The Industrial Journey from Ore to Gold

As the core extraction technology in modern gold mining, the cyanidation process achieves efficient gold recovery through stages including cyanide dissolution, activated carbon adsorption, and electrolytic refining. Depending on ore characteristics and production scale, it primarily encompasses three process routes: Carbon-in-Pulp (CIP), Carbon-in-Leach (CIL), and heap leaching.

I. Ore Pre-treatment – Laying the Foundation for Leaching

The pre-treatment stage directly determines subsequent leaching efficiency and comprises three key steps:

Crushing and Grinding

A three-stage crushing system (‘jaw crusher + cone crusher + ball mill’) reduces raw ore from 500–1000 mm to -200 mesh, with ore yield controlled at 80–95%. Special attention must be paid to avoid over-grinding, which could impair pulp fluidity.

Alkali Pretreatment

Lime (1–3 kg/tonne of ore) is added to adjust the pulp pH to 9–11. This prevents the hydrolysis of cyanide to produce highly toxic HCN gas while precipitating interfering ions such as Fe²⁺ and Cu²⁺. Pretreatment duration is 30–60 minutes at a pulp concentration of 40–45%.

Special Ore Treatment

High-sulphur ores (S > 5%) require prior desulphurisation via flotation or roasting (600–700°C). Arsenic-bearing ores (As > 0.5%) undergo pressurised oxidation (150–200°C) or bio-oxidation to disrupt arsenic mineral encapsulation of gold particles.

II. Leaching Process – The Critical Stage for Gold Dissolution

Agitation Leaching

Employ 6–10 serial agitation tanks with key parameters including:

Cyanide concentration: 0.03%–0.1%

Dissolved oxygen: ≥8mg/L

Leaching time: 24–72 hours

Slurry concentration: 40%-50%

Heap Leaching Process

Suitable for low-grade ores (gold grade<1g/t), costing only one-third of agitated leaching but with relatively lower recovery rates (70%-85%). Percolation leaching is applicable for small-scale mines, achieving recovery rates of 80%-90%.

III. Gold Recovery System – Transformation from Solution to Metal

Zinc Powder Replacement Method

Traditional process: Obtain leachate (gold content 0.5–5 g/m³) via continuous countercurrent washing. Add zinc powder and lead nitrate catalyst to replace gold into gold slime (grade 50%–70%) at pH 10–11.

Activated Carbon Adsorption Method

CIP Process: Gold adsorbed onto activated carbon post-leaching

CIL Process: Simultaneous leaching and adsorption, reducing processing time by 15%-20%

Gold-loaded carbon desorbed via the Zadra method yields crude gold with 95%-98% purity through electrolysis.

IV. Refining and Environmental Management

Refining and Purification

Crude gold undergoes impurity removal with nitric acid and acid washing with hydrochloric acid. It is then smelted with borax at 1100–1200°C to produce gold ingots with 99.99% purity.

Environmental Treatment

Cyanide is oxidatively decomposed using sodium hypochlorite, ensuring wastewater cyanide concentrations remain below 0.5 mg/L. Heavy metals are precipitated via lime and sodium sulphide. Tailings are resource-recycled through mine backfilling and recovery of valuable elements.

Through continuous optimisation and innovation, the cyanide gold extraction process enhances environmental sustainability while maintaining economic viability, providing reliable technical support for the gold industry's sustainable development.