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F LO TAT I O N ject, kill the project, or change the scope and recycle the project. The Eriez Flotation Division currently uses an approach to product and application development, based on some of the principles of the StageGate® system, promoted by Dr. Robert Cooper in his book Winning at New Products: Creating Value through Innovation. Eriez has found this system quite useful for taking new product and new application ideas forward in a systematic way. It has also allowed them to distinguish between product ideas that are more advanced, and can be taken forward in partnership with selected lead customers, as opposed to early stage projects, where most of the work is done in collaboration with the company's university partners. Several examples of new products and applications that have been developed by EFD will be described below. The flotation process consists of several different sub-processes operating in series. These include ore slurry conditioning, followed by bubble generation, bubble collection through bubble-particle collision and attachment, and finally, bubble-particle flotation and froth separation. Rather than trying to achieve all of these sub-processes in a single unit operation, it has been suggested that an optimal approach would consist of splitting the duty into two coupled units, each ideally designed and suited for each sub-process. The first unit maximizes the collection process and the second unit maximizes the separation and froth recovery. EFD has developed two distinct technology platforms based on this two-stage flotation concept, the StackCell and the Tank Feed Air Jet. The StackCell was originally developed as a modified column for cleaning coal for both the thermal and metallurgical applications. A cross-section is shown in Figure 1. High-energy particle-bubble collisions are promoted through a high-intensity shear mechanism located inside a dedicated "single-pass" pre-aeration mixing chamber inside or adjacent to the main vessel. The undiluted feed is targeted with high energy and bubbles because it has the highest concentration of floatable ore particles. After a short residence time in this collection zone, the collected ore particles are expelled into www.e-mj.com Figure 2—A cutaway of the HydroFloat, an aerated fluidized bed that can effectively float coarse particles. the primary tank. In this separation chamber, the flow is convective and laminar, which allows the particle-bubble aggregates to rise into the froth layer with less detachment of ore particles, and with more uniform flows, thus allowing efficient water washing of the froth to reject hydraulically entrained gangue. Since the StackCell can operate under near-atmospheric conditions, a high-efficiency, low-maintenance blower can be utilized for air addition. This approach has proven to be efficient for reducing the energy requirements and improving recovery, and is now being piloted in other applications using our product development system. Another approach is the Tank Feed Air Jet, which is useful for fine particle flotation. This system works by pre-aerating the feed while it is still in the highly turbulent environment of the feed pipe. The combination of high ore concentration, fine bubbles and high energy lead to bubble-particle collisions and attachment. The aeration device is an EFD CavTube—a sparger, which uses a natural or mechanically generated pressure drop to create a bimodal distribution of nucleated fine bubbles and larger bubbles that are produced by shear. After the ore particles have been collected in the feed pipe, they are sent to a froth flotation tank, which is used to create the low shear conditions necessary to float and recover the collected ore as froth. The Tank Feed Air Jet has been successfully piloted in a base metal sulphide application. One of the added advantages for this application was that natural gravity could be used to create the necessary pressure drop for the CavTube so that the overall energy requirements were reduced. For floating coarse particles, EFD has developed an aerated liquid fluidized bed, called the HydroFloat (See Figure 2), which has been successfully commercialized for recovering coarse particles in industrial minerals applications such as phosphate and potash, where particles in excess of 1 mm can be recovered. This is generally considered an impossible task for most conventional flotation units. The bed is fluidized with an upward flow of water or other fluidizing medium, which creates a plug-flow hindered-settling reactor that minimizes short circuiting, shear and turbulence that can lead to particle detachment. The counter-current settling regime in the denser fluidized bed creates more opportunities for bubble-particle attachment by increasing the collision frequency and minimizing turbulence. And because the HydroFloat operates with little or no froth layer, there is a higher recovery of coarse particles when compared with conventional approaches. It AUGUST 2013 • E&MJ; 45