Heap leaching is applied for leaching of oxidized copper ores, secondary copper sulfides, uranium and precious metal ores. Typically the ores are crushed to less than one inch (25 millimeters) and to as fine as minus ¼ inch (6.3 millimeters). Leaching can be performed in permanent heaps where successive lifts are placed over the original lift or in a reusable pad which allows the ore to be leached in one lift, the leach residue and a new lift placed on the pad. Recoveries are generally 65 to 85 percent, depending on the ore being leached, and leach cycle times range from months to a year.
Heap leaching has been used more recently for bio-leaching of secondary copper sulfide ores such as with the operations of Quebrada Blanca and Cerro Colorado in Chile and Cerro Verde in Peru. Cyprus Miami in Arizona, USA, and other US producers also employ a ferric leach or ferric cure technology for run of mine mixed oxide and secondary sulfide copper ores. Heap leaching technology allows processing of higher grade ores, but is typically used on lower grade ores (less than 1% copper) due to comparatively low capital and operating costs versus conventional technology.
