Copper Heap Leach Management
Abstract
Copper heap leaching involves both the simultaneous and sequential leaching of very large tonnages of ore over long periods of time. It is not unusual to be leaching 3 or 4 million tonnes over periods of 12 to 18 months. As a consequence of the way the heaps are built, a block of ore (of up to 0.5 Mt) is leached and treated as a "management unit" with a number of these blocks constituting the active leach area of the operation.
Due to the size of the "management units" the ROM characteristics within them may have considerable variation in terms of physical characteristics of the ore, the total copper and the mineralogy of the copper species. These variations would normally be accounted for in a mill by altering the process plant operating parameters to achieve the required product grade and/or recovery. In the heap leach system however this type of control is not readily available as the leaching process continues, with only time, leachate flow rate, leachate chemistry and leachate total flux as potential management control variables.
As a consequence a "management unit" with considerable ore variability will have a number of under-leached and some over-leached sections when the average recovery reaches the target level. An economic loss results from the presence of economically recoverable copper remaining in the under-leached ore, and the excess consumption of acid which is incurred when leaching beyond the economic limit, in the over-leached ore.
A model had been developed which describes the potential magnitude of the losses and the benefits of placing ore in the "management units" with consistent grade and recovery characteristics (particle size, mineralogy and lithology). Application of this approach will enable the optimisation of the mine plan and the production scheduling to provide a more consistent quality in the "management units".