Rethinking the way mine tailings are managed

We currently live in a world that is getting ready to blast off into space and colonize Mars— engineering feats that would have been laughed at 50 years ago. However, in some industries, there is a tendency to look back at how things have been done rather than looking forward and developing new methodologies.

I have heard many times “We have done it this way for 40 years, so why should we change?” The answer is quite simple, technology has changed significantly in that time period, and we must realize our acceptance of an old way of doing something is not necessarily the best path moving forward.

While there is value in reflecting on how something was done, if we want to improve, grow and stay ahead of competitive forces, it is imperative to embrace new technology and alternative methodologies to achieve our goals.

For example, as recent as March 27th of this year, crews at Piney Point, FL detected a leak in one of the containment walls holding back 480 million gallons of contaminated water. The remedial solution, on this occasion, was to discharge 177 million gallons (enough to fill 288 Olympic Swimming pools) of contaminated water into the Tampa Bay to ensure the nearby homes were protected.

While the water being discharged was not toxic, it could have had negative environmental impacts on the Bay due to the excess of nutrients [1]. Its location, however, helped since water could be discharged to a nearby water source.

In many mining locations around the world, discharging to a nearby water source may not have been possible, resulting in extreme risk to the local environment and human life. This, coupled with the other recent tailing dam failures that did cause damage to the environment and loss of life, has created a deeper sense of crisis.

The 2014 Mount Polley disaster resulted in a loss of about 17 million cubic meters of water and 8 million cubic meters of tailings. In 2015, a tailings dam in Brazil collapsed, unleashing a mammoth 43.7 million cubic meters [2] of mine tailings mud spill that killed 19 people, contaminated 668 kilometers of river and reached the Atlantic Ocean. In 2018, a dam failed at a major mine in Australia, resulting in the movement of more than 1.3 million cubic meters [3] of mining waste; luckily, a second barrier prevented disaster. Finally, in 2019, a dam disintegrated at a decommissioned Brazilian iron mine, releasing a torrent of 12 million cubic meters of tailings that killed 270 people.[4]

If we look at the mining industry, especially the way mining tailings are stored and handled, we see the same methodology employed today that was used more than 200 years ago. Mine operations, however, have increased significantly in size, which means these tailings ponds have also increased in size. This results in a much higher risk for severe environmental impact if there were to be a failure in the integrity of these large ponds.

Now don’t get me wrong, I am aware of the improvements in pond wall construction, as well as the updated methods available for monitoring these structures. However, this has not stopped tailing pond failures from happening. It is reported that in the 18,000 mines around the world, the failure rate in the past 100 years is estimated at 1.2%. The failure rate of the traditional water storage dam is 0.01%. On average, three of the world’s 3,500 tailings dams fail every year. The likelihood of tailings dam failure is several times higher than other conventional water-retaining dams [5]

We now have early insight into when a dam may fail, allowing us the opportunity to fix it. However, this does not always stop dam failure from occurring. We cannot continue to pursue the ideology that we know why it failed, or that “we will get it right next time”. Often, these are the only two aspects that are addressed. I’d like to challenge us, as innovative engineers, to review whether there is technology or methods available that can help mitigate the risk of this type of future disaster.

One possibility I would like to discuss today, is the treatment of tailings. Some may argue that trying to treat the tailings is too costly and expensive due to the size of the mines and tailings ponds. This is absolutely a legitimate concern. However, there are ways to address these concerns. One way to reduce this cost is to continue to develop the process for recovering the water from these waste streams and reuse it in the mine (where possible) or send for final effluent treatment in the same way other industries handle their water waste. Landing on the moon was an expensive feat, but everything they learned in doing that was used to develop technologies, methods and system that were more financially beneficial for the space program in the future. The technology and processes are already utilized in other industries, they just need to be accepted and built into the whole cost of operating a mine.

The other big challenge the current methods fail to address, are the large environmental issue regarding the massive volumes of water that can no longer be used. With tailings ponds containing anywhere from 2 million cubic meters to 60 million cubic meters or more—enough to fill 800 to 24,000 Olympic swimming pools respectively. Why not look at a way where this water can be reused and recycled within the process? It is very common that once the water has entered a mining operation, it is unlikely to be able to reenter the water table due to the high toxicity. Many companies have committed to the UN Global goals regarding the sustainability to water and environment. However, they continue to argue it costs too much. Yes, I understand companies must return a certain amount of profitability to their shareholders; however, shareholders and other stakeholders also need to hold the companies to account as well. There is an obligation to the environment that needs to be upheld, and it can be done responsibly and with technology that brings the cost into a tolerable zone for the industry to bear.

So, where am I going with this discussion? My goal is to educate people in the mining industry, (in fact, any industry that has a requirement to separate or dewater a solid/liquid stream) that there are incredible advancements in this space that may be game changers. The tradeoff doesn’t always need to be a painful one there are win-win solutions available. The equipment I work with every day, decanter and high-speed disc stack centrifuges, may solve some of these problems, but that’s not the main point. The goal is to start conversations about possibilities and if I have a solution for you, great. Even if I don’t, that is alright as well. My hopes are that these conversations encourage us to look at your processes more closely and create ideas on how we can improve. I would love to invite you to start those conversations with me, today. Connect with me on LinkedIn or send me an email at rhys.lewis@alfalaval.com.

For those of you that want to know more about the solutions I work with in solving these problems, please continue to read on for a short summary of Alfa Laval Solid Bowl Centrifuge.

Thanks for wanting to learn more! Reach out to me if you have any questions at all.

Alfa Laval’s solid-liquid separation solutions are an effective, proven, high capacity solution for dewatering coal tailings and mine wastewater. Our solid-bowl centrifuge technology has evolved over the years and we have further developed it to make the technology extremely robust and suitable for applications in the mining industry. Dewatering of mine tailings is one of the key areas that we focus on, helping our customers eliminate the need for tailings dams and thereby avoiding potentially catastrophic situations.

Proven success across the globe

Today we have successful installations for dewatering tailings in coal, oil sands (mature fine tailings), borax, nickel and cobalt, with reference sites in Australia, North America, South America, Europe, Asia and Africa. Alfa Laval is a world leader in solid-liquid separation technology with sales offices, service centers and partners in over 100 countries and 18,000 decanter centrifuges installed worldwide. With more than 130 years market presence in United States, Alfa Laval offers a large range of equipment and the knowhow to help you optimize key processes in coal and base mineral beneficiation, extraction as well as mineral processing applications.

With Alfa Laval’s alternative dewatering technology, you can work towards:

• Eliminating the need for tailing dams, which enhances the intrinsic safety of your operation
• Boosting capacity and reducing tailings volumes, all with a smaller footprint
• Producing a cake with up to 70% dry solids by mass, which can then be used for co-disposal with coarse rejects
• Recovering and re-using large quantities of process water, which reduces lifecycle cost, minimizes environmental impact and minimizes risk of dam failures
• Reducing operating and investment costs while minimizing your company’s environmental impact

Our aim is to help you avoid tailings, produce a stackable solids cake, recover/reuse process water and reduce wash water savings. This can be achieved by utilizing solid bowl centrifuge technology which has a smaller footprint for its hydraulic capacity when compared to traditional dewatering methods, allowing for continuous operation within an enclosed and clean operation.

Alfa Laval’ solid bowled centrifuge specifically designed for mining applications.

Are capable of handling up to 250m3/hr. hydraulically and 70 – 80 tn/hr. dry solids per machine
Have deep pond design and higher G forces
Have ultra high erosion protection specially for mining duties
Have global operating references on mine tailings
Lower power consumption - patented liquid discharge

Other applications that Alfa Laval could support your sustainability goals within the mining industry include heating, cooling, waste heat recovery, evaporation and condensation, desalination and zero liquid discharge.

Need help minimizing cost and environmental impact and maximizing the safety of your operation?

Let’s chat! I would be delighted to discuss efficiency and sustainability boosting solutions for the mining industry as well as our next generation technologies for tailings dewatering. I am available either in person or via conference call, so please do not hesitate to contact me at rhys.lewis@alfalaval.com or +1 (804) 297 2284.

References

[1] Florida Reservoir: How a Flood Was Averted at Piney Point Phosphate Plant - WSJ

[2] Mariana dam disaster - Wikipedia

[3]Newcrest must assume gold mine dam walls at risk, experts warn (smh.com.au)

[4] Brumadinho dam disaster - Wikipedia

[5] A Comprehensive Review on Reasons for Tailings Dam Failures based on case history - Hindawi