Separation And Refining Of Si And Liquation Agent During The MG-Si Solvent Refining Process

With the rapid development of photovoltaic industry, the needs of solar grade polycrystalline silicon sharply increase. Because the chemical method, like Modified Siemens Process and silanization, exist many problems like high energy consumption,serious environmental pollution, environment pollution and potential risk, the metallurgical method become the focus of attention.Solvent refining, as a new system for separation and purification of impurities,strengthens the segregation characteristic of impurities by transforming the existing state and position of impurities, and the alloying makes silicon refining at low temperature, so it is possible for reducing the total energy consumption of the purification process significantly. According to the problem of difficult separating silicon and liquation agent, the method of super-gravity separation and directional solidification were proposed. The separation effect of silicon and liquation agent was discussed in this paper. Besides, the influence factors and separation mechanism of those methods were analyzed. In the end, the refining effect of solvent refining with directional solidification as well as its refining mechanism was discussed.The main research work and the results obtained are as follows:(1) The separation effect in super-gravity separation process was analyzed. The result showed that this method could separate the silicon and liquation agent efficiently. Furthermore, comparing with the method of acid leaching, this method would reduce 90% of acid consumption.(2) The separation mechanism of super-gravity separation was discussed. The result showed that the occurrence statement of liquation agent during the separation process was variable. The occurrence statement was changed from free liquid to capillary liquid. In the end, the remaining liquation agent stayed in the touch point of silicon crystal and the crystal defect.(3) The separation mechanism of silicon and liquation agent in the solvent refining with directional solidification. The result showed that, with the help of directional solidification in induction furnace, the silicon and liquation agent could be separated efficiently. The bulk Si, a morphology without liquation agent, was obtained by controlling G/V value. Furthermore, the condition of bulk Si growth wasexpressed by math. Besides, the induction heating could strength the separation of silicon and liquation agent.(4) The refining effect of solvent refining with directional solidification was studied. Firstly, the segregation coefficient of the impurities in the Al-Si alloy system were calculated by Factsage software. The result showed that most segregation coefficient of impurities were decreased sharply in the Al-Si alloy system. According to the experiment result, the solvent refining with directional solidification could remove the impurities efficiently. The removal rates of metallic impurities was above98% and the removal rates of boron and phosphorus were 75% and 85%, respectively.