Liberation by Size Reduction. Consequences and Improvements on Flotation Kinetics

The first part of this lecture aims at emphasising the important role played by particle size on the general formulation of a separation process by means of its influence on the liberation status of a given ore. Liberation, seen as a static state of a particulate system, is described by means of a marginal probability density of grade, the computation of which compels us to define and use a grade distribution density conditional on size. Liberation is then considered as a dynamic state evolving along comminution time. Both cases of non-discriminating (transgranular) and discriminating (perigranular and transgranular preferential) comminution are referred. For the non- discriminating case, a limit probability argument is used to justify the introduction of the Euler Beta Law as a well suited tool for describing the liberation state of a comminuted ore, since it is able to predict the grade distribution of a given iso-size fraction. Considering this previous general model of liberation by size reduction as a good support, flotation kinetics is reviewed in order to provide evidence for the kinetic rate constants (seen as non-wettability parameters) as dependent on the grade distribution conditional on size. Simulation of traditional experiments, such as washability curves and release analysis, supported by the modelled liberation phenomenon and a good condensation of the kinetical parameters, is shown to be feasible. Finally, some numerical experiments of an elementary flotation kinetic model are performed in order to enhance the influence of size and degree of liberation on flowsheet performance.