Study on the hydraulic classification characteristics of micron-sized silica particles

The present study investigates the motion characteristics of micron-sized silica particles and how solid-water interaction regulates hydraulic classification. Two methods were evaluated for classifying micron-sized silica particles. Using the small-diameter cyclone for hydraulic classification of micron-sized silica particles resulted in poor separation due to the short residence time of particles in the cyclone. Particle settling in still water showed that settling velocity, drag force, and virtual mass force increased with particle size, providing a basis for size classification. In the particle sedimentation process, drag force and gravity were dominant, with drag force reaching equilibrium with gravity in a fast time. The upward water flow was introduced to classify silica particles, with its superficial velocity between the settling terminal velocities of large and small particles, allowing large and small particles to flow to the overflow and underflow, respectively. The upward flow velocity was higher near the center of the flow field and lower near the wall, leading to a parabolic distribution pattern of the particle group along the radial position. In hydraulic sedimentation classification experiments of silica particles, the average particle size of the overflow sample was lower than that of the feed, and its size range was narrower, indicating the feasibility of hindered sedimentation by upward flow for classifying micron-sized silica particles.