MATHEMATICAL-MODEL OF THE DENSE-MEDIUM DRUM

A phenomenological model of dense-medium drum separators has been deve loped on the basis of the observation that the partitioning behaviour of a particle is related to its calculated terminal velocity. The mode l utilizes a theoretical calculation of the terminal velocity of each particle class. This is then correlated with the observed partition da ta for a plant separator using empirically derived functions of operat ing conditions (based on plant surveys), which take into account such effects as bath turbulence, the holes in the drum lifters and feed arr angements. The model successfully decouples the effects of medium dens ity and viscosity and is appropriate for any bath-type separator. The correlation between calculated terminal velocity and actual partitioni ng behaviour was established and modelled using data obtained from two Wemco drums treating iron and manganese ores. The model can be used t o predict the prevailing size-by-size partition curves and, hence, the separation (grades/recoveries of each product) given the washability of the feed and operating conditions. Simulations are used to demonstr ate that, in the treatment of iron ore, there is a maximum medium dens ity beyond which product grades fall and that this maximum decreases a s the proportion of magnetite in the medium increases. This is attribu ted to the dominant effect of viscosity at higher medium solids concen trations.