工业硅熔体中非金属杂质强化析出及协同去除研究

Solvent refining is one of the metallurgical approaches producing low-coat soalr grade silion (SOG) from metallurgical grade silicon (MG-Si), which combination refined by acid leaching usually in order to increase the removal effiencient of impurities in MG-Si. Some studies only focused on the removal rate of solvent refining and acid leaching. But the precipitate behavior of typical impurities and synergy mechanism between impurities and hydro-leaching failed to receive sufficient attention attention. So we systematically investigated the improvement of impurity precipitate behavior and strengthening mechanism for non-metallic impurities precipitation during the solidification process of metallurgical grade silicon. Thermodynamics and kinetics analysis of diffusion and transfer for non-metallic impurities are investigated. The diffusion and transfer discipline of non-metallic impurities are studied with external field and different solidification rate, temperature and component of melt. The segragation of impurities on the melt-solid surface are studied to obtain behavior and mechanism of strengthening electromagnetic precipitation for non-metallic and the discipline of precipitation enrichment. Dynamic evolution process and component of precipitation phase are regulated to study the interactions and synergy mechanism between precipitate phase and acid leaching. Combined with high temperature microscope technique, diffusion then enrichment and precipitate of non-metallic impurities during the solifacation process can be expressed to find control strengthening precipitation and obtain regulation measures. So we can build mechanisms of controlled precipitation and synergy removal non-metallic impurities precipitation phase during the solifacation process, and it contribute to fillful the highly efficient and low cost removal of impurities during metallurgical grade silicon production.

熔体精炼是去除硅中杂质重要的技术手段之一，与湿法浸出的结合进一步提高了杂质去除率。针对利用熔体精炼和湿法浸出追求杂质的高去除率，而对硅中杂质相析出、杂质相与湿法浸出协同作用机制不够重视等问题，项目提出硅熔体中非金属杂质强化析出及协同去除研究。主要研究硅熔体凝固过程中非金属杂质扩散和迁移的热力学与动力学，获得凝固速度与温度、外场和熔体成份等因素对非金属杂质扩散迁移的影响规律；研究非金属杂质的固-液界面析出行为，获得非金属电磁强化析出行为与机制及富集沉淀规律；调控非金属杂质沉淀相析出过程及成份，研究非金属杂质沉淀相与湿法浸出剂之间的相互影响与作用机制；结合高温显微技术，更为直观的研究硅熔体凝固过程中非金属杂质扩散、富集和沉淀析出过程与行为，揭示非金属杂质可控强化析出机理并获得调控措施，构建硅熔体凝固过程中非金属杂质沉淀相的高效可控析出及协同去除机制，实现工业硅中非金属杂质的低成本、高效去除。

通过对工业硅熔体中非金属杂质的强化析出及协同去除的实验研究，项目主要取得了以下成果。. 对抬包吹氧精炼前后工业硅中的非金属杂质的赋存状态分析，发现在原生工业硅中：CaAl2Si2相（含磷0.48at.%）和FeSi2Ti相（含磷0.71at.%）对非金属杂质磷有较好的富集效果，且原生工业硅中磷主要与钙发生协同沉淀，而精炼后工业硅中磷则主要赋存于硅基体中。通过外场控制凝固降温条件的方式，证明了凝固速率可以通过改善传质影响杂质二次偏析物相的形成。. 利用电磁感应设备分别对工业硅进行了Si-Ca、Si-Sn、Si-Fe-P、Si-Fe-Ti、Si-Fe-Mn、Si-Fe-Mn-Ti等合金精炼实验，证明了钙、铁偏析相对硅中非金属杂质的强化沉淀作用，实现了硼、磷的可控析出。磷铁合金掺杂重熔实验的结果表明：当少量锰或钛熔入富铁相后，将硅中富铁偏析相的沉磷能力提高了10倍。针对精炼后工业硅难除磷现象，对其进行了95wt.%Si-3wt.%Fe-2wt.%Ti合金精炼处理，验证了Si-Fe-Ti相强化沉磷的能力，合金精炼前后物料在相同条件下酸浸对比发现通过合金精炼的物料磷的去除率提高58.9%。同时通过对工业硅进行常压与加压酸浸的实验对比，获得非金属杂质去除的最佳浸出工艺参数，在加压酸浸的最优条件下，硼、磷的含量分别可降低至9.5和18.8ppmw。. 针对工业硅熔体凝固过程中杂质行为高温动态演变问题：开展了氧化焙烧实验，发现间隙氧的扩散，近界面的硼进入二氧化硅层，内部的杂质硼由于浓度梯度的作用向表面扩散，实现了硼的强化析出，而磷等杂质则进入硅一侧，形成杂质的“堆积”；根据精炼前、后物料浸出的差异，发现了原生工业硅凝固过程中，硅中替代碳可以细化晶胞、置换硅中的磷。游离碳化物的形核效应增加非金属杂质磷的扩散动力，发现硅中碳杂质元素促进了原生工业硅中磷的强化沉淀，使得原生工业硅经过一次酸浸处理后，可将磷残留量降低至6ppmw。. 通过项目的实施，发表论文19篇、申请发明专利10件（授权6件）；参加学术交流51人次，其中邀请报告8次，参与承办2次国内学术会议；邀请国内外学者交流10人次；获得省部级奖励2次；培养毕业博士生2名，硕士生6人。