Carbon-in-Leach (CIL) Process in Gold Ore Treatment: From Leaching to Gold Recovery

The carbon-in-leach (CIL) process for gold ore is a key step in extracting gold from refractory gold ores, typically following bio-oxidation and washing procedures. The specific process is as follows:

1. Connection with Pretreatment Processes
        The flotation concentrate is first subjected to bio-oxidation, where bacteria oxidize most sulfide minerals (such as pyrite and arsenopyrite)      to release gold from sulfide encapsulation. The oxidized residue then enters the CCD (counter-current decantation) system, undergoing 3-stage      washing to remove impurities and reduce interference in subsequent cyanide leaching.

2. Main CIL Process

• Slurry Conditioning and Pre-alkaline Leaching： The oxidized residue after CCD washing is transferred to a slurry conditioning tank, where alkali (e.g., sodium hydroxide) is added to adjust the slurry pH to alkaline, creating conditions for cyanide leaching.

• Cyanide Leaching and Activated Carbon Adsorption： The slurry sequentially enters CIL1# to CIL6# leaching tanks,       and sodium cyanide (NaCN) is added. Gold reacts with cyanide to form gold-cyanide complexes (e.g., [Au(CN)₂]⁻). Meanwhile, activated carbon is introduced to adsorb gold-cyanide complexes from the solution, achieving gold enrichment.       During this process, mercury in the ore undergoes solid-liquid phase migration; mercury and mercury salts react with cyanide to form mercury-cyanide complexes (e.g., [Hg(CN)₄]²⁻), some of which are adsorbed by activated carbon, potentially causing "mercury poisoning" of the carbon.

3. Subsequent Treatment Processes

• Loaded Carbon Desorption: The gold-loaded activated carbon undergoes desorption, where gold is desorbed from the carbon into the solution.

• Electrolytic Recovery： The desorbed solution is electrolyzed, with gold precipitating on the electrodes.       Mercury also co-precipitates, and the precipitated elemental mercury evaporates, then is treated by venturi scrubbers and wet absorption towers.

• Activated Carbon Regeneration: The desorbed activated carbon is preheated and fed into a rotary kiln, where mercury and other impurities are desorbed at high temperatures. Waste gas is also treated by scrubbing before emission, and regenerated carbon can be reused.

• Gold Slime Smelting： The recovered gold slime is dried and smelted into gold ingots in an intermediate frequency furnace. Residual mercury during smelting evaporates and is collected for treatment.

4. Mercury Control Measures
        To reduce the impact of mercury on gold recovery, an appropriate amount of sodium sulfide (Na₂S) is added during the CIL process. This converts mercury ions      (Hg²⁺) in the solution into mercury sulfide (HgS) precipitate, which is fixed in the leaching residue, reducing the adsorption of mercury-cyanide complexes by activated carbon and improving gold recovery.