Enhancement in extraction of boron and phosphorus from metallurgical grade silicon by copper alloying and aqua regia leaching

• Cu alloying followed by aqua regia leaching helps to remove B and P from MG-Si.
• Up to 58.7% B and 42.2% P are leached into the leaching solution.
• Interfacial transfer and product layer diffusion both control the leaching process.

The feasibility and optimization of an enhanced boron and phosphorus extraction process, from metallurgical grade silicon (MG-Si), consisting of solvent refining and acid leaching were studied comprehensively. MG-Si was alloyed with copper (Cu), following which, the removal of boron and phosphorus from the Si–Cu alloy by acid leaching was investigated. The results showed that the Cu-alloying process led to the concentration of boron and phosphorus in the Si–Cu alloy phase, which was confirmed to be an important part of their removal. Based on the analysis of acid sensitivity of the Si–Cu alloy phase, it was found that aqua regia was an effective leaching agent for removing the Si–Cu alloy phases from Si grains compared to HCl and HNO3. Addition of copper resulted in the increase in the extraction yield of boron and phosphorus from MG-Si from 21.0 to 58.7% and 23.2 to 42.2%, respectively. The selected Si–Cu powders were within a size range 74–106 μm and the leaching was conducted at 70 °C for 5 h via a three-step sequential acid leaching procedure. Furthermore, the leaching kinetics of boron and phosphorus using aqua regia was observed to be controlled by interfacial transfer and product layer diffusion.

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