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Tailings management and water stewardship in mining

Traditional wet tailings storage facilities consume considerable quantities of water. New tailings management practices aim to recover much of this water for reuse in the mineral processing plant, reducing raw water draw and the regional water impact of mining operations – a key element in mining sustainability.

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The tailings dilemma 

Mine tailings are the waste byproduct left after extracting the economic fraction from ore. Although the exact composition varies according to the ore and processing methodology, tailings generally contain a significant water fraction alongside unwanted gangue material and chemical reagents. Conventional practice is to pump the tailings by pipeline to a surface storage facility and to return water for reuse after the solids settle. However, much water remains in the tailings or is lost and must be replaced, requiring significant annual water draw by mining operations.  

Although offering low CAPEX and OPEX, conventional tailings management poses the following problems:  

  • Highly inefficient water recovery. 
  • Containment required (higher risk of TSF failure).  
  • High potential for run-off and seepage.  
  • Challenging rehabilitation (high rehabilitation costs).  

Several factors exacerbate this tailings water dilemma. Many mining regions are in water-scarce areas. Climate change is anticipated to increase the frequency of extreme water events, such as droughts, which reduce water supply and risk water conflict with local communities, and floods, which risk inundating tailings storage facilities, causing them to fail. At the same time, declining ore grades will increase the amount of ROM material processed, generating more tailings and consuming even more water. 

With estimated annual tailings production well exceeding 10 billion tonnes, a new paradigm is urgently needed to reduce tailings volume and maximise tailings water recovery. Technological innovation will be important in developing this new paradigm, with FLS offering several solutions to enhance tailings water recovery and treatment.  

As with most sustainability innovations in mining, there is no one-size-fits-all solution for tailings water recovery and recycling. The most appropriate tailings management solutions will depend on several factors. For example, climatic conditions play a part in determining the economics and practicality of tailings dewatering. Water costs tend to be low in wet climates, making tailings dewatering economically unattractive. In contrast, tailings dewatering will be more economically viable in dryer climates due to the higher water cost, which offsets dewatering and water treatment costs.  

Mineralogy and topography also impact any tailings management plan. The type and quantity of clays in a deposit can significantly impact tailings dewatering: high clay content results in low dewatering rates and the need for higher-capacity, more expensive equipment. Flat ground requires expensive dams to enclose any wet tailings storage facility, while valleys only need a dam at the end to contain tailings (but capacity is limited). There is also the simple need for space. Remove the water, and you extend the operating life of any storage facility.  

FLS tailings management solutions

Thickened tailings

High-rate or high-density thickeners concentrate tailings before disposal, recovering a significant amount of process water and creating high-density tailings. For example, FLS Deep-Cone® thickeners can recover up to 70% of tailings water, making them ideal for water conservation. Deep-Cone thickeners feature deep side walls, steep cone angles, and a patented inner spiral rake design to create and allow effective operation with deep mud beds, extended mud residency times, and increased solids compaction – all of which optimise water recovery.  

Meanwhile, the E-CAT™ thickener combines high-rate thickening and water clarification into a single unit. These thickeners handle high throughputs while achieving highly efficient solid-liquid separations to produce a high-clarity overflow for excellent water recovery and minimal water treatment costs. 

Filtered tailings

Tailings filtration incorporates high-rate or high-density thickeners followed by various filters to achieve up to 95% tailings water recovery. Filtered tailings, thus, increase the water returned to the plant for re-use; however, selecting the correct filter is critical. Some tailings can be sufficiently dewatered using a vacuum filter, while others require pressure filtration, such as the latest AFP2500 filter press. Designing an effective – but not cost-prohibitive – filtered tailings solution is a balancing act that requires an in-depth understanding of tailings characteristics, process, equipment capabilities, and costs.  

With a maximum filter feed pressure of 15 Bar, the AFP2500 filter press achieves maximum cake density and minimum cake moisture, without using membranes, when dewatering many concentrate and tailings slurries. It also incorporates data-driven control and decision-making for optimised proactive maintenance. For example, the Intelliplate plate alarm system detects the time and location of any media failure so the issue can be addressed before it propagates or damages plates. Meanwhile, a moisture sensor determines cake moisture every 10-30 minutes, allowing near real-time responsiveness to filter performance issues.  

EcoTails® co-mingled tailings 

The EcoTails co-mingled tailings solution was developed in collaboration with an industrial partner. It blends ‘fast filtered’ tailings with waste rock in transit to create a geotechnically stable product called GeoWaste™. GeoWaste is easy to convey and has a high strength when stacked, making stacking possible for large-scale mining operations, even in areas with high seismic activity or precipitation.  

EcoTails, thus, offers the advantages of filtered tailings with the following additional benefits:  

  • Reduced opportunity for oxygen flow as fine tailings fill voids between rock particles.  
  • Reduced risk of acid rock drainage.  
  • Increased shear strength for improved physical stability provided by coarse waste rock.  
  • Smaller total waste footprint as tailings and waste rock disposal are combined.  

The FLS fast filtering solution provides the technological basis for EcoTails co-mingled tailings, increasing the filter process's speed and allowing high-volume tailings processing. Meanwhile, fixed or semi-mobile crushing stations process waste rock for efficient co-mingling.   

Paste tailings

Paste tailings have been dewatered to form a thick, non-segregating paste with minimal water content. This means they don’t flow easily and produce little to no seepage when stored. Paste tailings are often used to backfill underground mines. The paste is mixed with a binder, such as cement, to support and prevent heading collapse and subsidence. Any excess paste can be stored in surface tailings facilities. 

Most paste backfill projects have used FLS dewatering equipment, such as Deep-Cone thickeners or vacuum filters. In addition to recovering significant tailings water via thickening and filtration, paste backfill reduces surface tailings storage requirements while supporting underground mining operations, allowing previously unmined ore (pillars and supports) to be extracted. Mixing the paste with a binder stabilises the tailings, minimising the risk of groundwater contamination. Acid rock drainage is also reduced for certain ores. 

The future of tailings management 

Innovative tailings management solutions, such as Eco-Tails and paste tailings, may require higher CAPEX than conventional tailings storage facilities; however, when long-term water risks are considered alongside safety and future liability issues, the business case can be much more attractive. It is simply the case that mining companies must address water and tailings risks now to avoid future disruption to mining operations caused by changes to water availability and potential challenges to the practicalities, economics, and social licence to operate these may cause. 

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Frequently asked questions

FAQs for tailings management

A tailings dam is an earth-fill embankment dam that contains waste byproducts of mining operations (tailings). Tailings dams are typically built using tailings mixed with other materials, such as waste rock. Their primary purpose is to contain the tailings safely, ensuring the health and safety of employees and communities as well as preventing environmental contamination.

Water is used in almost all mineral processing with most of that water reporting to the tailings. When the tailings are stored, a significant portion is “trapped” or entrained with the solids, with some water lost through evaporation or seepage and replaced through freshwater draw. In water-scarce areas, where mining may be the largest water user, this can strain water resources, risking water conflict with local communities and other industries (such as agriculture) and damage to local ecosystems. Recovering tailings water for reuse reduces a mine’s freshwater consumption and thus mitigates these potential negative impacts.

Today, tailings are mainly disposed of in wet tailings storage facilities. These facilities contain the tailings slurry behind a tailings dam (embankment), with conventional storage methods including cross-valley and paddock (ring-dyke) impoundments. Alternative tailings disposal methods include filtered or paste tailings (which can also be used as backfill in underground mining). The approach to tailings disposal depends on multiple factors, including the miner’s governance approach, government regulation, ore characteristics, local topography and climate, site geology and seismic risk, and economics.  

Thickened tailings have been concentrated using thickening technology, such as high-rate or high-density thickeners, which can remove up to 70% of the water and create tailings with a high solids content.  

Filtered tailing are thickened tailings that undergo a secondary dewatering stage, extracting up to 95% of the tailings water. Various filtration techniques are available – from simple gravity filtration to digitally optimised pressure-based equipment like the AFP2500 filter press. Selecting the most appropriate filtration technology depends on the tailings’ characteristics.  

Paste tailings have been dewatered via thickening/filtration to produce a thick, non-segregating paste with minimal water content, which can be disposed of in smaller surface impoundments or used as a backfill in underground mining.  

Co-mingled tailings, such as the GeoWaste material produced using the Eco-Tails process, combine tailings and waste rock to create a geotechnically stable material. This allows stacking of tailings in areas where it would otherwise not be appropriate, such as areas of high seismic activity or precipitation.