Main Industrial Processes of Sodium Cyanide in Gold Extraction

• Heap Leaching
  

Procedure:

1. Agglomeration & stacking – Crushed ore (to 30–50 mm) is piled on an impervious pad.

2. Spraying – A dilute cyanide solution (typically 0.03%–0.2% NaCN) is sprinkled evenly over the heap.

3. Collection & recovery – The gold‑bearing solution (pregnant leach solution) percolates through the heap and is collected at the bottom. Gold is then recovered via activated carbon adsorption or zinc dust precipitation.

Characteristics: This method is simple to operate, but leaching takes weeks or even months. Gold recovery is usually 60%–70%.

• Agitation Leaching (Tank Leaching)

Procedure:

1. Fine grinding – Ore is milled to a very fine size (e.g., 90% passing 0.074 mm).

2. Agitation leaching – The ground ore is mixed with water and cyanide solution in agitated tanks, with continuous aeration, at ambient temperature for 24 hours or more.

3. Solid‑liquid separation & gold recovery – After leaching, the pregnant solution is separated from the solids, and gold is recovered, typically by zinc precipitation (Merrill‑Crowe process).

Characteristics: This is widely applied method, suitable for higher‑grade and finely ground ores, offering higher gold recoveries.