The role of mathematical models and simulators in describing the performance of mineral processing applications have had a large impact in optimising existing industrial plants and designing new plants over recent years. Before the development of sophisticated computer simulators, the design engineer used industrial “rules of thumb” to estimate the size and layout of plants. However, newly designed plants after commissioning, often do not meet the design product specification requirements and quite often years of “trial and error” optimisation is required. This process can be very costly especially with froth flotation processes where the complexity of the various stages of treatment makes “trial and error” optimisation very difficult to quantify and assess the benefits. Over the past 10 years, advances in the modelling of the flotation process have been conducted by many authors. The most significant flotation modelling advances in recent years have been provided by the AMIRA (Australian Mineral Industry Research Association) P9 project, whereby a new modelling methodology has been proposed. Within this methodology, the flotation response can be represented by a number of sub-processes including parameters describing the hydrodynamic, froth and ore characteristics. Although these parameters have been proposed, methods for measuring these parameters in large flotation cells are still developing, especially in the areas of the froth zone recovery and entrainment. In the light of this it was felt that the literature on froth recovery determination should be investigated to determine the most appropriate method for measuring froth recovery in large industrial flotation cells. It was found after the investigation of the literature that three techniques for measuring the froth recovery parameter stood out as potential methods for measurement within a large scale flotation cell. These were the methods decribed by Gorain et al (1998), Vera et al (1999) and Savassi et al (1997). It was decided that all three methods should be assessed on a quantitative and qualitative basis from data collected at the Mount Isa Mines (now Xstrata) Copper flotation circuit. In this assessment, all three methods were extensively trialed in a 2.8 m3 flotation cell which was operated in parallel to the main copper rougher flotation circuit. The cell could be operated at numerous operating conditions which allowed sufficient data to be collected. The conclusions from this work were that although the method proposed by Vera et al (1999) required significant amounts of data, the method appeared to be reliable in this scale of cell. The main recommendation from this work was to further test the Vera methodology in larger industrial flotation cells. A 100 m3 Outukumpu tank cell at the Mount Keith Nickel Concentrator was chosen for the further assessment of the Vera et al (1999) methodology and its applicability to large scale cells. This flotation cell was one of the largest flotation cells operating on a production scale at the time of the testwork. Numerous tests were conducted and data collected from this investigation showed that the Vera et al (1999) technique was applicable to this scale of flotation cell. Since the work at Mount Keith was conducted in a rougher flotation cell, it was decided to test the methodology with numerous cells of various sizes and duties at the Kambalda Nickel Concentrator. As with the previous investigation at Mount Keith, it was observed that the Vera method was able to measure froth recoveries in all cells measured at Kambalda (within typical operating ranges). However, the technique was not applicable at shallow froth depths since it does not take into account the effect of the pulp-froth interface within the froth recovery parameter estimation. The pulp froth interface and close to it is where a significant proportion of dropback occurs within the froth zone. In addition to this problem, the methodology required large numbers of samples and disturbed downstream processes which made the technique unpractical for operating industrial flotation plants. Hence, a new technique for measuring froth recovery in large flotation cells was required. For the technique to be successful on an industrial scale it required the following: • minimum disturbance on the process, • take into account the pulp froth interface within the froth recovery parameter, and • require a minimum amount of samples. To meet these needs a new technique was developed based on the Savassi et al (1997) technique and combining it with recent work by authors including Vera et al (2003). The methodology involves taking samples of the feed, concentrate and tail as per a typical flotation survey and combining them with two new samples: the air hold-up sample and the top of froth sample. With the addition of these samples, a mass balance across the pulp and froth phase could be conducted and the froth recovery parameter derived. In addition, the new method provided measurements of the pulp zone average bubble load and the amount recovered by the entrainment mechanism. The proposed method has a simple procedure which allows the technique to be used by academics and mill operators alike. The proposed froth recovery measurement technique was tested in numerous cells of various types (i.e. Wemco, Outokumpu, Dorr-Oliver etc), various sizes (up to 150 m3 in size), various duties (rougher, scavenger, cleaner, recleaner, etc) and various plants. In most cases the methodology proved to be a reliable measure of the froth recovery parameter. In addition, at the Century Zinc Operation, the methodology was compared directly with the original Vera et al (1999) technique and the results showed that there was a good comparison between the results with the off-set of the pulp-froth interface. A number of contributions to both the research and industrial areas have been provided from the outcomes of the thesis. The main contributions include: • A full assessment of the three current methods for measuring the froth recovery parameter within large flotation cells. With recommendations of developing a new technique. • The development of a froth recovery measurement technique which can be used in large cells to understand the impact of the froth zone in an individual cell, use within the AMIRA P9 modelling methodology and plant diagnostics. • The new method also allows the estimation of the average bubble load and quantifies the amount of material recovered by the entrainment mechanism which is invaluable to metallurgists in assessing the performance of a flotation circuit (plant diagnostics). Finally, the results of this thesis will provide practising metallurgists both within the research and operating fields, techniques to improve the profitability of flotation circuits worldwide. Metallurgists can quickly assess the performance of large flotation cells in terms of froth performance, bubble load and entrainment which has not been available before. In addition, the results from this thesis will also allow metallurgists to mathematically represent their plant through flotation models better and improve their understanding of their flotation circuits.
| Identifer | oai:union.ndltd.org:ADTP/291114 |
| Creators | Alexander, Daniel John |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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