Processing

LEFA’s CIL (carbon-in-leach) processing plant consists of several major unit processes.

• Following crushing, the ore is fed into the grinding circuit comprising SAG and ball mills where it is ground to 80% pass 150 microns.
• The density is then increased to around 50% solids in a thickener and the ore is then pumped to the leach circuit where sodium cyanide is added to dissolve the gold.
• The ore is leached for approximately 24 hours before passing to the adsorption circuit.
• Activated carbon is added to the circuit to adsorb the dissolved gold.
• The loaded carbon is recovered and washed with a hot solution of sodium hydroxide and sodium cyanide in the carbon strip columns.
• Gold is recovered from this concentrated solution by electrolysis, which causes it to be deposited onto steel wool cathodes.
• The dried precipitate from the cathodes is then smelted to produce doré bullion. Tailings are pumped to a specially constructed tailing storage facility.

The upgrade and refurbishment of the LEFA plant have taken over two years and have entailed the improvement of many plant processes and pieces of equipment. The power plant electrical generation system has been fully commissioned and is being converted to operate with heavy fuel oil (HFO) instead of diesel. The change to HFO power generation will reduce cash operating costs per ounce considerably. Additionally, the storage capacity of 3.5 million litres of HFO provides an additional buffer against possible disruption to supply during Guinea’s July-to-October wet season.