Purification of Silicon via Pyrometallugical Solvent Refining and Dealloying by HNO3

This work presents a method for producing high-purity, low-micron-size silicon particles by combining solvent refining and metal dealloying. Metallurgical-grade silicon, a feedstock material for photovoltaic and electronic applications, was mixed with copper, heated and then cooled under controlled conditions, mechanically crushed, and gravity-separated, yielding pure silicon crystals and copper silicides. The process leverages copper’s high diffusivity, low solubility, and susceptibility to oxidizing acids to segregate unwanted elements into copper silicides, and the significant density difference between silicon and copper to achieve effective separation. Characterization by optical microscopy, X-ray diffraction, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and inductively coupled plasma mass spectrometry (ICP-MS) confirmed the formation of large, pure silicon crystals with no contamination. Gravity separation produced high-purity silicon crystals free of inclusions, with only copper silicide residues remaining on the surface. Subsequent nitric acid treatment removed these residues, yielding silicon with no detectable elements other than silicon and copper, as confirmed by ICP-MS. The purified silicon met specifications for unidirectional or zone-refining feedstock material. Processing micron-sized particles enabled the use of conventional techniques for impurity removal, presenting a practical alternative to traditional chemical vapor deposition methods.