When we say “cyanide,” we refer to one of many different compounds that contain a cyanide functional group, consisting of a carbon (C) atom attached to a nitrogen (N) atom with a triple bond (C≡N). Cyanide can react with many metals, which sees it used to separate precious metals like gold from ore. The cyanide compound most often used for gold leaching is sodium cyanide (NaCN), applied to one of two common types of leaching: heap leaching, and tank leaching. Heap leaching uses cyanide solutions in open environments, where cyanide is sprayed over heaps of crushed ore that’s spread across large collection pads. The cyanide solution then passes over the heap, dissolving gold into solution that’s later collected by the collection pads, and this process is repeated until the ore is fully depleted. In contrast, tank leaching is performed in more controlled environments, typically in large tanks or vats. The process is fundamentally similar to heap leaching and benefits from a lower chance of spills or leaks, but produces a waste product known as tailings, a major type of hazardous waste that’s typically contained behind large dams known as tailings impoundments. When these dams fail, contamination can be every bit as extensive and severe as in heap leaching. So while the risks are clear and acute, cyanide leaching remains a key part of the mining industry, and extensive measures are taken to see its safe and continued use.