Leaching behavior of impurities in Ca-alloyed metallurgical grade silicon

• Silicon microstructure evolution under attack by different lixiviants was revealed.
• One-step leaching with the HCl + HF mixture resulted in achieving the required purity of SOG-Si for Ti, Mn, V and Mg.
• The acid leaching process of Si–Ca alloy was under chemical reaction control.

To explore the potential of acid leaching in purifying metallurgical grade silicon (MG-Si) for solar cell applications, the effect of silicon microstructure on its leaching behavior was systematically investigated in the present work by a combination of alloying refining with acid etching. The microstructure evolution of silicon was revealed before and after acid etching with different lixiviants. Calcium-containing precipitates were found in MG-Si after alloying with calcium. The etching results showed that the leaching behavior of impurity inclusions strongly depended on the composition of the major impurities. HCl + HF mixture was an effective lixiviant for dissolving impurity inclusions in both MG-Si and its alloy with calcium. The impurity removal efficiency of acid leaching of MG-Si was efficiently improved after alloying. Moreover, the kinetics of acid leaching of MG-Si after alloying with calcium was further discussed based on cracking shrinking model.