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Testing protocol for evaluating amenability of ores to HPGR crushing for heap leaching Moghadam Zadeh, Sanaz


Finer particle size distribution (PSD) and generation of more microcracks obtained by the use of high pressure grinding rolls (HPGR) are believed to be the major reasons for metal recovery improvement by heap leaching. Finer PSD increases the surface area of the particles, which are in contact with the leach solution and improves recovery. Microcracks in HPGR materials result in improved penetration of leach solution into the grains and thus metal recovery. The objective of this work is to develop a better understanding of ores crushed by HPGR and cone crusher, in terms of microcracks and PSD, and assess the benefits of using HPGR for heap leach projects. The test results can be used in the early stages of the project to develop an initial understanding of the benefits of utilizing HPGR in the comminution circuits for heap leaching. Gold oxide, copper sulfide and copper/gold sulfide samples were used in this research. Laboratory tests including PSD analysis, scanning electron microscope (SEM), slake durability, Helium (He) pycnometry, nitrogen gas adsorption, water absorption and column tests were used to evaluate the changes in the PSD, microcracks morphology, mechanical stability, porosity, exposed surface area, water absorption capacity and unsaturated flow behavior of the samples. Finally, modeling by HYDRUS was conducted to investigate the hydraulic behavior of the crushed ores. PSD analysis showed finer size distribution for HPGR materials, independent of the ore types. Lower slake durability indices, higher porosities, larger surface areas, higher water absorption values and residual water degree were obtained for HPGR’s materials in comparison with the cone crusher’s. Computer modeling showed lower unsaturated hydraulic conductivity for HPGR samples. Estimation of the microcracks percentage over the total porosity indicated higher values for HPGR samples. Percentage of water inside microcracks and on particle surfaces over the water remaining between particles was higher in most HPGR crushed samples. Finally, a time efficient testing protocol for evaluating the amenability of HPGR to provide ore having the preferred characterization for heap leaching is designed.

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