Recycling silicon wire-saw slurries: Separation of silicon and silicon carbide in a ramp settling tank under an applied electrical field

Abstract

The growing demand for silicon solar cells in the global market has greatly increased the amount of silicon sawing waste produced each year. Recycling kerf Si and SiC from sawing waste is an economical method to reduce this waste. This study reports the separation of Si and SiC using a ramp settling tank. As they settle in an electrical field, small Si particles with higher negative charges have a longer horizontal displacement than SiC particles in a solution of pH 7, resulting in the separation of Si and SiC. The agreement between experimental results and predicted results shows that the particles traveled a short distance to reach the collection port in the ramp tank. Consequently, the time required for tiny particles to hit the tank bottom decreased, and the interference caused by the dispersion between particles and the fluid motion during settling decreased. In the ramp tank, the highest purities of the collected SiC and Si powders were 95.2 and 7.01 wt%, respectively. Using a ramp tank, the recycling fraction of Si-rich powders (SiC <15 wt%) reached 22.67% (based on the whole waste). This fraction is greater than that achieved using rectangular tanks.Implications: Recycling Si and SiC abrasives from the silicon sawing waste is regarded as an economical solution to reduce the sawing waste. However, the separation of Si and SiC is difficult. This study reports the separation of Si and SiC using a ramp settling tank under an applied electrical field. As they settle in an electrical field, small Si particles with higher negative charges have a longer horizontal displacement than SiC particles in a solution of pH 7, resulting in the separation of Si and SiC. Compared with the rectangular tanks, the recycling fraction of Si-rich powders using a ramp tank is greater, and the proposed ramp settling tank is more suitable for industrial applications.

An efficient way of recycling silicon kerf waste for synthesis of high‐quality SiC

“…In recent years, a variety of separation processes for recycling Si and SiC from the SKW have been reported, including hydrocyclone, 4,5 centrifugation, 6,7 phase-transfer separation, [8][9][10] electrical field, 11 thermal plasma process, 12 methods, 13 and supercritical water methods. 14 For example, Mouna et al 15 have successfully separated Si (82 wt%) and SiC (91 wt%) from the SKW followed by centrifugal, chemical cleaning, filtering, distillation, and extraction methods.…”

Evolution and present status of silicon carbide slurry recovery in silicon wire sawing

“…Tsai et al (2013) have reported separation of silicon and silicon carbide in a ramp settling tank under an applied electrical field. They find that SiC and Si particles have different electrical charges and hence migrate at different rates under an applied electric field.…”

A rapid thermal process for silicon recycle and refining from cutting kerf-loss slurry waste

“…The removal of metals and the majority of SiC particles could be easily achieved by acid leaching and sedimentation [5,6]. Electrical and magnetic forces could also be considered [7][8][9][10]. The silicon purity of around 85 wt% could be easily obtained with low cost.…”