(Air-Sparged Hydrocyclone)
The air-sparged hydrocyclone (ASH) was developed at the University of Utah during the early 1980s to achieve fast flotation of fine particles in a centrifugal field. The ASH consists of two concentric right-vertical tubes with a conventional cyclone header at the top and a froth pedestal at the bottom (see figure below). The inner tube is a porous tube through which air is sparged. The outer tube serves as an air jacket to evenly distribute air through the porous inner tube.
Slurry is fed tangentially through the conventional cyclone header to develop a swirl flow of a certain thickness in the radial direction (the swirl-layer thickness). The swirl is discharged through an annular opening between the porous tube wall and the froth pedestal. Air is sparged through the porous inner tube wall and is sheared into small bubbles. These bubbles are then radially transported, together with attached hydrophobic particles, into a froth phase that forms on the cyclone axis. The froth phase is stabilized and constrained by the froth pedestal at the underflow, moved toward the vortex finder of the cyclone header, and discharged as an overflow product. Water-wetted hydrophilic particles generally remain in the slurry phase and are discharged as an underflow product through the annulus created by the froth pedestal.
During the past decade, large mechanical flotation cells, such as aeration-stirred tank reactors, have been designed, installed, and operated for mineral processing. In addition, considerable effort has been made to develop column flotation technology in the United States and elsewhere; a number have been installed in industries. Nevertheless, for both mechanical and column cells, the specific flotation capacity is generally limited to 1 to 2 tons per day (tpd) per cubic foot of cell volume. In contrast, the ASH has a specific flotation capacity of at least 100 tpd per cubic foot of cell volume.
Standard flotation techniques used in industrial mineral processing are effective ways of concentrating materials. However, metal value recovery is never complete. The valuable material escaping the milling process is frequently concentrated in the very fine particle fraction.
The ASH can remove fine mineral particles that are amenable to the froth flotation process. These particles are generally sulfide minerals, such as galena (lead sulfide), sphalerite (zinc sulfide) and chalcopyrite (copper-iron-sulfide). Finely divided mining wastes containing these minerals oxidize and release the metallic elements as dissolved sulfates into the groundwater. Particularly applicable are tailings from older operations conducted before the development of froth flotation. Earlier operations recovered minerals by gravity concentration, which did not effectively capture fine particles and left tailings with relatively large concentrations of the environmentally hazardous fine sulfide minerals.
This technology was accepted into the SITE Emerging Technology Program in June 1990. The most recent pilot plant trials on tailings generated by gravity concentration have confirmed both the technology's ability to recover sulfide minerals and the high throughput capacity claimed by proponents of the ASH. However, results on the economics of ash processing were inconclusive. Studies under the SITE Program were completed in August 1994, and a journal article is pending. The pilot plant was dismantled after 4 years of operation.
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TECHNOLOGY DEVELOPER CONTACT:
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