Gold Bio-Heap Leaching Technology

1. Introduction

With the gradual depletion of easily processable gold resources, the development of refractory gold ores (e.g., carbonaceous Carlin-type gold ores) has become a global mining focus. Bio-heap leaching technology, which utilizes microorganisms to oxidize sulfide minerals and release encapsulated gold, offers advantages such as low cost, reduced energy consumption, and environmental friendliness, making it particularly suitable for low-grade and complex ores. However, the successful implementation of bio-heap leaching relies on the synergistic control of multiple parameters. Based on the research by Hu Jiehua et al., this paper explores the key optimization pathways from five dimensions: ore pretreatment, temperature, aeration, irrigation, and cycle management.

2. Ore Type and Pretreatment

2.1 Impact of Ore Characteristics on Leaching
The mineral composition and physical structure of ores directly affect microbial activity and leaching efficiency. Ores with high clay content impede solution penetration and gas transport, leading to oxygen deficiency and insufficient CO₂ in the heap, thereby inhibiting bacterial metabolism. Additionally, sulfur content must be balanced: too low (

2.2 Pretreatment Strategies
Before stacking, the microbial leachability of ores should be evaluated through acid consumption tests, sulfur content analysis, and particle size screening. For clay-rich ores, thin-layer heap leaching (1.5 m height) can improve permeability; for high-sulfur ores, heat distribution within the heap must be optimized to prevent local overheating and microbial inactivation.

3. Temperature Control

3.1 Temperature and Microbial Adaptation
Leaching microorganisms are classified by optimal growth temperatures:

·         Mesophiles (30–40℃): e.g., Acidithiobacillus ferrooxidans;

·         Moderate thermophiles (~50℃): e.g., Thermithiobacillus;

·         Hyperthermophiles (>65℃): e.g., extreme thermophilic archaea.

Studies by Halinen et al. revealed that temperature fluctuations significantly alter dominant microbial species. For instance, Acidithiobacillus ferrooxidans dominates at 7℃, while Thermithiobacillus becomes prevalent at 50℃. Thus, maintaining heap temperature within the target microbial range is critical.

3.2 Temperature Regulation Techniques
In tropical regions, heat generated by sulfide oxidation can be balanced by adjusting irrigation flow rate (G₁) and aeration rate (Gₐ). An appropriate Gₐ/G₁ ratio prevents excessive heat loss at the heap’s top or bottom. For example, at Quebrada Blanca Copper Mine in Chile, where winter temperatures drop to -10℃, microbial activity was sustained by heating recycled raffinate to 28℃ and covering the heap with plastic film.

4. Aeration Optimization

4.1 Oxygen and Carbon Dioxide Supply
Chemolithotrophic leaching bacteria rely on O₂ and CO₂ for metabolism. Gas transport rates correlate positively with irrigation speed and temperature but negatively with ore particle size. Excessive heap height (>8 m) causes hypoxia in central zones, necessitating forced aeration via bottom-embedded pipes. Thin-layer heaps (1.5 m height) enhance gas diffusion, suitable for low-permeability ores.

4.2 Aeration Strategies
Lizama’s research indicates that increasing irrigation liquid temperature improves oxygen mass transfer efficiency. Additionally, intermittent aeration combined with rest periods in irrigation enhances pore oxygen levels, accelerating sulfide oxidation.

5. Irrigation System Design

5.1 Irrigation Intensity and Rest Cycles
Drip irrigation intensity is typically 10–15 L/m²·h. Rest cycles (e.g., 12 hours on, 12 hours off) promote solution penetration and bacterial proliferation. Increasing intensity to 20 L/m²·h during the mid-leaching phase enhances microbe-mineral contact, while reducing intensity in later stages saves energy.

5.2 Dynamic Adjustment
Irrigation parameters should be flexibly adjusted across leaching phases:

·         Initial phase: Low intensity to facilitate bacterial colonization;

·         Mid-phase: High intensity to accelerate oxidation;

·         Late phase: Reduced frequency to lower operational costs.

6. Leaching Cycle Management

Bio-heap leaching cycles typically span months to years. Optimizing the aforementioned parameters can shorten cycles and improve recovery rates. For instance, controlling sulfur content at 2%–5%, heap height ≤6 m, and implementing gradient irrigation systems can increase gold recovery rates to over 75%.

7. Conclusion

The industrial application of bio-heap leaching requires comprehensive consideration of ore characteristics, microbial adaptability, and synergistic process parameters. By precisely controlling temperature, aeration, and irrigation systems, combined with case experience and technological innovation, the economic efficiency and environmental sustainability of refractory gold ores can be significantly enhanced. Future research should focus on high-temperature microbial consortia and the development of intelligent monitoring systems.