The Gold must be in a gold chloride form
Liquid must be clean and contain no solids/dirt or fine particles
pH must be in the range of 2.5 to 4
ORP must be in the range of 900 to 1200
We suggest that the salt content be between 50 to 200g/L to help keep the gold in solution (If silver is present in liquid it must be close to 200g/L or it will not stay in solution)
The pregnant leach liquid should be stored in a dark container, light can precipitate the gold out of the solution
The leach liquid should be shipped quickly after being made to ensure we can test it before the gold falls out of the solution
Suggestions on Leaching the concentrate with the chloride-hypochlorite solution:
Keep a 1:5 (kg:L) solid to liquid ratio
Concentrate should be ground to 150 mesh or less
Mix the solution and concentrate to keep solids in suspension and not on the bottom of the tank
Mix the solution and concentrate for at least 2 hours
Need to monitor the pH, ORP and Temperature and keep them in the range of 3-4, 1000-1200 and 20 C – 35 C respectively
If the pH increases above 4:
Add HCL to lower the pH
If the pH decreases below 3:
Add NaOCL to raise the pH
If the ORP decreases below 1000
Add NaOCL to raise the ORP
Always make sure you have proper ventilation when making the chloride-hypochlorite solution, if you add the HCL to quickly to the solution, localized chlorine gas will come up from the solution.
If the concentrate has a high sulfide concentration, it will lower the pH and outgas the chlorine gas in solution, to counter act this start the solution at a higher pH between 6-7. The sulfides will turn to sulfuric acid and lower the pH and increase the ORP to the required range to leach the gold from the concentrate.
Keep the pressure of the leach solution above 1 atm to maintain best leaching conditions and as little outgas as possible.