Available Technology

Method for Enhancing Selectivity and Recovery in the Fractional Flotation of Flotation Column Particles

Although research is currently inactive on the patented technology "Method for Enhancing Selectivity and Recovery in the Fractional Flotation of Flotation Column Particles," the technology is available for licensing from the U.S. Department of Energy’s National Energy Technology Laboratory (NETL). Disclosed in this patent is a method of particle separation from a feed stream comprised of particles of varying hydrophobicity by injecting the feed stream directly into the froth zone of a vertical flotation column in the presence of a counter-current reflux stream. The current invention allows the height of the feed stream injection and the reflux ratio to be varied to optimize the concentrate or tailing stream recoveries desired based on existing operating conditions or other considerations. This novel method provides a high degree of particle collection with reduced carryover of lower hydrophobic or hydrophilic particles to the froth overflow, reduces or eliminates reliance on a clean wash-water supply, allows capture of coarse particles beyond the upper limiting size for liquid injection columns, allows capture of fine particles while mitigating the tendency of the low inertia particles to follow bubble streamlines and avoid capture, and provides other benefits over previously used methods of capture.
Froth flotation—one of the primary solid-solid separation processes for fine particles—has been widely practiced for a century in the mining industry for concentrating valuable minerals such as copper, lead, nickel, precious metals such as platinum group metals, gold and silver, and coal. In this process, specific particulate constituents of a slurry or suspension of finely dispersed particles attach to gas bubbles, separating them from other constituents of the slurry or suspension. The buoyant bubble/particle aggregate rises to the surface of the flotation vessel for separation. Higher recoveries (amount) and grades (concentration) of particles are desired in a separation process. Previously used methods of separation may produce a high amount of low-grade product, are difficult to control under certain conditions, or require other materials to be added, which must be removed at the end of the process. The current invention provides a method of particle separation from a feed stream of particles varying in hydrophobicity by injecting the feed stream directly into the froth zone of the vertical flotation column also provided with a counter-current reflux stream. This creates attachments between bubbles in the froth zone and the hydrophobic particles, which has several benefits to the process. The resulting grade of the product increases, and the loss to the tailings stream decreases. The froth injection method allows flexibility to influence recovery and grade independently, by varying the vertical entrance level of the feed stream and the magnitude of reflux stream. Furthermore, recovery and grade can be increased simultaneously. Such a benefit is particularly advantageous where higher concentration factors are required because of the initially low grade of the feed ore, and the product has high value. The number of flotation vessels conventionally used in series can be decreased materially, leading to simpler and more controlled process flow sheet designs.
Injection into the froth zone leads to significantly higher particle collection rates -Smaller fines are unlikely to dodge bubbles in densely packed froth, increasing recovery -Feed rates are significantly higher -Minimizing the large liquid collection zone reduces the column’s physical footprint -Overall recovery increases -The degree to which lower hydrophobicity particles are carried can be controlled -The resulting grade of the product increases -The grade of the slurry concentrate stream increases -Wash-water requirements are reduced or eliminated -More hydrophobic particles are more likely to form bubble-particle attachments -Less hydrophobic particles are more likely to drain downward with the interstitial liquid and ultimately exit the vertical flotation column through the tailings stream -Recovery and grade can be increased simultaneously -Fewer interconnected flotation vessels are needed in cases where high concentration factors are required -Simplified overall process control increases effectiveness and decreases costs -The maximum particle size recovered increases to +1.0 mm, possibly reducing the complexity of a plant by eliminating the need for spiral circuits, used in coal flotation
Edgar B. Klunder
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