Process
The mined ore is usually crushed into small chunks and heaped on an impermeable plastic and/or clay lined leach pad where it can be irrigated with a leach solution to dissolve the valuable metals. While sprinklers are occasionally used for irrigation, more often operations use drip irrigation to minimize evaporation, provide more uniform distribution of the leach solution, and avoid damaging the exposed mineral. The solution then percolates through the heap and leaches both the target and other minerals. This process, called the "leach cycle," generally takes from one or two months for simple oxide ores (e.g., most gold ores) to two years (for nickel laterite ores). The leach solution containing the dissolved minerals is then collected, treated in a process plant to recover the target mineral and in some cases precipitate other minerals, and then recycled to the heap after reagent levels are adjusted. Ultimate recovery of the target mineral can range from 30% of contained (run-of-mine dump leaching sulfide copper ores) to over 90% for the easiest to leach ores (some oxide gold ores).
Read more about this topic: Heap Leaching
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