Breakthrough Energy Savings with Waterjet Technology.
Experiments performed at the University of Missouri-Rolla's Waterjet Laboratory have demonstrated clearly the ability of waterjets to disaggregate, in a single step, four different mineral ores, including ores containing iron, lead and copper products. The study focused mainly on galena-bearing dolomite, a lead ore, and compared the new technology with that of traditional mining and milling to liberate the valuable constituent for the more voluminous host rock. The technical term for the disintegration of the ore to achieve this liberation is comminution. The potential for energy savings if this process can be improved, is immense. Further, if this separation can be made at the mining face, then the potential energy savings include avoidance of transportation (haulage and hoisting) costs to move, process and store this waste at the surface. The waste can, instead, be disposed into the available cavities within the mine. The savings also include the elimination of the comminution, crushing and grinding, stages in the processing plant. Future prototype developments are intended to determine if high-pressure waterjet mining and processing can be optimized to become cheaper than traditional fragmentation by drilling and blasting and to optimize the separation process. The basic new mining process was illustrated in tests on two local rock types, a low-strength sandstone with hematite inclusions, and a medium to high-strength dolomite commonly used for construction materials. Illustrative testing of liberation of minerals, utilized a lead-bearing dolomite, and included a parametric study of the optimal conditions needed to create a size distribution considered best for separation. The target goal was to have 50 percent of the mined material finer than 100 mesh (149 microns). Of the 21 tests that were run, five clearly achieved the target. The samples were obtained as run-of-mine lumps of ore, which exhibited a great deal of heterogeneity within the samples. This, in turn, reduced the ability to apply detailed statistical tests to the product outcomes. Nonetheless, a regression analysis showed that operating pressures between 105 (10,000psi) and 140 (15,000psi) MegaPascals (MPa) at traverse speeds no greater than 10 cm/min (4 in/min), best generated the target result. Variation in other parameters, rotation speed, nozzle diameter, and nozzle separation angle, during the preliminary tests did not substantially change the product, and so were kept fixed during the ore mining tests. The experimental protocols were developed to include proper treatment of the lead-bearing materials, which may be considered hazardous. In anticipation of the creation of a mineral processing design for separation of the concentrates from the tailings (waste), assays were made of the metal content of each screen size for each of the 21 runs; with three screens and a pan for undersize, to give a total of 84 assays. This information will enable Dr. McNulty, project consultant, to create a flow sheet for the prototype mining machine. As a preliminary component to such a system, the experimental layout included a product-recovery system that delivered all of the fragmented product to the nest of screens which allowed study of the liberation at the different size levels. Where incomplete liberation is found, a secondary process was demonstrated for using pressurized cavitation to further comminute the material. This concept was successfully demonstrated, with a small cavitation chamber illustrating the much smaller space that such a tool requires, relative to conventional ball and rod mills. Additional testing is ongoing, external to this program, to find whether an one-step process using higher jet pressures and longer dwell times to achieve all the required comminution in mining, is more efficient than a two-step process in which normal jet pressures and feed rates do the initial mining, but full particle liberation is achieved only through secondary processing of the product in a cavitation chamber. Subsequent testing is also planned, to determine preferred methods for separating ore minerals from the waste. Tests with this system have included both the galena samples, and copper ores from Poland. The development of this tool lies within an expanding market for the use of high-pressure waterjet equipment across a broad spectrum of applications. As the industry develops new tools, it is anticipated that the research team will investigate the development of a prototype machine based on these tools, since this will simplify and speed up equipment development. It is hoped that once this is developed that can be taken into an active mine. Such a machine should be able to produce large enough samples to allow assessment of optimal operating conditions.
L. W. Saperstein et al., "Breakthrough Energy Savings with Waterjet Technology.," University of Missouri, Jan 2007.
Mining and Nuclear Engineering
Report - Technical
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