| Nowadays,with the rapid development of the photovoltaic industry,the demand for solar silicon wafers has increasing dramatically.During silicon wafer cutting,a large amount of silicon powder,crushed silicon carbide and iron filings drop into mortar and become waste mortar;However,The present technology can only recycled part of silicon carbide from the waste mortar,and the rest of silicon carbide and silica fume are discarded,which will not only pollute the environment,but also cause the waste of resources.In this thesis,Crystal silicon cutting waste is used as raw material.Firstly,analysis of the main ingredient of cutting waste and a pickling technology to remove iron and the SiC synthesized by carbothermic reduction,Then,three different solid-liquid separation processes were explored,,and the silicon carbide powders were prepared by carbothermal reduction after pure raw materials were obtained.Finally the silicon carbide powder was prepared by carbothermal reduction of pure raw materials,and choose the appropriate preparation process conditions for preparation of porous silicon carbide ceramics.The property of Cutting waste was studied,and a pickling technology to remove iron from the Cutting waste was developed to provide the high-quality raw materials for the subsequent process,It has been found that the Cutting waste mainly consist of SiC、Si、SiO2 and FeO,The size of the Cutting waste is between 1 μm and 13 μm.The optimal condition of the pickling technology is obtained:leaching temperature is 70℃,leaching time is 4h,concentration of H2SO4 is 4%and Liquid-Solid ratio is 3:1.Due to acid pickling the iron reduced from 8.96%to 0.14%causing the removing rate iron reached 98.6%.When leaking temperature are between 30 and 50℃,it belongs to chemical reaction control with E=37.57 kJ/mol,and it also belongs to internal diffusion control with E=17.01 kJ/mol when leaking temperature are between 60 and 80℃.The solid liquid separation process of cutting waste pickling slurry was further studied,and three processes were studied,and three processes were studied with flocculation settlement,centrifuge separation and plate frame pressure filtration.Study on the flocculation of different electrical,molecular weight,ion degree and dosage,the results show that the cationic PAM has the best effect and the best flocculation conditions are molecular weight 15 million,ionic degree 20%and dosage 0.9 kg/t.But the water content of the floc is high;The main research of the centrifugal separation centrifugal speed,the centrifugal time on the separation effect,better process conditions are:centrifugal speed was 2500 r/min,centrifugation time was 10 min,but the recovery rate is only 80.86%,The particle size of the supernatant was analyzed,and the solid particles were mainly concentrated below 1 μm,so the particles below 1 μm were difficult to be separated by centrifugation.Though the filter cake has low water content and small particle loss,the water consumption is large and the process is tedious.Combining three kinds of technology,the use of flocculation and centrifugation can reached solid-liquid separation.Raw materials for iron removal by acid washing,the preparation of SiC powder by carbothermal reduction method,The effects of sintering temperature,holding time and carbon content(cutting waste and carbon powder mass ratio)on the synthesis process of silicon carbide were investigated by means of XRD and SEM.the results showed that the SiC powder was successfully synthesized by holding 1550℃ for 3 h and ratio of raw material and carbon is 100:27,Then the effect of SiC addition on the properties of SiC porous ceramics was studied.Under the optimum conditions,add SiC are 40%SiC,porous ceramics can be prepared,apparent porosity is 48.35%,the water absorption is 33.21%,the bulk densityis 1.05 g/cm3.Finally,the thermodynamics of the synthesis process is analyzed. |
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