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THE CYANIDE PROCESS IN GOLD MANUFACTURE

• Gold is leached from crush rocks using an aerated, dilute solution of cyanide:
  
  4Au + 8NaCN + O2 + 2H2O --> 4Na[Au(CN)2] + 4NaOH
  
  Gold is then precipitated by adding Zn dust.
  
  
  Source: N.N. Greenwood and A. Earnshaw, Chemistry of the Elements, 2nd edition, Butterworth Heinemann, 1998.