冶金法制备太阳能级硅工艺中湿法提纯及半工业化研究

【作者】 麦毅；

【导师】 马文会； 谢克强；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2014， 博士

【摘要】 光伏产业的大规模发展需要成本低廉、环境友好的多晶硅生产技术。当前,多晶硅主要靠改良西门子法生产,该法生产成本较高,环境压力较大。冶金法是近年来正在发展的一种成本低、能耗低和环境友好的多晶硅制备新技术。湿法提纯是冶金法硅制备太阳能级多晶硅工艺中不可缺少的一环,它能去除冶金级硅中大部分杂质。湿法提纯冶金级硅虽然研究较多,但是主要停留在小规模的工艺研究方面,研究深入不够。本文以云南某硅厂生产的冶金级硅为原料,系统性地研究了湿法提纯冶金级硅的机理、工艺并进行了半工业化试验,主要内容如下：(1)分析测试了冶金级硅中杂质的赋存状态。在冶金级硅中金属杂质Fe、 Al、Ca、Ti等主要偏聚在晶界处形成二元金属间化合物FeSi、CaSi2和三元金属间化合物Fe5Al8Si7、FeAl3Si2、FeTiSi2等,并首次发现了含P物相SiP。(2)计算绘制了冶金级硅中杂质Al、Ca、Ti、P在25℃下的Me-Si-(F)-H2O电位-pH图,并结合已报道的Fe-Si-(F)-H2O系电位-pH图,从热力学角度分析了冶金级硅中杂质Fe、Al、Ca、Ti和P去除需要的浸出剂体系和具体条件,结果表明含氟的强酸性溶液为最佳浸出体系。(3)运用双参数模型估算出了FeTiSi2和FeAl3Si2的△fGm分别为-94.23kJ·mol-1和-240.052KJ·mol-1。在此基础上,讨论并提出了杂质相FeSi2、CaSi2、 FeAl3Si2、FeTiSi2、SiP与HC1或HF去除反应机理。(4)通过实验验证了理论指出的去除冶金级硅中金属杂质Fe、Al、Ca、Ti的最佳浸出剂体系为HF-HC1混酸,但该体系在常温常压下对非金属杂质B、P的去除效果不明显。在最佳条件3%HF-2%HC1,80%硅粉粒度<75μm,液固比5：1,浸出温度70℃,浸出时间5h,两段浸出,产品中Fe、Al、Ca和Ti的残留分别为5ppmw以内,60ppmw以内,10ppmw以内,5ppmw以内,金属杂质总含量在100ppmw以内。本文还提出了氢氟酸加压去除非金属杂质B、P的工艺,在该工艺中温度对去除非金属杂质B、P影响最大。当在浸出温度为200℃,HF含量为5%,液固比为5：1,硅粉粒度80%<200目,浸出5h后,产品中B、P含量分别从21和81ppmw降低到9.5和18.8ppmw。(5)从HF或HCl对冶金级硅中杂质相的去除作用,浸出过程产生的气相组成和溶液中可变价离子(离子形态的铁)的存在状态角度用实验验证了本文提出的杂质相FeSi2、CaSi2、FeAl3Si2、FeTiSi2、SiP与HCl或HF反应去除的化学机理的合理性。(6)进行了年产500吨规模的半工业化试验,结果表明HF-HCl体系在最佳的生产条件为1.5%HF-1.5%HCl,硅粉粒度<75μm,液固比5：1,浸出时间4h。在该条件下通过两段浸出,产品中Fe、Al、Ca和Ti的含量分别下降到1OOppmw以内,200ppmw以内,150ppmw以内和5ppmw以内,产品质量达到3.5N。该工艺成本低廉,具有良好的投资前景。更多还原

【Abstract】 Large-scale development of photovoltaic (PV) industry requires the polysilicon production technology with low cost and environment friendly. At present, the primary technology for production of polysilicon is improvement Siemens method. It restricts the development of PV industry because of its high cost and environmental pressure. With economical and low energy consumption and environmental friendly? metallurgical method for preparation of solar grade silicon (SoG-Si) is a new technology. Hydrometallurgical process is an indispensable part for metallurgical methodes, which can remove the most of impurities in the metallurgical grade silicon (MG-Si). Hydrometallurgical method for purification of MG-Si has been studied long time, but only on the processes in laboratory, being lack of systematic research and semi industrialization. Hydrometallurgical process, the mechanism and semi industrialization for purification of MG-Si have been studied in this paper. The MG-Si produced in Yunnan of china has been used as raw material. The main contents as follows:(1) Deportmentes of impurity elements in MG-Si were investigated, and the results show that metal impurities Fe, Al, Ca and Ti was mainly distributed in binary intermetallic FeSi2,CaSi2and ternary FeAl3Si2, FesAl8Si7, FeTiSi2. The SiP phase was first time found in MG-Si.(2) Me-Si-(F)-H2O potential-pH diagram for Al, Ca, Ti, Fe and P at25℃have been calculated or quoted. According to those, leaching agents and specific conditions for removal the impurities of Fe, Al, Ca, Ti and P from MG-Si were analyzed under the viewpoint of thermodynamics.(3) The AfGm, of FeTiSi2and FeAl3Si2were calculated through two-parameter model, and the results of△fGm of FeTiSi2and FeAl3Si2were-94.23kJ·mol-1and-240.052kJ·mol-1respectively. Based on those, chemical reaction mechanism of the removal of FeAl3Si2, CaSi2, FeSi2and FeTiSi2through leaching by HF or HC1were discussed and proposed.(4) Experiments confirmed the theoretical results that the mixed acid system HF-HCl is the most effective leaching agent for removal of metal impurities Fe, Al, Ca, Ti in MG-Si, but the system under normal pressure and temperature is not obvious on the removal of non metal impurities B, P. By leaching MG-Si with3%HF and2%HC1at70℃for5h and using two stage leaching, the content of Fe, Al, Ca and Ti in products were less5ppmw, less60ppmw, less lOppmw and less5ppmw respectively.Hydrofluoric acid pressure leaching process for removing the non metal impurities B and P was researched, in the process temperature has the greatest influence on the removal of non metal impurities B, P. When the extraction temperature is200℃, the HF content is5%, the ratio of liquid to solid5:1, powder particle size80%<200mesh, leaching after5h, B and P content in the product are respectively from23and81ppmw decreased to9.5and18.8ppmw.(5) Those chemical mechanism, which proposed in this paper, of the removal of impurities phases FeSi2, CaSi2, FeAl3Si2and FeTiSi2by HC1or HF were verified by experiments from three aspects as follows:the effect of HC1or HF on removal impurities phases in MG-Si, the composition of gas generated in the leaching process and the ionic form of iron in leaching solution.(6) Semi industrialization experiments with annual output of500ton UMG-Si have been studied. The results showed that the optimal conditions for HF-HCl system were1.5%HF,1.5%HC1, silica fume particle size<75microns, liquid to solid ratio5:1, leaching time for4h. The Fe, Al, Ca and Ti in product were respectively1OOppm or less,200ppmw or less,150ppmw or less,5ppmw or less, and the product quality has reached3.5N after leaching by a two-stage contained under optimum conditions. This process is a technology with low cost and good investment prospect.更多还原