Mathematical modelling of bagnold effect and separation behavior of a coal-washing spiral using a mechanistic approach

Among the gravity separators, the spiral concentrator is considered to be one of the most efficient and simple unit operations. Complex mechanisms, including the combined effects of different forces, differential particle settling rates, interstitial trickling and possibly hindered-settling affect the stratification of particles. "Bagnold effect" arises at relatively high pulp densities of the feed. This effect is attributed to the velocity distribution along the depth of the flowing film, which gives rise to a distribution of shear rates along the depth of flow. An improved mathematical model incorporating Bagnold effect is proposed to characterize the separation behavior of a coal-washing spiral. Sensitivity studies of the operating parameters on the segregation behavior of particles across the radial width of the trough during their motion along the spiral have been carried out. It is believed that the model reasonably mimics the segregation behavior of a particle during its motion along the spiral with a reasonable degree of realism.