Engineering & Mining Journal

DEC 2013

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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COMMINUTION Energy and Cost Comparisons of HPGR-based Circuits UBC researchers compare the cost of novel comminution techniques with the Huckleberry mill's existing circuit By C. Wang, S. Nadolski, O. Mejia, J. Drozdiak and B. Klein The Huckleberry mine, located in British Columbia, produces roughly 40 million lb/y of copper. A comprehensive energy and cost study compared an existing SAG mill-based circuit at the Huckleberry mine with two proposed circuits involving comminution technologies that are associated with energy efficiency: high-pressure grinding rolls (HPGR) and high-speed stirred mills. The specific energy requirements, expressed as kilowatt-hours per metric ton (kWh/mt), for the proposed circuits were determined from pilot-scale HPGR and stirred mill testing conducted at the University of British Columbia (UBC). Samples and operating data were collected from Huckleberry's copper-molybdenum concentrator to evaluate current mill performance for comparison. To support the base case, the current Huckleberry mill circuit was modeled using JK SimMet software. The main comparison focused on the complete energy requirements for each circuit, including materials handling equipment 102 E&MJ; • DECEMBER 2013 such as conveyors, screens, feeders and pumps. Capital and operating cost estimates for each of the comminution circuits are also given. The results showed that the HPGRball mill circuit achieved a 21% reduction in energy consumption over the existing SAG-ball mill circuit at the same P80 grind size of 160 mircons (µm). At a grind of 80% passing 75 µm, the HPGR-stirred mill circuit showed a 34% reduction in energy compared to the base case. The energy reduction for the new flowsheets significantly improved the economics of the Huckleberry comminution process. Introduction Up until now, tumbling mills such as AG/SAG mills and ball mills have had a dominant bearing on the design and economics of comminution circuits. However, it is commonly agreed that the majority of employed comminution processes are energy intensive and energy inefficient, accounting for up to 80% of overall process plant energy consumption and having an efficiency of as low as 1%. The U.S. Department of Energy reported that there is a potential to reduce energy consumption in the metals industry by up to 61% from current practice to best estimated practical minimum energy consumption; suggestions included the implementation of best practices and the adoption of energy efficient mining and mineral processing technologies such as advanced blasting techniques, HPGR and stirred mills. The concept of combining an HPGR and a stirred mill in a single flowsheet has been proposed, which was envisioned to be an example of the future in energy conscious comminution processes. The pilot-scale HPGR and highspeed stirred mill testing facility at the UBC Norman B. Keevil Institute of Mining Engineering provided a very unique opportunity to assess the HPGR and/or stirred mill circuits and understand the potential benefits. To examine a combined HPGR and stirred mill circuit, both machines have to be operated outside their currently accepted operating conditions. Studies have demonstrated that an HPGR-stirred mill circuit is technically feasible and showed promising benefits over the traditional stage crushers-ball mill circuit and HPGR-ball mill circuits. To determine whether the novel HPGR-stirred mill circuit arrangement could achieve energy savings in comparison to conventional SAG mill-based circuits, a pilot-scale study was conducted to compare the energy requirements of the existing circuit at the Huckleberry mine to two alternative circuits: an HPGR-ball mill circuit and a novel HPGR-stirred mill circuit. The study was conducted in collaboration with the www.e-mj.com

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