湿氧-熔渣联合法深度去除冶金级硅中杂质硼的应用基础研究

Boron removal from metallurgical grade silicon (MG-Si) with low cost, low energy consumption and high removal efficiency is the difficult point and hot topic focus for the preparation of solar grade silicon (SoG-Si) by metallurgical route. In this project, a united refining technique for boron removal from metallurgical grade silicon using wet-oxygen atmosphere of H2O(g)-O2 and molten slag agent of CaO-CaCl2 is brought forward. The major research contents include: the physical and chemical behavior of impurity boron in silicon during the united refining process; the thermodynamic relationship and the characterization of oxidizability and boron removal limitation using the united wet-oxygen and molten slag refining technique; establishing the kinetic model and the reaction rate equation of boron removal in-depth from silicon; study on the influence factors of limiting the oxidation rate of impurity boron in silicon; determining the restrictive step of reaction rate in all links and supplying the measures of improving the restrictive step; the synergistic behavior and relationship between wet-oxygen and molten slag for boron removal during the united refining process; the effects of process parameters on boron removal using the united wet-oxygen and molten slag refining technique; obtaining the synergistic technical conditions for boron removal in depth from metallurgical grade silicon by the optimization of process control. The minimal silicon loss will also be achieved during the refining process. In this project, the synergistic effect between wet-oxygen and molten slag for boron removal from metallurgical grade silicon is put forward. The removal limitation of impurity boron by a single refining technique is broken down and the purpose with a maximum removal efficiency for boron removal will be reached by the process control. This research will supply a theoretical and applied guidance to boron removal step in the preparation of solar grade silicon using the metallurgical route.

低成本、低能耗和高效率去除冶金级硅(MG-Si)中杂质硼是冶金法制备太阳能级硅(SoG-Si)研究的难点和热点。本项目联合H2O(g)-O2湿氧和CaO-CaCl2型熔渣精炼两种除硼方法，研究杂质硼在湿氧-熔渣联合精炼过程中的物理化学行为，对湿氧-熔渣联合深度除硼的能力与去除限度进行热力学计算与表征；建立湿氧-熔渣联合精炼深度除硼过程的反应动力学模型与速率方程；研究影响杂质硼氧化去除速率的因素，确定过程的限制性步骤，并提出改善限制性步骤的措施；研究湿氧-熔渣联合作用时杂质硼的协同行为，探讨工艺条件对杂质硼去除效率的影响规律；通过过程调控与优化，获得协同强化与深度除硼的工艺条件，并实现精炼过程硅损失率的最小化。本课题提出利用湿氧与熔渣的协同效应，突破单一方法对杂质硼去除的限度，达到高效与深度除硼的目的，研究成果将为冶金法制备太阳能级硅技术在除硼环节上提供理论与应用支撑。

低成本、低能耗和高效率去除冶金级硅(MG-Si)中杂质硼是冶金法制备太阳能级硅(SoG-Si)研究的难点和热点。本项目联合吹气-熔渣精炼两种方法对冶金级硅进行除硼的提纯，研究湿氧-熔渣联合作用时杂质硼的协同行为，探讨工艺条件对杂质硼去除效率的影响规律。研究发现：吹入Ar-H2O-O2气体及造渣剂CaO-SiO2-CaCl2进行联合精炼，吹湿氧能加速杂质硼以HBO气体形式挥发，同时又形成一种新的化合物3CaOB2O3进入渣中去除，硼的最高去除效率达到93.77%；吹Ar-H2O-O2气体精炼过程中，杂质硼主要以BxOy、BxHy、HxByOz气态挥发。吹气-造渣联合精炼除硼实验结果表明：用40%Ar-60%O2和40%Ar-60%H2O与42.5%CaO-42.5%SiO2-15%CaCl2造渣剂精炼3h时，硼含量从22ppmw分别降低至约2.5ppmw 和2ppmw。然而，联合吹气40%Ar-20%O2-40%H2O与42.5%CaO-42.5%SiO2-15%CaCl2造渣剂精炼3h后时，硼含量降低至0.75ppmw，除硼效率达到96.6%，除硼效果达到最佳。B2O3在37%CaO-63%SiO2渣中的扩散系数为5.24×10-9m2/s，B在37%CaO- 63%SiO2熔渣中的传质系数为6.2×10-6 m/s。分子动力学模拟计算证明，杂质B能够与湿氧和氯化物生成HBO、BOCl气体去除。湿氧-熔渣联合精炼过程硅损失率的研究发现精炼结束后虽然硅有一定损失，但损失的程度都在3%，平均损失率3.33%，且渣硅比略大于1。本课题提出利用湿氧与熔渣的协同效应，突破单一方法对杂质硼去除的限度，达到高效与深度除硼的目的，研究成果将为冶金法制备太阳能级硅技术在除硼环节上提供理论与应用支撑。