FLSmidth recently provides a dewatering solution to Hindustan Zinc Ltd.’s Zawar operation in Rajasthan, India.
(Photo: FLSmidth)

That said, momentum is gathering. There is now a wide selection of high-performance dewatering technologies available on the market and vendors are building expert design, engineering and operating packages around these to support mining companies on their journey toward thickened or filtered tailings. There is also a greater willingness from mining companies to consider different dewatering strategies and recognition that, going forward, these will form a central part of their license to operate. Next-generation filter presses capable of handling upward of 10,000 metric tons per day (mt/d) of tailings, some of which have been waiting some time for full-sale test partners, are finally getting implemented, and these references are helping to build miners’ confidence in evaluating “new” technologies for their own operations.

Most importantly, the trend for noncompetitive collaboration and innovation that has emerged globally in tailings management over the past two years — similar to that seen in general mine safety — is not abating; it’s growing. And the results of this work are both exciting and heartening.

Water, Waste and Willing
“Water is the issue that everything revolves around,” Todd Wisdom, director of tailings solutions at FLSmidth, set the scene for E&MJ. “The more water a mine has, the more chance there is of a negative impact if an accident occurs. So, mines are looking for economical ways to remove that water from tailings and maybe reuse and reprocess it inside of their facility. That has to be balanced if they have potential for acid generating tailings, which would need to remain saturated with water to inhibit acid formation.”

Depending on where a mine is located, whether it’s in what’s known as a “positive water environment” or not, there are different costs and risks that are associated with different dewatering solutions. This, in turn, will determine which solutions a vendor or engineering company would recommend to each operation. “There are many customers that actively evaluate these different solutions,” Wisdom said. “You have to look at the local constraints — the regulations and permits, for instance. What are the seismic conditions? Seismicity plays a big role in dam stability. A large, tall tailings dam, obviously has a bigger chance of failure than a small one in a seismically active area. You need to look at rainfall. You need to look at what the local population is like.

“And, last but not least, the economics of a particular solution. If something’s not economical, the mine will be shut down or it won’t be built. Economics always play into any solution, even if they’re being driven by regulations.” A good example of this is in Chile and Peru, where many mines use desalinated water due to the arid climate and water scarcity. By the time that water is pumped up to the mine, the altitude that needs to be overcome means the water can cost up to $8 per cubic meter (m3). “Even if regulations aren’t driving them to adopt a particular solution, at $8 per cubic meter you could pay for a lot of dewatering technologies,” Wisdom said. “By comparison, in Canada, water costs probably $0.10/m3-$0.20/m3, so you’re talking easily an order of magnitude more in costs for water in an arid environment.”

Waste footprint is another key driver. Andrea Pezzi, director of marketing and communications at Diemme Filtration, part of Aqseptence Group, joined the discussion. “In general, we see that the quantity of tailings is increasing, for various reasons,” he said. “Because the ore grade is getting lower, mines need to process more material and that creates more waste. One of the consequences of this is that mines require more space for the disposal of this material. Additionally, the traditional way of disposing of tailings in a wet storage facility carries a lot of safety and environmental issues. “We are seeing an increase in the level of questions, demands and the inquiries for dewatering solutions for big projects, and mining companies are becoming more familiar with the concept. I think many were reluctant in the past because of the capital investment or the lack of knowledge or confidence in this technology. But now, this is improving.

“Another tendency that we see in the market, and I think it’s a reasonable approach, because EPC/EPCM models are standard when building a new mine or expansion, is the engineering company collecting prices from vendors and going with the lowest bid. But the lowest bid doesn’t always mean the most appropriate solution. “When you’re investing in a big project and you have a lot of technical and social responsibility, I think the method of going to the lowest bidder is not applicable. That’s why we see a lot of mining companies contacting us directly, to find a different type of collaboration for tailings dewatering. Rather than the typical client-vendor relationship, it’s more like two experts working together to find a good solution for both parties.”

Partners in Innovation
These new, direct and mutually benefi- cial relationships are crucial in finding suitable and sustainable dewatering solutions, because tailings characteristics vary widely in different locations, and from site to site; no two projects are exactly the same and, over time, the characteristics can change.

McLanahan supplies a variety of tailings dewatering equipment including thickeners
and filters. (Photo: McLanahan)

Job Kruyswijk, manager for Integrated Slurry Solutions, at Weir Minerals in the Netherlands, explained: “Sustainable storage of tailings is about engineering an integrated system that reduces the environmental impact of mining. At some sites, water conservation may be the most important issue, while other sites may be more concerned with minimizing energy consumption. It’s also vital that miners reduce their overall emissions, and this can only be achieved by engineering energy efficient systems, however, the specifics of what this entails will differ from site to site.” Over the past couple of years, the mining sector has faced increased pressure from investors and the community to implement more sustainable solutions for handling mine waste. And, after several catastrophic tailings dam failures, the industry is starting to see the benefits of adopting a longer-term approach to tailings management. “The challenges are varied and obviously differ from one operation to another,” Kruyswijk said. “However, I think they fall into three broad categories: firstly, bridging the knowledge gap; secondly, brownfield optimization; and thirdly, meeting the changing legislative and regulatory requirements for tailings disposal. “Following the Fundão and Brumadinho dam failures, mining operators have become increasingly interested in the prospect of dewatered tailings, which has initiated a global trend toward drier tailings. The industry’s attitude to tailings needed to change; however, there remains a lot of work to be done to ensure that miners strike the right balance between energy and water conservation, long-term stability and feasibility.”

While thickened or filtered tailings are now commonly assessed for every new mine, the industry is yet to tackle many legacy operations. Upgrading existing mines that already have a set pathway for tailings handling and storage can be expensive, time-consuming and extremely challenging from an engineering, design and regulatory perspective. Mario Gerards, industry director for mining and minerals at ANDRITZ Separation, said, “Tailings are not part of the valuable stream. Therefore, many operators want to process tailings as cheaply as possible. Often these additional production costs are not calculated and can influence cash flows and other economic values in a negative way,” he said.

Pezzi added: “The mentality toward dewatering is changing but, in our opinion, it’s very slow; many mines still opt for conventional storage methods when filter technology should be the new standard. The investment required for this equipment is now justified and, when you are looking to these types of applications, it’s important to consider the total cost of operation instead of just the capital investment or the operational cost. “Having more references is helping a lot because, if a client is unsure, having the possibility to speak to other mines with more experience can definitely build their confidence.”

Derisking ‘New’ Technologies
There is a well know adage in mining that, when it comes to implementing new technologies, mining companies prefer to be first to be second. Nowhere has this proven truer than in tailings dewatering and, particularly, with high-performance filter presses (despite the fact that filter presses are not new). Proving out the first units at a large scale has been tricky. Vendors understand this challenge well and have developed a variety of methods to help derisk these projects for miners.

“Most miners do not want to be the first company to deploy any new technology at scale as a way of managing their projects risks,” Wisdom said. “They typically want to be first to be second or third, so the only way to derisk a solution for them is to have one or more units up and operating well. “Along with this, many of the largescale solutions for big mines are expensive to install and operate. One way to manage this risk is for miners to form a consortium and share in the costs and risks associated with a large-scale technology demonstration plant. Or potentially a government could subsidize a large-scale technology demonstration plant to prove the technology would support new stricter regulations.”

Dry filter cake ready for stacking/storage.
(Photo: McLanahan)

“New, high-performance technologies need to have the opportunity to be implemented in brownfield operations to prove they can be used on a larger scale. This requires close cooperation between equipment suppliers, EPC companies and end-users. They should be sharing this risk, as well as the gains.” One partner is missing in this formulation — the regulator. In many countries, significant changes in the process flow require permit or license renewals for the entire mining operation. This process can take years to complete, and most operators understandably choose not to go through with this exercise. Kruyswijk believes that short-tracking permits for upgrades that deliver sustainable tailings deposition could be another way to encourage operators to embark on more ambitious projects.

Diemme Filtration recently sold its first 5-m x 5-m filter press (more on the commercial launch later) to a mine in Latin America. Pezzi shared that experience and how the companies worked together to overcome the risk barrier. “Knowing the model, which we are currently manufacturing, was the first one, when we made the agreement with the client, we agreed to share the risk,” he said. “We found special terms that would allow us to work together, because we knew that we’re not just making a product that is good for the client, but also good for the overall mining world. “The first unit is going to be a pilot because now, the concept of pilot-scale is changing. This client has a full-scale capacity of 80,000 mt/d of tailings. The unit we are building has a capacity of 8,000-10,000 mt/d and, if it works as expected, then we will need to add nine more units. This is not new for us; we have another case in New Caledonia where we piloted a 2.5-m x 2.5-m filter press and we are supplying 10 more units for the full-scale plant. That modularity and scalability is really important in derisking these technologies.

“And, aside from the factors like capital investment and operational costs — things that you can easily measure and put on paper — there are other valuable lessons that can be learnt from pilots, like operation in local weather conditions or something related to a plant that you cannot foresee until it’s on site.” Finding and overcoming issues at pilot- scale can also save time further down the line as plants scale up, and this too can have an economic impact; all of these factors add up.

“We really encourage clients to have an open dialogue with us to save time,” Pezzi added. “Mining projects tend to have a long gestation because there are many different levels of studies, different gates. Many times, projects do not come to execution, but having a straight dialogue with subject matter experts, in my opinion, can really help to reduce the timeframe and enable better decisions.”

FLSmidth’s Drive Toward Zero-waste
Tailings dewatering is a key part of FLSmidth’s MissionZero initiative that aims to provide sustainable, zero-emissions (water, energy and CO2) solutions for both the mining and cement industries. The company’s Colossal tailings filter, which was designed to handle 10,000 mt/d and was demonstrated a few years ago at Escondida in Chile, has now been purchased by a customer who is executing a fast-track project. And the 5 x 3 filter, which can handle 30,000 mt/d and was originally developed for the EcoTails project with Goldcorp, has completed feasibility study engineering and is ready for a full-scale demonstration plant. “We also just launched our new M2525 filter, which will provide the highest production rate for that plate size for a pressure filter and at the lowest operating cost,” Wisdom added.

FLSmidth recently provided a dewatering solution to Hindustan Zinc Ltd.’s (HZL) Zawar operation in Rajasthan, India. The location was reaching its capacity for conventional wet tailings deposition with no space nearby to expand, and the company wanted a dry tailings management system that could offer environmental sustainability benefits, process water recovery, and minimize the footprint of its tailings storage facility. After evaluating a number of options, HZL chose a concept comprising: an FLSmidth high-density thickener and four E-disc filters with ancillary equipment, dry tailings transfer conveyors and stockpiling equipment, and E&I plus automation (E-House concept) technologies.

The final installed system has a capacity of 680 mt/h. Designed cake moisture was 16%, but the system achieved a moisture content of 13%-14% during the performance guarantee and managed levels as low as 10%-13%. In addition to its small footprint, key benefits of the system include recirculation of greater than 86% of the process water present in tailings, safe and stable stacking of tailings cakes in an area of high seismic activity, a 50% reduction of the storage footprint, faster rehabilitation, and restoration of storage sites at mine closure and ensuring water availability for expansion of production.

FLSmidth signed another agreement in 2020 to deliver an integrated dry stack tailings solution and a paste fill plant to a HZL lead-zinc mine in Rajasthan. The order includes supplying two Automatic Filter Presses (AFP-IVTM), two E-Disc filters and one 26-m-dia. High-Density Thickener as the main pieces of equipment. The mine’s tailings dam was reaching capacity for conventional wet tailings deposition, and it required a solution to create a small dry-stack tailings area with minimized environmental and physical footprint and also a method to backfill the mine by using an adjusted dry filter cake mix.

By choosing this hybrid technology, HZL will be able to achieve this and recover around 85% of process water, which can be reused by the process plant with minimum operating and capital expenses. “We have a lot of R&D that’s going on right now,” Wisdom said. “We’re always trying to come up with new and better solutions. These include dry grinding technologies that enable mines to use less water, better flotation technology, like coarse particle flotation and reflux flotation, so mines don’t have to use as much water for separation. Both the grinding and flotation of the ore effects the quality and quantity of tailings that must be dewatered. We’re also looking at different digital solutions for our dewatering portfolio, so that the equipment can be better operated and controlled, either individually or as a group. “We’ve come up with multi-variable control philosophies which revolve around individual equipment like the thickener, filter or conveying and stacking system, but we also have control systems now that can manage that whole group as a whole. This means that mining companies not only have the option for local optimums for their thickeners, filters or conveyors, but they can also have a global optimum that revolves around all of those different technologies.”

Weir Minerals’ End-to-end Solutions
Weir Minerals is focusing on delivering dewatered tailings products that meet clients’ geotechnical requirements, packaged in a way that takes into account the end-to-end process, from the metallurgical plant through dewatering to placement at the tailings storage facility. “Weir Minerals’ has the expertise and range of equipment that’s required to deliver a high-density paste system,” Kruyswijk said. “From ‘traditional’ paste thickeners from our Isodry filter and thickener range to the innovative Terra- Flowing process, which combines several dewatering technologies to produce a paste, Weir Minerals has a solution to almost any tailings challenge.” Weir Minerals’ TerraFlowing dewatering process addresses both the value proposition of tailings as a resource, and the safe storage of tailings.

Weir Minerals’ Warman tailings pumps in action. (Photo: Weir Minerals)

Water recovery can be up to 85% of the total water in the tailings with a stackable final tailings product achieved if the three tailings streams are combined in the maximum solids concentration configuration. “The primary cyclone can be operated to deliver a particle size distribution suitable for tailings storage facility embankment construction or alternatives such as concrete structures or shotcrete for support,” Steward said. “The secondary cyclone underflow and centrifuge pulp is suitable for beaching deposition within the tailings storage facility.” In addition to researching and developing new dewatering techniques, Weir Minerals also has the capability to conduct inhouse testing through the Weir Technical Centre, and the Weir Sustainable Mining Centre in Venlo, the Netherlands. Steward added: “Weir Minerals works in conjunction with the miner and geotechnical consultant to design a dewatered product system to fit the mine tailings management structure, as well as provide options for alternative uses for the mine’s tailings.”

ANDRITZ Introduces ME2500
ANDRITZ offers a range of thickening technologies, including conventional and high-rate thickeners as well as flocculant dosing stations. “These machines are often used as first process step, followed by additional mechanical dewatering equipment, such as filter presses, vacuum belt filters, belt presses, vacuum disc and drum filters, pressure drum filter, hyperbaric disc filter or decanter centrifuges,” Gerards said. “All our machines and systems come with the Metris addIQ control system, our automation solution for separation processes. As an example, in ANDRITZ’s intelligent filter press, we have combined our proven filter press automation solutions with Industrial Internet of Things (IIoT) technologies to create new mechanisms and features that promise an increase in product quality and a decrease in operating costs.”

In June, ANDRITZ introduced the ME2500 filter press, which completes its A4F and the SE series for the mining and minerals industry. The ME2500 is well suited to processing tailings with a high clay content or concentrates like iron, copper, lead or zinc. It boasts an hourly capacity of up to 450 kg/m2 and a filtration area of up to 840 m2 with chained plates for speedy filter cake discharge. The innovative closure system, which largely replaces hydraulic components with electrical ones, further reduces cycle times, thus increasing capacity and operating availability.

In June, ANDRITZ introduces the ME2500 filter press. (Image: ANDRITZ)

Diemme, SUEZ Join Forces for Dewatering
In May, SUEZ and Diemme Filtration announced they were creating a partnership to provide an integrated approach for tailings management with a specific focus on sustainable solutions for the mining industry. This partnership combines SUEZ’s capabilities in water, process, and waste management and its experience in design, build operate (DBO), and build operate transfer (BOT) large infrastructure projects, together with Diemme Filtration’s expertise and solid- liquid separation technologies.

“We could see that the market was in need of somebody to help guide mining companies based on their specific needs, rather than using the traditional EPC or EPCM approach,” Pezzi said. “With the DBO/BOT approach, SUEZ will share the risk with the client, and we are their preferred supplier for the dewatering solutions. It’s a good strategy, because of Diemme Filtration’s reference list in the mining industry and also because we are joining the global presence of both groups. Together, we have the opportunity to execute very large projects, upward of 30,000 mt/d of tailings. In particular, we see Latin America, as a key market where large-scale solutions are required. So, we are pretty active there.”

Together, the companies will offer complete systems for tailings dewatering from design, delivery and execution, all the way through to operation and transfer. “In particular, Diemme Filtration is focused on designing and providing the dewatering equipment, mainly filter presses and thickeners. But again, case by case, we have the flexibility to adjust our scope of supply,” Pezzi added.

Diemme Filtration showcased its new GHT.5000.F filter press (mentioned earlier) for high-volume tailings dewatering applications at MINExpo in early September. The model will be officially launched on November 30, with a virtual press event and a new catchy name. The first unit is currently being assembled in Italy and is soon heading to a mine in Latin America. “I can’t tell you the name yet, but I can tell you that the tagline will be ‘Mine with Mind,’” Pezzi told E&MJ exclusively. “The message is that companies in the mining industry have a lot of environmental and social responsibility to consider alongside running a business. The two must go hand-in-hand.

“In terms of other technologies, our R&D department, jointly with sales andmarketing, is constantly exploring and evaluating new ideas,” Pezzi said. “In terms of innovation, we are focusing on increasing the level of automation in dewatering with greater data collection and monitoring. We believe it is fundamental to optimize the operations of our partners. Very soon, we will be launching a new service. Again, with a catchy name. We are basically helping our clients to get the most from their equipment and improve the efficiency of their plant.”

McLanahan: New Filter in Development
McLanahan supplies a variety of tailings dewatering equipment and works with engineering companies and geotechnical consultants to determine the best dewatering solution for each site. The company’s offering includes cyclones, separators, thickeners, filter presses and dewatering screens. “These can be supplied as individual products or incorporated in an entire stationary, modular or portable plant,” explained the company representative. “Following demand to process higher tonnages, McLanahan is also developing a larger, faster cycling filter press with 2.5-m x 2.5-m plates that can process up to 100-120 dry t/h.”

Brighter Future for Tailings
One thing every expert interviewed for this article agreed on was that, if mining companies, solutions vendors and engineering firms continue working together to accelerate the uptake of next-generation dewatering solutions — not just for individual gain but, for the good of all stakeholders — then tailings management practices could be in a much better place in just 10 years’ time. Together, the potential we have to effect change is massive.

“In 10-years’ time, we will be producing more metals with less water through advances in dry grinding technology and improved flotation technology,” Wisdom said. “We will be recycling more water with lower dewatering costs through better thickening and filtration technology, and we will be placing the dewatered tailings, sometimes comingled with other mine wastes, in geotechnically and geochemically stable deposits.” Ian Ross, dewatering global product manager for Weir Minerals in Canada, added: “Due to the global pressures on resource-based industries to operate with a lower environmental footprint, there will be an increased demand from our customers for tailings management solutions that move away from the traditional high fluid ratio tailings management practices.

Ross’ colleague, Steward, went one step further with his prediction. “Owing to decreasing ore grades and the increasing need for raw materials, the volume of tailings is going to increase,” he said. “This is going to lead to miners being primarily tailings management companies, as opposed to mineral producers. The challenge for miners and Weir Minerals in the future is how to reduce tailings volumes through alternate applications of tailings. This requires a different mindset; one that sees tailings as a resource and not a waste product.” Gerards believes that, in 10 years, dewatering tailings will be a more reliable process compared to today. Then, the question will no longer be if tailings are dewatered, but how they are dewatered. “Hopefully, we will never see another dam break with catastrophic environmental consequences,” he said. “We also need to take care of water, which is a very valuable commodity. Hopefully, in 10 years, we will no longer see water waste caused by the mining industry.”

McLanahan’s representative agreed: “By then, all sites will be operating dry stack or filtered tailing solutions for maximum water recovery and best long-term stability.” Pezzi joked, “10 years from now… Well, it would be nice to have every mine with Diemme filter presses in operation. “But really, what we would like to see is a very responsible approach from the mines, considering all the technologies available on the market and then selecting the best one after a very thorough evaluation. It’s important that we remove any bias in these decisions and be open to finding a solution that maybe, was not considered in the past because of cost limitations or a very conservative approach to new technologies.

“By doing things the way we’ve always done them, we are not helping the market or the industry to make improvements. Ten years from now, we would like to see the results of this open-minded approach in mines across the globe. If it’s necessary to spend more money to increase the safety of a mine using dewatering technology, then that shouldn’t be considered an effort. It should be an integral part of doing business. “Think of it like driving with a safety belt; you also have to protect the people, the villages, the communities, using the best available technologies.”