Metso is on a mission to turn tailings management from a costly, high-risk area of the mining business into a safe, sustainable and profitable operation. Here’s how…

Mining companies across the globe are striving to make their businesses more environmentally responsible and sustainable. However, they have a challenge on their hands when it comes to tailings management.

Water plays a critical role in processing operations, from the transport of minerals as slurry to the flotation of metals, and the volume required is increasing, as average ore grades decline and metal demand increases. Processing more rock also generates greater volumes of waste, or tailings.

Tailings disposal is one of the biggest areas of water loss within mines; certain types of tailings can be difficult to dewater, and high evaporation rates mean that once tailings are deposited in a pond, it is difficult to recover that water. Some miners are already paying hundreds of millions of dollars a year to replace water lost to tailings. And this problem is only going to increase as droughts become more widespread and meteorological conditions harder to predict.

Considering that 70% of the mines operated by major mining companies are in countries where water is deemed scarce, it is not hard to see why conservation is such a key focus for the industry at present.

The cost of water aside, tailings storage is a risky business and the issue of safe management has come to the forefront over the past five years, following dam failures at mines like Samarco and Brumadinho.

The problem is that until widely applicable, non-aqueous mineral processing methods are proven, water and tailings will remain inextricably linked. Even then, how do we eliminate the environmental and societal risks associated with legacy tailings storage facilities (TSFs)?

The answer lies in the clever application of technology.

Rethinking tailings

Although filters and thickeners that offer greater efficiencies have been brought to the market in recent years, what is needed going forward is not purely new dewatering equipment but a step change in the way we view, handle and manage tailings is required if the industry is to maintain its social license to operate.

This is where the concept of a holistic tailings management solution comes into play.

In June, mineral processing firm, Metso, launched its new VPX filter and concurrently announced that it was bringing together its market-leading suite of products and expert knowledge to provide a comprehensive portfolio called Metso Tailings Management Solutions. This addresses not only the dewatering and handling/storage of tailings, but also gives mines the chance to reprocess material deposited in both operational and closed TSFs.

Only 5% of the tailings generated globally in 2018 were dewatered to create thickened tailings, paste for backfill, or dry cakes for stacking. However, Metso estimates that by 2025 that share will increase to 13%. Given that the quantity of tailings produced each year through copper extraction alone totals 2.9 billion tonnes, and 1.6 billion tonnes for the iron-ore industry (and those are only two examples), the impact that increasing this percentage could have, even by a small amount, is clear.

These numbers also throw into relief the vast quantity of tailings that already reside in TSFs across the globe, and the scale of the clean-up operation required to satisfy stakeholders and investors.

There are multiple benefits to reprocessing tailings: dewatering allows process water to be recovered and recycled, thus minimizing abstraction requirements. It also gives greater control and over where and how the resulting material can be stored.

Dry stacking of reprocessed material, which is widely considered the most promising option for future tailings storage, allows mines to better protect their local environment, particularly nearby water sources that can be subject to seepage of harmful minerals from tailings held in suspension. It also removes the safety risks posed by tailings dams to both mine personnel and communities surrounding the operation.

Crucially, reprocessing offers mines the chance to recover valuable metals that in the past were too difficult to liberate – concentrations of metals in legacy tailings can be surprisingly high. This creates an additional source of revenue that could be used to offset the cost of new equipment, water and even fluctuating metal prices.

Niclas Hällevall, Vice President for Beneficiation Solutions at Metso explains: “We strongly believe that dry stacking is the way forward. At the moment, that’s the only sustainable solution as we see it.”

Disruptive development

Before the VPX came to the market, the VPA was Metso’s go-to filter. While this can be used to dewater tailings, it was primarily designed to dewater concentrates, and the company could see a growing need for a product designed to handle the high volumes and fine particles associated with tailings.

“We didn’t just make a bigger filter,” says Hällevall. “We undertook significant investigations to understand what the customer wanted and what their needs were.”

The results showed that greater capacity and faster cycle times were priorities, as well as higher working pressures and more uptime.

“We have increased the working pressure of the VPX from the industry standard 10-16 bar up to 25 bar,” says Hällevall. “This makes a significant difference to the capacity, and it means that you need a shorter time to pump the water out from the slurry.”

The result is also a drier filter cake; the lower pressures used by other models deliver cakes with a moisture content of around 20%, but the VPX’s 25 bar can bring that down to 10%. This means that 90% of the process water can be returned to the plant and reused.

To enable the filter to run at higher pressures, the team had to rethink the entire setup and, as part of that, they removed the hydraulic system.

All other filters on the market are dependent upon a hydraulic system to open and close their plates. However, these require high maintenance and pose a safety risk to technicians. By replacing the hydraulics with electromechanical drives, Metso has enabled the VPX to run faster and more safely. Additionally, as the whole system is now digital, it is much easier to optimize the operation.

“We have built a filter that is prepared for the future,” Hällevall says proudly. “And we also added modularity and scalability. You could say it’s a completely new filter; a disruptive development.”

From product to solution

There are currently four models in the VPX range, but these are completely customizable. Metso configures each filter to suit the material being processed and the duty it will perform.

The use of modules means that filters can be lengthened or shortened, depending on how difficult the material is to dewater, and the pressure can be adjusted to ensure just the right amount of energy is used to obtain desired result, saving the customer money.

This also means that there are very few applications where the VPX cannot be used; it is a very flexible work horse.

Of course, the VPX is just one product in Metso’s tailings management stable. The beauty of having not just filters but also hydrocyclones, thickeners and pumps is that Metso has been able to design a bimodal concept for dewatering tailings.

This means that if a material is particularly difficult to dewater (tailings with a high quantity of ultrafine particles or clays might require longer filter times and higher pressures), then the process stream can be split and treated separately for maximum efficiency.

Hällevall explains: “We divide it into two streams: the fine stream reports to a special thickener called the Inclined Plate Settler. This thickens the material very quickly using fewer chemicals than a conventional or high-rate thickener. And the core stream reports directly to the hydrocyclones and on to a filter.”

Metso can take this even further using a concept called ‘staged filtration’. Here, two tailings streams are mixed to create the perfect ‘recipe’ of tailings material to optimize the action of the pressure filter.

VPX10 earns its stripes

To support its new solution, Metso has devised a pilot program that allows customers to test their suggested equipment setup before purchasing it. The idea is that, by having a strong set of numbers and proof the system will work, mines are able to build a better business case for their investment.

The VPX10 is equipped with all the sensors and control systems that come with the larger VPX models, but its miniature size means that it can be packed into a shipping container and installed at, or close to, a customer’s site. Thickeners and hydrocyclones can also be added to optimize the simulation.

Rodrigo Gouveia, Metso’s Vice President of Tailings Management Solutions, says the VPX10 has proven invaluable.

“We can provide the full pilot plant for trial and everything fits inside a container. So, it’s very easy to transport and have close to the customer site without disturbing their operation,” he says. “It’s a great way for the customer to prove the concept and build their business case.”

Indeed, the VPX10 has proven so popular that it now has a waiting list. The unit has already been tested at a mine in Europe, and it is currently deployed in South America until the end of the year, after which it will head to Ireland.

A new source of revenue

Metso’s investigations also showed that mining companies did not just want equipment to dewater their tailings; they wanted a solution that enabled them to reprocess legacy tailings.

“In some gold, copper, iron and coal mines, it’s impressive how rich those tailings are,” Gouveia says.

“Reprocessing tailings to collect the valuable material is, in some cases, more cost effective than processing virgin material. This is impressive, because the customer has the opportunity to deal with the tailings dam, which is an environmental and societal problem. And they can also turn the waste to value.”

Reprocessing involves removing tailings from an existing dam, bringing them back to the concentrator, and using regrinding, thickening and filtration (or whatever processes are required) to liberate the valuable metals. The leftover tailings are then dewatered and dry stacked, and the water recycled within the plant.

“This is not only a means to sustainability,” says Hällevall. “It’s a huge business opportunity at the same time.”

Gouveia agrees: “It’s well known by the industry that the cost of tailings management will increase. Companies will need to be able to dewater and stack their tailings going forward. They will have to invest in new equipment. Reprocessing provides a chance for them to recover some of that money and make this new operation more affordable.”

Fonte: Mining.com