Engineering & Mining Journal

AUG 2018

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SCREENINIG MACHINES 38 E&MJ • AUGUST 2018 www.e-mj.com Thinking about a screening solution gener- ally only happens when either something goes wrong with one or when designing a plant. The rest of the time, screening is that endless background sound and should stay that way. That is exactly why suppliers seek to fully prove their screening solutions prior to release. Upon release, the typical elevator pitch focuses on the reliability of the solution. A glance at the recent news from suppliers reveals the emphasis they place on successful field testing, the deep knowledge in the brains behind the solu- tion, and how it is something miners can easily order, install, maintain and forget. More Gs in Less Space Derrick Corp. announced a major gold miner recently adopted its Linear Motion screening machines for an open-pit heap- leach mine in southern Nevada. The purchase is the latest in a series by the miner and is in response to more than a decade of the same machines meeting and surpassing expectations at its other operations, said David Perkins, metallurgical engineer and general man- ager, Latin America, Derrick Corp. "They have rewarded us," Perkins said. The miner previously "made this a standard across all of their other mines," he said. "Obviously, they felt very strongly about the Derrick design." The miner first tapped Derrick "in the early 2000s" and trialed a carbon column train with three 4-ft-by-10-ft dual motor Linear Motion screening machines at a similar but larger mine in central Alaska, Perkins said. There, the ADR (adsorption, desorp- tion, recovery) plant mandated a system effective at capturing almost the entirety of the impregnated carbon. "If they are not captured before they leave the ADR plant, this solution that contains the fines is recirculated back out to the heap leach, where it is distributed by a series of pipes and smaller pipes and emitters," Perkins said. "And what happens is that fine car- bon will be redeposited on the heap leach where it will sit there and adsorb gold until the point where it can no longer adsorb." Additionally, the particles could "cause a blockage at the emitter that would pre- vent the solution from getting to a partic- ular part of the heap leach," Perkins said. Leach lines were buried to prevent freezing. It was critical that less than a trace amount of fines recirculated back to the emitters, Perkins said. "The minute they got plugged, they would never find it," he said. "They'd never know because they are buried under the ore, so it was super-critical the job that these machines played in their success at that mine." The carbon particles ranged in size from 50 microns up to a millimeter and were suspended in a cyanide-leach solution at a concentration of 350 to 400 parts per million and flowing at up to 4,000 gallons per minute. "There is almost zero undersize particles," Perkins said. "The slurry is just about 100% minus 150 microns, where- as the carbon particles themselves for the most part are about 0.8 to 1 mm in diam- eter." The system mandated "a machine capable of handling very high volumetric flows and making a good separation and also has the ability to not be a maintenance nightmare to the customer," he said. Each machine was equipped with Derrick's non-blinding 200 mesh Polyweb urethane screen panels. Each featured a "very high open area, the highest of any- one in the world that makes urethane panels," Perkins said. "That coupled with the high G-forces at a very high frequency gives the Derrick machine the ability to process a very high volumetric flow on a very small footprint." Eight Gs at a frequency of 1,800 ro- tations per minute means "we're shaking this machine really hard and really fast, and the machine has to be robust enough to handle that," Perkins said. "That takes some pretty high-tech manufacturing to do that." Derrick, he said, cuts "all of our steel with lasers, and we use robots to do the welding." The machines are coat- ed "in a solid spray-on urethane instead of just a paint, so we essentially have a machine that is going to not only be able to do this, but is going to last a very long time doing it." In 2013, a second ADR plant was built, with a line of three Linear Motion machine specified in the blueprints. "They essentially had two ADR plants at this mine, each of them operating in parallel," Perkins said. "There is a train of carbon Designed to Stay Off Your Mind The latest in screening solution offerings are promoted as producing results while reducing labor costs By Jesse Morton, Technical Writer Above, three dual-motor Linear Motion screening machines process 4,000 gallons per minute at an Alaskan gold mine. (Photo: Derrick)

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