Tapered fluidized beds and the role of fluidization in mineral emplacement

One of the most prominent features of fluidised beds is the mixing and segregation that takes place within them. This is of great importance for many industrial processes, but takes on a particular significance for mineral extraction where a small amount of valuable matter is mixed with a large amount of waste. These are often emplaced in large pits (length scale of the order of a kilometre) with a volcanic vent at the bottom through which the minerals were introduced along with other matter, along with a gas flow. What is desirable is an understanding of the processes that led to the dispersal of minerals before their emplacement to allow efficient extraction. The paper describes experimental observations of a tapered fluidised bed. The objective was to identify the physical behaviour of gas and particles; so, of particular interest are the extent to which fluidisation takes place within the bed, and the arrangements of particles seen. Gas flow rate, particle size, and degree of taper were all varied. These observations can be used to identify the structures and processes that can take place; it is then possible to understand field data in terms of the physics that led to the emplacement of material. This will be shown using new data taken from southern Africa. Scale-up of evidence is of obvious difficulty in this system and this is discussed in terms of the possible behaviour of the bubbles that have generated mixing of material before emplacement.