To convert gold sulfide to gold oxide before feeding it into the cyanide gold dissolution process, the two most commonly used methods are oxidation roasting and pressure oxidation (POX). The processes and their appropriate temperature ranges are as follows:

1. Oxidation Roasting

• Process:

o Gold sulfide concentrate is heated in a roaster with a controlled supply of air or oxygen.

o Sulfides are oxidized to oxides, and sulfur is released as sulfur dioxide gas (SO₂).

o This leaves gold in an oxidized, cyanide-soluble form.

• Temperature: Typically between 500°C and 750°C.

o Below 500°C: Incomplete oxidation of sulfides.

o Above 750°C: Risk of gold loss through volatilization or encapsulation in other minerals.

2. Pressure Oxidation (POX)

• Process:

o Gold sulfide concentrate is treated in an autoclave under high pressure and temperature in the presence of oxygen and water.

o Sulfides are converted to sulfuric acid or elemental sulfur, leaving behind gold oxides.

o This method minimizes emissions (e.g., SO₂) and achieves nearly complete oxidation.

• Temperature: Typically 180°C to 225°C.

o Operates under pressures of 300–700 kPa (absolute pressure).

Key Differences:

• Oxidation roasting requires higher temperatures and releases SO₂ gas, requiring scrubbing systems for environmental compliance.

• Pressure oxidation (POX) operates at lower temperatures but requires high-pressure equipment, making it more capital-intensive but environmentally cleaner. Both methods aim to liberate gold from its sulfide matrix, enabling efficient cyanide dissolution during subsequent leaching.