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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Since its commercial introduction to the mining industry in the late 1960s, heap leaching of low-grade ores to recover valu- able commodities—mostly gold and cop- per, but also nickel, uranium and to a less- er extent, vanadium and other metals—has grown steadily and proven to be a flexible and less-capital-intensive approach that appeals to both ends of the industry's cor- porate spectrum, from new or smaller com- panies looking for a way to get a property into production as quickly and cheaply as possible, to established producers that want to monetize marginal mineralization. It's a steadily evolving technology that has been able to accommodate mineralog- ical changes in the mining landscape, and it has been user-friendly in terms of adopt- ing new forms of technology that offer the prospect of lower pad construction and closing costs, more efficient fluids applica- tion and collection, and ultimately, higher recovery rates. Many of the long-term trends and changes in heap-leach operations are high- lighted in a recent paper presented at the 2016 Society for Mining, Metallurgy and Exploration (SME) Annual Meeting* that updated a survey of copper leach produc- ers conducted in 1998. The authors sent questionnaires to 40 copper-leach opera- tors, including properties that were con- tacted in the original survey and are still in operation; 28 operations responded. Among the broad trends identified by the survey results is a geographical shift in overall capacity of copper SX-EW plants— Latin America gained 12%, moving from 46% to 58% at the expense of the south- western U.S., which dropped from 42% to 38%; and Africa, which didn't register on the recent survey after holding a 9% share in 1988. Australia gained one point, grow- ing from 3% to 4%. The results also showed a swing in pri- mary copper mineralogy to mixed leach-ore types: in 1988, oxide ore accounted for 29% and sulphide 14%, with oxide/sulphide mixed ores representing 57%. In the updat- ed survey, oxides dropped to 20%, sulphides to 12%, and mixed ores grew to 68%. Other notable results from the survey are shown in the accompanying figure on p. 39. To identify ways in which industry sup- pliers are responding to the heap-leach sector's changing conditions and require- ments, E&MJ; conducted an informal sur- vey of its own; we took a look at recent product announcements, spoke with sup- plier representatives, and put together a brief sampling of the newest technologies available to the industry. Among those, we found an increasing emphasis on automa- tion and better control systems for materi- al handling equipment—not a surprising result, as leach pad footprint size and height continue to grow while the industry attempts to pare construction and labor costs as it searches for solutions to opti- mize metal recovery and its return on heap- leach project investment. Maintaining the Flow As the industry shifts from truck-dump pad loading to conveyor-based stacker/spreader systems, the focus changes from what is almost a batch-loading process to one that is more or less continuous. Careful planning is necessary—involving a wide range of dis- ciplines—to extract the best performance from these highly engineered materials- handling systems. We spoke with Matthew Hanson, business development manager at Superior Industries, a Minnesota-based supplier of conveyor systems and compo- nents, about how the company goes about laying the basic groundwork for recom- mending a leach-pad loading system pack- age to its customers. E&MJ; : What are the basic set of project-spe- cific factors that Superior's engineers take into account when specifying an equipment package for a given heap-leach operation? Hanson: The first area we look at is mate- rial characteristics—the type of material, its PCF, size and tons per hour require- ment. With this information we can then size the belt width of the conveyor system. The next step would be to look at the pad layout and the stacking plan in order to properly size length and number of grass- 38 E&MJ; • MARCH 2016 www.e-mj.com *Washnock, R., Zarate, G. and Scheffel, R., Copper Leaching: 2014–2015 Global Operating Data , Preprint 16-041, SME Annual Meeting, Feb. 21–24, 2016, Phoenix, Arizona. The latest generation of mobile conveyor-based heap-leach stacking equipment, such as the Superior Industries system shown here, has auto-leveling features that allow consistent material placement on the pad even when the radial stacker has to travel over uneven ground. Following the Flow Heap leaching has always offered a low-cost extractive solution with minimal environmental impact. Building on its inherent flexibility to accommodate new challenges, techniques and technologies, it shows no signs of lagging interest from producers or suppliers. By Russell A. Carter, Managing Editor H E A P L E A C H