Froth Recovery Research Articles

Study of froth behaviour in a controlled plant environment – Part 1: Effect of air flow rate and froth depth

This paper presents the results of a thorough investigation into the froth recovery measurements in a controlled plant environment using a device that allows direct collection of dropback particles from the froth phase.Experiments were performed at the Northparkes concentrator (NSW, Australia), using a feed taken from the head of the cleaner scavenger bank. The feed slurry had a relatively higher copper grade varying from 5.2% to 6.8%. Experiments were performed to investigate the effect of important flotation parameters such as air flow rate and froth depth, on the froth performance. The size of the particles in the relevant streams was analysed to acquire in-depth knowledge about the froth dropback mechanism. The results suggested that the froth recovery could be as low as 70%, although it was relatively easy to achieve the values in the range 75–85% by the correct choice of operating variables. It was found that the air flow rate has a positive impact on both collection (pulp) and froth zone recoveries. However, the effect was more prominent in the froth zone. It appeared that the froth recovery is a strong function of particle size.

Effect of entrainment in bubble load measurement on froth recovery estimation at industrial scale

Froth recovery was calculated in a 130m3 mechanical cell of a rougher flotation circuit. This was done by bubble load determinations along with mass balance surveys. Valuable grade in the bubble load decreased in the −38μm due to fine particles entrained to the chamber of the device. The effect of fine particle entrainment on froth recovery was evaluated. A comparison between results from the raw bubble load data (assuming all particles were transported by true flotation) with those from corrected bubble load information (subtracting fine particle entrainment) was carried out. Entrainment occurred due to hydraulic transport in the bubble rear, which corresponds to the worst case scenario for froth recovery estimation. Results showed that the relative error was less than 0.3%, which allowed validation of the bubble load measurement as an effective methodology for froth recovery estimation at industrial scale.

Modelling flotation with a flexible approach – Integrating different models to the compartment model

In this work, a comprehensive model structure for froth flotation is developed by linking the compartment model (Savassi, 2005) to a set of phenomenological models describing the froth recovery, the water recovery and the entrainment factor. This model structure is successfully calibrated against experimental data from a pilot plant campaign with a copper ore.

The implications of the froth recovery at the laboratory scale

This paper presents a critical review of the role of froth recovery in laboratory flotation kinetics tests. By conducting tests in the standard lab equipment (the Denver cell), it is demonstrated that, for typical scraping rates, the froth recovery is significantly lower than the 100% that is commonly assumed when interpreting lab kinetics data. Furthermore, it is shown that the curve of overall rate constant versus froth residence time, as defined by the scraping rate, is not linear, but increases quickly at faster scraping rates. These findings have important implications for scale-up. For one, differences in froth recoveries at the lab scale can lead to significant error in the modeled plant recoveries. For two, they undermine a key assumption used to derive and validate the linear relationship between collection rate constant and bubble surface area flux. This casts doubt on the assertion that it is only the collection rate—rather than the froth recovery, interface recovery, or some combination thereof—that is responsible for the observed collinearity between the bubble surface area flux and the overall rate constant.

Froth recovery measurements in an industrial flotation cell

The froth phase serves an important role in upgrading the final concentrate in flotation. At present, the techniques that are used in the mineral industry to determine the effect of froth phase on the metallurgical performance of plant scale flotation cells have limitations.The aim of this paper is to investigate the performance of the froth in an industrial flotation cell. A unique device has been developed which is able to decouple the froth zone from the pulp zone. The device consists of two concentric tubes. The inner tube acts as a dropback collection chamber or catcher. The particles that return from the froth phase fall directly into the catcher and are collected as froth dropback. This technique is capable of measuring plant scale flotation cell froth recovery as well as providing valuable information on froth dropback particles.The froth recovery measurements were carried out in a rougher bank of a copper concentrator treating sulphide minerals. The dropback device is designed so that it can be immersed into an industrial size flotation cell and plant froth recovery measurements can be taken at any given location. During the experiments, the bubbles laden with valuable mineral particles entered the device from the flotation cell, subsequently rising to form a froth layer at the top of the device. The particles that detached or drained from the froth zone were collected in the dropback collection chamber whereas the concentrate sample was collected through a launder. By sizing and chemical analysis of the concentrate and dropback samples, the froth recovery was estimated on the basis of the valuable component. The effect of air rate on the froth recovery was also investigated. Metallurgical grades of the froth dropback device samples for different particle size ranges were compared to those of the concentrator to better understand the froth dropback mechanism.

On the froth transport modelling in industrial flotation cells

A froth transport model for industrial flotation cells characterisation has been developed in terms of operating variables for a three-phase system (i.e., gas, liquid and valuable/non-valuable solid). The new approach, based on previous literature, involves three transport mechanisms: a vertical transport zone, a combined vertical and horizontal transport zone that allows the liquid and solid phases to be carried to the concentrate stream, and a mechanism in which the gas phase is gradually removed from the top of the froth (bubble collapse).To develop and evaluate the model, non-conventional measurements were conducted in a 130m3 flotation cell in the Cu/Mo rougher circuit at Division El Teniente, Codelo-Chile. The solid axial profile in the froth, the froth recovery and the froth transport times for the three phases (measured by radioactive tracers), are among the most important measured variables. The mean froth residence times and froth recovery estimations were used as boundary conditions in the proposed model.The aim of the froth transport model was to provide a simple and practical understanding of the froth performance in the flotation equipment. A practical description of the froth zone behaviour will allow new designs and configurations to be evaluated for the radial and peripheral launders in mechanical cells, improve the recovery of valuable minerals and decrease the gangue entrainment into the concentrate stream.

Modelling and simulation of rougher flotation circuits

At present, large mechanical flotation cells of 100 to 300m3 are used in rougher operation in different industrial flotation plants around the world. However, in spite of the advances in fundamental research and the notable growth in equipment size, there is still a lack of reliable data for industrial flotation modelling and simulation. In this work, a procedure for modelling and simulating rougher flotation banks that is based on operating variables and parameters fitted by empirical data from plant measurements is presented.Recently, a new methodology for describing industrial flotation by separating the collection and froth zones has been developed. This approach consists of using a new apparatus for direct bubble load measurement below the pulp–froth interface in industrial cells. The procedure allows independently estimating the froth recovery and the collection zone recovery. Metallurgical characterisation is developed by plant sampling, mass balance adjustment and applying a short-cut method for kinetic characterisation of flotation banks. In addition, the effect of grinding is characterised using flotation models with distributed flotation rates (for each particle size class) and a low number of parameters.From the experimental data, a non-linear distributed model to simulate rougher flotation banks was developed, which allows describing the industrial operation as a function of the main operating variables (e.g., mass flow rate, solid percentage, grinding degree, pulp level and superficial air rate). The simulator was calibrated and validated using experimental data from the rougher operation at El Teniente Division, Codelco-Chile.The new approach is a practical tool that is useful for flotation operation diagnosis, for robust design and analysis of new control and optimisation strategies and for evaluation of the effect that design and operating variables have upon the collection and froth zone performance in large flotation cells. This methodology can be applied to other flotation operations, such as cleaner and scavenger circuits that use mechanical flotation cells.

Operation of Rougher Flotation Circuits Aided by Industrial Simulator

AbstractToday, large size mechanical flotation cells of 100 to 300 m3 are used in rougher operation in different flotation industrial plants, in Chile and worldwide. However, in spite of the advances in fundamental research and the notable growing in equipment size, with more complete instrumentation systems, there are still a lack of reliable data for industrial flotation modeling and simulation to advance in better control systems design. In this work, a procedure for modeling and simulation of rougher flotation banks, based on operating variables and parameters fitted from industrial data, is presented. This simulator is used to develop a set of logic rules in order to aid operating decisions.Recently, a new methodology for describing the industrial flotation, separating the collection and froth zones, has been developed. This approach consists of using new apparatus for direct bubble load measurement below the pulp-froth interface in industrial cells, for estimating the froth recovery as well as the collection zone recovery, independently. The bubble surface area flux SB (m2/min/m2) is determined by measuring the bubble size distribution and superficial gas rate. Metallurgical characterization is developed by plant sampling, adjusted mass balances and applying the short-cut method for kinetic characterization. Also, the effect of grinding is characterized using flotation models with distributed flotation rates and low number of parameters (e.g., rectangular distribution).A non linear distributed model to simulate rougher flotation circuits was developed, based on measurements of the main operating variables. The simulator was calibrated and tested using experimental data from the rougher operation at El Teniente Division, Codelco-Chile. The simulator was first used to sensitize the effect of changing the froth depth profile on target variables, and then to find out the best profile to reject common disturbances coming into the plant.

Froth Recovery Factor – What Is It and Why Is It So Difficult To Measure?

Froth Recovery Factor – What Is It and Why Is It So Difficult To Measure?

Froth Recovery Factor – What Is It and Why Is It So Difficult To Measure?

The past twenty to thirty years have seen unprecedented research activity aimed at understanding the performance of flotation froths. In 1990, Finch and Dobby coined the term froth recovery factor, Rf, to represent the efficiency of the froth in delivering particles from the pulp-froth interface to the concentrate. Originally defined for flotation columns, Rf has also been found useful in modelling mechanical flotation cells and a number of techniques, based on quite different approaches, have been developed for measuring the froth recovery in industrial flotation cells. None of these techniques are universally successful. This paper reviews the concept of the froth recovery factor and the basis of each of the techniques that have been proposed to measure Rf and examines the reasons for this parameter being so difficult to pin down.RésuméAu cours des vingt à trente dernières années, on a observé une activité de recherche sans précédent ayant pour objet la compréhension de la performance des mousses de flottation. En 1990, Finch et Dobby ont créé le terme facteur de récupération de la mousse, Rf, qui représente l'efficacité de la mousse à délivrer les particules de l'interface pulpe-mousse vers le concentré. Défini originalement pour les colonnes de flottation, Rf est également utile dans la modélisation des cellules mécaniques de flottation et un certain nombre de techniques, basées sur des approches plutôt différentes, ont été développées pour mesurer la récupération de la mousse dans les cellules industrielles de flottation. Aucune de ces techniques n'a de succès universel. Cet article étudie le concept du facteur de récupération de la mousse et la base de chacune des techniques proposées pour mesurer Rf et examine les raisons pour lesquelles ce paramètre est si difficile à cerner.

A novel scale-up approach for mechanical flotation cells

Planning industrial flotation operation and earlier flotation equipment sizing are commonly based on batch flotation testing, where ideal operating conditions can be provided. Each plant has its own batch flotation standards and typically uses a time scale-up factor in order to compare laboratory and plant flotation performance. However, flotation scale-up is more complex, and it is not yet completely understood. In this work, a novel scale-up approach was developed, where the effects of the hydrodynamic regime (mixing), solid segregation (effective residence time) and froth recovery on the plant flotation rate were identified and evaluated. Each effect was then described by means of correction factors applied on the batch flotation rate, which was considered the optimal condition. These factors can be determined from laboratory and plant experimental data. This methodology was successfully applied at the rougher copper flotation plant of Codelco Norte Division, Codelco-Chile, for cells of 160 and 300 m 3.

Troubleshooting and Diagnostic of Industrial Flotation Cells

The residence time distribution of liquid, gas and solid per size class was measured in large flotation cells in different flotation plants. The RTD measurement was developed using radioactive tracers. Results allowed the estimation of effective pulp volumes of 82–85% of the total nominal volume in large flotation cells. It was found that single large industrial flotation cells have different flow regimes and can be significantly different from a perfect mixer (N>1 or N<1). Measurement of RTD also allowed the identification of operating control problems such as solid segregation (affecting the mean residence time for kinetic modeling), cells embankment, and increasing short-circuit because of cell design characteristics and circuit arrangement (i.e. input-output location). Measurement of local superficial gas rate and improved measurement of bubble size distribution, using new software, allowed the estimation of the bubble surface area flux (S B around 40s −-1 ), key parameter describing the quality (level) of gas dispersion in industrial flotation cells. Also, typical boundaries for superficial gas rate (1–2 cm/s) and mean bubble size (1–2mm) have been identified for stable flotation operation from different plant experiences. Bubble load measurement was carried out for estimating the froth recovery in large flotation cells. Froth recovery is relevant for flotation process modeling and control because of the critical role the froth transport plays in large cells. Recent development on automated froth visual analysis (i.e., bubble size, bubble collapse and froth overflow velocity) poses new challenges to link this information with the actual internal process variables (i.e. froth recovery).

Quantifying contributions to froth stability in porphyry copper plants

A method to describe froth stability in industrial flotation cells, and its link with froth recovery, is discussed in this paper. The direct measurement of froth stability in industrial flotation cells is still controversial, and different techniques have been developed. In this paper, the froth half-life time and bubble size on the top of the froth are discussed as indicators for froth stability. Experiences at two flotation concentrators treating porphyry copper ore are compared. The relative contributions to froth stability from frother in solution and solids loading in the froth were investigated in both concentrators, and links were found between both the froth half-life and bubble size on the top of the froth and the amount and nature (hydrophobicity) of particles in the concentrate. The comparison also suggests how two significantly different operating strategies for the froth phase may lead to similar outcomes in terms of froth recovery.

Froth zone characterization of an industrial flotation column in rougher circuit

In this investigation the froth zone of an industrial column (4 m “diameter” × 12 m “height”) in rougher circuit was characterized. Experiments were carried out at Miduk copper concentrator, Iran. Miduk is a unique copper processing plant which utilizes columns in rougher circuit. Cleaning and selectivity actions in the rougher froth were illustrated using solids and grade profiles along with RTD data. The impact of froth depth (FD) on overall rate constant ( k) and k– S b relationship was evaluated. Dependency of overall flotation kinetics on froth depth and gas velocity ( J g) was modeled by k = 4.97(FD) −0.87( J g) 0.80. Froth recovery ( R f) was estimated and modeled in terms of froth residence time of slurry (FRT Slurry) as R f = R f,maxexp(− k × FRT Slurry). Finally, the correlation between k, S b (indicative of the collection zone performance) and FRT Slurry (indicative of the froth zone performance) was modeled by k = 0.02 (FRT Slurry) −0.62( S b) 0.82.

Simple approximations for estimating froth recovery

Froth recovery is an important aspect of the overall performance of flotation cell. Froth recovery is also very difficult to predict based on the operating conditions of the cell. In this paper, a simple theoretical approximation is proposed that relates froth recovery to the relevant froth parameters, such as gas rate into the cell, the air recovery and the change in bubble size over the cell. This simple model includes both the particle detachment, as well as the behaviour of detached particles in its description of froth recovery. An important concept that is introduced and that has a strong influence on the froth recovery is the fraction of particles attached to a failing film that become detached. Some of the implications of this model for the performance of flotation cells and, in particular, their response to typical operating parameters such as froth depth, air rate and particle size are discussed.

Mixing and gas dispersion in mineral flotation cells

Mineral flotation in mechanically agitated vessels (cells) involves complex interaction between bubbles, particles and the liquid phase. Ideally, just enough power input from the impeller is needed to so that the frequency of particle–bubble collision and attachment is maximised, while at the same time detachment events are minimised. This paper firstly investigated how the slip velocity of 2–10mm diameter bubbles, a size commonly encountered in flotation devices, was influenced by turbulence intensity. The measurements confirmed the earlier correlation by [Lane, G.L., 2005, Numerical modelling of gas–liquid flow in stirred tanks, Ph.D. Thesis, University of Newcastle, Australia], which was then inputted into a computational fluid dynamic model to describe the gas dispersion in a mechanically agitated tank. The model provided turbulence intensity values that were then coupled with both slip velocity and critical Weber number models to generate both bubble size and gas holdup profiles for the entire vessel. Moreover, a simple equation was introduced to allow prediction of cavity formation behind the rotating impeller blades, which is a common occurrence in most flotation cells they normally operate at high gas loadings. This inclusion allowed the model to predict power reduction resulting from the presence of the cavities. Finally, extension of the computational model to include flotation hydrodynamics, such as probabilities of collision, adhesion and stabilisation of the particles at the bubble surface, is also described. The model is able to compute net attachment rates, and hence the particle flux entering the froth recovery phase, as a function of bubble and particle diameter, gas flowrate and power input.

The flotation of fine particles using charged microbubbles

One of the major problems in the flotation of fine particles is the decreased probability of collision between particles and bubbles, which can be improved by a reduction in bubble size. Additionally, smaller particles, having lower momentum, may not be able to break through the liquid barrier surrounding a bubble. In order to overcome this limitation, flotation exploiting electrostatic interactions has potential. Colloidal gas aphrons (CGAs) are charged microbubbles generated using a high speed impeller, typically of the size 50 μm. In this work, CGAs generated using the anionic surfactant sodium dodecyl sulphate (SDS) have been used to separate copper oxide and silica powder (−10 μm). By the manipulation of pH (therefore zeta potential), particles can be recovered by bubbles of opposite charge. Agglomeration between particles of different charge is a potential problem, however, initial results indicate a good separation using a novel system of froth recovery.

Froth recovery of industrial flotation cells

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. It was found that mineral transport along the froth was mainly non-selective, and also the contribution of valuable minerals recovered by entrainment was negligible, if compared with minerals recovered by true flotation. Thus, a direct estimation of the froth recovery was obtained, without arbitrary assumptions about the grade of mineral transport by entrainment and drainage. This simple procedure allows a non-biased and independent evaluation of the effect that design and operating variables have upon the collection and froth zones performance, in large flotation cells. The use of this approach for flotation cells diagnosis and development of new control strategies is considered.

An evaluation of different models of water recovery in flotation

Water recovery is one of the key parameters in flotation modelling for the purposes of plant design and process control, as it determines the circulating flow and residence time in the individual process units in the plant and has a significant effect on entrainment and froth recovery. This paper reviews some of the water recovery models available in the literature, including both empirical and fundamental models. The selected models are tested using the data obtained from the experimental work conducted in an Outokumpu 3 m 3 tank cell at the Xstrata Mt Isa copper concentrator. It is found that all the models fit the experimental data reasonably well for a given flotation system. However, the empirical models are either unable to distinguish the effect of different cell operating conditions or required to determine the empirical model parameters to be derived in an existing flotation system. The model developed by [Neethling, S.J., Lee, H.T., Cilliers, J.J., 2003, Simple relationships for predicting the recovery of liquid from flowing foams and froths. Minerals Engineering 16, 1123–1130] is based on fundamental understanding of the froth structure and transfer of the water in the froth. It describes the water recovery as a function of the cell operating conditions and the froth properties which can all be determined on-line. Hence, the fundamental model can be used for process control purposes in practice. By incorporating additional models to relate the air recovery and surface bubble size directly to the cell operating conditions, the fundamental model can also be used for prediction purposes.

Selective transport of attached particles across the pulp–froth interface

A technique for determining the recovery of attached particles across the froth phase in flotation that relies on measuring the rate at which bubble–particle aggregates enter the froth is used to investigate the selectivity of attached particles across the froth phase. Combining these measurements with those of other techniques for determining the froth recovery of attached particles provides an insight into the different sub-processes of particle rejection in the froth phase. The results of experiments conducted in a 3 m 3 Outokumpu tank cell show that the detachment of particles from aggregates in the froth phase occurs largely at the pulp–froth interface. In particular it is shown that the pulp–froth interface selectively detaches particles from aggregates according to their physical attributes.