Carlos Vanegas Alvarez (2011). DEVELOPMENT OF A NOVEL FROTH ACOUSTIC EMISSIONS SENSOR PhD Thesis, Sustainable Minerals Institute, The University of Queensland.

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Author Carlos Vanegas Alvarez
School, Centre or Institute Sustainable Minerals Institute
Institution The University of Queensland
Publication date 2011-03
Thesis type PhD Thesis
Supervisor Dr Peter Holtham
Total pages 372
Total colour pages 43
Total black and white pages 329
Subjects 04 Earth Sciences
Abstract/Summary Processes that use air bubbles in liquid as a method of mass transfer generally result in foam (liquid and gas) or froth (liquid, gas and solids) formation. Foams and froths, which reside on the top layer, can be encountered in diverse applications such as waste water treatment, as well as food and mineral industries among others. The coalescence and bursting of bubbles in the foam or froth phase is of particular importance because it ultimately determines the efficiency of the process. Therefore, measurement of coalescence and bursting is essential for proper monitoring of the process. In this study, a method capable of detecting the acoustic emissions produced by breaking foams and froths was developed. The method is intended to be used in the detection of bubble bursting and coalescence mainly in the mineral flotation field; however, its application is not limited to this process. For the development of the method, a broadband hydrophone was initially used. However, this technique was unable to distinguish signals caused by coalescence and bursting from background noise. Then two commercially available Acoustic Emission Sensors with different operating frequencies were tried; however without success. Consequently it was decided to develop a method in house comprising of an electronic sensor that uses a small ultrasonic transducer. Through the research described in this thesis, a sensor was developed to measure the amount of acoustic emissions occurring in the froth. The main feature of this sensor is its ability to isolate the background noise normally found in flotation plants. Methods were established to handle the signals generated by the sensor and flotation experiments were performed to determine relationships between the processed signal and metallurgical performance. The Froth Acoustic Emission technique involves the use of ultrasonic sensors to measure the elastic energy released by film rupture during bubble coalescence in industrial flotation cells. The signal emitted by the sensor has been proven to respond to changes in froth conditions. Experiments were performed in a wide variety of scenarios including laboratory conditions in two systems: water-frother and with solids; as well as in industrial conditions. Results show variations of the froth sensor response to be dependant on changes in frother and collector concentration, and related to corresponding variations in the mineral and water recovery. Importantly, a linear relationship was found between the reciprocal of the acoustic emission activity in the froth with first, the dynamic foam stability factor and second, with water recovery. This signal, the acoustic emission activity of the froth phase, provides an alternative method to measure the stability of the froth. The response of the sensor to changes in metallurgical performance are shown in this thesis and compared with other instrumentation outputs. These results confirm the ability of the new acoustic sensor to be used as a quantifying method to measure froth stability. This research is the first of its kind in the forthcoming technology of froth acoustics and for that reason, considerable effort was devoted to development of the prototype, putting a lot of emphasis on its practicality to ensure its future exploitation. It is desired that by the development of the tool presented in this thesis, researchers would be provided with extra information on what is going on in the froth phase, keeping in mind that results are still open to discussion and interpretation. This tool could offer a wide variety of applications and the possibility of its use in many experimental scenarios. Furthermore, it could be used to create new standards. The industry could also be benefiting by this project since the developed apparatus can potentially be incorporated as a sensor for everyday operation which would end up finally in cost reduction.
Keyword Froth, sensor, acoustics, emission, flotation, mineral
Additional Notes Pages with colour 5, 39, 46, 54, 67, 71, 72, 77, 81, 87, 96, 97, 98, 99, 100, 101, 102, 103, 106, 107, 108, 112, 113, 114, 115, 116, 117, 118, 120, 129, 103, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148

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Created: Tue, 24 May 2011, 15:25:56 EST by Mr Carlos Vanegas Alvarez on behalf of Library - Information Access Service