Carbon-in-Leach

Cyanide is used to dissolve gold from the ore into a gold/cyanide solution.  Carbon is then used to absorb the gold from the solution and then the gold recover similar to the carbon-in-pulp process can take place.

The cyanide solution can then be recycled to leach more ore.

Carbon Columns, part of the gold recovery process at Cortez

Picture courtesy of Rio Tinto & Placer Dome. J.V Project: Cortez gold mine

Run-of-mine oxide ore is crushed and stockpiled before grinding in an autogenous mill and a ball mill. Discharge from the AG mill is screened, with screen oversize being conveyed to a cone crusher and recycled to the AG mill. Screen undersize and ball mill discharge are sized in hydrocyclones, the overflow being thickened to provide feed for the carbon-in-column (CIC) and carbon-in-leach (CIL) circuits.

The CIL circuit consists of eight CIL tanks, 16 screens and eight carbon-forwarding pumps. Retention time at the 9300t/d throughput rate is 44 hours, increasing to 54 hours when milling South Pipeline ore at 7500t/d. The CIC circuit consists of six carbon columns with a retention time of 18 minutes.

After stripping the carbon using a pressurised Zadra process, the gold is recovered by electrowinning on to stainless steel wool cathodes. The filter cake is dried, melted in an induction furnace and poured into doré bars assaying approximately 90–94% gold and 3–6% silver for shipping to commercial refineries.