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The gas dispersion characteristics in mechanical flotation cells have a significant effect on the overall flotation performance. Three major properties that can be measured in characterising the gas dispersion in a flotation cell are bubble size, gas hold-up, and superficial gas velocity. Another property that is equally important in flotation is bubble surface area flux which is calculated from bubble size and superficial gas velocity. Despite the importance of gas dispersion in flotation, not much work has been reported previously in this area. Moreover, the study of gas dispersion in flotation has typically considered only a few points in a flotation cell and the average values were assumed to represent the gas dispersion characteristics in the entire volume of the cell. It is known however, that the gas dispersion characteristics are not uniformly distributed in a mechanical flotation cell. This thesis seeks to understand better the gas dispersion characteristics in mechanical flotation cells with a view to optimisation, modelling, cell comparison and selection. The main aim of this thesis was to measure comprehensively the gas dispersion characteristics in a mechanical flotation cell, analyse the behaviour in the entire volume of the cell, and develop a methodology for modelling the gas dispersion characteristics in the whole volume of the cell as well as develop the models themselves. For this purpose, a fully instrumented 3 m³ glass rectangular flotation cell at the Julius Kruttschnitt Mineral Research Centre (JKMRC) at the University of Queensland was used. The cell was fitted with a Dorr-Oliver impeller-stator mechanism and was provided with facilities to change impeller speed and gas flow rate. Sensors to measure the gas dispersion characteristics were also acquired and modified. This cell could only be operated in a two-phase (air-water) system but the opportunity was taken to make some comparative measurements in an operating plant in a three-phase slurry to compare the gas dispersion characteristics in two and three-phase systems. The comprehensive measurements of the gas dispersion characteristics (i.e. bubble size, gas hold-up, and superficial gas velocity, with subsequent calculation of bubble surface area flux) throughout the entire volume of the 3 m³ rectangular flotation cell show that the properties do vary with distance from the impeller, the cell bottom, and the walls. Statistical analysis to test the homogeneity of the properties in the cell confirmed that the differences (variation with distance) were real. It was found that the gas dispersion was poor in the corners of a rectangular flotation cell. These corners are referred to as dead zones. It can be interpreted that in these zones, flotation is less effective compared to other zones in a cell. The results of mapping the gas dispersion characteristics throughout the entire volume of the flotation cell were used to determine the best location to measure gas dispersion characteristics in a flotation cell in order to represent the overall values. It was established that this location in a flotation cell is about halfway between the impeller and the wall, and halfway between the bottom of the flotation cell and the pulp-froth interface. Statistical analysis also showed that there is “quarter symmetry”, i.e. there is no significant difference between equivalent positions in different quarters in a horizontal plane. In any future work, therefore, measurements of the gas dispersion characteristics need only be made in one quarter, and symmetry in the rest of the cell can be assumed. Following from the statistical analysis that established quarter symmetry in the 3 m³ glass rectangular flotation cell, a methodology to model gas dispersion characteristics in the entire volume of a rectangular mechanical flotation cell was developed, based on an experimental design known as CCRD (central composite rotatable design) which then modified. Using the methodology, models to predict bubble size, gas hold-up, superficial gas velocity and bubble surface area flux in the entire volume of a rectangular flotation cell were developed as a function of air flow rate and impeller speed. The validity of the models was tested using a predictive (cross) validation method, from where it was concluded that the models were valid. These models were then used to analyse the gas dispersion characteristics in detail in the flotation cell, as a function of flow rate, impeller speed, and location in the cell. Finally, a comparison of gas dispersion characteristics in two and three-phase systems in flotation cells was made. Comprehensive measurements of gas dispersion characteristics were performed in a three-phase slurry in an industrial OK 38 m³ rectangular flotation cell at the PT Freeport Indonesia concentrator, and the results were compared to those measured previously in the two-phase system in the 3 m³ rectangular cell. It was found that the profiles of gas dispersion were generally similar in both cells but the magnitude of the gas dispersion properties differed between the two systems. The presence of solid particles had greater effect on the bubble size than on gas hold-up and superficial gas velocity.

Over many years, researchers in the field of flotation have developed an in-depth understanding of processes occurring in the pulp phase of flotation machines. Until recently, however, the froth phase has received little attention. The froth phase serves to separate bubble-particle aggregates from suspended slurry in a flotation cell. The mechanism of recovery by entrainment, its relationship to water recovery and particle size dependency is well understood. Froth recovery, (the fraction of particles entering the concentrate launder that entered the froth phase attached to air bubbles), is not well understood. Up until now, there has been doubt over whether this property is dependent on particle size and hydrophobicity. Difficulties in measuring froth recovery had previously prevented researchers from gaining a deeper understanding of the transport of attached particles across the froth phase. A novel device was designed and tested to measure froth recovery by isolating bubble-particle aggregates in the pulp-phase of flotation machines through the determination of the bubble loading in the pulp phase (mass of particles attached per unit volume of air bubbles). This technique can be used with other measurements to investigate froth selectivity by directly comparing these captured particles to those found in the froth phase. Evidence was collected at Red Dog Mine, Alaska and Newmont Golden Grove Operations, Western Australia which showed that the froth phase selectively transported more hydrophobic and smaller sized particles across the froth than less hydrophobic and larger particles. Particles collected in the device were compared to those found in the concentrate stream on a size by mineral by liberation class. Froth recovery was also calculated on a size by mineral by liberation class for two valuable sulphide minerals in a continuous 3m³ flotation cell. These results show that the froth phase is responsible for the upgrading of attached particles across the froth phase as well as for the separation of bubble-particle aggregates from suspended slurry. The pulp phase is responsible for creating bubble-particle aggregates through the attachment of hdyrophobic mineral particles to air bubbles. Many complex factors affect the extent to which this occurs including the size and hdyrophobicity of the particles, the size and number of air bubbles produced by the flotation machine, the rate of collisions between particles and bubbles and the overall chemistry of the system. This measurement of bubble loading presents an opportunity to measure the impact of all these factors on the successful creation of bubble-particle aggregates. Based on a literature review suggesting that there was a high probability of particles being detached at the pulp-froth interface due to the aggregates change in momentum, a three phase description of a flotation cell was proposed. The three phases were: pulp, pulp-froth interface and upper froth zones. A second froth recovery measurement technique (changing froth depth) was used in combination with the bubble load technique to determine the recovery across each of the two froth zones. It was found that the pulp-froth interface appears to be responsible for the selectivity observed across the froth phase as a whole. These findings will enable more in-depth research into the sub-process of the froth phase as well as assisting flotation cell design through a better understanding of the roles of the pulp-froth interface and the upper froth region.

Over many years, researchers in the field of flotation have developed an in-depth understanding of processes occurring in the pulp phase of flotation machines. Until recently, however, the froth phase has received little attention. The froth phase serves to separate bubble-particle aggregates from suspended slurry in a flotation cell. The mechanism of recovery by entrainment, its relationship to water recovery and particle size dependency is well understood. Froth recovery, (the fraction of particles entering the concentrate launder that entered the froth phase attached to air bubbles), is not well understood. Up until now, there has been doubt over whether this property is dependent on particle size and hydrophobicity. Difficulties in measuring froth recovery had previously prevented researchers from gaining a deeper understanding of the transport of attached particles across the froth phase. A novel device was designed and tested to measure froth recovery by isolating bubble-particle aggregates in the pulp-phase of flotation machines through the determination of the bubble loading in the pulp phase (mass of particles attached per unit volume of air bubbles). This technique can be used with other measurements to investigate froth selectivity by directly comparing these captured particles to those found in the froth phase. Evidence was collected at Red Dog Mine, Alaska and Newmont Golden Grove Operations, Western Australia which showed that the froth phase selectively transported more hydrophobic and smaller sized particles across the froth than less hydrophobic and larger particles. Particles collected in the device were compared to those found in the concentrate stream on a size by mineral by liberation class. Froth recovery was also calculated on a size by mineral by liberation class for two valuable sulphide minerals in a continuous 3m³ flotation cell. These results show that the froth phase is responsible for the upgrading of attached particles across the froth phase as well as for the separation of bubble-particle aggregates from suspended slurry. The pulp phase is responsible for creating bubble-particle aggregates through the attachment of hdyrophobic mineral particles to air bubbles. Many complex factors affect the extent to which this occurs including the size and hdyrophobicity of the particles, the size and number of air bubbles produced by the flotation machine, the rate of collisions between particles and bubbles and the overall chemistry of the system. This measurement of bubble loading presents an opportunity to measure the impact of all these factors on the successful creation of bubble-particle aggregates. Based on a literature review suggesting that there was a high probability of particles being detached at the pulp-froth interface due to the aggregates change in momentum, a three phase description of a flotation cell was proposed. The three phases were: pulp, pulp-froth interface and upper froth zones. A second froth recovery measurement technique (changing froth depth) was used in combination with the bubble load technique to determine the recovery across each of the two froth zones. It was found that the pulp-froth interface appears to be responsible for the selectivity observed across the froth phase as a whole. These findings will enable more in-depth research into the sub-process of the froth phase as well as assisting flotation cell design through a better understanding of the roles of the pulp-froth interface and the upper froth region.

Over many years, researchers in the field of flotation have developed an in-depth understanding of processes occurring in the pulp phase of flotation machines. Until recently, however, the froth phase has received little attention. The froth phase serves to separate bubble-particle aggregates from suspended slurry in a flotation cell. The mechanism of recovery by entrainment, its relationship to water recovery and particle size dependency is well understood. Froth recovery, (the fraction of particles entering the concentrate launder that entered the froth phase attached to air bubbles), is not well understood. Up until now, there has been doubt over whether this property is dependent on particle size and hydrophobicity. Difficulties in measuring froth recovery had previously prevented researchers from gaining a deeper understanding of the transport of attached particles across the froth phase. A novel device was designed and tested to measure froth recovery by isolating bubble-particle aggregates in the pulp-phase of flotation machines through the determination of the bubble loading in the pulp phase (mass of particles attached per unit volume of air bubbles). This technique can be used with other measurements to investigate froth selectivity by directly comparing these captured particles to those found in the froth phase. Evidence was collected at Red Dog Mine, Alaska and Newmont Golden Grove Operations, Western Australia which showed that the froth phase selectively transported more hydrophobic and smaller sized particles across the froth than less hydrophobic and larger particles. Particles collected in the device were compared to those found in the concentrate stream on a size by mineral by liberation class. Froth recovery was also calculated on a size by mineral by liberation class for two valuable sulphide minerals in a continuous 3m³ flotation cell. These results show that the froth phase is responsible for the upgrading of attached particles across the froth phase as well as for the separation of bubble-particle aggregates from suspended slurry. The pulp phase is responsible for creating bubble-particle aggregates through the attachment of hdyrophobic mineral particles to air bubbles. Many complex factors affect the extent to which this occurs including the size and hdyrophobicity of the particles, the size and number of air bubbles produced by the flotation machine, the rate of collisions between particles and bubbles and the overall chemistry of the system. This measurement of bubble loading presents an opportunity to measure the impact of all these factors on the successful creation of bubble-particle aggregates. Based on a literature review suggesting that there was a high probability of particles being detached at the pulp-froth interface due to the aggregates change in momentum, a three phase description of a flotation cell was proposed. The three phases were: pulp, pulp-froth interface and upper froth zones. A second froth recovery measurement technique (changing froth depth) was used in combination with the bubble load technique to determine the recovery across each of the two froth zones. It was found that the pulp-froth interface appears to be responsible for the selectivity observed across the froth phase as a whole. These findings will enable more in-depth research into the sub-process of the froth phase as well as assisting flotation cell design through a better understanding of the roles of the pulp-froth interface and the upper froth region.

Over many years, researchers in the field of flotation have developed an in-depth understanding of processes occurring in the pulp phase of flotation machines. Until recently, however, the froth phase has received little attention. The froth phase serves to separate bubble-particle aggregates from suspended slurry in a flotation cell. The mechanism of recovery by entrainment, its relationship to water recovery and particle size dependency is well understood. Froth recovery, (the fraction of particles entering the concentrate launder that entered the froth phase attached to air bubbles), is not well understood. Up until now, there has been doubt over whether this property is dependent on particle size and hydrophobicity. Difficulties in measuring froth recovery had previously prevented researchers from gaining a deeper understanding of the transport of attached particles across the froth phase. A novel device was designed and tested to measure froth recovery by isolating bubble-particle aggregates in the pulp-phase of flotation machines through the determination of the bubble loading in the pulp phase (mass of particles attached per unit volume of air bubbles). This technique can be used with other measurements to investigate froth selectivity by directly comparing these captured particles to those found in the froth phase. Evidence was collected at Red Dog Mine, Alaska and Newmont Golden Grove Operations, Western Australia which showed that the froth phase selectively transported more hydrophobic and smaller sized particles across the froth than less hydrophobic and larger particles. Particles collected in the device were compared to those found in the concentrate stream on a size by mineral by liberation class. Froth recovery was also calculated on a size by mineral by liberation class for two valuable sulphide minerals in a continuous 3m³ flotation cell. These results show that the froth phase is responsible for the upgrading of attached particles across the froth phase as well as for the separation of bubble-particle aggregates from suspended slurry. The pulp phase is responsible for creating bubble-particle aggregates through the attachment of hdyrophobic mineral particles to air bubbles. Many complex factors affect the extent to which this occurs including the size and hdyrophobicity of the particles, the size and number of air bubbles produced by the flotation machine, the rate of collisions between particles and bubbles and the overall chemistry of the system. This measurement of bubble loading presents an opportunity to measure the impact of all these factors on the successful creation of bubble-particle aggregates. Based on a literature review suggesting that there was a high probability of particles being detached at the pulp-froth interface due to the aggregates change in momentum, a three phase description of a flotation cell was proposed. The three phases were: pulp, pulp-froth interface and upper froth zones. A second froth recovery measurement technique (changing froth depth) was used in combination with the bubble load technique to determine the recovery across each of the two froth zones. It was found that the pulp-froth interface appears to be responsible for the selectivity observed across the froth phase as a whole. These findings will enable more in-depth research into the sub-process of the froth phase as well as assisting flotation cell design through a better understanding of the roles of the pulp-froth interface and the upper froth region.

Over many years, researchers in the field of flotation have developed an in-depth understanding of processes occurring in the pulp phase of flotation machines. Until recently, however, the froth phase has received little attention. The froth phase serves to separate bubble-particle aggregates from suspended slurry in a flotation cell. The mechanism of recovery by entrainment, its relationship to water recovery and particle size dependency is well understood. Froth recovery, (the fraction of particles entering the concentrate launder that entered the froth phase attached to air bubbles), is not well understood. Up until now, there has been doubt over whether this property is dependent on particle size and hydrophobicity. Difficulties in measuring froth recovery had previously prevented researchers from gaining a deeper understanding of the transport of attached particles across the froth phase. A novel device was designed and tested to measure froth recovery by isolating bubble-particle aggregates in the pulp-phase of flotation machines through the determination of the bubble loading in the pulp phase (mass of particles attached per unit volume of air bubbles). This technique can be used with other measurements to investigate froth selectivity by directly comparing these captured particles to those found in the froth phase. Evidence was collected at Red Dog Mine, Alaska and Newmont Golden Grove Operations, Western Australia which showed that the froth phase selectively transported more hydrophobic and smaller sized particles across the froth than less hydrophobic and larger particles. Particles collected in the device were compared to those found in the concentrate stream on a size by mineral by liberation class. Froth recovery was also calculated on a size by mineral by liberation class for two valuable sulphide minerals in a continuous 3m³ flotation cell. These results show that the froth phase is responsible for the upgrading of attached particles across the froth phase as well as for the separation of bubble-particle aggregates from suspended slurry. The pulp phase is responsible for creating bubble-particle aggregates through the attachment of hdyrophobic mineral particles to air bubbles. Many complex factors affect the extent to which this occurs including the size and hdyrophobicity of the particles, the size and number of air bubbles produced by the flotation machine, the rate of collisions between particles and bubbles and the overall chemistry of the system. This measurement of bubble loading presents an opportunity to measure the impact of all these factors on the successful creation of bubble-particle aggregates. Based on a literature review suggesting that there was a high probability of particles being detached at the pulp-froth interface due to the aggregates change in momentum, a three phase description of a flotation cell was proposed. The three phases were: pulp, pulp-froth interface and upper froth zones. A second froth recovery measurement technique (changing froth depth) was used in combination with the bubble load technique to determine the recovery across each of the two froth zones. It was found that the pulp-froth interface appears to be responsible for the selectivity observed across the froth phase as a whole. These findings will enable more in-depth research into the sub-process of the froth phase as well as assisting flotation cell design through a better understanding of the roles of the pulp-froth interface and the upper froth region.

In this study the unique Magotteaux Mill® system was used to control the grinding chemical conditions, which may be adjusted by varying grinding media, purging gas and pH, during grinding. An electrochemical apparatus was used to investigate oxidation-reduction behaviour of grinding media and sulphide mineral electrodes, as well as their galvanic interaction in-situ of the Magotteaux Mill®. Galvanic interaction between the grinding media (mild steel, 15% chromium, 21% chromium and 30% chromium media) and the sulphide minerals (bornite, arsenopyrite and pyrite) was initially quantified in-situ of the mill by electrochemical techniques under different grinding atmospheres (nitrogen, air and oxygen). An innovative mathematical theoretical model was developed to describe the effect of galvanic interaction on oxidation rates of the grinding media during grinding, which was verified by the experimental data. Galvanic interaction enhanced the oxidation of the grinding media and produced more oxidized iron species in the mill discharge. It was observed that oxidized iron species (EDTA extractable iron) was linear with galvanic current between the grinding media and the sulphide minerals, in agreement with the prediction of the theoretical model. The effect of grinding conditions on pulp chemistry, surface properties and floatability was investigated by the measurement of dissolved oxygen (DO), pH, pulp potential (Eh), ethylene diamine-tetra acetic acid (EDTA) extraction, X-ray photoelectron spectroscopy (XPS) and floatation recovery. / PhD Doctorate

The gas dispersion characteristics in mechanical flotation cells have a significant effect on the overall flotation performance. Three major properties that can be measured in characterising the gas dispersion in a flotation cell are bubble size, gas hold-up, and superficial gas velocity. Another property that is equally important in flotation is bubble surface area flux which is calculated from bubble size and superficial gas velocity. Despite the importance of gas dispersion in flotation, not much work has been reported previously in this area. Moreover, the study of gas dispersion in flotation has typically considered only a few points in a flotation cell and the average values were assumed to represent the gas dispersion characteristics in the entire volume of the cell. It is known however, that the gas dispersion characteristics are not uniformly distributed in a mechanical flotation cell. This thesis seeks to understand better the gas dispersion characteristics in mechanical flotation cells with a view to optimisation, modelling, cell comparison and selection. The main aim of this thesis was to measure comprehensively the gas dispersion characteristics in a mechanical flotation cell, analyse the behaviour in the entire volume of the cell, and develop a methodology for modelling the gas dispersion characteristics in the whole volume of the cell as well as develop the models themselves. For this purpose, a fully instrumented 3 m³ glass rectangular flotation cell at the Julius Kruttschnitt Mineral Research Centre (JKMRC) at the University of Queensland was used. The cell was fitted with a Dorr-Oliver impeller-stator mechanism and was provided with facilities to change impeller speed and gas flow rate. Sensors to measure the gas dispersion characteristics were also acquired and modified. This cell could only be operated in a two-phase (air-water) system but the opportunity was taken to make some comparative measurements in an operating plant in a three-phase slurry to compare the gas dispersion characteristics in two and three-phase systems. The comprehensive measurements of the gas dispersion characteristics (i.e. bubble size, gas hold-up, and superficial gas velocity, with subsequent calculation of bubble surface area flux) throughout the entire volume of the 3 m³ rectangular flotation cell show that the properties do vary with distance from the impeller, the cell bottom, and the walls. Statistical analysis to test the homogeneity of the properties in the cell confirmed that the differences (variation with distance) were real. It was found that the gas dispersion was poor in the corners of a rectangular flotation cell. These corners are referred to as dead zones. It can be interpreted that in these zones, flotation is less effective compared to other zones in a cell. The results of mapping the gas dispersion characteristics throughout the entire volume of the flotation cell were used to determine the best location to measure gas dispersion characteristics in a flotation cell in order to represent the overall values. It was established that this location in a flotation cell is about halfway between the impeller and the wall, and halfway between the bottom of the flotation cell and the pulp-froth interface. Statistical analysis also showed that there is “quarter symmetry”, i.e. there is no significant difference between equivalent positions in different quarters in a horizontal plane. In any future work, therefore, measurements of the gas dispersion characteristics need only be made in one quarter, and symmetry in the rest of the cell can be assumed. Following from the statistical analysis that established quarter symmetry in the 3 m³ glass rectangular flotation cell, a methodology to model gas dispersion characteristics in the entire volume of a rectangular mechanical flotation cell was developed, based on an experimental design known as CCRD (central composite rotatable design) which then modified. Using the methodology, models to predict bubble size, gas hold-up, superficial gas velocity and bubble surface area flux in the entire volume of a rectangular flotation cell were developed as a function of air flow rate and impeller speed. The validity of the models was tested using a predictive (cross) validation method, from where it was concluded that the models were valid. These models were then used to analyse the gas dispersion characteristics in detail in the flotation cell, as a function of flow rate, impeller speed, and location in the cell. Finally, a comparison of gas dispersion characteristics in two and three-phase systems in flotation cells was made. Comprehensive measurements of gas dispersion characteristics were performed in a three-phase slurry in an industrial OK 38 m³ rectangular flotation cell at the PT Freeport Indonesia concentrator, and the results were compared to those measured previously in the two-phase system in the 3 m³ rectangular cell. It was found that the profiles of gas dispersion were generally similar in both cells but the magnitude of the gas dispersion properties differed between the two systems. The presence of solid particles had greater effect on the bubble size than on gas hold-up and superficial gas velocity.