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Thickening

Water stewardship through innovation: pioneering thickener technology

Thickening has long been essential to mineral processing flowsheets. Today, they are taking on increased importance within the drive to improve water stewardship and tailings management, enabling mines to recycle more water, reduce tailings footprint, and enhance process efficiency.

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Thickeners and the water challenge

Water access is an increasing risk factor for mining operations, many of which are in areas of water stress. Climate change is expected to exacerbate this risk, causing more frequent droughts and altering the water supply to mining sites. The water challenge could thus disrupt operations, increase costs, and raise the risk of water conflict between mines and local communities. In this context, water recovery and recycling become critical operational concerns.

Thickeners are one of the technologies that enable mines to face this water challenge. Their job is simple: to separate solids from liquids. In doing so, they concentrate the solids while producing a clear water overflow that can be recycled back into the process. They are used extensively to dewater tailings, making them easier to manage, but they can also concentrate mineral slurries before further processing. 

The evolution of thickener technology 

The first thickeners were simple gravity-based settling tanks. They were slow-settling and needed a large unit area while producing a low underflow density. Improvements to thickener design in the mid-20th century and the introduction of chemical flocculants to promote particle aggregation increased the rate of solid-liquid separation. However, it was not until the 1980s that thickener development took a significant lead forward with high-rate thickeners. 

FLS high-rate thickeners were designed to offer mining companies a more compact and cost-effective solution capable of processing larger volumes of slurry while producing a clearer overflow.  They feature the improved E-Volute™ feedwell to optimise energy dissipation and solids distribution, while advanced E-DUC® and P-DUC feed slurry dilution systems maximise flocculation efficiency and settling rates. Other benefits include better slimes management.   

In recent years, the focus has shifted to maximising the solids concentration in the underflow, leading to the introduction of high-density thickeners. These systems are designed to produce denser tailings with lower water content, enabling easier handling (with suitably designed underflow systems) while reducing the footprint of tailings storage facilities. 

FLS Deep Cone® thickeners feature deep side walls, steep cone angles, and a patented inner spiral rake design. These features create and allow effective operation with deeper mud beds, extending mud residency time and increasing solids compaction. Deep Cone thickeners can achieve underflow densities of up to and exceeding 70 wt%, making them ideal for applications where water conservation and tailings management are critical.

A final development of note is the E-CAT™ thickener from FLS,  a high-rate thickening solution that combines high-rate thickening and water clarification into a single unit. E-CAT units can handle high throughputs, achieving highly efficient solid-liquid separation to produce a high-clarity overflow, maximising water recovery while minimising water treatment costs.

The benefits of modern thickener technology

  • Maximised water recovery

    Modern thickeners, particularly paste thickeners, can recover a significant portion of process water, reducing the demand for freshwater intake. This is especially important in regions where water is scarce or where strict water usage regulations are in place.

  • Reduced tailings footprint

    Denser tailings with low moisture content allow mining operations to minimise the footprint of tailings storage facilities. This reduces the environmental impact and decreases the long-term risk and liability.

  • Improved operational efficiency

    Innovations in thickener design have improved the throughput and efficiency of mineral processing plants. This translates into lower energy consumption, reduced chemical usage, and overall cost savings.

  • Enhanced compliance with environmental regulations

    As regulatory bodies worldwide tighten environmental standards, mining companies must demonstrate responsible water and tailings management. Modern thickening technologies help operators meet these regulations while enhancing their sustainability credentials.

  • Increased safety

    Paste thickeners, in particular, enhance the safety of tailings management by producing a more stable and less fluid tailings material. This reduces the risk of tailings dam failures, which can have catastrophic environmental and social consequences.

Leading innovations in thickener design

E-DUC dilution systems

The E-DUC system uses feed momentum to dilute the feed slurry before it enters the thickener’s feedwell, resulting in more controlled and effective mixing profiles and residency time. Doing so maximises contact between the flocculant and the solids in the slurry, leading to better agglomeration and improved settling characteristics and thus reducing the amount of chemical required – and hence flocculant costs. 

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Thickeners in the digital era

Digitalisation is also now playing a part in thickener optimisation. Advanced process control technologies, such as the AutoFloc™ solution from FLS, continuously monitor critical variables, such as bed level and pressure, rake torque, overflow clarity, underflow density, setting rate, and feed disturbances, making real-time dynamic operational adjustments to flocculant dosage and underflow pump speed.

These technologies aim to deliver the following objectives:

  • Maintain underflow density within a specified range to ensure consistent output quality and meet processing requirements.
  • Maximize the amount of clear water recycled back into the plant.
  • Use the minimum flocculant required for effective flocculation, lowering chemical costs and environmental impact.
  • Keep the thickener inventory within set parameters to ensure stable operation and prevent upset conditions.
  • Continuously monitor and regulate critical parameters, such as rake torque, pump amperage, and bed pressure, to prevent equipment overload and extend component life.
Performance studies

Upgrades to boost existing thickener performance

  • Performance study

    Reducing water to tailings at a Canadian gold mine

    A Canadian gold mine  wanted to increase water recycling from its tailings thickener to reduce raw water draw and extend the life of its tailings dam. Upgrading an existing third-party thickener with an E-DUC® dilution system and E-Volute™ feedwell, drive, and low drag rake mechanism resulted in the following:  

    • An increase in underflow density from 61% solids (w/w) to 65% solids (w/w).
    • A 12% reduction in the amount of water to tailings.
    • An improvement in overflow clarity from 400 NTU to less than 100 NTU. 
    • A reduction in flocculant consumption. 


    Read the study

  • Performance study

    Increasing gold recovery and saving water at an Australian mine

    At an Australian gold mine , the installation of P-DUC dilution mechanisms on the leach feed and tailings thickeners resulted in the following: 

    • Thickener throughput rose from 1060 tph to 1160 tph, with no increase in flocculant consumption on a gram/tonne basis. 
    • Leach feed thickener underflow density increased from 54% to 56% solids (w/w). This extended residence time in the CIL circuit and improved recovery without increasing the ore mined. 
    • Tailings thickener underflow density increased from 54% to 57% solids (w/w), reducing the volume of water reporting to the tailings dam by 11%. This resulted in a lower freshwater draw, while water was lost to evaporation and seepage. 


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  • Performance study

    Increasing tailings dam stability and water recovery in Kazakhstan

    Insufficiently dewatered tailings were impacting the stability of the tailings dam at a Kazakhstan copper mine. This increased the amount of water lost to tailings and required an earlier-than-expected expansion of the tailings storage facility (TSF).

    The upgrade achieved:  

    • A 15% increase in water recovery at the plant
    • A 15% reduction in tailings volume
    • Reduced ratholing and more consistent mud bed residence time
    • Maximised deposited tailings density and better utilisation of available TSF footprint

    Read the study

  • Performance study

    Achieving a significant reduction in water to tailings in Chile

    A Chilean copper-molybdenum mine  located 1700m above sea level in an area of water scarcity was receiving seawater from the water-cooling system of a coastal thermoelectric power plant via a 143 km pipeline. This was expensive and likely to become more so. The mine thus wanted to ensure that as much water as possible was being recycled from tailings. To do so, the mine implemented the AutoFloc advanced process control solution with the following results: 

    • 14% reduction in water to tailings at a potential saving of USD 18 million per year (based on an average water cost of USD3.50/m3).  
    • 15% decrease in flocculant consumption at an OPEX saving of USD 350,000 per year (based on flocculant costs of USD4.00/kg). 
    • 3% solids (w/w) increase in underflow density.
    • Lower pumping costs and associated energy consumption.

    Read the study

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The future of thickeners

As the mining industry prioritises sustainability, the role of thickeners in water stewardship will only become more critical. With over 100 years of expertise and 10,000 thickener installations, FLS is ideally placed to continue innovating advanced thickening solutions that enhance water recovery, reduce tailings storage risks, and improve operational efficiency.