Settlement behavior and stratification of waste printed circuit boards particles in gravitational field

Abstract Waste printed circuit board (WPCBs) is a kind of sustainable resource for providing economically valuable metals due to its huge output and excellent metal grade. Gravity separation is an effective pre-concentration technology to separate WPCBs particles with significant density difference. This study focuses on revealing the mechanism of gravity concentration from the perspective of dynamics and statics. The settling velocity of three kinds of particles in WPCBs (organic matter, glass fiber and metal particles) are calculated, which can be expressed by traditional settlement velocity model with correction coefficient. Subsequently, the equal-sedimentation model of the particles was established, and the calculation results show that the particle size ratio should be within 5.58. The lowest potential energy model was proposed to explain the stratification process of particles from the static point of view. The potential energy calculation results show that the stratification process dominated by density difference is spontaneous, which can achieve the lowest potential energy. Shaking table test shows that the metal particles with different sizes can be effectively enriched in the concentrates, and the metal grade increases with the decrease of particle size, from 56.5% to 68.2%, and the metal recovery decreases from 86.41% to 83.04%.