Heap Leaching

Heap leaching is an industrial mining process that extracts metals such as copper, gold, silver and uranium from crushed ore by piling the ore onto a lined pad and slowly percolating a chemical leaching solution through it using drip or sprinkler systems, then collecting and processing the metal-bearing liquid that drains out the bottom. The technique produces a usable metal concentrate at lower cost than many conventional processing methods, since it avoids fine grinding and extensive mechanical handling, and it is especially widespread in low-grade copper and gold mining operations. A related principle is ancient: one traditional method of making copperas, iron sulfate, was to heap up iron pyrite and collect and boil the leachate that drained from the pile. Large mining companies including Rio Tinto, Orano, BHP and Vale operate heap leach facilities today, though the source consulted for this entry does not name the specific individuals or companies who first adapted the technique to large-scale modern metal extraction.