Metso’s VPX filter features operating pressure of up to 25 bars, making it capable of handling difficult to dewater tailings and allowing it to recover up to 90% of the
water. It can produce a dry cake with less than 7% moisture. CREDIT: METSO
With the introduction of its new VPX filter system for dewatering tailings, Metso is going all in on dry tailings as the best technology to deal with the growing environmental, regulatory, social and cost pressures on the mining sector.
“We believe dry stacking is the most sustainable way to manage tailings today,” says Niclas Hallevall, vice-president, beneficiation solutions, mining equipment business area, Metso.
Niclas Hallevall, vice-president, beneficiation solutions,
mining equipment business area, Metso
Today, only about 5% of tailings are dewatered, while 70% of mines are located in countries where water scarcity is an issue. Yet more tailings are being produced as operations mine lower-grade ore. And recent devastating tailings dam failures have increased the pressure to search for alternatives.
While water scarcity has been a driver towards considering dry tailings technology in the past, the question now is around responsible use of resources.
“I think that is what’s creating the drive right now,” Halleval says. “Ten or fifteen years ago, we were talking about water scarcity. Now we are starting to talk more about recovery of water but what we really mean is, what is the responsible use of water? Are we over-consuming it?
And the same thing applies to responsible use of energy, or chemicals in the process or the ore itself – how do we mine it in a responsible way?”
Designed to maximize water recovery and reduce the footprint of tailings dams – or even eliminate them completely – Metso’s VPX filter is meant to provide an answer to one part of this puzzle.
“Our ambition is to challenge the conventional way of looking at tailings management in mining,” said Victor Tapia, president, mining equipment business area at Metso, in a release.
“In practice, this means that besides environmental and regulatory concerns related to tailings, we need to improve the conservation of water, chemicals and ore, as well as looking for opportunities to reprocess tailings and generate value by extracting any remaining minerals.
Ultimately, it allows (the transformation of) legacy practices in tailings management into a new, positive value creation model.”
Dry stacking is not a new technology, but it is new for many mining companies.
Dry-stacking solutions produce a low moisture cake that is then piled in a tailings facility or can be used to make construction materials. If the resulting dry cake is not geotechnically stable, it may be comingled with other materials before stacking.
Thickening and paste technology are other alternatives to conventional tailings disposal in ponds, but they are very expensive and don’t recover the water that dry stack technology does, Hallevall says.
In the past, dry stacking has been seen as too costly or impractical – especially at high-volume operations.
But the VPX system removes many of the barriers to adoption of dry tailings technology for mining companies.
The system can handle larger volumes, dewater more difficult material, and can be easily fit in standard shipping containers for easier deployment.
“The main difference with the VPX is it’s a much bigger filter. From a capacity point of view, it’s three to four times bigger than the VPA, so it’s a much bigger machine,” Hallevall says.
The system can handle up to 35.3 cubic metres in total volume and has a filtration area of up to 1,391 sq. metres.
While a typical operation that currently uses dry stacking is in the range of 12,000 to 15,000 tonnes per day, he says that the VPX is feasible for operations as large as 100,000 tonnes per day.
“One solution we’re showing as an example has eight filters, one thickener and a hydrocyclone cluster, and for a typical copper mine, that will handle 60,000 tonnes per day. So this is real already today,” Hallevall says.
The VPX has several other major improvements over the VPA. Instead of hydraulics, the VPX opens and closes with a rack and pinion drive system, which is not only safer, faster and less costly in terms of maintenance, but also adds capacity.
“The faster you can open and close, the more capacity you will have in the machine,’ Hallevall notes. “That means a smaller machine with this technology can result in higher capacity than a bigger machine.”
Compared to 16 bars of operating pressure in the VPA filter (and 12-16 bars as the industry standard), the VPX has up to 25 bars – making it capable of handling difficult to dewater tailings and allowing it to recover up to 90% of the water.
A range of features, including high pressure and some features that the VPA also had – such as air blow and membrane squeeze – mean that the moisture in the dry cake is more easily controlled.
“Our filter is a multi-action filter, meaning we can go high-pressure feed pumping, we can have a membrane squeeze with high pressure, we can do air blow, we can even do washing of the material inside of the filter. So with all those different functions, we can always find the optimum way to dewater.”
Recovering the maximum amount of water and producing a cake with the right moisture content are both important.
“The moisture requirement is related to how they transport the cake in the next step, so it’s all about how can we make it transportable – typically on a conveyor,” Hallevall explains. “If they don’t reach the right moisture content, they can’t use the conveyors and they need to make special arrangements.”
The VPX can produce a dry cake less than 7% moisture – or it can be customized to whatever level is necessary at the operation.
The filter is also scalable and modular, meaning it can be fit into shipping containers for easier deployment to remote locations.
In fact, Metso has full-scale test pilot systems that ship in four containers available for potential customers to test the technology at their site.
“It helps the customer build a business case and make the right decision, so they know what they’re buying,” Hallevall says. “This is a big investment.
The system comes equipped with sensors to gather all the information needed to evaluate the technology at the specific site.
On the surface, dry stacking, where another step is added to processing to produce a stackable cake, is more expensive than traditional tailings dams. But when more factors are considered, Hallevall says dry stacking is actually cost-competitive.
“Our investigation shows that this could actually be done at less cost or at least at the same level compared to any of the other methods,” he says. “Everything depends on how it’s calculated – if you consider the cost of land and the construction of the different solutions, and not just looking at the operation, then from a capex and opex perspective, this is very favourable.”
Smart control system
Part of what makes the VPX a very efficient technology is that it can separate material into two streams for bimodal filtration.
Having two configurations for the filter – coarse and fine – can dramatically reduce the use of chemicals in the process and even reduce energy consumption. As fines are more difficult to dewater, treating the two streams separately is more efficient.
“The fine stream is maybe 30-40% of the feed, for example, and we send that to our IPS (inclined plate settler) thickener. That thickener is fantastic on thickening fine particles in a very fast and efficient way and it only requires 50% of the chemicals that are typically used in conventional thickeners,” Hallevall says.
In addition, staged filtration means the VPX can control and build the feed in the most optimal way.
Metso already had a “smart” control system for its VPA filter, but the company has an eye toward introducing artificial intelligence in the future with the VPX to enhance its performance.
“Artificial intelligence will take it to the next level where the machine can – after it’s been operating for a while and it learns the conditions in a mine – optimize the performance for that specific operation,” Hallevall says.
“It’s one thing if you’re in a concentrator plant, the material looks the same over a time. But when it comes to tailings, there could be much bigger variation, especially if we also add reprocessing, you can have different streams coming to the dewatering island. With those variations, the filter can always adapt to the condition of the streams that come in.