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Unlocking hidden reserves
Most gold occurs in tiny particles locked within rocks. These gold concentrations are so low that it typically takes about one ton of ore – usually brown, iron-stained rock – to yield just a few grams of gold.
Once this ore has been excavated from the mine, it is crushed to create small particles. The next step entails leaching the ore particles to recover the gold. Water and cyanide are typically added to the ore at this stage to transfer the gold from the solid phase to a water-based gold-cyanide complex. Oxygen is needed for the formation of this complex. However, side-reactions of the cyanide can occur in refractory ores, compromising process efficiency. In addition, cyanide is an expensive and hazardous chemical and its use is restricted or illegal in many parts of the world.
Adding value to the recovery process with GOLDOX®
Linde has developed an innovative dissolved gas management solution to reduce the overall requirement for cyanide and increase the gold leach rate by raising dissolved oxygen levels. GOLDOX® not also oxidizes the gold itself (to create a water-soluble complex), it also oxidizes and deactivates other compounds, such as iron and copper salts, which would otherwise also compete with the available cyanide. It thus reduces the cyanide cost substantially, while simultaneously reducing the waste cyanide load to be destroyed. In some cases, GOLDOX raises the percent of gold recovered by reducing the volume of cyanide lost to side reactions. This, in turn, increases the rate of complex formation between gold and cyanide.
Leaching and beyond
Looking beyond the pre-oxidation and leaching steps, oxygen can optimize productivity and reduce costs by fine-tuning many other steps such as ore roasting, high-pressure pre-oxidation, atmospheric pressure pre-oxidation, cyanide destruction and waste(water) treatment. In some cases, carbon dioxide can be used to enhance dissolved gas floatation upstream of the hydrometallurgy (hydromet) process.
Gas-enabled applications are also found in hydromet applications for the recovery of copper, lithium and other metals. For example, carbon dioxide can be used to recover and purify both lead and lithium.
Linde works closely with its customers to evaluate the ore, the current process flow and the optimization potential of oxygen technologies. Once a customer decides in favor of water-based hydrometallurgy, Linde’s experts then design the best injection, dissolution and monitoring system to maintain consistent oxygen levels and optimize process efficiency.
Linde’s offering at a glance
- Engineering evaluation and consulting
- Gas injection and dissolution equipment
- Dynamic dissolved oxygen (DO) measurement and control technology
- Gas supply scheme (bulk or on site)
- Ongoing training and maintenance support