Separation And Recovery Of The Valuable Resources From Kerfs Loss Slurry

In recent years, as the European debt crisis affects the end-market demand forsolar PV industry in Europe and America, European countries constantly cut solarsubsidies, which result in continuous decrease of solar wafer price and cuttingindustry’s profits. At the same time, in accordance with relevant regulations ofEnvironmental Pollution Prevention and Control Law of Solid Wastes, kerfs lossslurry belongs to the category of solid wastes which need harmless treatment.Therefore, in order to reduce wafer cutting cost and dispose kerfs loss slurry properly,separation and recovery of valuable resources such as polyethylene glycol, silicon andsilicon carbide is the only way to realize a win-win situation of economic benefits andenvironmental protection.In this thesis, separation and recovery of high purity polyethylene glycol, siliconand silicon carbide from kerfs loss slurry are systematically investigated.In the first part, qualified recovered polyethylene glycol is obtained by a series ofsteps such as centrifugation, decolorization, filtration, removal of metal ion impuritiesand viscosity reducer. Conditions of centrifugation are as follows,1:1distilled wateris added as the viscosity reducer, centrifugal time15min, rotating speed3500r/minand centrifugation for twice. Operating pressure of vacuum distillation is5KPa,heating voltage is220V and reflux ratio is from the initial1:4to1:1while the bottomtemperature reach46oC.In the second part, SEM、XRD、XRF、particle size analysis are used to study theproperties of kerfs loss slurry. At the same time, the optimal conditions to remove themost metal component are determined. Mass fraction of HNO3is30%, HNO3dosageis2g/g slurry and stirred time is30min.A new method is established for the accurate determination of silicon, silicondioxide and silicon carbide content in kerfs loss slurry. Silicon dioxide is determinedafter reaction and coloration by silicon molybdenum yellow. The total silicon content(elemental silicon and silicon dioxide) is determined by the method of hydrofluoricacid evaporation, then content of silicon and silicon carbide could be obtained bysubtraction. The experimental factors such as reaction temperature and reaction timeare investigated. The optimal conditions are as follows, reaction temperature:70oCand reaction time:60min. Under the optimal conditions, the detection limit of silicon dioxide is0.04mg/L SiO2, the spiked recoveries for silicon and silicon dioxide are97.2%~98.3%and96.7%~98.6%respectively, while both RSDs are less than5％.With this method, the slurry is composed of19.97%silicon,75.10%silicon carbideand4.93%silicon dioxide.In the third part, a method of combining vertical electrophoresis and ultrasoundis used to separate and recover silicon and silicon carbide for the first time.Plackett-Burman design, the steepest ascent search and Box-Benhnken design areadopted to optimize the separation process and the optimal conditions are determinedas follows: pH9.32, voltage5.64V, solid volume fraction0.73%. Under suchcondition, the yield coefficient of silicon carbide is90.68%, purity is93.09%.