For low-grade gold mine development seeking to improve profitability and reduce operating costs, which gold extraction process is the most reliable choice? Given the continuously declining global gold resource grades, traditional cyanide leaching (CIP) and heap leaching methods are no longer sufficient to balance economic efficiency and environmental compliance. Carbon-in-leach (CIL), with its integrated design and high recovery rate, stands out. This article will comprehensively break down the process principles, full-process operation steps, advantages, and applicable scenarios of CIL, helping mine operators quickly understand whether this process solution is suitable for their gold mining projects.
Carbon-in-leach (CIL) is the mainstream cyanide gold extraction process in the global gold processing industry. Simultaneously adding activated carbon to the cyanide leaching tank, it achieves integrated gold dissolution, adsorption, and recovery. It is suitable for processing low-grade oxide ores and complex ores, and its cost is lower than CIP, with a gold recovery rate of over 95%.
Basic Understanding of Carbon-In-Leach
Carbon-In-Leach (CIL) is one of the mainstream technologies in cyanide gold extraction processes. Its core logic involves simultaneously adding activated carbon during the cyanide leaching stage, achieving “simultaneous leaching and adsorption,” eliminating the need for slurry filtration and precious liquor clarification steps in traditional processes.
Process Principle
The principle is to use the cyanide solution to dissolve gold ions in the slurry, while the activated carbon adsorbs complex alloys in the solution in real time, significantly reducing gold loss in the tailings.
This process is considered a “non-destructive adsorption method” in gold processing systems, particularly suitable for processing low-grade ores containing fine-grained gold or complex compositions (such as clay or organic-containing ores). Compared to separate leaching and adsorption processes (such as CIP), the integrated design of the gold carbon-in-leach process reduces equipment complexity and energy consumption, achieving an average recovery rate of 90%-95%, making it the preferred solution for current gold extraction.
Complete Process Flow of Gold Carbon-In-Leach (CIL)
Step 1: Ore Crushing & Grinding
In the CIL process, the key to crushing and grinding is ensuring liberation, that is, fully exposing the gold minerals. First, the gold ore needs to be crushed to a suitable particle size to ensure that subsequent cyanide treatment can efficiently contact and dissolve the gold particles. The coarse crushing stage typically uses a jaw crusher, while fine crushing uses a hammer crusher, roll crusher (for small- to medium-sized gold mines), or cone crusher (for large-scale gold mines) to pulverize large ore pieces.
Then, a closed-circuit ring mill is formed using a ball mill and a spiral classifier to further grind the ore into a slurry (65%-85% -200 mesh), the specific value of which is adjusted according to the ore’s intercalation particle size, creating optimal conditions for subsequent leaching.
Step 2: Leaching with Cyanide
The finely ground slurry is pumped into a series of leaching tanks (usually 6-8) and mixed with a sodium cyanide (NaCN) solution (0.03-0.3% concentration) in an alkaline environment with a pH of 10-11. Cyanide ions react with gold ions in the slurry to form stable gold-cyanide complexes. Note that sulfur- or copper-containing ores may interfere with the reaction and require pretreatment (such as roasting or bio-oxidation).
Step 3: Adsorption onto Activated Carbon
The CIL gold process adds activated carbon simultaneously with the start-up of the leaching. Mechanical stirring or airflow ensures thorough contact between the carbon particles and the gold-containing solution. It enables simultaneous leaching and adsorption, significantly shortening the overall process time.
Step 4: Carbon Stripping & Gold Recovery
The gold-saturated carbon is sieved out and fed into a desorption column to desorb the gold. Currently, the mainstream method uses high-temperature, high-pressure desorption. Under conditions of 150℃ and 0.5MPa, the gold-loaded carbon is eluted with a mixed solution of sodium cyanide and sodium hydroxide, and desorption is completed in 2-6 hours, achieving a desorption rate exceeding 98%.
Electrolytic purification
The resulting high-concentration gold-bearing solution is fed into an electrolytic cell. Under high voltage and current density conditions, gold ions precipitate on the cathode plate, forming gold mud. Its gold content can typically reach 30%-50%, and gold ions are reduced to metallic gold (purity ≥99.5%).
Step 5: Melting, Carbon Regeneration
Finally, the gold mud undergoes acid washing to remove impurities. Nitric acid is added to dissolve associated metals such as silver and copper. After filtration, crude gold with a purity exceeding 95% is obtained. Subsequently, the crude gold is placed in a graphite crucible furnace for induction melting, with the temperature controlled at 1200-1300℃. After removing the slag, it is poured into a mold to obtain a standard gold ingot with a purity of 99.99%.
Activated carbon regeneration and reuse
The desorbed carbon is first acid-washed to remove adhering substances such as calcium carbonate, and then sent to a rotary kiln for high-temperature thermal activation to restore its adsorption activity. The regeneration recovery rate of activated carbon can reach over 95%, and the regenerated carbon can be recycled 10-20 times, significantly reducing the activated carbon procurement cost of the production line.
Core Advantages of Carbon-In-Leach (CIL)
✔️ High Compatibility with Complex Ores
The CIL gold process is most suitable for the following types of mines: low-grade mines with gold grades of 0.5-3 g/t, difficult-to-process mines with mud content higher than 10% and fine particle size, and medium-sized and larger projects with a daily processing capacity of 100 tons or more. It can also be used to process ores with arsenic, sulfur, and other harmful impurity content below 2%, maximizing the gold recovery advantages of CIL.
✔️ Gold Recovery Rate 95%+
Carbon-in-leach plant integrates the leaching and adsorption processes into a unified reaction system, which not only shortens the residence time of gold in the slurry but also effectively avoids gold loss due to solution transfer.
✔️ Fewer Process Steps, High Degree of Automation
The equipment adopts a series layout, with a simple and clear structure. Low professional requirements for on-site operators; small and medium-sized mines can quickly and stably start production after training.
✔️ Lower operating costs compared to the CIP process
CIL eliminates the need for separate adsorption tanks and intermediate concentration stages, resulting in lower consumption of cyanide and activated carbon, and saving approximately 10% in investment costs.
✔️ Simpler plant design
The CIL gold process eliminates the thickener and intermediate storage tanks required by CIP, reducing the number of tanks by 30-40%. Its modular design makes it easier to automate, allowing small and medium-sized gold mines to quickly complete construction and start production.
✔️ Lower environmental impact
The CIL process requires lower cyanide concentrations and can be configured with tailings dam seepage prevention and cyanide degradation treatment processes. Simultaneously, activated carbon selectively adsorbs gold-cyanide complexes, significantly reducing heavy metal emissions in tailings. It achieves environmental compliance throughout the entire production process, aligning with the current global mining industry’s low-carbon and environmentally friendly development requirements.
(Carbon-In-Leach) CIL vs. (Carbon-In-Pulp)CIP
Process Type | CIL (Carbon-In-Leach) | CIP (Carbon-In-Pulp) |
Core Process Difference | Leaching and adsorption are carried out simultaneously | Cyanide leaching is completed first, then activated carbon is added for adsorption |
Average Gold Recovery Rate | 90%-98% | 85%-95% |
Applicable Scenarios | Low-grade fine-grained gold mines, medium-sized and above mines with high mud content | Mines with medium grade and easy solid-liquid separation |
Cost | Medium (activated carbon circulation system required) | Relatively high (multi-stage adsorption) |
Environmental Performance | Cyanide residue needs to be controlled | Similar to CIL |
Carbon-in-leach (CIL) is a simplified version of the CIP process. Compared to CIP, it eliminates the post-leaching pulp separation step, reducing site requirements by approximately 15% and operating costs by 10%, making it the preferred process for modern medium-sized gold mine beneficiation.
Carbon-In-Leach (CIL) - A Modern Solution For Efficient Gold Processing
Carbon-in-leach (CIL) has become the preferred technology for modern medium-sized gold mining projects due to its integrated leaching-adsorption design, a high recovery rate of 95%, low operating costs, and adaptability to low-grade, complex ores. In short, CIL is more suitable for continuous large-scale production; CIP is suitable for projects with significant fluctuations in gold ore grades. Currently, it has become the global high-yield gold processing solution due to its energy-saving, environmentally friendly, and rapid return on investment, especially suitable for low-grade, muddy, or complex ores.
Do you need to optimize your existing gold extraction process or build a CIL plant? JXSC Mine Machinery Factory‘s customized solutions can maximize your ROI. Contact us for professional project feasibility assessments, process design, and mining equipment selection solutions!