Research On The Removal Of Boron From Industrial Silicon By Air Blowing And Slagging Combined Refining

In the process of preparing solar polysilicon by the metallurgical process,non-metallic impurities B is one of the most difficult to remove element in industrial silicon.In this paper,the optimal experimental conditions for boron removal are studied by combined slag refining and gas blowing refining method,and the experimental results are verified by theoretical calculations.The gas?Ar-H₂O?g?-O₂?was blown into the slag CaO-CaCl₂,and part of the Si was oxidized to Si O₂ and then combined with CaO to form the silicate slag phase,achieving the purpose of boron removal using slagging refining and gas blowing.The experimental results show that when the mass ratio of CaO:Ca Cl₂ is 4,the mass ratio of slag to silicon is 1,and the flow ratio of Ar:H₂O:O₂ is 55:30:15,refining time is 3h and temperature is1823K,the impurity boron concentration in industrial silicon decreased from 22 ppmw to 2.1 ppmw.After further acid leaching,the boron removal rate can reach 94.5%.Addition of Si O₂ to binary slag Ca O-CaCl₂ constitutes a ternary slag system,and recombination gas refining to removal boron.It can be reduced to 1.37 ppmw after slag refining.After acid leaching,it can be further reduced to 0.81 ppmw.The boron concentration in the refining silicon can be reduced to 0.71 ppmw using slag refining with gas blowing refining.Removal impurity from silicon was studied.The experiment shows that the impurity removal effect of the Ar-O₂ mixed gas refining is less than that of the Ar-O₂-H₂O mixed gas refining.The removal rate of Al and Ca by Ar-O₂ mixed gas was 82%⁸5%,the removal rate of Ti was 44%⁴8%,non-metal impurities B and P were about 33%and 20%,respectively.Cu has no effect;when using Ar-O₂-H₂O mixed gas refined,the removal rates of Al,Ca,and Ti are respectively 85%,85%-89%,and 50%,and non-metallic impurities B and P reached over 50%,40%⁴5%respectively.impurity Fe,Cu also has no effect.The dynamic simulation of each particle on the Si?111?-B interface was performed by the adsorption of OH^-,O^2-,and Cl^-,respectively.The simulation results show that the impurity B can removal in the form of HBO and BOCl gas.