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A purification method using copper (Cu) alloying and CaO–SiO 2 –CaCl 2 slag treatment had been studied in connection with the purification of metallurgical grade silicon (MG-Si). The principle of this method was that low-purity MG-Si alloyed with Cu to form Si–Cu alloy phase, and then the Si–Cu alloy was treated using CaO–SiO 2 –CaCl 2 slag to remove impurities. Finally, selective acid leaching was applied to remove the Si–Cu alloy phase, whereupon high-purity silicon could be recovered from the Si–Cu alloy. Effects of slag composition and Cu content on the removal of boron (B) and phosphorus (P) were also investigated. When the Si–50 wt% Cu alloy treated with 45 wt% CaO–45 wt% SiO 2 –10 wt% CaCl 2 slag for 30 min at 1550 °C, the final concentrations of B and P in the purified Si decreased from 3.12 to 0.35 ppmw and 17.14 to 7.27 ppmw, respectively. Furthermore, the corresponding removal mechanism was investigated. It was found that the reaction kinetics followed a first-order rate law with respect to B and P, and were controlled by mass transfer with mass transfer coefficients of 6.25 × 10 −4 cm s −1 and 2.55 × 10 −4 cm s −1 , respectively. [ABSTRACT FROM AUTHOR]

The effect of hydrogen peroxide as a novel oxidizing agent on purifying metallurgical grade silicon (MG-Si) by leaching with hydrofluoric acid was investigated as a function of temperature, leaching duration, stirring and hydrofluoric acid concentration. It was found that adding oxidizing agent resulted in enhancing the extraction of impurities from MG-Si as compared to that without oxidizing agent, especially for some non-dissolving elements in the acid like copper. After 2 h of leaching MG-Si with an acid mixture composed of 1 mol L − 1 hydrofluoric acid and 2 mol L − 1 hydrogen peroxide, the purity of MG-Si increased from 99.74 to 99.99%, which was higher than 99.97% obtained without hydrogen peroxide addition. Based on cracking shrinking model, the leaching MG-Si with the mixture was under chemical reaction control. Furthermore, to investigate the reaction mechanism on leaching MG-Si, the micro-structural evolutions of MG-Si before and after exposure to each etchants were revealed. [ABSTRACT FROM AUTHOR]

Impurity removal from metallurgical grade silicon (MG-Si) is an important issue for solar-grade silicon production, and solvent refining is used as an effective method to purify silicon. To evaluate the purification ability of solvent refining with Si Cu melt at 1343–1603 K, the effective segregation ratio of the main impurity element Fe between solid Si and Si Cu melt was experimentally and theoretically determined. The results demonstrated that the effective segregation ratio of Fe increased with the increasing temperature at the range of 1343–1603 K. The corresponding removal mechanism of Fe was investigated in detail. It was found that the effective segregation ratio of Fe calculated by Scheil equation presented the same tendency with experimental results, and the theoretical calculation was more consistent with experimental results when back diffusion was considered. Moreover, Fe was found to form Si Fe Mn and Fe Mn Ti phases into Si Cu alloy phase from MG-Si with the presence of Cu. It can be concluded that removal mechanism of Fe was not only a segregation process, but also a recombining process of impurity phase transformation. [ABSTRACT FROM AUTHOR]