Numerical Investigation of Density Segregation on a Shaking Table Using the Discrete Element Method

A shaking table is used in gravity separation utilizing the difference in density of solid particles and has been widely employed in mineral processing and recycling processes. Although the principle of the table separation is simple, there is still limited knowledge about the segregation and separation mechanisms. To better understand these mechanisms, in this study, the discrete element method was applied to simulations of density segregation associated with the stratification of particles between riffles on a shaking table. The behavior of binary particles having the same diameter and different densities was simulated under various operating conditions. The mixing index was employed to evaluate the segregation state on the shaking table and the progress of segregation was investigated from the viewpoint of the vertical velocity difference between binary particles. Simulation results showed that although a larger amplitude and longer frequency of the shaking table promoted density segregation with time, an excessive amplitude and frequency of vibration was ineffective in promoting density segregation on the shaking table. It was also shown that the time variation of the average vertical velocity difference within one period of the shaking table can explain the progress of density segregation under conditions of various shaking table amplitudes and frequencies. In addition, the velocity difference between particles became larger near the wall than near the center, independent of the amplitude and frequency conditions. Consequently, the discrete element simulation newly revealed density segregation due to the vertical velocity difference between heavy and light particles, especially near the wall. This result will contribute to the optimization of shaking tables.