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Selecting optimal operating conditions for Knelson Concentrators

Sargent, D. and Subasinghe, G.K.N. (2006) Selecting optimal operating conditions for Knelson Concentrators. In: Metallurgical Plant Design and Operating Strategies, 18 - 19 September, Perth, Western Australia pp. 274-289.


Metallurgists operating Knelson Concentrators (KC) often rely on manufacturers recommendations for selecting operating parameters, such as fluidising water flow rate and cycle time. Recent studies have shown that these parameters are not only dependent on the machine parameters but also on the feed characteristics, such as size distribution of the gold and gangue particles and the composition of its constituent minerals. It is known that a particle entering a KC initially traverses a circular path within the bowl. For a particle to maintain a given orbit, the required centripetal force must be supplied by external means. It has been argued that this centripetal force which is dependent on the mass of the particle, its radial position and the rotational speed of the bowl, is provided by the fluid drag force created by inwardly moving fluidising water and the Bagnold's force created by the particle/particle collisions. Depending on the fluidising water flow rate, one of two situations can occur where the porosity of the bed increases or decreases which influences the amount of material retained within the bowl. The amount of material of a given size and density retained in the bowl is thus dependent on the extent of the centripetal force provided. Based on the above concept, a criterion that can be used to predict the amount of material recovered in the bowl has been derived and validated by experimental data. It may also be construed that this criterion demarcates the transition of the bed from a packed-bed state to a fluidised state. By identifying the transition values for the different constituent mineral particles in the feed, it is possible to estimate the optimal fluidising water flow rate that would maximise gold recovery while minimising gangue recovery. In addition, the kinetics of gangue displacement by incoming heavy mineral particles were also studied using synthetic mineral mixtures. The experimental data suggests that this process follows first order kinetics and that the build-up of heavy mineral reaches a maximum. A model has been proposed to predict the optimal batch cycle time for a KC in terms of the feed characteristics and machine operating parameters.

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