The recovery of fine particles has become of great importance during recent years, since the demand for minerals is increasing and the extent of available ore is decreasing. To recover fine particles by flotation is very difficult due to their low flotation rate, which leads to poor recoveries and long residence times in flotation circuits. In this thesis, the reasons for the low flotation rate of fine particles are studied by focusing on the role of hydrodynamics and surface chemistry in bubble-particle collection. / In this study, fine particle flotation was investigated using 0.5 to 5 mm diameter graphite and quartz as model particles. The graphite particles are naturally hydrophobic whereas the quartz particles are hydrophilic but their surfaces can be modified to various degrees of hydrophobicity. Particle contact angles were determined using the film flotation technique, modified with the addition of a calibration curve of advancing water contact angle and critical surface tension. The film flotation technique was found to be suitable for the determination of the contact angle of these very fine and angular particles, whereas conventional particle contact angle techniques failed. / The flotation behaviour of model particles was investigated using single bubbles and bubble swarms in quiescent conditions in a modified Hallimond tube and at constant gas flow rate in turbulent conditions in a Rushton turbine cell. The results from these experiments showed that to float particles smaller than 5 mm in diameter, an advancing water contact angle of 54° - 3° or higher was needed. This critical contact angle for fine particle flotation is in agreement with the predictions of the Scheludko model, when a correct line tension is used. Importantly, this critical contact angle is independent of the flotation environment within which capture occurs. / The “experimental” bubble-particle attachment efficiencies were obtained by dividing the measured bubble-particle collection efficiencies by the Generalised Sutherland Equation (GSE), assuming that the bubble-particle stability efficiency is equal to unity. A new approach to attachment model was developed using the electrostatic double layer, the van der Waals and the hydrophobic interaction energies. This 1/W attachment model is based on the ratio between the rate of interaction force controlled interparticle collision and the rate of interaction force controlled interparticle collision without electrostatic double layer repulsion. / The 1/W model, the modified Dobby and Finch model and the Yoon and Mao model were compared with the “experimental” attachment efficiencies. The modified Dobby and Finch and 1/W models agreed with experimental findings in this study and others. The Yoon and Mao model shows entirely opposite behaviour. / Bubble-particle collision efficiency increases with increasing particle size. Thus, it is theoretically possible to improve the flotation rate of fine particles by particle aggregation. It was found that the maximum size of aggregates increased with decreasing agitation speed and increasing particle hydrophobicity, electrolyte concentration and condition time. An increase in graphite aggregate size resulted in an increase in graphite flotation recovery and rate in a mixed mineral suspension of graphite and quartz. Selectivity was assured providing that the advancing water contact angle of the quartz particles was below 54°. / A copper sulphate ore was floated in a Rushton turbine cell to validate results obtained using model particles. The flotation experiments showed conventional results for flotation of different size fractions, where the intermediate size fraction floated best. A particle size fraction of -6 mm did not respond to the methods outlined in this study to increase the flotation rate of fine particles, whereas the response of a particle size fraction of -53 +6 mm was as expected. The results indicated that the particle size fraction of -6 mm was highly oxidised and their contact angle was below the critical contact angle needed for flotation, in contrast to the larger particles. / Thesis (PhDEngineering)--University of South Australia, 2007.
| Identifer | oai:union.ndltd.org:ADTP/267068 |
| Creators | Miettinen, Tatu. |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | copyright under review |
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