Study on phosphorus removal from metallurgical grade silicon by acid leaching for solar application

Metallurgical grade silicon (MG-S) contains a series of metal (Fe, Al, Mn, Cu, Ni) and non-metal (P, B) impurities which make it unsuitable for use in solar cells. It is known that various metallic impurities are rejected by the silicon during its solidification process, and those crystallize at grain boundaries as intermetallic compounds. However, P is difficult to segregate in silicon, unlike most other impurities, since their partition coefficient (kp) is high (about 0.35). There are reports in the literature indicating the possibility of phosphorus removal by the introduction of elements that decrease the kp of P in silicon, such as calcium and barium. In this work, it was used barium, which was introduced in MG-S as a synthesized slag with BaO/SiO2 ratio of 6 and 5 wt% of CaF2 using a treatment of 1550 o C for 2 h. After melting, the ingot was milled obtaining particle in the range -35+400 mesh. The particles were leached in three steps by using water, HCl, and HF. The results showed that about 80 wt% of phosphorus was removed from the silicon after leaching treatment.