Application Progress of Secondary Refining in Metallurgical Grade Silicon Purification Process

The development of the silicon industry has rendered low-quality metallurgical grade silicon (MG-Si) incapable of fulfilling the requisite quality standards for downstream products. Secondary refining is an indispensable process for the production of high-quality metallurgical grade silicon, which has obvious advantages in terms of production costs. However, the deep removal of impurities represents one of the most challenging aspects of metallurgical grade silicon refining. This work presents a comprehensive analysis of the latest research progress in the thermodynamics and dynamics factors (including activity interaction coefficient, diffusion coefficient, mass transfer coefficient, etc.) affecting the removal of impurities in the process of gas blowing refining, slagging refining, and gas-slag combined refining, as well as the precipitation characteristics of impurities in the solidification process of metallurgical grade silicon. The removal level of impurities in secondary refining is also reviewed. Furthermore, the impurity content, composition, refining temperature, and solidification rate in silicon will affect the distribution and type of precipitated phase in silicon. Therefore, it is of great significance to study the removal of impurities such as Fe and Ti during the refining process and to establish the interaction between the precipitation characteristics of impurity phases and the removal rate during the solidification process.