A simplified froth model is proposed, which describes the froth transportation characteristics in three different regions of a flotation froth. In the stagnant region, new froth arrives at the same rate as froth collapses and returns to the pulp, so there is no net exchange between this region and other regions. In the second region, the froth rises vertically from the pulp-froth interface until it reaches the concentrate launder weir level. Then, the froth moves horizontally towards the launders in the surface froth region. Based on the mass balance of air passing through the froth phase, a mathematical model of froth transportation is developed for a cylindrical flotation cell. The model describes froth transportation time from the point of entry at the pulp-froth interface to the concentrate launder as a function of the geometrical dimensions of the flotation cell, the concentrate launder and froth crowder designs, as well as cell operating conditions and froth properties. The model was validated in two industrial scale flotation cells, viz. an Outokumpu 3 m3 tank cell at the Western Metals Hellyer concentrator and an Outokumpu 50 m3 tank cell at the Anglo Platinum Bafokeng-Rasimone concentrator, under various cell operating conditions and concentrate launder/froth crowder configurations. The results show that the model in general fits the experimental data well. Model fitting can be improved by taking into account the actual air dispersion profile in the flotation cell. Although the current form of froth transportation model does not explicitly relate the surface froth velocity to the pulp level setting, it was found during the plant test work that froth height can affect froth transportation and that the effect is associated with ore type and froth viscosity. A preliminary investigation into froth rheology was carried out separately in the Oukokumput 3 m3 tank cell at the Xstrata Mt Isa copper concentrator. The results are included in this thesis for future reference. In addition to not accounting for the froth height effect (pulp level setting), the current froth transportation also has some limitations when used for prediction purposes. There are three parameters in the model related to the froth properties – the air hold-up in the froth (f), the froth height above the concentrate launder (hf) and the froth instability factor (). These parameters depend on the ore and the cell operating conditions as well as the cell design, and cannot be modelled at present. Nevertheless, they can be measured directly in an existing flotation cell, which allows the model to be used for process control. Experimental measurement procedures and measured results from the industrial flotation cells are given in this thesis. The effect of the cell operating conditions is discussed. Finally, this thesis proposes a number of potential model applications, including the modelling of froth recovery of attached particles, the modelling of water recovery and entrainment, criteria for concentrate launder and froth crowder design, and a model for flotation process control based on froth images.
| Identifer | oai:union.ndltd.org:ADTP/254041 |
| Creators | Xiaofeng Zheng |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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