the pretreatment which may for example be effected by bubbling the ozonised gas through the liquor will depend on the nature of the liquor but is preferably continued until the liquor is substantially free from base metals organic matter and free cyanide this occurs typically when the ph of the liquor has decreased to below approximately 8 the ozonised gas may be generated using known and commercially available ozone generators the pretreatment results in a significant increase in the equilibrium or saturation loading of gold on the activated carbon thereby improving significantly the recovery of gold from the gold rich liquor the gold may be recovered from the loaded carbon by treating the carbon with water of low ionic strength in the manner described above gold bearing solutions originating from leaching a gold bearing ore with a sodium cyanide leach solution in a standard cyanidation process were treated by bubbling ozonised air at a rate of approximately 200 ml min at ambient conditions of temperature and pressure through a 500 ml sample of the solution in a beaker equipped with a magnetic stirrer the ozonised air was produced using a gallenkamp ozone generator type ge 150 the treatment resulted in each case in the formation of a white precipitate and a decrease in the ph from the tabulated results it is seen that copper nickel silver and iron are precipitated by the ozone treatment while gold remains unaffected a treatment lasting of the order of 1 2 hours was found sufficient to yield a liquor substantially free of.