Modelling of a pinched sluice concentrator

Abstract

Although pinched sluice concentrators have been used for the concentration of heavy minerals for many centuries, their mechanisms involved have not been fully understood. Previous studies on the performance of pinched sluices have been of a purely empirical nature. In the present analysis, an attempt has been made to explain the behaviour of a pinched sluice in terms of the established theories of fluid mechanics and minerals processing. In spite of the inherently complex nature of two phase flow, a method has been developed to calculate the underflow discharge by assuming a logarithmic velocity distribution and free gravity fall through the discharge slot. The concentration profile of solids over the depth of flow has been shown to comply with Bagnold's theory of dispersive shear, rather than turbulent sediment transfer. Even although the results can be explained qualitatively by the Bagnold's theory, their complete quantitative analysis will not be possible until more work is done. Consequently, an empirical equation has been developed to predict underflow pulp densities. The segregation process of the heavier mineral beneath the lighter has been shown to obey a first order law, as was originally proposed by Mayer in relation to jigging. In the light of the results obtained, a computer model of the pinched sluice has been developed. This predicts the underflow grade, pulp density and flow rate in terms of the feed and operating conditions. The model can also be used to determine the effect of a change in operating conditions, and for the optimisation of rougher, cleaner and scavenger circuits.