Optimization and innovation of gold extraction process from gold mines

一  Differentiated Design and Technology Selection for CIL and CIP Processes

Although both CIL (carbon-in-leach) and CIP (carbon-in-pulp) processes are activated carbon adsorption gold extraction processes, they differ significantly in process design, operational logic, and applicable scenarios: 

Differentiating Mechanisms: CIL simultaneously reduces the liquid gold concentration through leaching and adsorption, driving the cyanidation reaction kinetics. CIP optimizes leaching and adsorption conditions step by step to reduce impurity interference, but the process is more complex.

二  Key Influences of Activated Carbon Adsorption Kinetics on Gold Recovery

The adsorption efficiency of activated carbon for gold-cyanide complex (Au(CN)₂⁻) is determined by both pore structure and chemical modification. The key parameters are as follows:

1. Adsorption Kinetic Model

• Diffusion-controlled Stage: Au(CN)₂⁻ migrates to adsorption sites through micropores (<2 nm) and mesopores (2-50 nm). The diffusion rate is positively correlated with the pore distribution (BET surface area >1000 m²/g).
• Chemical Adsorption Stage: Oxygen-containing functional groups (such as carboxyl and phenolic hydroxyl groups) on the activated carbon surface coordinate with Au(CN)₂⁻, with an apparent activation energy of 15-18 kJ/mol (laboratory measured values).

2. Optimized Parameters

• Pore Structure: Coconut shell charcoal with a micropore ratio >70% has a gold adsorption capacity of 6-8 kg Au/t charcoal; fruit shell charcoal with a micropore ratio <50% has a capacity of only 3-4 kg Au/t charcoal.
• Chemical Modification: Nitric Acid Oxidation can increase the phenolic hydroxyl content by 30%-50%, improving the gold adsorption rate by 40% (experimental data: gold recovery increased from 90% to 99.1%).
• Operating Parameters: At a slurry concentration of 40%-45% and a stirring intensity of 200-400 rpm, the adsorption equilibrium time is shortened to 8-12 hours.

3. Industrial Indicators:

The activated carbon adsorption coefficient (K value) must match the ore grade. For high-grade ores (Au >5 g/t), modified coconut shell charcoal with a K value ≥30 is recommended. The gold concentration in the tailings can be controlled at 0.05-0.1 mg/L.

三  Pretreatment Technology for Arsenic-Containing Gold Ore and Efficiency Improvement Mechanism

Arsenic compounds (such as FeAsS) encapsulating gold particles is the primary cause of low leaching yields. Pretreatment technologies release gold through mineral dissociation:

1. Roasting Oxidation Method

• Process Parameters: Two-stage roasting (first stage at 650°C to remove arsenic and produce As₂O₃ gas, second stage at 800°C to remove sulfur and produce porous Fe₂O₃ roasted sand).
• Verification: After roasting a high-arsenic ore (12% As content), the gold leaching rate increased from 41% to 90.5%, but a flue gas purification system (As₂O₃ capture efficiency >99%) was required.

2. Pressurized Oxidation Method

• Acidic Oxidation: Under conditions of 190°C and 2.0 MPa, arsenopyrite decomposes into Fe₃⁺ and SO₄²⁻, converting arsenic into H₃AsO₃, increasing the gold leaching rate to 88%-95%.
• Limitations: Titanium reactors cost $30 million per 10,000 tons of production capacity, making them suitable only for large-scale mines.

3. Biooxidation Method

• Microbial Action: Acidithiobacillus ferrooxidans catalyzes the conversion of Fe²⁺ to Fe³⁺, dissolving the arsenopyrite coating and achieving an arsenic removal rate of >90%.
• Efficiency Improvement: Biooxidation of a difficult-to-treat gold ore (2.5 g/t Au, 8% As) increased the cyanide leaching rate from 25% to 92%, and the oxidation cycle was optimized to 7 days (with the addition of an Fe³⁺ catalyst).

四  Large-Scale Application and Technological Breakthroughs in Biooxidation Pretreatment

Due to its environmental advantages, biooxidation technology has achieved commercial application in specific scenarios:

1. Applicable Limits

• Ore Type: Sulfide-encapsulated gold ore (As 1%-15%), mineral dissociation degree <30%.
• Environmental Requirements: pH 1.0-1.5, temperature 35-45°C, slurry concentration 10%-15% (excessive concentration inhibits bacterial activity).

2. Typical Case Studies

• A gold mine in Liaoning, China: Two-stage biooxidation treatment of concentrate containing 15% arsenic achieved a gold leaching rate of 92% and an arsenic solidification rate >99% (producing scorodite FeAsO₄·2H₂O).
• A large mine in Peru: Daily processing of 2,000 tons of ore containing 20% ​​arsenic, achieving a slag cyanide recovery rate >90%, and a 30% reduction in overall costs compared to roasting.

3. Technical Bottlenecks and Breakthroughs

• Bacterial Acclimation: Arsenic-tolerant strains (such as Leptospirillum ferriphilum) can survive at As₃⁺ concentrations of 15 g/L, increasing oxidation rates by 25%.
•  Process Coupling: The combined biooxidation + CIL process can process ultra-low-grade ores (Au 0.8 g/t), achieving an overall recovery rate exceeding 85%.