Boron separation from Si–Sn alloy by slag treatment

Abstract

This study investigates a purification process for metallurgical-grade silicon (MG-Si) in which Si is alloyed with tin (Sn) and CaO–SiO₂–CaCl₂ slag is used to remove boron (B) impurity. Acid leaching was performed to remove the Sn phase after slag refining to recover high-purity Si from the Si–Sn alloy. The effect of refining time was investigated, and acceptable refining results were realized within 15 min. The effects of slag composition and Sn content on the removal of B were also studied. The results indicate that increasing Sn content favors B removal. With the increase of Sn to 50% of the alloy, the final B content decreased to 1.1 × 10⁻⁴wt%, 93.9% removal efficiency.

Keywords

boron removal / metallurgical grade silicon / Si–Sn alloy / slag refining

References

[1] Luque A., Hegedus S. Handbook of Photovoltaic Science and Engineering, 2011 56.

[2] Suzuki K., Sano N. Thermodynamics for removal of boron from metallurgical silicon by flux treatment, 1991 273.

[3] Lai H., Huang L.Q., Xiong H.P., Gan C., Xing P.F., Li J.T., Luo X.T. Hydrometallurgical purification of metallurgical grade silicon with hydrogen peroxide in hydrofluoric acid. Ind. Eng. Chem. Res., 2016, 56(1): 311.

[4] Safarian J., Tangstad M. Vacuum refining of molten silicon. Metall. Mater. Trans. B, 2012, 43(6): 1427.

[5] Pires J.C.S., Braga A.F.B., Mei P.R. Profile of impurities in polycrystalline silicon samples purified in an electron beam melting furnace. Sol. Energy Mater. Sol. Cells, 2003, 79(3): 347.

[6] Arafune K., Ohishi E., Sai H., Ohshita Y., Yamaguchi M. Directional solidification of polycrystalline silicon ingots by successive relaxation of supercooling method. J. Cryst. Growth, 2007, 308(1): 5.

[7] Lei Y., Ma W.H., Lv G.Q., Wei K.X., Li S.Y., Morita K. Purification of metallurgical–grade silicon using zirconium as an impurity getter. Sep. Purif. Technol., 2017, 173(1): 364.

[8] Wang J.T., Li X.D., He Y.M., Feng N., An X.Y., Teng F., Gao C.T., Zhao C.H., Zhang Z.X., Xie E.Q. Purification of metallurgical grade silicon by a microwave–assisted plasma process. Sep. Purif. Technol., 2013, 102(1): 82.

[9] Hopkins R.H., Rohatgi A. Impurity effects in silicon for high efficiency solar cells. J. Cryst. Growth, 1986, 75(1): 67.

[10] Hall R.N. Segregation of impurities during the growth of germanium and silicon. J. Phys. Chem., 1953, 57(8): 836.

[11] Wu J.J., Li Y.L., Wei K.X., Yang B., Dai Y.N. Boron removal in purifying metallurgical grade silicon by CaO−SiO2 slag refining. Trans. Nonferrous Met. Soc. China, 2014, 24(4): 1231.

[12] Wu J.J., Ma W.H., Jia B.J., Yang B., Liu D.C., Dai Y.N. Boron removal from metallurgical grade silicon using a CaO−Li2O−SiO2 molten slag refining technique. J. Non–Cryst. Solids, 2012, 358(23): 3079.

[13] Wang Y., Ma X.D., Morita K. Evaporation removal of boron from metallurgical–grade silicon using CaO−CaCl2−SiO2 slag. Metall. Mater. Trans. B, 2014, 45(2): 334.

[14] Johnston M.D., Barati M. Distribution of impurity elements in slag–silicon equilibria for oxidative refining of metallurgical silicon for solar cell applications. Sol. Energy Mater. Sol. Cells, 2010, 94(12): 2085.

[15] Teixeira L.A.V., Morita K. Removal of boron from molten silicon using CaO−SiO2 based slags. ISIJ Int., 2009, 49(6): 783.

[16] Ma X.D., Yoshikawa T., Morita K. Purification of metallurgical grade Si combining Si−Sn solvent refining with slag treatment. Sep. Purif. Technol., 2014, 125(2): 264.

[17] Huang L.Q., Lai H.X., Gan C.H., Xiong H.P., Xing P.F., Luo X.T. Separation of boron and phosphorus from Cu–alloyed metallurgical grade silicon by CaO−SiO2−CaCl2 slag treatment. Sep. Purif. Technol., 2016, 170(1): 408.

[18] Li M., Utigard T., Barati M. Removal of boron and phosphorus from silicon using CaO−SiO2−Na2O−Al2O3 flux. Metall. Mater. Trans. B, 2014, 45(1): 221.

[19] Kubaschewski O., Alcock C.B. Metallurgical Thermochemistry, 1979 89.

[20] Meteleva–Fischer Y.V., Yang Y.X., Boom R., Kraaijveld B., Kuntzel H. Microstructure of metallurgical grade silicon and its acid leaching behaviour by alloying with calcium. Miner. Process. Extr. Metall., 2013, 122(4): 229.

[21] Li J.Y., Cao P.P., Ni P., Li Y.Q., Tan Y. Enhanced boron removal from metallurgical grade silicon by the slag refining method with the addition of tin. Sep. Purif. Technol., 2016, 51(9): 1598.

[22] Cai J., Li J.T., Chen W.H., Chen C., Luo X.T. Boron removal from metallurgical silicon using CaO−SiO2−CaF2 slags. Trans. Nonferrous Met. Soc. China, 2011, 21(6): 1402.