Engineering & Mining Journal

APR 2018

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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HEAP LEACH 54 E&MJ • APRIL 2018 by four hydraulic rams. Ore is choke-fed to the gap between the rolls. The potential benefits of using HPGR technology includes faster and higher recoveries due to the formation of mi- cro-cracks in the ore particles. The pro- cess should also demonstrate higher agglomeration due to a more favorable overall particle-size distribution. This would also impact the flow rate of solution through the heap. This flowsheet also of- fers lower capital costs than a four-stage, conventional crushing-screening plant. Dust control is better managed with fewer transfer points. "We found that our ore gave signifi- cantly better recoveries as well as lower operating costs due to the efficient use of power," Clay said. "Our recoveries have been tracking very well and we believe that we will be able to achieve our fea- sibility study targets for recovery rates of 75% to 80%." Thyssenkrupp designed and built Gold- en Queen's HPGR, which has the ability to operate with a specific press force of 609 psi (4.2 N/mm 2 ) as the key operating parameter. A higher specific press force gives a finer overall particle-size distribu- tion and leads to a greater density of mi- crocracks and this will directly affect tails and recoveries. The conclusion is that the specific press force is the determining op- erating parameter in an application of the HPGR as the comminution equipment. The importance of particle-size distri- bution and the proportion of fine material in the HPGR product must also be em- phasized and systematic sampling and screen analysis is required. Applying the Technology to Heap Leach At the 2018 Society for Mining, Metallur- gy and Exploration (SME), Gerhard Sauer- mann, business development manager for thyssenrupp Industrial Solutions, pre- sented two case studies for HPGRs being used in heap-leach operations: Soledad Mountain and Gold Fields's Tarkwa mine in Ghana. The Tarkwa installation established the benefits of HPGR in heap-leach op- erations, Sauermann explained. He has overseen the POLYCOM HPGR set up at several sites including Soledad Moun- tain and Tarkwa. "The use of HPGRs has grown steadily and now they are being in- corporated into heap-leach processing," Sauermann said. "Iron ore miners ad- opted the technology in the early 1990s. The systems have been in use at hard rock operations since thyssenkrupp de- veloped the technology to overcome the wear rates." Queen City uses its HPGR in an open configuration. "The development of the Soledad Mountain coincides with the development of the HPGR," Sauermann said. "Their machine was commissioned in early 2016 and has been operating since. It processes 800 tons per hour (t/h). There was a lot of test work with this unit." Comparing the HPGR results with that of a vertical shaft impactor (VSI), Sauer- mann said the HPGR had high recov-

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