Gold mining, while a lucrative industry, has long been associated with significant environmental concerns, especially in the extraction and processing phases. However, gravity separation is emerging as an environmentally friendly and cost-effective alternative to traditional chemical methods in gold processing. This technique, which has been used for centuries in various industries, offers a more sustainable approach by eliminating the need for harmful chemicals and reducing the environmental footprint of mining operations.
A Sustainable Alternative
Gravity separation relies on the natural physical properties of materials, particularly their specific gravities — the ratio of their density to the density of water. Gold, with a specific gravity of 19.3, is much denser than most host rocks, which typically have a specific gravity between 2.8 and 4.0. By utilizing this difference, gravity separation methods can efficiently isolate gold from ore without the need for chemical agents.
For resource companies fortunate enough to extract gravity-recoverable gold, the process offers significant environmental and economic benefits. Water is used in the separation process and can be recycled, while the tailings left behind are benign, allowing them to be safely stored as non-toxic sand piles. This stands in stark contrast to traditional gold extraction methods, which often involve the use of toxic chemicals like cyanide, mercury, and arsenic, resulting in hazardous waste.
How Gravity Separation Works
The gravity separation process begins with crushing the ore, followed by sorting to separate waste rock from the gold-bearing quartz. The gold is then concentrated using a centrifuge, followed by further separation on a wet, oscillating table. The final step involves melting the concentrated gold. This technique, while mechanical, is simple and cost-effective, requiring minimal energy input compared to chemical-based methods.
“There are no downsides. The process has a low environmental footprint, and it’s simple and cheap to undertake,” says Roger Jackson, executive chairman of Vertex Minerals (ASX:VTX), an Australian gold exploration and production company. Vertex is integrating a gravity processing plant near its Reward gold mine in New South Wales, which is set to begin production in early 2025. The project aims to produce one of Australia’s highest-grade, most environmentally responsible gold.
Advantages Over Traditional Methods
Traditional gold mining methods generate substantial waste, including arsenic, lead, mercury, cyanide, and acid, with an estimated 180 million tonnes of dangerous waste produced annually. In contrast, gravity separation requires no harmful chemicals and reuses water. While there may be some low-sulfide residual material, the acidity is minimal, and the process uses little energy. Additionally, rock waste can be returned underground as filler, further reducing environmental impact.
“Gravity plants are considerably simpler and cheaper than other gold processing plants,” Jackson adds. “This process not only improves recovery rates and operational efficiency but also enhances cost-effectiveness.”
Vertex’s New Gravity Plant
Vertex Minerals is installing a refurbished 110,000-tonne-per-annum (ktpa) Gekko gravity gold plant adjacent to its Reward gold mine. This plant, part of the company’s Hill End gold project, is expected to reduce capital expenditures by AU$4 million. The integration of this gravity plant will streamline production, increasing throughput from 30,000 tonnes to 120,000 tonnes per annum, while also lowering operational costs and improving cash flow.
More importantly, the project aligns with industry trends toward more sustainable mining practices. By adopting gravity processing, Vertex can accelerate production timelines and operate with lower environmental impact, positioning itself as a leader in eco-conscious gold mining.
Broader Industry Adoption
Vertex is not alone in recognizing the potential of gravity separation. Other companies are also exploring its use. Cobalt Blue Holdings (ASX:COB) began testing gravity separation techniques in 2022 at its Broken Hill Cobalt project in New South Wales, focusing on the separation of cobalt-pyrite ores.
In Western Australia, Allup Silica (ASX:APS) plans to implement gravity separation at its McLaren Mineral Sands project to extract ilmenite, zirconium, and titanium minerals. Similarly, the Storm project in Nunavut, Canada, is incorporating ore sorting and wet jigging, another gravity-based separation method, as part of its copper mining operations in partnership with Aston Bay Holdings and American West Metals.
A Greener Future for Mining
As the mining industry continues to face increasing pressure to adopt more environmentally responsible practices, gravity separation stands out as a promising solution. Its cost-effectiveness, efficiency, and minimal environmental impact make it an attractive alternative for resource companies seeking to balance profitability with sustainability. As more companies implement gravity-based technologies, the future of gold mining may be greener than ever before.
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