Heap leaching for gold and silver recovery is a fairly simple process that eliminates many complicated steps needed in conventional milling. A "typical" precious metal heap leaching operation consists of placing crushed ore on an impervious pad. A dilute sodium cyanide solution is delivered to the heap, usually by sprinkling or drip irrigation. The solution trickles through the material, dissolving the gold and silver in the rock. The pregnant (gold bearing) solution drains from the heap and is collected in a large plastic-lined pond