Cyanide is used to leach gold from its ores.  The leaching reaction can be represented as

 2 Au + 4 CN- + 0.5 O2  + H2O → 2(Au(CN2)-) + 2OH-

In order for the gold to be complexed/solubilised by the cyanide, it  has to be oxidised in order to form the soluble complex  as per the above reaction.

Depending on the nature of the ore, it may have a significant oxygen demand which cannot be satisfied alone by the oxygen from the air because of  solubility limitation of oxygen in water. In some cases, even the use of enriched air or pure oxygen may not be a solution.

Without sufficient oxidant, not all the gold present in the ore will be leached.   Hydrogen peroxide or calcium peroxide can be added to ensure a sufficient level of oxidant  and hence to improve  the overall gold recovery.

The presence of peroxygens is able to help in a number of ways

• reduce the amount of cyanide soluble gold going out in the tailings and so improve recovery
• oxidise species in the ore which consume oxygen and reduce the amount of cyanide being used by destroying cyanocides
• reduce of the amount of additives such as “lead “ required
• for calcium peroxide, improve the flow characteristics of the slurry

In some cases it has been shown that the presence of peroxygens can improve gold recoveries even if the dissolved oxygen levels appear sufficient.

Choice of reagent

The choice of oxidant will depend on the type of ore or the process used to leach the precious metal.  Consultation with one of our specialists will enable the selection of the most suitable solution for your particular situation.