Removal of Fe, B and P impurities by enhanced separation technique from silicon-rich powder of the multi-wire sawing slurry

The silicon-rich powder, which was separated by tuning the particle surface potential combined with centrifugation, contains varied impurities like iron, boron and phosphorus. To remove these impurities, the process of pre-dispersion and magnetic separation was attempted. The aggregates in the silicon-rich powder were dispersed by surface potential tuning combined with microwave treatment. According to the DLVO theory and experimental results, the electrostatic repulsion of the particles was largest when the pH value of solution reached 13.0, and the fine silicon-rich particles can be kept sufficiently dispersed at this pH, which was good for the further separation by magnetic field with the 90% removal of iron impurity. The residual iron impurity can be further completely removed by the microwave acid leaching with the mixing acid solutions of hydrofluoric and hydrochloric acid. By combining these enhanced purification techniques, other bothersome impurities such as boron and phosphorus can also be reduced to the requirements of solar grade polysilicon. This work is good for the recycling of silicon scrap materials to the solar grade polysilicon.