Optimising froth stability of copper flotation tailings

Linking results from laboratory scale experiments to industrial flotation behaviour is challenging. Typically, such experiments involve batch tests in which the system does not operate at steady-state, making it difficult to infer the effects that operating conditions have on flotation performance. In order to overcome this limitation a 4-litre recirculating tank was previously developed at Imperial College London. This tank is capable of reaching, and operating at, steady-state by recycling overflowing concentrate back into the feed. As well as instruments to control operating conditions, it is fitted with a system of sensors that allow the surface of the froth to be dynamically monitored. From this information, it is possible to measure the air recovery a proxy for froth stability. Thus, this bench-scale tank can be used to understand the effect of differing operating conditions on flotation performance at steady state. However, so far, this cell has only been used to investigate idealised systems with only one or two species. Reprocessing of tailings dams is not only environmentally desirable but also increasingly economically feasible due to the declining head grades of primary deposits. There is also the added benefit of no further milling being required prior to flotation. However, the effects of fine and ultrafine particles on froth stability are not yet fully understood. In this work, the bench-scale continuous tank has been used for the first time to determine the flotation response of a complex feed, consisting of samples from a copper tailings dam, to changes in operating conditions. It was shown that the froth stability in the system is comparable to that of previous work and industrial tests, with a peak in air recovery being found at a superficial gas velocity of 1.13 cm/s. There is scope to optimise the froth stability of tailings flotation for enhanced metallurgical performance

The effect of particle size distribution on froth stability in flotation

Separation of particles of different surface properties using froth flotation is a widely-used industrial process, particularly in the minerals industry where it is used to concentrate minerals from ore. One of the key challenges in developing models to predict flotation performance is the interdependent nature of the process variables and operating parameters, which limits the application of optimising process control strategies at industrial scale. Froth stability, which can be quantified using air recovery (the fraction of air entering a flotation cell that overflows in the concentrate as unburst bubbles), has been shown to be linked to flotation separation performance, with stable froths yielding improved mineral recoveries. While it is widely acknowledged that there is an optimum particle size range for collection of particles in the pulp phase, the role of particle size on the measured air recovery and the resulting link to changes in flotation performance is less well understood. This is related to the difficulty in separating particle size and liberation effects. In this work, the effects of particle size distribution on air recovery are studied in a single species (silica) system using a continuous steady-state laboratory flotation cell. This allows an investigation into the effects of particle size distribution only on froth stability, using solids content and solids recovery as indicators of flotation performance. It is shown that, as the cell air rate is increased, the air recovery of the silica system passes through a peak, exhibiting the same froth behaviour as measured industrially. The air recovery profiles of systems with three different particle size distributions (d80 of 89.6, 103.5 and 157.1 μm) are compared. The results show that, at lower air rates, the intermediate particle size distribution (103.5 μm) yields the most stable froth, while at higher air rates, the finest particles (89.6 μm) result in higher air recoveries. This is subsequently linked to changes in flotation performance. The results presented here highlight, for the first time, the link between particle size distribution in flotation feeds, air recovery and flotation performance. The results demonstrate that there is an optimal air rate for each particle size distribution, therefore changes in particle size distribution in the feed to flotation cells require a change in air rate in order to maximise mineral recovery

Dynamic froth stability of copper flotation tailings

In this work, dynamic froth stability is used for the first time to investigate the flotation behaviour of copper tailings. Reprocessing of material from tailings dams is not only environmentally desirable, but also increasingly economically feasible as head grades can be high compared to new deposits. Flotation tailings, however, usually contain a large proportion of fine (10–50 m) and ultra fine (< ) material and the effect of these particle sizes on froth stability is not yet fully understood. For this study, samples were obtained from the overflow and underflow streams of the primary hydrocyclone at a concentrator that reprocesses copper flotation tailings. These samples were combined in different ratios to assess the dynamic froth stabilities at a wide range of particle size distributions and superficial gas velocities. The findings have shown that the effect of particle size on dynamic froth stability can be more complex than previously thought, with a local maximum in dynamic froth stability found at each air rate. Moreover, batch tests suggest that a local maximum in stability can be linked to improvements in flotation performance. Thus this work demonstrates that the dynamic froth stability can be used to find an optimum particle size distribution required to enhance flotation. This also has important implications for the reprocessing of copper tailings as it could inform the selection of the cut size for the hydrocyclones

Dynamic froth stability of copper flotation tailings

In this work, dynamic froth stability is used for the first time to investigate the flotation behaviour of copper tailings. Reprocessing of material from tailings dams is not only environmentally desirable, but also increasingly economically feasible as head grades can be high compared to new deposits. Flotation tailings, however, usually contain a large proportion of fine (10–50 μm) and ultra fine (<10μm) material and the effect of these particle sizes on froth stability is not yet fully understood. For this study, samples were obtained from the overflow and underflow streams of the primary hydrocyclone at a concentrator that reprocesses copper flotation tailings. These samples were combined in different ratios to assess the dynamic froth stabilities at a wide range of particle size distributions and superficial gas velocities. The findings have shown that the effect of particle size on dynamic froth stability can be more complex than previously thought, with a local maximum in dynamic froth stability found at each air rate. Moreover, batch tests suggest that a local maximum in stability can be linked to improvements in flotation performance. Thus this work demonstrates that the dynamic froth stability can be used to find an optimum particle size distribution required to enhance flotation. This also has important implications for the reprocessing of copper tailings as it could inform the selection of the cut size for the hydrocyclones

Identification of the Dynamics of Biofouled Underwater Gliders

Marine growth has been observed to cause a drop in the horizontal and vertical velocities of underwater gliders, thus making them unresponsive and needing immediate recovery. Currently, no strategies exist to correctly identify the onset of marine growth for gliders and only limited datasets of biofouled hulls exist. Here, a field test has been run to investigate the impact of marine growth on the dynamics of underwater gliders. A Slocum glider was deployed first for eight days with drag stimulators to simulate severe biofouling; then the vehicle was redeployed with no additions to the hull for a further 20 days. The biofouling caused a speed reduction due to a significant increase in drag. Additionally, the lower speed causes the steady-state flight stage to last longer and thus a shortening of mission duration. As actual biofouling due to p. pollicipes happened during the deployment, it was possible to develop and test a system that successfully detects and identifies high levels of marine growth on the glider using steady-state flight data. The system will greatly help pilots re-plan missions to safely recover the vehicle if significant biofouling is detected

A Marine Growth Detection System for Underwater Gliders

Marine growth has been observed to cause a drop in the horizontal and vertical velocities of underwater gliders, thus making them unresponsive and needing immediate recovery. Currently, no strategies exist to correctly identify the onset of marine growth for gliders and only limited data sets of biofouled hulls exist. Here, a field test has been conducted to first investigate the impact of marine growth on the dynamics and power consumption of underwater gliders and then design an anomaly detection system for high levels of biofouling. A Slocum glider was deployed first for eight days with drag stimulators to imitate severe biofouling; then, the vehicle was redeployed with no additions to the hull for further 20 days. The mimicked biofouling caused a speed reduction due to a significant increase in drag. Additionally, the lower speed causes the steady-state flight stage to last longer and the rudder to become less responsive; hence, marine growth results in a shortening of deployment duration through an increase in power consumption. As actual biofouling due to p. pollicipes occurred during the second deployment, it is possible to develop and test a system that successfully detects and identifies high levels of marine growth on the glider, blending model- and data-based solutions using steady-state flight data. The system will greatly help pilots replan missions to safely recover the vehicle if significant biofouling is detected

Phosphorus removal by a fixed-bed hybrid polymer nanocomposite biofilm reactor

Eutrophication is one of the main challenges regarding the ecological quality of surface waters, phosphorus bioavailability being its main driver. In this context, a novel hybrid polymer nanocomposite (HPN-Pr) biofilm reactor aimed at integrated chemical phosphorus adsorption and biological removal was conceived. The assays pointed to removal of 1.2 mg P/g of reactive phosphorus and 1.01 mg P/g of total phosphorus under steady-state conditions. A mathematical adsorption–biological model was applied to predict reactor performance, which indicated that biological activity has a positive effect on reactor performance, increasing the amount of reactive phosphorus removed.The authors acknowledge the Portuguese Foundation for Science and Technology for the financial support under Project SFRH/BD/39085/2007

CFD modelling of particle classification in mini-hydrocyclones

This work presents validated Computational Fluid Dynamics (CFD) predictions of the effect that changes in vortex finder and spigot diameters have on the classification performance of mini-hydrocyclones. Mini-hydrocyclones (e.g. 10 mm in diameter) have been applied successfully to the separation of micron-sized particles since their bypass fraction is larger than the water recovery, which results in a high particle recovery to the underflow, as well as low water recovery. However, a larger bypass fraction can be a disadvantage when the purpose of the hydrocyclone is particle classification, because of the large amount of fine particles that are misplaced in the underflow. Although it is well known that changes in the outlets of the hydrocyclone affect its performance, there is limited research on the effect of these design parameters in mini-hydrocyclones, in particular with regard to particle classification. The aim of this study is to computationally explore the influence of spigot and vortex finder on the classification process. To this end, CFD simulations were carried out and the predictions experimentally validated in a 3D printed mini-hydrocyclone using glass beads (below 20μm) as the particulate system. The numerical results showed very good agreement with the experimental data for recovery of solids, concentration ratio, pressure drop and particle size distribution. A trade-off was observed between the solids recovery and concentration ratio, while the solids recovery was found to be inversely proportional to the pressure drop when vortex finder diameters were kept constant. It was found that the design that yielded the lowest recovery among those tested also resulted in a particle size distribution furthest away from that of the feed. We show how the model can be used to assess changes in design parameters in order to inform the selection of designs that exhibit lower energy requirements without compromising separation performance

The submarine volcano eruption at the island of El Hierro: physical-chemical perturbation and biological response

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Techniques for Arbuscular Mycorrhiza Inoculum Reduction

It is well established that arbuscular mycorrhizal (AM) fungi can play a significant role in sustainable crop production and environmental conservation. With the increasing awareness of the ecological significance of mycorrhizas and their diversity, research needs to be directed away from simple records of their occurrence or casual speculation of their function (Smith and Read 1997). Rather, the need is for empirical studies and investigations of the quantitative aspects of the distribution of different types and their contribution to the function of ecosystems. There is no such thing as a fungal effect or a plant effect, but there is an interaction between both symbionts. This results from the AM fungi and plant community size and structure, soil and climatic conditions, and the interplay between all these factors (Kahiluoto et al. 2000). Consequently, it is readily understood that it is the problems associated with methodology that limit our understanding of the functioning and effects of AM fungi within field communities. Given the ubiquous presence of AM fungi, a major constraint to the evaluation of the activity of AM colonisation has been the need to account for the indigenous soil native inoculum. This has to be controlled (i.e. reduced or eliminated) if we are to obtain a true control treatment for analysis of arbuscular mycorrhizas in natural substrates. There are various procedures possible for achieving such an objective, and the purpose of this chapter is to provide details of a number of techniques and present some evaluation of their advantages and disadvantages. Although there have been a large number of experiments to investigated the effectiveness of different sterilization procedures for reducing pathogenic soil fungi, little information is available on their impact on beneficial organisms such as AM fungi. Furthermore, some of the techniques have been shown to affect physical and chemical soil characteristics as well as eliminate soil microorganisms that can interfere with the development of mycorrhizas, and this creates difficulties in the interpretation of results simply in terms of possible mycorrhizal activity. An important subject is the differentiation of methods that involve sterilization from those focussed on indigenous inoculum reduction. Soil sterilization aims to destroy or eliminate microbial cells while maintaining the existing chemical and physical characteristics of the soil (Wolf and Skipper 1994). Consequently, it is often used for experiments focussed on specific AM fungi, or to establish a negative control in some other types of study. In contrast, the purpose of inoculum reduction techniques is to create a perturbation that will interfere with mycorrhizal formation, although not necessarily eliminating any component group within the inoculum. Such an approach allows the establishment of different degrees of mycorrhizal formation between treatments and the study of relative effects. Frequently the basic techniques used to achieve complete sterilization or just an inoculum reduction may be similar but the desired outcome is accomplished by adjustments of the dosage or intensity of the treatment. The ultimate choice of methodology for establishing an adequate non-mycorrhizal control depends on the design of the particular experiments, the facilities available and the amount of soil requiring treatment