Low recovery rate of carbon-containing gold ore: what should be done? When organic carbon content exceeds 0.2%, the carbonaceous material exerts a strong “preg-robbing effect,” adsorbing dissolved gold and slashing recovery rates via traditional cyanidation to a mere 50%–60%. Despite the fact that carbonaceous ores account for approximately 20% of global gold reserves, their utilization rate remains below 20%. To address this industry challenge, this article systematically reviews 5 high-efficiency carbon-containing gold ore processing methods, helping you identify the optimal gold extraction solution.
Facing the challenges of processing carbon-containing gold ore, five efficient methods for gold extraction are proposed: the roasting method decomposes carbon that robs gold at high temperatures. Flotation pre-separates carbonaceous minerals; bio-oxidation ecologically neutralizes the carbon; chemical oxidation selectively destroys carbon activity; and CIL/CIP processes enhance recovery rates through pre-oxidation.
What are carbon-containing gold ores?
Carbon-containing gold ore is a refractory gold ore that contains carbonaceous materials such as organic carbon, elemental carbon, or graphite. These ores are widely distributed, accounting for more than 20% of proven global gold reserves.
Forms of carbon
Carbon does not exist in a single form within gold ores; the three most common forms are:
- Elemental carbon: Features a porous, honeycomb-like structure with a surface rich in adsorption sites, resulting in strong adsorption capacity.
- Organic carbon (humus): Includes humic acid and fulvic acid, which can form complexes with gold in solution.
- Graphitic carbon: Characterized by a layered crystalline structure; the higher the degree of maturity, the more active its adsorption properties.
Why Is Carbon-Containing Gold Ore Difficult to Process?
Challenges in Processing Carbonaceous Gold Ores
- “Preg-robbing” effect: Carbonaceous matter preferentially adsorbs dissolved gold, causing gold loss into the tailings.
- Fine gold particles: Gold occurs as fine or sub-microscopic particles encapsulated within carbonaceous matter and sulfides, making liberation difficult.
- Complex mineral associations: Gold is intimately associated with carbon, pyrite, and arsenic-bearing minerals, making effective separation via a single process challenging
- Difficulty separating carbon and gold: Their similar floatability makes precise separation difficult.
- High costs: Most carbonaceous gold ores require additional pre-treatment steps, driving up operating costs.
- Increasing environmental pressure: Some pre-treatment methods involve high-temperature roasting or chemical reagents, and emission regulations are becoming increasingly strict.
5 Methods to Process Carbon-Containing Gold Ore
1. Oxidative Roasting
Principle: High temperatures are used to oxidatively decompose carbonaceous matter, thereby eliminating its capacity to adsorb gold. During roasting, the carbon reacts with oxygen to form carbon dioxide, which is then released.
Key Parameters: Maintaining a roasting temperature of over 600°C for approximately two hours effectively eliminates the carbon’s gold-robbing activity. Specific parameters must be adjusted based on ore characteristics.
- Advantages: This is a mature, reliable technology with extensive industrial application experience.
- Disadvantages: Energy consumption is high, and flue gas management faces increasingly stringent environmental regulations, necessitating the installation of an exhaust gas treatment system.
2. Flotation
Preferential flotation for carbon removal:
When the carbonaceous material is barren (contains no gold), non-polar oil is added first to float off and discard the carbon, followed by gold flotation on the tailings. This process is simple and efficient, significantly reducing carbon interference in subsequent stages, making it an economical gold extraction method choice for treating low-carbon ores.
Bulk flotation of carbon and gold:
When carbon and gold are intimately associated and difficult to separate, they are floated together to produce a mixed concentrate for subsequent processing. While this method offers operational simplicity and a streamlined flow, the resulting concentrate grade is relatively low, necessitating further treatment.
Flotation with depressants:
Depressants such as CMC or sodium silicate are added to suppress carbon floatability, allowing gold minerals to float preferentially and thereby improving concentrate quality and grade. This method effectively enhances concentrate quality but requires precise control over reagent dosages.
3. Chemical Oxidation
Process Principle:
This method utilizes the oxidizing power of strong oxidants to decompose carbonaceous matter, thereby stripping it of its gold-adsorbing capacity. Oxidants release active oxygen in the aqueous phase, which reacts with the carbonaceous material to disrupt its surface structure and destroy adsorption sites, effectively eliminating the “preg-robbing” effect.
Commonly Used Oxidants:
Chlorine gas, calcium hypochlorite, potassium permanganate, and hydrogen peroxide are all suitable for oxidizing carbonaceous gold-bearing minerals. The specific choice depends on a comprehensive assessment of ore characteristics, reagent availability, cost-effectiveness, and environmental regulations.
- Advantages: Low equipment investment, rapid reaction kinetics, and high treatment efficiency; the oxidation of carbonaceous matter can be completed within a relatively short timeframe.
- Disadvantages: High reagent costs; some reagents pose environmental risks, necessitating the installation of wastewater treatment facilities.
4. Bio-oxidation
Process Principle:
Microorganisms such as “Acidithiobacillus ferrooxidans” are utilized to decompose the carbonaceous structure and reduce its surface activity, thereby minimizing the adsorption of gold.
- Advantages: Environmentally friendly, safe, and pollution-free; low operating costs; simple operation and easy maintenance.
- Disadvantages: Long processing cycle; requires supporting bioreactors and temperature control systems; sensitive to harmful impurities in the ore.
5. Carbon-in-Leach/Carbon-in-Pulp (CIL/CIP)
The ore undergoes cyanide leaching to dissolve the gold, followed by the addition of activated carbon to the pulp to adsorb the gold-cyanide complex. Activated carbon competes with naturally occurring carbonaceous matter for gold adsorption, effectively minimizing gold “preg-robbing” by the latter.
Activated carbon is added simultaneously with cyanide leaching, allowing adsorption of the gold-cyanide complex to occur concurrently with the leaching process. This method integrates leaching and adsorption into a single stage, resulting in a more compact flowsheet and simplified operational management.
- Advantages: Suitable for large-scale production with recovery rates reaching up to 95%. CIP and CIL are mature gold extraction technologies and currently the most widely applied methods for processing carbonaceous or refractory gold ores.
- Disadvantages: Precise control of activated carbon concentration and adsorption time is required. The use of masking agents can mitigate interference from carbonaceous matter while further enhancing recovery rates.
Comparison Table of 5 Carbon-Containing Gold Ore Processing Methods
Method | Principle | Advantages | Disadvantages | Application |
Roasting | High-temperature decomposition of carbonaceous matter | Mature technology, stable results | High energy consumption, high pollution | High-carbon ore |
Separation based on surface property differences | Moderate cost, flexible process | High reagent dependency, concentrate requires further treatment | Simple carbon-gold association | |
Chemical Oxidation | Strong oxidants destroy carbon structure | Fast见效, strong adaptability | High reagent cost, strong corrosiveness | Small-to-medium scale mines |
Bio-Oxidation | Microorganisms decompose carbonaceous matter | Green, low-carbon, low operating cost | Long cycle, demanding conditions | Environmentally-prioritized projects |
Activated carbon adsorbs gold | Compact process, low overall cost, suitable for large scale | Requires precise parameter control | Low-to-medium carbon content ore |
Conclusion
While the “preg-robbing effect” in carbon-containing (carbonaceous) gold ores presents a challenge, it is not insurmountable. The key lies in selecting the optimal combination of processing methods based on the mode of occurrence of the carbon and the dissemination characteristics of the gold within the ore. Techniques such as roasting, flotation, chemical oxidation, bio-oxidation, and CIP/CIL each have their own advantages and limitations; in practice, combined flowsheets are often employed to achieve superior gold recovery results. With 40 years of deep expertise in mineral processing, JXSC welcomes you to contact us for customized gold processing solutions and equipment tailored to any of your gold ore types.