Characterising and Predicting the performance of industrial flash flotation cells

Abstract

Flash flotation plays an integral role in many of the gold and sulphide mineral concentrators around the world. A comprehensive review of the available literature has found that there is a distinct lack of research in the area of coarse particle flotation with sulphide ores, and more specifically that very little data is available on the process of flash flotation, despite its widespread use. This thesis has been developed to investigate the conditions present within an operating flash flotation cell; the nature of the particles it recovers (and their flotation kinetics); mathematically describe the dual flotation / classification behaviour of these cells and also to develop a method of predicting whether an ore is amenable to the flash process using conventional laboratory methods (including mineralogical characterisation). In order to achieve this goal, two plant survey campaigns have been conducted at Kanowna Belle, which treats a refractory (pyrite) gold ore. Both campaigns involved running the concentrator both with and without the flash flotation circuit in operation. A belt cut was taken of the plant feed material in both survey campaigns to enable laboratory test-work to be conducted on the same material being processed by the plant, and enable a direct comparison of plant and laboratory performance. Hydrodynamic characterisation of the operating cell was performed to compliment plant survey data, which involved axial profiling of both slurry and gas dispersion properties. Mineralogical analysis has been performed throughout to gain an understanding of the nature and behaviour of particles in this system. The culmination of all the information gathered has two key outputs: 1. A batch flotation testing method that can reproduce the distribution by size and liberation properties of the valuable material (in this case pyrite) in the flash flotation cell concentrate; and 2. A phenomenological model that mathematically describes the dual flotation and classification behaviour of particles within an operating flash flotation cell. The results of several plant survey campaigns with associated batch flotation test-work have culminated in the identification of key trends in plant performance that can be directly attributed to the operation of a flash flotation circuit. Stream data easily obtained from cyclone surveys or on-line particle size measurements of the cyclone overflow stream can be used as the basis for laboratory batch flotation testing to determine an ores amenability to undergo the flash flotation process. The batch testing method developed for this refractory gold ore is able to produce a concentrate with a valuable elemental (Au, S and Fe) distribution by size that is equivalent to that produced by the plant flash flotation cell, whilst treating the same ore feed material. Further to this the pyrite particles were found to have nearly identical liberation characteristics within the floatable size range (-212 / +12 µm), with almost all particles being greater than 90 % liberated. The development of a laboratory method to determine whether a precious metal ore is suitable to undergo the flash flotation process has potential to aid in flow sheet development and optimisation for new ores. Axial profiling of slurry with increasing depth into the cell has been identified as a useful tool in understanding and optimising the flash flotation response to changes in the grinding environment and overall circuit water balance. Axial profile data has clearly shown the extent of settling that is occurring within the industrial cell, with the results of two profiles revealing a drop of 21.0 % and 31.5 % solids over a 1.5 m measurement range. A large change in the distribution of solids with size is also observed, with the total solids P80 changing by 195 and 227 µm respectively. Analysis of axial profile data has led to the development of a phenomenological model which mathematically describes the dual flotation / classifier action of the settling zone within the cell. This model takes a novel kinetic type approach to empirically fitting the measured data with two parameters (αi and βi) relating the kinetic rate constant (by size i) of the valuable particles with the axial residence time (τs) within the cell, and takes the form: ki= αi e-βi Τs. This model will be presented and discussed and represents the first published model describing the internal behaviour within an operating flash flotation cell. This thesis has been undertaken as a ‘Thesis by Publication’ and as such Chapters 2 to 6 consist of peer reviewed papers that have been published in Minerals Engineering Journal (see list in section: Publications included in this thesis). An introduction and context to the work is added as Chapter 1 and the thesis finishes with discussing the conclusions and recommendations for future work in Chapter 7. Additional conference papers have been added as supporting information in the appendices.