Tailings, refuse, mine dumps, slickens, culm dumps, slimes – by whatever name, mine ore waste and its storage and handling has become a major environmental and safety issue on the agenda of mining companies, governments and environmental groups.
For one 18kt gold wedding band, approximately eight tonnes of waste is generated. Consider how much waste must be produced to manufacture components for a mobile phone, the car or tram you take to work or the size of a single wind turbine? Bearing in mind the global population’s increasing reliance on consumer goods coupled with lower ore grades, the annual volume of tailings produced is staggering.
“When you look at a modern mining operation, it can appear more like a waste handling facility than a mine, with more than 90 per cent of the material generally disposed of in the form of tailings. The safe management and storage of tailings is paramount for any mine operation,” says Job Kruyswijk, Tailings Process Specialist for Weir Minerals.
The traditional means of tailings disposal is typically an impound method, often stored in a constructed dam in diluted form. This form of waste storage poses a number of concerns, the biggest of which is safety. Additionally, tailings dams occupy vast landmass, require large quantities of water to dilute the tailings for storage, and often have a limited capacity.
The toxic nature of tailings also requires extensive preventative measures to mitigate risk, including employee safety, leaks into local ecosystems and waterways and minimising the potential of a dam collapse.
Amid intensifying societal concerns relating to the safety of communities and fragility of ecosystems, increasingly necessary and stringent social and environmental regulations follow suit.
“The mining industry has changed significantly over the last few years, and the social license to continue to operate has become increasingly important,” says John Abbott, Global Product Manager for Tailings at Weir Minerals.
“It’s evident there is a drive within the mining industry to investigate doing things differently.”
Under this emerging scrutiny, the mining industry is under pressure to implement responsible management of tailings, as well as address the environmental impact left on the surrounding areas. ‘Green mining’ initiatives – Natural Resources Canada (2015) which “targets the development of innovative energy-efficient technologies required for mining to leave behind only clean water, rehabilitated landscapes and healthy ecosystems” – are expected globally.
While the traditional means of mining and waste management may be in crisis, it’s also an exciting time of innovation for those open to alternative methods such as backfill, tailings as a resource and tailings re-mining.
“Constantly redefining innovation is critical to informing best practice,” says Nils Steward, General Manager at the Weir Technical Centre.
“At the Weir Technical Centre (WTC), we have the pilot plant capabilities to simulate what exists onsite. From there, we also investigate innovative new methods for tailings handling, reuse and disposal.”
The first of these alternative uses is the existing, yet still under-utilised practice of using tailings for backfill.
While both cemented paste backfills (CPB) and hydraulic fills are the two most established forms of backfill, paste backfill offers the most advantage. With substantial reductions in both the volume of tailings left to store and rehabilitation costs, an estimated 60 to 80 per cent of the tailings’ processed water can be recovered prior to backfilling, while the structural stability once filled offers a safer workspace for employees to continue.
In this way, utilising the mine’s own tailings for backfill is not only a resource to the mine but it also reduces the need to store it in a storage facility.
Tailings as a resource
Another productive means of utilising tailings is to create more sustainable by-products. This includes everything from commercial shotcrete and concrete products for self-sustaining uses such as mine roads, brick and tile manufacture, insulation, or even foamed products.
Tailings as a resource has further positive implications for the environment – by recycling existing ‘waste’ to manufacture products, less tailings requires storage, and, as in the case of backfill, less water is trapped within the tailings.
“While de-watered tailings don’t necessarily decrease the industry’s footprint, they do produce a more stable product with less water utilisation, which in arid areas is environmentally-sound practice. It also means that you have more water to put back into your process,” Mr Steward explains.
“At Weir Minerals, the future of our work is to be able to thicken tailings sufficiently so that we can dispose of it as landforms. You can imagine the difference continuous, rapid landforms will have on rehabilitation – turning waste into a usable space.”
Finally, there is the option to remine legacy tailings. This is possible through using new techniques to recover more valuable minerals, as is currently being achieved in Australia’s Northern Territory gold mines.
Meanwhile, remining old tailings for metals that were previously ignored or discarded, like lithium – a 21st century golden-child in the renewable energy boom – to fund our technologically-driven world, turns ‘waste’ into a new treasure trove. As Job Kruyswijk explains, “if you start to look at tailings as having value, all of a sudden you are no longer a waste management facility but managing something of value and for the first time, old tailings suddenly become a resource”.
By utilising tailings as a material with value, as opposed to waste, customers are able to extract ‘treasure from trash’, reducing the need for a whole new mine site to mine those minerals.
In the face of new challenges and a changing mining landscape, the collapse of tailings dams demonstrates that safety cannot be compromised and new technology must be considered.
As with any operational decisions, it is important to understand the advantages and disadvantages of the various options available to determine what solution works best for your unique business. Thankfully, the authorities on the topic of tailings do the research for you.
“With the continual research and development we do in this field, a priority for us is working towards an innovative way to help the industry through a safer disposal of tailings, while also reducing the impact on the environment,” states Mr Abbott.
1. Assuming 18kt, 10g, with 1g/tonne gold.
2. Natural Resources Canada Green Mining Initiative program descriptor as found at www.nrcan.gc.ca
|Closing the loop on tailings|