Separation of silicon and silicon carbide using an electrical field

Abstract

Recycling silicon from wiresaw slurry may be a good solution to reducing the high cost of silicon feedstock for solar cells. In this study, a cell was designed for separating Si and SiC particles in a buffer solution by gravity combined with electrical fields. According to the particle size distribution and zeta potential analysis, the average size of SiC particles was greater than that of Si particles in wiresaw slurries. The negative charges on the Si surfaces were more than that on SiC surfaces in buffer solution with a pH > 2.5, increasing the average settling velocity for SiC particles and attractive force toward the anode for Si particles. Therefore, the horizontal and vertical movement of Si and SiC particles occurred simultaneously when a horizontal electrical field was applied to the cell. Due to the small size, low density and increased charges, the electrical field enhanced greater displacement for Si particles, leading to a Si distribution on the bottom of separation cell. Analysis of carbon content at various positions on the cell bottom indicates that the experimental results and predicted result were consistent. The highest efficiency of separation, with only 7.15 wt% SiC remaining in the mixture, was obtained near the cell outlet; the original mixture had roughly 75.3 wt% SiC. The recovered material with high Si content can be transferred to an induction furnace to generate solar-grade Si.