Efficient Gold Extraction from Low-Grade Gold Ore Using Heap Leaching

 Core Definition and Application Scenarios of the Heap Leaching Process

The gold ore heap leaching process is the mainstream gold extraction technology for low-grade gold ores with grades ranging from 0.1 to 0.3 g/t. It involves crushing the ore and piling it into mound-shaped heaps, then using cyanide solutions (such as sodium cyanide) to spray and leach out the gold elements, and finally recovering elemental gold through adsorption, precipitation, and other processes. This process offers advantages such as low cost (30%–50% energy savings compared to tank leaching), strong adaptability (capable of processing difficult-to-process oxidised ore), and ease of operation. It accounts for over 80% of the domestic market share for low-grade gold ore processing, particularly suited for large-scale open-pit gold mines. 

 Comprehensive Analysis of the Heap Leaching Process 

1. Pre-treatment Stage: Ore Crushing and Heap Construction 

- Crushing and Screening: The ore is crushed to a particle size of 20–40 mesh (0.42–0.85 mm) to ensure uniform penetration of the cyanide solution. Practice at the Longnan Gold Mine in Gansu Province has shown that a particle size of 20 mesh can increase leaching efficiency by over 20%. 

- Heap Construction: Construct the ore heap on a waterproof liner (HDPE membrane + clay), typically 3–10 metres in height. Install a porous drainage pipe network at the base to ensure over 95% leachate collection efficiency.

2. Leaching Stage: Cyanide Spraying and Gold Dissolution 

- Spraying system: Drip irrigation or spray nozzle devices are used to uniformly spray cyanide solution (concentration 0.05%–0.1%) at a flow rate of 0.05–0.1 L/(m²·h). The leaching cycle generally lasts 45–90 days. Data from the Homestake Mine in the United States shows that optimising the spraying frequency can increase gold leaching efficiency from 75% to 82%. 

- Chemical Reaction: Cyanide forms soluble complexes [Au(CN)₂]⁻ with gold, which migrate with the leaching solution to the bottom of the heap, collected in a sump and processed in subsequent stages.

3. Gold Recovery and Tailings Treatment

- Gold Recovery: Gold is extracted from the leaching solution using activated carbon adsorption or zinc powder replacement methods, with activated carbon adsorption achieving efficiency of over 99%. 

- Environmental protection measures: Tailings from heap leaching contain cyanide (50–200 mg/kg) and heavy metals, which must be treated via microbial leaching (such as the composite microbial consortium technology used in this study) or chemical oxidation to ensure compliant discharge.