Depending on the nature of the ore, precious metal recovery may be lower than expected;  pretreatment can overcome this :

• ores that contain high levels  of sulphides, arsenic and/ or antimony
• ores containing high levels of carbonaceous material (preg robbing)
• ores where the precious metal is physically surrounded by non porous minerals

A number of methods can be used to pretreat the ores including

• chlorination
• pressure oxidation
• calcining
• biological treatment
• Caro’s acid or hydrogen peroxide

The advantages of using peroxygens include :

• no generation of new gaseous or liquid effluents which could create further  environmental issues
• operation at ambient temperature and atmospheric pressure
• no major capital investment