Copper is a key resource in modern industry and society. However, copper is finite like all natural resources, and increasing demand for this material depletes global copper reserves. Recovering copper is a crucial strategy to keep up with demand. One approach is to reprocess mining tailings to extract the vital copper resources within.
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The Demand for Copper
The extraction of copper is a critical economic activity in the modern world. The properties of this metal make it essential for several industries.
Copper is widely used in the electronics and electrical industries due to its excellent electrical conductivity.
Its good corrosion resistance makes it an essential resource in the construction industry, and its superior thermal conductivity makes it ideal for constructing cooling and heating systems.
The demand for copper has accelerated over the twentieth century, and this trend is expected to continue. However, demand has exhausted large proportions of the natural reserves of this critical metal, and the global copper market is currently facing a supply deficit. If the mining industry continues along a business-as-usual trajectory, the global copper industry will likely face a supply crunch in the future.
Recovering Copper and Reprocessing Tailings
In recent years, the need for efficient recovery, recycling and reuse strategies for waste streams to address climate change, environmental damage, and supply deficits has become clear to researchers and governments. Several technological solutions have been developed, and governments and international bodies have enacted policies.
Mining operations produce vast amounts of tailings every year, and legacy dams contain billions of tons of recoverable resources. Tailings consist of rock particles, leftover chemicals and water.
Aside from valuable mineral resources that are difficult to recover, tailings ponds cause environmental damage due to the leaching of toxic chemicals into fragile ecosystems.
Previously, non-ferrous metals were relatively inexpensive, which was a primary reason for wasted resources: there was no economic incentive to recover valuable minerals and metals. Another reason was that recovery and reprocessing technologies lacked development.
Today, the supply deficit of copper, its high price, the need for environmental remediation and the maturity of reprocessing technologies have facilitated increased interest in recovering these resources from mine tailings.
However, reprocessing mine tailings is a complex endeavor as tailings' mineral and chemical content differ, and the presence of contaminants compounds the issue. For this reason, it is highly challenging to predict what the optimal reprocessing method needed will be.
Before resources such as copper are recovered for reprocessing, the mine tailings must be evaluated for viability. This is known as feasibility testing.
Feasibility testing starts with sample collection, and then samples are analyzed using compositional analysis and granulometric analysis methods, such as X-ray fluorescence. Finally, the copper content is enriched using equipment such as flotation cells and multi-gravity separators, and then the tailings composition is redetermined.
Several methods are appropriate for reprocessing mine tailings and recovering copper. These methods have been extensively explored in recent research.
Leaching methods are chemical processes that convert solid copper into liquid-phase copper ions, facilitating the extraction of metallic copper from the leaching solution. Acid leaching typically uses dilute sulfuric acid and has the advantage of high leaching rate, cost-effectiveness, and simple processing and operation. However, acid leaching is limited to simple copper oxide ore and has low leaching selectivity.
Ammonia leaching has high selectivity for metallic copper but is energy-intensive and requires complex operations. Other leaching methods suitable for metallic copper extraction and reprocessing are bacterial and electrochemical leaching.
Flotation methods are suitable for the reprocessing of low-grade copper tailings. A three-phase system (solid, liquid, gas) separates substances using chemical reagents. Particles attach to air bubbles, forming a concentrated foam on the surface of the flotation tank, and are recovered while tailings sink to the bottom. However, flotation methods are not always suitable for fine-grained particles commonly present in mine tailings. Another drawback to flotation methods is a large amount of reagent necessary for recovery.
Multi-gravity separators are a technology that can be used to separate fine and ultra-fine minerals from mine tailings and are suitable for copper reprocessing and recovery. They have already been successfully used to recover high-grade concentrates from low-grade tailings with high recovery rates.
The multi-gravity separator works on the principle of differences in specific gravity between particles. Different minerals or groups of minerals can be selectively recovered.
At least one specific gravity unit must exist between heavy and light particles to achieve effective separation. Several multi-gravity separators are available, from lab versions to full-scale industrial units. Ultrafine particles of 1 μm in size can be recovered using commercial multi-gravity separators.
A rapidly rotating drum, into which tailings slurry is introduced, provides the centrifugal force, increasing the separation efficiency. Forces acting on the particles can reach 15 g or more. Separation and recovery efficiency is much higher than conventional shaking tables.
Water is introduced into the system, which has the purpose of creating a film of liquid that can collect and transport the entrained light fraction and wash the grains before discharge.
As the world faces a critical supply deficit in copper, the need to recover valuable metallic copper from mine tailings is becoming more apparent to researchers, mining companies, and governments.
Moreover, the environmental damage and greenhouse gas emissions from mining operations facilitate the need for a more circular approach to resource extraction, recovery, and reuse.
Efficient and cost-effective reprocessing of copper is central to achieving sustainability in the copper industry.
References and Further Reading
Hann, D (2022) Copper tailings reprocessing [online] sciendo.com. Available at: https://www.sciendo.com/article/10.2478/rmzmag-2021-0002
Toovey, L (2011) Copper as a Critical Metal [online] streetwisereports.com. Available at: https://www.streetwisereports.com/article/2011/06/23/copper-as-a-critical-metal.html
Xinhai Metal Processing EPC (2020) Common Copper Tailings Reprocessing Methods [online] xinhaimining.com. Available at: https://www.xinhaimining.com/newo/998.html