（Basic processes, Advantages, and Precautions）
The coconut shell activated carbon used in gold extraction (commonly referred to as gold-loaded carbon) is the core material in the cyanide leaching process for gold extraction (CIL -Carbon-In-Leach / CIP – Carbon-In-Pulp). It plays the role of efficiently and selectively adsorbing gold cyanide complexes from the cyanide leaching solution. The following is an introduction by China Chengde Jibei Yanshan Activated Carbon Co., Ltd. about the process, advantages, and precautions for “coconut shell activated carbon used in gold extraction”:
I. Process Principles and Flow Description
1. Cyanide leaching
The finely ground gold ore (slurry) is reacted with sodium cyanide solution under alkaline conditions (usually by adjusting pH to approximately 10.5 using lime). Gold dissolves to form a stable gold cyanide complex.
2. Activated Carbon Adsorption (CIL/CIP)
2.1Carbon-in-Pulp (CIP) Process: Efficient Gold Adsorption from Leached Slurry
The Carbon-in-Pulp (CIP) process is a widely used method for gold recovery following cyanide leaching. The process begins with ore that is finely ground and then subjected to gold dissolution in a series of agitated cyanide leach tanks. Once leaching is complete, the resulting slurry, containing the dissolved gold, is transferred to a dedicated CIP adsorption circuit.
This circuit typically consists of a cascade of five or six agitated tanks. Granular activated carbon is introduced into this series of tanks, where it moves counter-currently to the flow of the leached slurry. This staged, counter-current contact is a key feature of the CIP process, ensuring that the freshest carbon meets the solution with the lowest gold concentration, thereby maximizing the efficiency of gold adsorption. As the carbon adsorbs the gold from the slurry solution, it becomes progressively loaded with gold. The gold-laden carbon is then mechanically separated from the barren slurry through coarse screening, ready for the gold elution (stripping) stage. This highly efficient system achieves high gold recovery rates by optimizing the concentration gradient between the carbon and the solution.
2.2 Carbon-in-Leach (CIL) Process: A Combined Leaching and Adsorption Method
The Carbon-in-Leach (CIL) process is an efficient gold extraction method that integrates leaching and adsorption into a single operational step. Instead of using separate tanks, the leaching tanks are equipped with carbon retention screens, eliminating the need for a dedicated carbon-in-pulp (CIP) circuit. In this process, activated carbon is introduced directly into the leach tanks, allowing for the nearly simultaneous dissolution of gold by cyanide and its immediate adsorption onto the carbon.
This method is particularly advantageous for processing gold ores containing native carbon (often present as organic matter). The native carbon can prematurely adsorb the dissolved gold (a phenomenon known as “preg-robbing”), leading to significant gold losses and lower recovery rates. In the CIL process, the added activated carbon acts as a preferential adsorbent, effectively competing with the native carbon to capture the gold. This ensures that the gold is successfully loaded onto the activated carbon, from which it can later be recovered through a stripping process.
3. Gold-loaded Carbon Separation
Adsorbed saturated gold-loaded carbon is separated from the slurry through screening (usually using a vibrating screen or safety screen), and is washed to remove entrained mineral mud and cyanide solution.
4. Gold-loaded Carbon Desorption
Saturated gold-loaded carbon is sent to the desorption column (tower). Under high temperature (~110°C) and high pressure (~0.3-0.5 MPa), using a hot solution containing low concentrations of sodium cyanide and sodium hydroxide (commonly used) or alcohol (Zadra method), the gold is washed off from the coconut shell activated carbon to form a high-concentration gold solution (precious liquid).
5. Electrolytic Deposition
The high-concentration gold solution obtained from desorption is sent to the electrolytic cell, where gold is deposited on the cathode.
6. Gold Sludge Melting
The gold sludge is acid-washed to remove impurities, and then melted at high temperature to form gold ingots.
7. Activated Carbon Regeneration
Regenerated coconut shell activated carbon has decreased activity and requires regeneration treatment for recycling.
7.1 Acid washing: Use dilute acid (such as hydrochloric acid or nitric acid) to remove inorganic deposits (mainly calcium carbonate).
7.2 Thermal regeneration: In a rotary kiln or vertical furnace, under an oxygen-free or low-oxygen atmosphere at high temperature (~650-750°C), heat is applied to burn off the adsorbed organic substances and sulfides, restoring the pore structure and activity of the carbon. The regenerated carbon is cooled and returned to the adsorption loop for use.
II. Advantages
Why use coconut shell activated carbon?
1. High Selectivity
Coconut shell activated carbon has excellent selective adsorption capacity for gold cyanide complexes, effectively enriching gold while leaving most other metal ions and impurities in the solution, thereby improving the purity of subsequent products.
2. High Recovery Rate
The process is mature and stable, with the total gold recovery rate typically reaching over 95%, even exceeding 99%, making it one of the most effective gold extraction methods at present.
3. Simple Operation
Compared to the traditional zinc powder replacement method, the carbon adsorption process has a more easily automated control flow, with relatively mild operating conditions (except for desorption), and lower skill requirements for operators.
4. Strong Adaptability
4.1 It can handle ores with high clay content and difficult solid-liquid separation (such as clay-type gold ores), which is a difficulty of the zinc powder replacement method.
4.2 It can handle ores with varying gold grades.
4.3 It is suitable for large-scale continuous production.
5. Lower Gold Dissolution Loss
The adsorption process can quickly transfer gold from the solution to the carbon, reducing the risk of gold re-precipitation or loss in the solution (such as being “robbed of gold” by carbonaceous substances in the pulp).
6. Environmental Advantages
Compared to the zinc powder replacement method that generates a large amount of cyanide wastewater requiring treatment, in the CIP/CIL process, most cyanide is recycled, resulting in a relatively smaller amount of cyanide-containing wastewater (still requires strict treatment). The concentration of cyanide in the desorption liquid is low.
7. High Gold Enrichment
Coconut shell activated carbon highly enriches gold in the solid phase (carbon) in the solution, significantly reducing the volume of the solution that needs electrolytic treatment and improving electrolytic efficiency.
8. Recyclable Carrier
Coconut shell activated carbon can be regenerated and reused multiple times (usually up to 10-20 times or more), reducing material consumption costs.
III. Notes and Challenges
1. Selection of Activated Carbon is Crucial
1.1 Physical properties: Particle size (affects adsorption kinetics and screening efficiency), hardness/mobility (reduces powder loss during transportation and mixing), density (affects suspension and fluidity in the pulp).
1.2 Adsorption Properties: Adsorption capacity (the amount of gold that can be adsorbed per unit weight of carbon), adsorption rate (affects the amount of carbon required and the retention time), selectivity (low adsorption of other impurities such as base metals and organic substances).
1.3 Common types: Coconut shell carbon is the most commonly used gold extraction activated carbon due to its high strength, high hardness and excellent adsorption properties (especially for gold selectivity). Almond shell carbon, coal-based carbon are also used, but their performance is usually slightly inferior.
2. Carbon Loss
2.1 Mechanical wear: Friction during stirring, pumping, and screening can cause carbon powdering (fine carbon powder), resulting in loss of activated carbon and gold (attached to the fine carbon powder). High-strength carbon should be selected and equipment operation optimized.
2.2 Chemical degradation/oxidation: In high-temperature regeneration or strong oxidizing environments, carbon will undergo burning and structural damage.
2.3 Fine carbon loss: Low screening efficiency can cause fine carbon to enter the tailings, resulting in loss.
2.4 Management goals: The factory needs to closely monitor the inventory and loss of carbon, and replenish new carbon in a timely manner. The annual loss rate is usually around 10%-15%.
3. “Gold-robbing” Substances
3.1 Organic carbon: Natural organic carbon (graphite, humus, etc.) in the ore will also adsorb gold cyanide complexes, competing with activated carbon and reducing the gold recovery efficiency (referred to as the “gold-robbery effect”).
3.2 Clay/mud: Will cover the surface of activated carbon or clog carbon pores, reducing adsorption efficiency (passivation).
3.3 Countermeasures: Flotation pre-selection, roasting pre-treatment, increasing the amount of activated carbon, using additives, etc.
4. Impurity Adsorption and Poisoning
4.1 Calcium scale: Calcium ions in the pulp will form calcium carbonate precipitation, blocking carbon pores and adsorption towers/pipes. The activated carbon needs to be acid-washed and regenerated.
4.2 Organic matter: Oil, flotation reagents, humic acid, etc. will adsorb on the carbon, occupying adsorption sites or blocking pores. Thermal regeneration is required for removal.
4.3 Base metals: Cyanide complexes of copper, zinc, nickel, iron, etc. may also be adsorbed, competing for sites with gold and causing problems during desorption/electrolysis (such as reducing gold concentrate grade, increasing acid washing difficulty).
5. Desorption Efficiency and Cost
5.1 Desorption requires high-temperature and high-pressure conditions, with high energy consumption.
5.2 Incomplete desorption will result in gold remaining on the poor carbon, causing loss.
5.3 High-concentration gold in the desorption solution requires efficient electrolytic recovery.
6. Regeneration Efficiency
6.1 Regeneration (especially thermal regeneration) cannot fully restore the original activity of the carbon, and the activity will slightly decrease after each regeneration.
6.2 The thermal regeneration process itself also has carbon loss (~5-10%).
6.3 The operation and maintenance of the regeneration furnace are crucial.
7. Safety and Environmental Protection
7.1 Cyanide: The entire process involves highly toxic cyanide, which must be strictly managed (storage, use, protection, emergency response) and wastewater treatment (such as using the INCO method, hydrogen peroxide oxidation method to destroy cyanide).
7.2 High temperature and high pressure: The desorption process involves high-temperature and high-pressure equipment, ensuring that safety valves, pressure gauges, etc. are in good condition, operations must be standardized, and records must be kept.
7.3 Activated carbon dust: Activated carbon dust is flammable and explosive. Fire and explosion prevention measures (inert gas protection, dust control) must be noted.
7.4 Thermal regeneration exhaust gas: Contains combustion products (CO, CO2) and possible harmful volatiles (from adsorbed organic matter), which must be properly treated (such as incineration or washing). 8. Process Control and Monitoring:
8. Process Control and Monitoring
8.1 Key parameters need to be continuously monitored: pulp pH, cyanide concentration, oxygen content, carbon concentration in the adsorption tank, gold-carrying carbon grade, desorption efficiency, inactive carbon activity, regenerated carbon quality, and tail liquid gold grade, etc.
8.2 Operating parameters (such as carbon addition rate, adsorption time, desorption conditions) should be adjusted promptly to optimize gold recovery rate and cost.
IV. Summary and Activated Carbon Brands, Services, and Performance
The activated carbon adsorption process is a key technology in modern gold extraction industry. With its significant advantages such as high selectivity, high recovery rate, and strong adaptability, it is widely used globally. However, this process also faces challenges such as activated carbon loss, impurity influence, desorption and regeneration efficiency, high safety and environmental protection requirements, and complex process control. The key to successful operation lies in selecting high-quality activated carbon, optimizing process flow design, strictly controlling operating parameters, implementing effective activated carbon management and regeneration strategies, and strictly adhering to safety and environmental regulations. Continuous technological improvements (such as new activated carbon materials, more efficient desorption/regeneration technologies, online monitoring, etc.) are still continuously driving the development of this process.
Based in China, Chengde Jibei Yanshan Activated Carbon Co., Ltd. is a professional manufacturer specializing in activated carbon for water treatment systems. It supplies clients with high-quality activated carbon, marketed under the brand “Yanshan”.
“Chengde Tanke Import and Export Trading Co., Ltd.”, responsible for the foreign market service, provides excellent pre-sale, in-sale, and after-sale services for users.
The “Yanshan” brand’s activated carbon lineup comprises coconut shell activated carbon, fruit shell activated carbon, coal-based activated carbon, powdered activated carbon, honeycomb activated carbon, and silver-loaded activated carbon, among other variants.
“Yanshan” Brand Coconut Shell Activated Carbon – Its performance track record in gold mines includes collaborations with outstanding enterprises such as China National Gold Group, Shandong Gold Group, Zijin Mining Group, China Gold International Resources, Zhaojin Mining Industry, Chifeng Gold, Yintai Gold, Hunan Gold, Western Gold, Yunnan Gold, China Mining Group, and Zimbabwe Gold Mines.