Gold Leaching Process

Heap leaching (Heap leaching) is a low-cost, large-scale gold extraction process for low-grade gold ores. The core process involves constructing a seepage-proof heap, followed by spraying/drip leaching with a low-concentration cyanide solution. This dissolves the gold into cyanide complexes, which then enter the precious metal solution. The gold is then recovered through activated carbon adsorption-desorption electrolysis or zinc powder replacement, ultimately smelting it into gold ingots.

Core Principle and Applicable Scope

Principle: In an alkaline cyanide solution (pH 10–11), gold reacts with cyanide ions and oxygen to form soluble NaAu(CN)₂ complexes, which are then collected at the bottom of the heap via the liquid flow.

Applicable to: Oxidized ores, low-grade ores (0.3–1 g/t), tailings; not suitable for high-sulfur/high-arsenic/high-carbon refractory ores (pretreatment required).

Indicators: Leaching rate 70%–90%, cycle 3–18 months, cost per ton 30–80 RMB, low investment, large processing capacity. Core Process Flow

1. Ore Pretreatment

The gold ore is first crushed and screened to a suitable particle size (usually 10-30mm). Excessively fine ore will result in poor permeability of the ore bed, while excessively coarse ore will affect leaching efficiency. Some ore needs to be washed to remove impurities to prevent interference with the leaching reaction.

2. Lodging and Leaching

The pretreated ore is piled on an impermeable substrate, typically 5-10 meters high, ensuring structural stability and permeability. Leaching agents such as sodium cyanide or thiourea are evenly sprayed onto the surface of the pile using a spray or drip irrigation system, allowing the leaching agent to slowly penetrate the ore layer.

3. Leaching Reaction

The leaching agent reacts chemically with the gold in the ore, converting solid gold into soluble gold ions, forming a gold-bearing precious solution. This process requires control of pH (typically pH=10-11 for cyanide leaching), temperature, and leaching time (generally several days to several tens of days) to ensure efficient gold leaching.

4. Precious Metal Solution Collection and Adsorption

The gold-bearing precious metal solution is collected in a collection tank via a seepage-proof bottom pad and then pumped to the adsorption system. Utilizing the adsorption properties of activated carbon or ion exchange resin, gold ions in the solution are adsorbed onto a carrier, resulting in gold-loaded activated carbon/resin (lean solutions can be recycled for leaching).

5. Desorption and Electrolysis

The gold-loaded carrier undergoes desorption treatment, commonly using high-temperature, high-pressure sodium cyanide or thiourea solutions to desorb the gold from the carrier, forming a high-concentration gold-bearing desorption solution. This desorption solution is passed into an electrolytic cell, where electrolysis causes gold ions to be reduced and deposited at the cathode, yielding gold mud.

6. Refining and Purification

After washing and drying, the gold mud is purified through pyrometallurgical processes (smelting with flux) or hydrometallurgical processes to remove impurities such as silver and copper, ultimately yielding gold ingots (typically with a purity of 99.9% or higher).