Tailings, or the material remaining after a valuable component has been separated from the gangue, have long plagued the mining industry with management costs, liability risks, and disposal challenges.
Due to their toxicity, tailings pose a number of risks if not properly managed. Furthermore, the mass quantities in which they are produced puts additional pressure on managing such waste.
Although historically tailings have been considered a waste, decreasing ore grades, improved technologies, and a growing focus around sustainability are causing some companies to consider tapping into the potential value tailings contain, or at least alleviating some of the challenges they present.
Tailings: The Risk
In order to extract the valuable component, be it gold, copper, uranium, or otherwise, mined ore undergoes several processing steps, often involving additives and/or chemicals. While this allows the target component to be separated out, it causes the gangue to be contaminated. Gangue material is often also contaminated as a result of reacting with oxygen upon removal from the ground, causing other undesirable materials to form.
As such, tailings composition differs based on the target material and the method of processing. However, despite this diversity, most tailings present similar environmental risks as a result of their toxicity…
The failure of tailings ponds, one of the most common tailings storage facility (TSF) types, is well documented and has the potential to cause catastrophic and irreparable damage to the surrounding area and ecosystems.
Tailings deposited into dams are in the form of a slurry. In 1998, a tailings dam failed at the Los Frailes zinc mine in Spain, causing more than one billion gallons of acidic, heavy metal-laden sludge to spill into the surrounding area, eventually making its way into the Guadiamar River. The spill decimated the area, resulting in massive wildlife die-offs, water and soil contamination, and other consequences that would take years to bring back to equilibrium.
In 2014, a tailings dam at the Mount Polley copper and gold mine in British Columbia failed as a result of an unstable foundation, sending 24 million cubic metres of slurry into the surrounding waterways. A year later, the Samarco mine’s tailings dam failed as a result of seismic activity combined with structural defects and other issues. The flood of toxic sludge was devastating.
The failure of tailings dams is not unusual; experts estimate that a tailings dam failure occurs roughly every eight months.
Even a well-managed tailings facility can pose risks in the way of contaminated dust (in the case of dry tailings), radioactivity, leaching, and acid rock drainage. For these reasons, tailings disposal and management has become an increasing concern in the ongoing quest for a more sustainable future, pushing miners to look for better alternatives.
Tailings: A Neglected Resource
In addition to the risks that tailings can pose, a number of other factors such as easily accessible material, reduced risk, and more, are pushing the demand for improved management and reuse/reclamation of tailings.
Tailings Retreatment
Tailings have long been considered a waste, but they still contain a small amount of the targeted materials. Inferior extraction techniques, combined with plenty of available high ore grade resources have historically made processing lower grade ores and tailings uneconomical and a low priority.
However, as high ore grades become extinct and technology around extraction improves, tailings are becoming an increasingly attractive resource.
Sibanye-Stillwater has drawn global attention for their West Rand Tailings Retreatment Project (WRTRP) in South Africa. Through a combination of tailings storage facilities, the company estimates there to be 6.2 Moz of gold and 97.2 Mlb of uranium. VP of the project, Grant Stuart, commented to Mining Weekly:
“There is significant potential for a vibrant tailings retreatment industry, given the vast quantities of tailings scattered across the ‘Golden Arc’, stretching from Johannesburg to Welkom.”
Pan African Resources is also working on a gold tailings retreatment project in South Africa. The project intends to retreat old tailings at a rate of one million tonnes per month and aims to recover about 688,000 ounces of gold from the combined tailings deposits over the life of the project.
Metals X Limited also recently announced that the updated Definitive Feasibility Study (DFS) for their Renison Tailings Retreatment Project estimates it to be a lucrative endeavor with high margins. The company projects that they will be able to recover around 5,400 tonnes of tin and 2,200 tonnes of copper annually.
Tailings Retreatment through Heap Leaching
The retreatment of tailings varies depending on the source of tailings and the material(s) to be recovered.
The heap leaching and SX-EW processes have been key advancements in the ability to treat tailings; heap leaching, in which ore is agglomerated and stacked on a heap and then irrigated with a leachate, is ideal for low-grade ores. Heap leaching offers a number of attractive benefits, including:
- Reduced operating costs
- Lower capital costs
- Simple design and operation
- And more…
Combined with advancements in the solvent extraction – electrowinning (SX-EW, or L-SX-EW) process, the two processes allow for a highly effective, cost efficient extraction and separation of the target material from low-grade ores.
Image: Agglomeration drums used in the heap leaching process.
Other tailings retreatment options include flotation and smelting, among others.
Tailings Reuse
While most work has focused around the recovery of valuable components from tailings, there is also some interest in their reuse for applications outside of the mining industry.
Primarily, tailings are being investigated for use in construction materials such as concrete, mortar, and the like. Such applications would not only relieve the burden of managing massive amounts of tailings, but would also reduce the need to mine natural aggregates, which requires substantial energy.
Conclusion
The tailings retreatment industry looks to potentially hold significant value for the mining industry. In addition to relieving them of the burden of managing massive amounts of waste, the retreatment of tailings would also reduce risks to the environment and promote a more sustainable industry overall. The heap leaching and SX-EW processes combined look to be especially promising for tailings retreatment projects.
FEECO provides robust agglomeration drums and material handling equipment for use in the heap leaching process; some of the world’s largest and most environmentally advanced mines rely on FEECO for our heavy-duty agglomeration drums. For more information on our capabilities within the mining industry, contact us today!