Leach Chemistry & Application Rate
Oxygen acts as a critical oxidizing agent in the chemical reactions that liberate gold, copper, and other metals from ore.
The most common method for gold extraction is cyanidation, where a dilute sodium cyanide (NaCN) solution is applied to the ore. The chemical reaction, known as Elsner's Equation, shows that oxygen is a required reagent:
If oxygen (O₂) is not present, the reaction cannot proceed, and gold will not be dissolved into the solution, regardless of how much cyanide is applied. The same principle applies to copper leaching with acid and other hydrometallurgical processes.
The goal is to maintain unsaturated flow conditions within the heap to ensure oxygen is always present.
When the application rate of the leach solution exceeds the ore's ability to drain, the pore spaces within the ore become completely filled with liquid. This is called saturation. When the pores are full of water, there is no room for air, and the oxygen supply to the leaching reaction is cut off. This dramatically slows or stops mineral recovery.
Maximum leaching efficiency is achieved when the leach solution moves through the ore by means of capillary action. In this state, the solution coats the surfaces of the ore particles, but the pore spaces remain open to the atmosphere, allowing a continuous supply of oxygen. Drip irrigation is the key to achieving this state.
Dina's presentation called out the oxygen problem directly: too much surface-applied solution can saturate the ore. Controlled drip application keeps the leach solution moving by capillary action without cutting off air.
Wobbler / surface spray
Broad application can outrun ore infiltration, fill pore space with solution, and push oxygen out.
Max-Emitter / controlled drip
Slow application uses capillary action to wet the ore while preserving connected air paths for oxygen.
Schematic animation based on the Ore-Max sales presentation concepts.
Drip irrigation provides precise control over application rate, preventing saturation and maximizing air-to-ore contact.
Drip emitters apply solution at a slow, controlled rate (e.g., 2-8 liters per hour) that is typically well below the ore's infiltration capacity, preventing ponding and saturation.
Pressure-compensating emitters ensure every part of the heap receives the same application rate, preventing localized over-watering and dry spots.
By avoiding saturation, drip irrigation ensures that air-filled pores are always present throughout the ore stack, allowing oxygen to diffuse and fuel the leach reaction.
