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.

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A great amount of slurry waste is formed during the cutting process from silicon ingot to wafers. More than 50% of this waste comes from cutting liquids. This study investigated centrifugation to recover polyalkylene glycol (PAG) cutting liquid with low turbidity (<100 NTU). The experimental results show that clean PAG liquids could be obtained by using water as a diluent. Because water with high chemical polarity and strong hydrogen bonding would destroy the adsorption of PAG molecules on particles, and weaken the steric stabilization, the particles are aggregated and then separated from liquids by centrifugation. After 50 wt.% water-assisted centrifugation at 3,253 G-force for 24 h, the solid content of the upper liquid decreased to 0.018 g/L, and the turbidity reduced to 7.2 nephelometric turbidity units (NTU). The obtained liquid was then vacuum distillated to remove water. The final recovered PAG with only 0.43 NTU could be reused in the cutting process.