Use of a thermal plasma process to recycle silicon kerf loss to solar-grade silicon feedstock

The objective of this study was to recycle the dust generated in the slicing of silicon wafers (silicon kerf) by means of a two-stage thermal plasma process. In the first stage, the silicon particles are injected in a plasma jet where silicon oxides and carbon impurities are removed by vaporization. In the second stage, the purified silicon droplets are collected in a silicon bath maintained in a hot-wall crucible. The optimal operating conditions for reduction were determined by injecting into the plasma jet a commercial silicon powder of known degree of oxidation and measuring the attained degree of reduction. Also, silicon powders from wafer slicing were processed in the two-stage plasma set-up. The results of these tests showed that the deoxidation rate of the final silicon ingot was as high as 80% and the initial carbon concentration decreased by 85%. The purification was essentially controlled by the residence time of particles in the hottest zones of the plasma jet and the partial pressure of oxygen in the processing atmosphere. (C) 2016 Elsevier B.V. All rights reserved.