The main aims of this thesis were:
• To develop the three-product cyclone such that:
- it can be used to generate a second overflow that would serve as a more suitable feed for flash flotation than the usual conventional cyclone underflow, or alternatively, can be classified with a micro-screen to separate the values from the gangue, its use will result in improvement in overall classification performance, particularly with respect to the denser mineral fractions.
• To provide a database that:
- will help in understanding and interpreting the mechanism of the separation process in the three-product cyclone,
- can be used to develop a mathematical model of the three-product cyclone for simulation and performance optimisation.
To achieve the above aims, an approach comprising a combination of the crowding theory (Fahlstrom; 1960, 1963) and variation in the vertical path travelled by particles in the upward central current of the cyclone was adopted.
Experiments were designed and carried out to investigate the influence of the length and diameter of the second vortex finder, spigot size, inlet pressure and feed solids content on the operational performance of the three-product cyclone. In some selected cases, conventional cyclone tests were conducted under similar conditions to those of the three-product cyclone to serve as a base case.
The results showed that the geometry of the second vortex finder, in particular its length, and the spigot size are critical variables for the three-product cyclone. By optimising these design variables:
• a second overflow (middlings stream) can be generated that may be more suitable for flash flotation than the conventional cyclone underflow. At the same time, a fines stream with similar properties to those of the conventional overflow can be obtained. Hence if the middlings stream was used as feed for flash flotation or classified further with a micro-screen, the fines stream could be used in lieu of the conventional overflow without compromising the feed requirements for the conventional flotation circuit;
• an inner and an outer overflow streams can be obtained which when combined and used in place of the conventional overflow would result in improvement in the overall classification performance particularly with respect to the denser mineral fraction in the feed;
• the three-product cyclone could be used for fine separation and de-sliming duties.
Based on the author's understanding of the data trends obtained from the experimental program, the mechanism of the separation process in the three-product cyclone was for the first time described. To determine the accuracy of this description, two conceptual models of the possible mechanisms of separation were formulated and tested using the same database. The results showed that the conceptual model based on the author's description fitted the data more accurately.
Using non-linear least squares techniques, this conceptual modelling approach was used in conjunction with modified empirical hydrocyclone models (incorporating the influence of the geometry of the second vortex finder) and 120 data sets to develop mathematical models of the three-product cyclone. Based on the criteria of accuracy, significance and simplicity, the best model was selected, validated with thirty-one independent data sets, and then used for simulations to demonstrate some of its applications.