Using Supercritical CO2 for Selective Gold Recovery in Refractory Ores

Using Supercritical CO2 for Selective Gold Recovery in Refractory Ores

Gold recovery from refractory ores presents a significant challenge in the mining industry due to the encapsulation of gold particles within complex mineral structures. Traditional methods such as cyanidation, though effective, pose environmental and health risks. Recently, supercritical carbon dioxide (scCO2) has emerged as a promising alternative for the selective recovery of gold, offering advantages in efficiency and sustainability.

Understanding Supercritical CO2

Supercritical CO2 is carbon dioxide that is held at or above its critical temperature and pressure (31.1°C and 73.8 atm, respectively). In this state, CO2 exhibits unique properties that allow it to operate as both a gas and a liquid, making it an effective solvent for extracting metals and other compounds.

The ability of scCO2 to dissolve non-polar compounds and its low viscosity enables superior penetration into the porous structures of refractory ores, facilitating the extraction process. This property is akin to using a sponge to absorb liquid, where the sponge (scCO2) fills the voids in the mineral matrix, capturing the desired elements.

Mechanisms of Gold Recovery

The key to using supercritical CO2 for gold recovery lies in its chemistry and the methodology of extraction. Several processes can enhance the efficacy of scCO2, including:

• Carbon Dioxide Leaching: In this process, scCO2 selectively dissolves gold from the ore matrix when used alongside co-solvents, such as sodium carbonate or a suitable ionic liquid, enhancing solubility and separation.
• Particle Size Reduction: Reducing ore size increases surface area exposure, which improves scCO2 penetration and enhances gold recovery rates. Studies have shown that optimum particle sizes can significantly influence extraction efficiency.
• Temperature and Pressure Control: Adjusting the temperature and pressure of the scCO2 not only affects its density but also influences solvation dynamics. Fine-tuning these parameters can lead to improved selectivity for gold recovery.

Case Studies and Real-World Applications

Several ongoing projects have effectively implemented scCO2 for gold extraction, showcasing its potential across the mining sector:

• Australian Mining Projects: Several Australian mining companies have experimented with scCO2 for extracting gold from low-grade and refractory ores, reporting up to a 90% recovery rate. These initiatives emphasize the environmental benefits, including reduced use of toxic reagents.
• Academic Research: Universities worldwide are conducting research on the theoretical frameworks and practical applications of scCO2 in metal recovery, leading to innovative models that could redefine extraction processes in the future.

Environmental and Economic Advantages

Employing scCO2 for gold recovery provides substantial advantages over traditional methods:

• Environmental Impact: scCO2 is non-toxic and non-flammable, significantly reducing the ecological footprint of the extraction process. Its ability to function at lower energy requirements also contributes to a decreased carbon footprint.
• Diminished Regulatory Burdens: Regulations surrounding the use of cyanide and other hazardous agents are stringent. Using scCO2 enables operators to sidestep complex regulatory frameworks, simplifying compliance efforts.
• Economic Viability: Although the initial investment in scCO2 equipment may be higher, the lower operational costs, combined with higher recovery rates, can lead to increased profitability over time.

Challenges and Future Directions

Despite its advantages, several challenges exist in fully adopting scCO2 for gold recovery:

• Economic Feasibility: The cost of setting up scCO2 extraction systems can be a barrier for small-scale operations. Ongoing research into cost reduction is critical.
• Technical Limits: The solubility of gold in scCO2 can be low under certain conditions, necessitating the use of additives, which can complicate the extraction process.

Looking ahead, improvements in scCO2 technology, alongside innovations in process optimization and additive formulations, will likely enhance the viability of supercritical CO2 for use in selective gold recovery.

Conclusion

Using supercritical CO2 for selective gold recovery from refractory ores is a transformative approach that combines sustainability with efficiency. As advancements in technology and research continue, scCO2 stands poised to redefine gold extraction in an eco-friendly manner. Industry stakeholders should actively monitor developments in this field, as embracing advanced recovery methods like scCO2 could lead to improved outcomes for both the environment and their profitability.