Modelling of froth transportation in industrial flotation cells (original) (raw)
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The operation of a froth flotation column can be described by a nonlinear convection–diffusion partial differential equation that incorporates the solids–flux and drift–flux theories as well as a model of foam drainage. The resulting model predicts the bubble and (gangue) particle volume fractions as functions of height and time. The steady-state (time-independent) version of the model defines so-called operating charts that map conditions on the gas and pulp feed rates that allow for operation with a stationary froth layer. Operating charts for a suitably adapted version of the model are compared with experimental results obtained with a laboratory flotation column. Experiments were conducted with a two-phase liquid–bubble flow. The results indicate good agreement between the predicted and measured conditions for steady states. Numerical simulations for transient operation, in part for the addition of solid particles, are presented.
Froth recovery of industrial flotation cells
Minerals Engineering, 2008
The mass flowrate of particles (ton/h), entering the froth by true flotation, was evaluated from direct measurement of bubble load (ton/m 3 ) and gas flowrate (m 3 /h). This information, together with the concentrate mass flowrate, allowed the estimation of the froth recovery of floatable mineral in a 130 m 3 rougher flotation cell.
Scale-up in froth flotation: A state-of-the-art review
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Froth flotation has been one of the most important and widely used methods to concentrate minerals since its introduction over a hundred years ago. Over the last few decades, in order to process more mineral while reducing capital costs, flotation equipment has become exponentially larger. The increase in tank volume, however, has brought new challenges in the operation and design of industrial flotation tanks. This review analyses the literature on flotation tank scale-up for the first time, contrasting several techniques and approaches used in both historical and state-ofthe-art research. The study of flotation scale-up is crucial for the optimisation of industrial plant performance and the maximisation of laboratory-scale research impact. While important advances in our understanding of flotation have been achieved, large flotation tank design and scale-up has, to a large extent, remained in-house know-how of manufacturing companies. This review of the literature relevant to flotation tank scale-up has resulted in a new classification, dividing the scale-up literature into two main areas of study, namely "Kinetic scale-up" and "Machine design scale-up". This review indicates that current scale-up rules governing the design of flotation tanks focus mainly on pulp zone kinetic parameters and neglect the effects on the froth zone, despite the importance of froth stability and mobility in determining flotation performance. Froth stability and mobility are closely linked to the distance the froth needs to travel, which increases with tank diameter. Although including internal elements, such as launders and crowders, has been the industrial solution for enhancing froth transport and recovery in larger tanks, the design and scale-up of these elements have not been thoroughly studied. Gaps in our knowledge of flotation are discussed in the context of addressing the scale-up problem, considering froth transport and froth stability. Addressing these gaps will pave the way for the design and operation of large flotation tanks of enhanced performance.
A Review of Flotation Physical Froth Flow Modifiers
Minerals
Over the past few decades, the need to process more minerals while lowering capital costs has led to an increase in the size of flotation cells, e.g., 0.03 m3 to 1000 m3. However, this increase has created new challenges in the operation and design of industrial flotation cells, particularly in terms of froth removal, because the distance the froth must travel increases with an increase in the flotation cell diameter. This has a negative impact on recovery. Physical froth flow modifiers can be used to improve froth removal. Their major functions are to modify and optimise the flow of the froth, improve froth drainage, reduce dead zones, and improve froth flow and removal dynamics. Therefore, physical froth flow modifiers are discussed, evaluated, and compared in this paper. The literature indicates that physical froth flow modifiers such as crowders and launders are used extensively as industrial solutions to enhance froth transport and recovery in large flotation cells. Other modif...
Minerals Engineering, 2007
The concentrate mass flow rate of solids of a flotation column was modeled based on geometrical principles and considering complete air recovery to the concentrate and bursting of a fraction of the bubbles that reach the top of froth. For the first consideration, the results show that concentrate mass flow rate of solids experimentally measured, is smaller than that estimated with the geometrical model. For the second consideration, bursting of a 0.45 fraction of the bubbles reaching the top of froth gave improved results (average relative error obtained under these circumstances is about 20%).
A Method to Predict Water Recovery Rate in the Collection and Froth Zone of Flotation Systems
Minerals
This paper describes a method to predict water recovery rate into and through the foam in a bubble column operating under different gas rates, froth depths, and frother types and concentrations. Three frothers were considered: Metil Isobutil Carbinol (MIBC), a proprietary blend of alcohols, aldehydes, and esters commercialized under the name PINNACLE® 9891, and a PGE-based Dow Froth 1012 (DF1012). The water rate entering into the froth (foam) layer from the bubbly (collection) zone was estimated as the water rate overflowing the column when operating at a thin stable foam layer, i.e., 0.5 cm. It was observed that the rate at which water entered into the froth phase could be modelled as a unique linear function of the gas holdup below the froth, regardless of the frother chemistry. This is a fundamental result not previously found in the literature that also facilitates the calculation of the froth zone water recovery for deeper froths. The water recovery in the froth was found to be...
Powder Technology, 1998
The recovery and grades of a coal flotation concentrate are significantly dependant on the water content of tile overitowing frotll. The drainage of water from the froth is associated with the coalescence and bursting of bubbles in the froth. This work was undertaken to investigate the possibility of regulating the performance of a flotation cell by using Image Analysis to define a desired bubble size in the concentrate, and subsequently to use measured deviations to control bubble coalescence by the compensating addition of suffactants. The image analysis was done on a transputer-enhanced Micro Vax computer off-line, using video images of experimental semi-batch runs. Individual runs were done using a single surfactant which had to act both as a frother and collector, two surfactants 2-eth) ! hexanol and Triton X-405 being used. Data fro,n the image analysis was interpreted together with experimental measurements of particle and water recoveries in terms of a previously formulated froth kinetic model. Correlation of the point rates of overflow of dry-mineral-matter-free (dmmf) coal in terms of the model produced physically plausible parameters.
Residence time distributions and mass transport in the froth phase of the flotation process
International Journal of Mineral Processing, 1984
A comprehensive description of some aspects of the physical behaviour of the froth phase of the flotation process has been provided by two mathematical models. Both are formulated in terms of familiar design and control variables (e.g. cell dimensions, froth depth, gas rate) and the froth stability, a, defined as the ratio between the volume flowrate of air in the concentrate stream and the volume flowrate of air in bubbles crossing the froth/slurry interface which have a finite probability of entering the concentrate stream. The first model provides a description of the two-dimensional streamline behaviour of the froth as it moves towards the concentrate weir. The second model is a two-stage approximation of this behaviour and provides a simple and tractable model of froth behaviour which can easily be incorporated in existing models of the flotation process. This model involves two more parameters: the residence time ratio $, which provides a means for estimating the minimum froth phase residence time (it can be given the value 0.5 unless it is possible and practical to measure it more accurately); and the froth removal efficiency, e, which is a measure of the efficiency with which the available froth chamber volume is used. RTD measurements using twophase froths have shown that these models constitute a good description of physical reality, and that e and a can be obtained as functions of control variables such as gas rate, froth height and frother concentration. Insights obtained from this work have led to the development of a method for froth removal which produces an unambiguous improvement in the performance of the flotation cell. The second model can be used to investigate the effect of control actions and scale-up on cell performance.
Froth mean residence time measurement in industrial flotation cells
Minerals Engineering, 2008
Froth plays an important role in flotation processes preventing the pulp transport to the concentrate (short-circuit). Thus, it contributes to increasing the concentrate grade by gravity drainage of entrained particles, back into the pulp. Key parameters affecting the froth performance are the mean residence times of solids, liquid and gas in the froth. The froth mean residence time depends on the froth depth, gas flowrate, gas holdup , and flow regime. In this work, the froth mean residence times were evaluated from direct measurements of liquid and solid time responses in the froth of self-aerated copper flotation cells of 130 m 3. For this purpose the radioactive tracer technique was applied, using 82 Br as liquid tracer, and non-floatable mineral particles in three size classes (+150; À150 + 45;À45 lm) as solid tracers. All tracers were injected at the cell feed entrance, which allowed the tracer to circulate first through the rotor, and become well distributed over the whole cross-sectional area before entering the froth. Each tracer time response was measured on-line below the pulp/froth interface (input signal) and at the concentrate overflow discharge (output signal). The froth mean residence time was then obtained by difference between the average times of the froth input and output tracer signals, previously modelled. For the copper rougher flotation, the froth mean residence time (9-12 s) of non-floatable solids, derived from experimental measurement, was comparable with that obtained by measuring the gas flowrate and estimating the effective gas volume in the froth. While, the froth mean residence times of liquid and floatable solid were significantly larger, 21 and 24 s, respectively.
Design and Development of a 0.012 m3 Froth Flotation Machine from Locally Sourced Materials
International Journal of Mineral Processing and Extractive Metallurgy
The desire to design and develop machine with high versatile method of physically separating mineral particles based on differences in the ability of air bubbles to selectively adhere to specific mineral surfaces in mineral/water slurry using indigenous materials is constantly evolving to meet specific requirements of specific industrial plant. Therefore, the aim of this study was to design and construct a 0.012 m 3 capacity laboratory froth flotation machine using locally sourced materials with the view to promoting indigenous technology in Nigeria. The construction was based on parameters established from literatures. The design was done using Auto-Cad version 7 software. The machine was built of different components which are corrosion resistant, easy to access and can be assembled and disassembled when the need arises. The machine was constructed such that its height can be adjusted to suite flotation characteristics of different materials. The machine was of height 1.5 m and designed to operate at batch condition. A flotation tank of capacity 0.012 m 3 holds the pulverized pulp mixture for flotation operation. The flotation tank was equipped with regulated speed agitator shaft and stirrer assembly to condition the pulverized pulp mixture. Regulated air flow from a 0.02 m 3 /min compressor was also applied to the mixture in the cell for effective hydrophobicity and hydrophilicity.