The use of cyanide in gold mining

Chapter 5

This figure is referred to in the book as X.XX (Page XX)

In recent years the use of cyanide in gold mining has become the dominant means by which gold is extracted from a body of ore. The mercury amalgamation process had previously been used but recovered only about 60 per cent of an ore body’s gold. In contrast, leaching finely ground ore with cyanide can recover up to 97 per cent of the ore body’s gold.

The process involves:

    1. Removal of all topsoil from the area to be mined.
    1. Large open pits, up to a mile wide, created to extract the ore.
    1. Transport of raw ore in large trucks to crushing machines.
    1. Crushed material built into heaps over which cyanide is sprayed.
    1. The cyanide trickles down through the ore and bonds with microscopic specks of gold. A pad underlying the heap channels the solution into a holding pond.
    1. The gold laden cyanide solution flows over activated carbon; the carbon bonds to the gold while the cyanide is drawn off for re-use on the heap.
    1. Other chemicals are used to separate the gold from the carbon.
  1. The gold is then purified.

Mining companies state that under sunlight cyanide in water rapidly breaks down into largely harmless substances such as carbon dioxide and nitrate. It also tends to react readily with many other chemical elements, however, and is known to form hundreds of different compounds. While generally less toxic than the original cyanide, many of these compounds are known to be toxic to aquatic organisms, to persist in the environment for long periods and can be accumulated in plant and fish tissues.

People’s health is endangered when cyanide-laden waste is released into water used for drinking and bathing. People who live in close proximity to cyanide heap leaching pads also report increased respiratory and skin diseases.

Source:
Centre for Economic and Social Rights (2001) ‘Report of a fact-finding mission (CESR-FFM) to Honduras in March/April 2001’, New York, pp.1-2, 10-11.