An improvement in the kinetics of the fine and coarse size classes, provided there is no adverse metallurgical influence on the intermediate size ranges, is obviously beneficial to the overall recovery response.
Managing the local energy dissipation, and hence the power imparted to the slurry, offers the benefit of targeting the particle size ranges exhibiting slower kinetics. In principle it decouples regimes where fine and coarse particles are preferentially floated.
HEF includes three sections:. Standard flotation machines energy, rpm, rotor size at the beginning of the row, whereflotation is froth phase limited and operational and set-up parameters have small influence on the recovery.
Higher power flotation machines high rpm, standard rotor size at the end of the row to increase recovery of fine particles. Lower power flotation machines low rpm, larger rotor at the end of the row mixed with higher energy cells to increase recovery of coarse particles.
This concept was successfully implemented at the Mineral Park concentrator in Arizona and will be expanded at various mines in the near future. The fundamental parameters that influence fine and coarse particle recovery will be reviewed.
The potential dual recovery benefit is then presented in terms of its practical implementation in a scavenging application. This innovative technology recovers fine particles more efficiently than mechanical flotation cells. This new approach provides all the performance advantages of column flotation while greatly reducing capital, installation and operation costs.
Unlike conventional, mechanically agitated flotation cells, the energy imparted to the slurry is used solely to generate bubbles rather than to maintain particles in suspension.
This leads to reduced mixing in the cell and shorter residence time requirements. The low-profile StackCell design features an adjustable water system for froth washing and also takes advantage of a cell-to-cell configuration to minimise short-circuiting and improve recovery rates. Space requirements for the StackCell design are approximately half of equivalent column circuits, with corresponding reductions in weight leading to reductions in installation costs.
Units can be shipped fully assembled and lifted into place without the need for field fabrication. This technology can provide recoveries and product qualities comparable to column flotation systems while using a low profile design.
The small size and low weight of the new StackCell makes possible lower cost upgrades where a single cell or series of cells may be placed into a currently overloaded flotation circuit with minimal retrofit costs. The incorporation of regrind mills on rougher concentrates has further exacerbated this problem. To date the conventional flotation tank cell manufacturers have attempted to counter this fall off in recovery of fine particles by inputting increasing amounts of energy bigger agitation motors into the system to improve bubble particle contact.
Unfortunately this tends to compromise coarse particle recovery. Typically in percentage terms the G-Cell air rates are five to ten times that of conventional flotation although the overall or total air usage is approximately half. The improved kinetics results in a much lower residence time than conventional flotation facilitating a double benefit of both reduced footprint and improved recovery. A technical paper will be presented at the MEI Flotation 11 Conference in South Africa providing more detail on the specific case studies.
Metso notes a main drawback of column cells being low recovery performance, typically resulting in bigger circulating loads. Its CISA sparger is derived from the patented Microcel TM technology and enhances metallurgical performance by allowing flexibility on the graderecovery curve. Metso Cisa says the main advantages of its column technology include:. At the bottom of the column, the sparger system raises mineral recovery by increased carrying capacity due to finer bubble sizes.
This maximises the bubble surface area flux which is a standard parameter in evaluating flotation device performance. It also provides maximum particle-bubble contacts within the static mixers and effective reagent activation from the mechanical operation of the pump. However, recent laboratory work demonstrates that Fluidised Bed Froth FBF flotation extends the upper size limit of flotation recovery by a factor of resulting in significant concentrator performance benefits.
In a continuous FBF Cell, dense mineral particles will tend to sink to the bottom and accumulate in the cell, thus they can be recovered in a concentrated form by emptying the cell periodically. This could be a significant benefit where the concentration of the heavy metallic material is too low to warrant a separate treatment plant to recover them.
This upgrade was implemented after Stawell changed its production profile to process lower grade ore at higher throughput rates. Instead of the projected 3. Payback was also impressive, occurring within less than four months.
The project has also achieved payback in less than four months and has delivered further ongoing benefits, including easier operation and reduced maintenance costs, says Outotec Services, which worked in close partnership with Stawell Gold to ensure the site remained fully operational during the upgrade.
The mine, which has produced more than 2 Moz in its year history, previously employed a flotation circuit consisting of a bank of eight mechanical trough cells in the rougher circuit, followed by two banks of 2 x OK3 Outotec cells as cleaners.
The TankCell design also allows a much deeper froth depth and better concentrate grade through optimised launder lip length and surface area. These cells known for great performance, ease of operation and reduced power and air consumption.
Outotec Services was commissioned to handle the complete turnkey solution of the new rougher circuit, including design, supply, installation and commissioning. The schedule was demanding but achievable, in just 30 weeks.
It was decided to adopt the partnering approach between Stawell and Outotec Services, because this collaborative method ensured open communication, with all parties having greater ownership of the project and its aims.
This close teamwork resulted in meticulous planning and site remaining fully operational at all times. Pipework and electrical easement ducts, for example, were rerouted early in the project.
Tie-in points for new cells and rerouting of pipework were also planned upfront in the project and all disruptive work was completed during shutdowns. The project overcame a number of challenges, including an extremely limited footprint, which was adjacent to a gabion wall, close to the runof-mine pad and also close to a reagents shed, which could not be moved.
Additionally, existing process requirements at Stawell required specific elevations for the new TankCells. Structural stability was the main issue when designing the tank support structure due to the height of the tanks and the limited footprint.
Sufficient stiffness was required such that the operation frequencies of the TankCells would not interfere with the natural frequency of the tank support structure. Through FE modelling of the structure, section sizes and bracing orientations were optimised to produce the required stiffness. Despite the challenges, the turnkey installation of the new rougher circuit, along with blowers for the complete flotation circuit, was completed within deadlines. Because all tie-in points had been already carefully planned upfront, commissioning was a seamless exercise.
Designed to cope with projected increases in production and considerably more operator friendly than its predecessor, the new TankCell — 20 cells have quickly proved their worth at site. Basically, they do exactly what they are supposed to do.
This would be a great step forward in using a combination of reagents and sensors to optimise flotation systems. It brings together the knowledge we have developed in both how reagents effect hydrodynamics and measuring the hydrodynamics to maintain optimum conditions. The thinking was that we could try to develop collectors with absolute specificity.
In other words, we could develop a collector that would float only specific minerals and provide clients with an almost perfect flotation separation. This was our approach to flotation optimisation. Unfortunately, we discovered that there was no such thing as absolute specificity. In fact, we had trouble measuring any improvements in the circuits because they were multi-variant and highly complex.
Every change made was always a trade off between grade, recovery and cost. Changing one thing in the circuit seemed to improve something but always got a negative response in some other variable.
It was also very hard to measure the performance of the flotation circuit because the only real parameters you could measure on line were concentrate grades and tails of the circuits, which were always after the fact. There was little ability and understanding about what real time measurements we could take other than air rates, cell levels and flow rates. So even if we got an improvement or a response to a change, we never knew if that was a response to a change or a natural variation in the system.
Every test needed long term statistical trials to get some confidence in any real change. We needed new sensors that could measure the performance of the flotation circuit so we could learn to control it. Once we got this, then we could actually measure improvements and use this to develop reagents. Froth cameras that tried to measure froth grade and velocity were one of the first new sensors developed to assist in optimising circuits. Through the work of universities such as McGill and organisations like JKtech, new sensors have been developed that could actually measure reliably and in real time the hydrodynamic parameters in the flotation cell.
Flotation cell hydrodynamics gas dispersion parameters is critical to the performance of the cell. When we talk about these parameters, we are talking about measuring what is happening in a flotation cell. Flotation is really about making bubbles and using the surface area of the bubble to do the work of transporting hydrophobic minerals to the froth.
In flotation cells, we add air, create bubbles of a certain size and speed that provide the surface area to do the flotation. The more bubbles and the smaller the bubble, the more surface area we have to do the work. This surface area we create is known as the surface bubble flux Sb and controls the kinetics of flotation.
Now that we have instruments that can measure the air into a cell known as Jg , measure the size of the bubble diameter Db and the gas hold up Eg , we can figure out how the relationship between these parameters and how they affect the Sb and flotation circuit performance.
We can also now do research on how reagents can be used to control these parameters as well. Frothers perform two major functions. They create and maintain small bubbles in the pulp to transport the minerals and they create the froth on top of the cell to hold the minerals until they can be recovered. The froth is created because frothers allow a film of water to form on the bubbles which makes them stable enough not to break when they reach the surface of the cell.
Fortunately, the water drains over a short period of time and the froth will eventually break down. Froth breakdown is essential for cleaning and transporting the concentrates. General Delivery Conditions. Privacy Policy. All rights reserved. Natural flotation. Valid if the difference in density is naturally sufficient for separation.
Air flow used Nl. Input power per m 3 treated Wh. Theoretical retention time min. Stevenson has outlined practical methods for the determination of design and scale-up data for flotation systems. See also Foam Fractionation. Fuerstenau, M. Gaudin Memorial Volume. Jowett, A. Lemlich, R. Stevenson, D. Purchas and R.
Wakeman, Eds. Uplands Press and Filtration Specialists, London. Login: Guest. DOI: View in A-Z Index. References Fuerstenau, M.
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