Experimental study on the sedimentation of silicon particles under the interference of flocculants

Silicon separation represents the initial step in the recovery of silicon from diamond wire saw silicon waste slurry. In the current recovery process, the relatively low recovery rate indicates an inadequacy in silicon separation. This article primarily focuses on the sedimentation of particle groups and delves into the interference sedimentation mechanism of particle swarms. The experimental results reveal that the optimal flocculant for promoting interference sedimentation is CPAM (Cationic Polyacrylamide). For 3.72 µm silicon particles, the effect is optimal when the CPAM concentration is set at 0.2% and the addition rate is 17%. And 0.59 µm silicon particles require a higher concentration of 0.4% concentration and 17% addition rate for CPAM, to make the particles settle. And by comparing the particle size results, it can be seen that the 0.59 µm silicon particles have more surface voids and tiny particles on the flocs, and a larger total contact area, requiring more flocculant addition. Therefore, the contact performance between particles and flocculants determines the effective level of flocculants. To enhance the contact performance between flocculants and particles, a certain proportion of PDDA was added while adding the optimal proportion of CPAM. The experimental results showed that the addition of PDDA could reduce the contact angle between particles and CPAM, improve the overall hydrophilicity of the suspension, and make it easier for CPAM to contact with silicon particles. Moreover, 0.5% PDDA was required for 3.72 µm silicon particles, and 1.5% PDDA was required for 0.59 µm silicon particles. Under these conditions, the flocculation speed and sedimentation efficiency of particles were improved.