冶金法制备太阳级硅中非金属杂质B和P的熔盐电化学去除机制

For several decades,solar grade (SoG) silicon is a key feedstock for photovoltaic (PV) industry. Molten salt electrorefining is believed an efficient way to reduce the amount of impurities B and P, which is a limitation of "solidification refining with Al-Si melts" method for production of SoG silicon from metallurgical grade (MG) silicon. After systematic analyzing the relationships between composition, structure and properties of fluoride molten salt, ideal conditions for electrorefining are obtained.Electrochemical behaviors of impurities in complex fluoride molten salt and anode alloy are revealed, which is helpful to reduce the possibility of impurities deposition on cathode. The dissolution, deposition and alloying procedures of Si during electrorefining are studied, and dynamics of electrochemical reaction and silicon diffusion into liquid cathode are modeled. In order to maintain chemical equilibrium, anode dissolution and cathode deposition of Si are matched with the Si diffusion into cathode alloy. Then an innovative route for production of high pure Si-Al alloy is raised by molten salt electrorefining with liquid cathode.This study is believed that can satisfy the great demand of high pure raw materials of SoG Si and saves a great deal of energy with the combination of molten salt electrochemical method and alloy solidification physical method. Developing a low-cost solar grade (SoG) silicon feedstock is both requirement of continued rapid expansion of the photovoltaic (PV) market and a very important role in national energy security strategies.

太阳级硅是光伏产业的关键材料，本项目提出采用熔盐电解精炼方法，解决由冶金硅低成本制备太阳级多晶硅的"合金凝固提纯新工艺"中B和P等非金属杂质难以去除的瓶颈问题。通过研究含硅氟化物熔体组成、结构与性质之间的关系，建立其物理化学性质调控方法；研究阳极合金和电解质熔体中杂质的电化学行为，确定杂质阳极溶解及阴极析出的有效抑制方法；研究硅的阳极溶解、阴极析出及其与阴极金属Al的合金化过程，建立电极过程与合金化反应的动力学模型，确定速率控制步骤及其强化机制；在此基础上，实现硅的阳极溶解、阴极析出及其与阴极金属Al合金化过程的动态平衡，提出熔盐电解精炼制备高纯Al-Si合金的技术原型。项目成果将为创建低能耗、低成本的"熔盐电解精炼-合金凝固提纯"太阳级硅制备新技术奠定基础，为推动光伏产业的发展作出积极贡献。

太阳级硅是光伏产业的关键材料，其低成本高效制备是光伏产业发展的迫切需求，也是国家能源战略的重要组成部分。本项目采用熔盐电解精炼方法，以制备高纯Si和含Si合金为目标，开展氟化物熔盐体系中Si的电解提取与电解精炼研究，探讨了氟化物熔盐体系中多种组元的热力学沉积条件，研究了Si在固态电极和液态金属电极上的电化学行为，研究了Na3AlF6-SiO2体系中Si的电解提取工艺，提出了三层液和水平熔盐电解精炼工艺，此外，基于电解精炼方法的普适性，向熔融盐电池方面工作进行了拓展。取得了以下研究成果，（1）Sr、Mg、Ca等元素因电极电位比Si负，不会与Si共沉积，而Fe、Cu、P等元素在电解质中的浓度大于理论计算获得的“极限浓度”时，会先于Si电沉积析出，从而影响沉积Si的纯度；（2）揭示了Si在氟化物熔盐体系中的电沉积机理，建立了沉积Si在液态阴极中的传质模型，获得了低熔点合金元素扩散系数和活度系数等难以直接测量的基础数据；（3）设计了三层液和水平电解精炼槽，实现了对Si的深度提纯；（4）基于电解精炼方法的普适性，设计并开发了熔融盐电池，并对电池体系进行了优化。