Producing upgraded metallurgical-grade silicon may be the most promising method to replace the modified Siemens process to produce solar-grade silicon, which has many advantages such as no pollution and low cost in the production process. The main process is described in detail, including smelting and secondary refining of metallurgical-grade silicon and acid leaching treatment. Other technologies also are introduced and discussed: solvent refining, vacuum treatment, plasma refining, and electron beam treatment; these technologies are used to refine metallurgical-grade silicon. Purification is also very important in the production process; a solidification process is used in purification to obtain highly pure silicon.
Ma, W. H., Wu, J. J., Wei, K. X., & Lei, Y. (2019). Upgrade metallurgical grade silicon. In Handbook of Photovoltaic Silicon (pp. 109–126). Springer Berlin Heidelberg. https://doi.org/10.1007/978-3-662-56472-1_7