Innovative Tailings Solutions at El Soldado’s Copper Mine

Mining plays a major role in the Chilean economy; it also poses major environmental challenges. The issue is particularly acute when it comes to tailings management and storage. This is a region where water is scarce, but where huge amounts of water are lost every year from wet tailings storage facilities (TSFs). South America is also a region scarred by catastrophic tailing dam failures.

It adds up to a complex and multifaceted challenge. But it is a challenge that Anglo American is tackling head on through an innovative new tailings management concept known as hydraulic dewatered stacking (HDS). Patented by Anglo American and developed in collaboration with WSP, HDS offers a safer and more sustainable long-term approach to tailings management and mine closure. It also allows a significant proportion of tailings water to be captured and reused.

Location

Chile

Client

Anglo American

What is hydraulic dewatered stacking, exactly?

HDS combines and co-disposes sand generated by coarse particle recovery with the mine’s tailings, filtering and dewatering the tailings in the process, to produce a stable, well-consolidated tailings stack with a low degree of saturation. The liberated supernatant and seepage water is collected and managed separately for re-use in the mining process. Read more about the hydraulic dewatered stacking concept.

Following initial discussions with Anglo American to flesh out the concept, a multidisciplinary team at WSP undertook a range of concept studies and laboratory trials to develop an operational concept for HDS site design. This multi-disciplinary work drew on the company’s global team of mining professionals, bringing in subject matter experts not only in tailings management, but also in geotechnics, hydrogeology, and mine water management (including pumps and piping).

Putting HDS to the test at El Soldado

On the basis of this early work, WSP developed the concept for a large-scale field trial. As Anglo American had already implemented coarse particle recovery at its El Soldado mine, the site was the natural place to locate the trial. The test facility was designed by the WSP team, again drawing on the wider expertise available within the company’s global mining group to provide project and risk management, and construction quality assurance.

As part of the trial, WSP, Anglo American and the tailings contractor developed an innovative method of sand deposition which is being tested. The technique involves a hydraulic sand flinger depositing sand as a slurry directly onto the TSF to form interbedded sand blanket drains. It is easily controlled and much simpler than an alternative self-propelled cyclone-based system, which is also part of the trial and is used to form vertical sand drainage columns.

WSP analysis has proved that drainage of the sand slurry is quick, with the sand returning to its baseline moisture content within ten minutes. However, the potential for evaporative water losses with the flinger is greater than with the alternative cyclone unit. Further testing and analysis is needed to determine this conclusively.

The cyclone unit – the alternative method for sand deposition being studied – is self-propelling and dewaters the sand before deposition. This generates a larger-than-expected amount of water from the cyclone overflows, which required the WSP team to quickly develop appropriate water management strategies to overcome the issue. Other key operational challenges relate to equipment maintenance to deliver consistent operation: for example, the need to introduce screening to reduce the risk of blockages.

Initial results are promising

Extensive onsite instrumentation for data collection, designed by WSP, provides multiple data points for expert analysis and reporting through the trial. These data are being regularly monitored and reported by the WSP project team, with the aim of proving the feasibility of HDS at large scale.

It is ultimately hoped that dewatering below the point of liquefication will be demonstrated. This is a key element in best-practice tailings management standards and GISTM objectives, as the lower the degree of saturation, the lower the consequence of catastrophic mudflows in the unlikely event an HDS facility fails. Early results are positive. Analysis by the WSP team has shown the initial tailings layer quickly dewaters and consolidates, achieving an average degree of saturation of around 75%. Subsequent layer placement will impact this figure. Going forward, it will be interesting to see how sand layers help to mitigate the wetting front and what steady-state levels of saturation can be achieved.

The El Soldado trial has also demonstrated high levels of water recovery, with the WSP team reporting 78% of tailings water being recycled back to the mine.

What’s next for El Soldado and HDS?

HDS not only offers operational benefits in terms of TSF safety and water recovery. Because it uses a cell-based approach to tailings deposition, it also facilitates a progressive approach to site closure and re-use. This ultimately allows speedier repurposing of otherwise sterilised land. Since the drainage systems remain in place even after closure, the risk of long-term re-saturation of the tailings and subsequent groundwater contamination risk is minimized. Long-term subsidence is also likely to be significantly reduced because consolidation occurs so quickly, again simplifying closure design.

WSP continues to monitor the El Soldado pilot to provide further proof of concept and test these points. Closure design at El Soldado is also currently being finalized by WSP mine closure specialists. Meanwhile, another trial is being planned at an Anglo American site in South Africa to test whether conversion of an existing TSF to HDS is possible.

What makes hydraulic dewatered stacking stand out?

Improved tailings stability

Simply and effectively dewater tailings in line with GISTM best-practice tailings management guidelines.

Dewatered and well-consolidated tailings are safer and more stable, eliminating the risk of liquefaction and catastrophic mudslides in the event of a TSF failure.

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Future-ready water management

Tailings water recovery of 75% achieved so far.

Hydraulic dewatered stacking lowers fresh water draw and/or desalination requirements, enhancing water stewardship in a water-scarce region.

Simplified and faster closure

Take a progressive approach to closure and expedite final hand-over.

Risk of re-saturation and water contamination is controlled, even after closure, while long-term subsidence is likely lower as HDS tailings consolidate quickly, as they are deposited.

Innovation in Tailings Dewatering

The development of an innovative new tailings technology, hydraulic dewatered stacking, is advancing the mining industry’s commitment to improvements in stability, water recovery and closure of tailings facilities.