Gold Ore Heap Leaching Process Characteristics
- Introduction
Gold heap leaching is an extractive metallurgical process designed to recover gold from low
grade ores through percolation of leaching solutions (typically cyanide-based) through
stacked ore. This method is characterized by its simple operation, low capital/operating costs,
and suitability for marginal ore deposits. The process involves crushing, stacking, chemical
leaching, and gold recovery from pregnant solutions, making it particularly valuable for
small-scale operations and remote locations.
- Main Application
Heap leaching is a practical, low-tech solution for gold extraction, balancing economic
viability with environmental stewardship, especially in resource-limited settings.
Heap leaching is primarily applied to:
Low-grade gold ores (0.5–2 g/t Au) where conventional methods are uneconomical.
Oxidized or free-milling ores with high permeability.
Waste rock or tailings reprocessing to recover residual gold.
Small-scale or artisanal mining due to minimal infrastructure requirements.
Arid regions where water availability is limited (closed-loop systems).
Key Advantages:
- Low capital and operating costs (simple infrastructure, minimal energy use).
- Scalability (adaptable to ore volumes from thousands to millions of tons).
- Fast deployment (quick construction and production startup).
Environmental considerations: Requires strict controls to prevent cyanide contamination.3. Detailed Introduction ofthe Process Flow
(1) Ore Preparation
Crushing: Ore is crushed to 10–25 mm to enhance leachability.
Agglomeration (if needed): Fine particles are bonded with cement/lime to improve
permeability.
Pre-treatment: For refractory ores, oxidation (e.g., bioleaching) may precede stacking.
(2) Heap Construction
Pad Design:
Base liner (HDPE geomembrane + clay) to prevent solution leakage.
Drainage system (pipes/gravel layer) to collect pregnant solution.
Stacking: Ore is stacked in 5–10 m high lifts using conveyor systems or trucks.
(3) Leaching Solution Application
Solution Preparation: Sodium cyanide (NaCN, 100–500 ppm) + lime (pH 10.5–11) to
dissolve gold.
Irrigation:
Drip emitters/sprinklers evenly distribute solution over the heap.
Application rate: 5–20 L/hr/m², adjusted for ore permeability.
(4) Gold Recovery from Pregnant Solution
Collection: Pregnant solution (Au-bearing) drains to a pond via the pad’s drainage
system.
Adsorption:
Carbon-in-Column (CIC): Solution passes through activated carbon columns to
adsorb gold.
Zinc Precipitation (Merrill-Crowe): Alternative for high-grade solutions.
Electrowinning: Gold is stripped from carbon and electroplated onto cathodes.
(5) Heap Rinsing & Closure
Rinsing: Post-leaching, heaps are washed with water to remove residual cyanide.
Detoxification:
Cyanide destruction (H₂O₂/SO₂) to meet environmental standards.
Neutralization of spent ore with lime.
Closure: Heap is capped and monitored for long-term stability.