Shear pressure to improve mine tailings management
New technology being developed at the University of Melbourne offers safer storage of mining tailings, with improved recovery of valuable minerals, chemicals and water.
The storage of waste tailings is an ongoing issue for the mining industry that jeopardises its fundamental social licence to operate. Tailings are commonly held in potentially toxic suspensions in dams. The failure of these dams in the past has had catastrophic impacts on the environment and local communities, with large fines for mine operators.
The tailings issue continues to grow in size, as more minerals are mined from lower grade ores and more tailings are produced.
Researchers at the University of Melbourne have put a new spin on existing technology to develop a safer and more sustainable way to treat and store tailings. They have created high-pressure dewatering rolls, adapted from the widely used high pressure grinding rolls.
Lead researcher Dr Anthony Stickland says that rather than crushing rock, two independently driven semi-permeable rollers use a combination of vacuum, high pressure and shear to filter liquids from tailings slurries.
Dissolved minerals, processing chemicals and water can be reclaimed from the liquid for reuse, while the solids are consolidated to high enough concentrations to be stored more safely in mounds or stacks rather than in dams.
This approach also addresses the increasing fine size of particles in tailings, which is an emerging issue for the mining sector.
As ore quality in mines declines, the ore may be ground more finely to extract as much of the sought-after minerals as possible, Dr Stickland explains. The finer the particles, the more difficult they are to separate them from liquids using existing pressure and filtration technologies.
A laboratory-scale prototype has already provided proof-of-concept for the high-pressure dewatering rolls, with an initial focus on fibrous pulps used in papermaking and recycling. The results of these initial trials, published in Chemical Engineering Science in 2019, demonstrate that the dewatering rolls reach comparable concentrations to existing high-pressure devices for a range of suspensions and that shear improves dewatering.
The Australian Research Council Centre of Excellence for Enabling Eco-Efficient Beneficiation of Minerals based at the University is funding the construction of a revised version to advance the proof-of-concept for tailings. The research team has revised the design specifically to cater for the fine particulates in tailings.
Team members all have extensive experience in solid-liquid separations and include Dr Stickland, Professor Robin Batterham and Professor Peter Scales. They also bring chemical engineering expertise and industry knowledge specific to the needs of the mineral processing sector.
Dr Stickland says a significant advantage of the roller system is the ability to vary the operating conditions to optimise results for different tailings. It provides for continuous rather than batch filtration, which will be operationally more efficient. It does away with the need for filter cloths, which are essential to the current high-pressure filter presses being used to concentrate the solids but present a disposal issue for operators.
Miners investing in presses as alternatives to dams at large mine sites require many presses to process the large volumes of tailings, with filter press installations costing hundreds of millions of dollars for the largest mines. Both the presses and dams also take up extensive areas of land.
Dr Stickland expects the roller system will have a smaller physical footprint and will use less power to achieve the same level of solids concentration, or liquid extraction, as the current filter presses.
He says providing a more cost-effective option for tailings separation will allow more mineral tailings to be stored as solids as an alternative to tailings dams. It will provide an inherently safer and more stable storage option for the resources sector, protecting the environment and the broader community.
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