppm,and their removal rates were more than 90%.The Zinc was separated from Zn-Al-Fe melt by pressure filtration,and the effects of pressure differential,filtration temperature and melt composition were evaluated.At the conditions of pressure differential of 0.30 MPa and filtration temperature of 450?,85.1%zinc was recovered from Zn-4Al-2Fe melt.The recovery of zinc from hot galvanizing dross melt by pressure filtration was also studied.At the conditions of pressure differential of 0.30 MPa and filtration temperature of 430?,69.1%zinc was recovered,and the contents of iron and oxygen in the recovered zinc were 0.0197 wt%and 0.000362 wt%,respectively,so that it can be directly returned into galvanizing process.The characteristics of filtering cakes formed in the filtration processes of Zn-Al-Fe melt and hot galvanizing dross melt were studied,respectively.The filtering cake composed of iron-contained particles and formed in the filtration process of Zn-Al-Fe melt was compressible,with its compression index of 0.80.A complex filtering cake was formed in the filtration process of hot galvanizing dross melt.It can be simplified as the combination of cake layer composed of iron-contained particles and cake layer composed of ZnO particles,respectively,and the compression index in the cake layer composed of ZnO particles was 0.28.As the iron-contained particles and ZnO particles being concentrated in the top region of melts,the filtration process in Zn-Al-Fe melt and hot galvanizing dross melt can be divided into two stages.In the first stage,the filtration equation was q=ut;in the second stage,the filtration equation was q2=Kt.When the best separation results were achieved,the filtration velocity u in the first stage was 8.69 m/s,while the filtration constants K in Zn-Al-Fe melt and hot galvanizing dross melt at the second stage were 6.01×10-4 m2/s and 2.12×10-4 m2/s,respectively.