Key Benefits

  • Increased raking capacity
  • Reduced ratholing
  • Improved mud bed residence time
  • Reduced energy and water consumption
  • Reduced maintenace

Tailings thickener inner rake blade

Thickeners not only help create a more sustainable site by producing reusable process water, they also minimise the environmental impact and safety risks associated with multiple or large settling ponds. The spiral design of our thickener rake blade addresses the challenges operators often face with raking capacities of traditional high-tonnage standard machines - including ratholing, high energy consumption and water loss.

In addition to providing high-quality raw materials for processing, mine operators must also meet increasing demands for environmentally conscious practices. We know that properly optimised thickeners will help to increase mine performance, reduce operating costs and improve a mine’s sustainability – which is why we have developed our spiral rake blade for thickeners. The spiral design allows for higher underflow densities at lower torque, which significantly reduces energy and water consumption. 

Better distribution = better performance 

One common issue with traditional high-tonnage thickener rakes is the inability to move mud evenly to the outlet, causing the lower-viscosity material to flow out too quickly – also known as ratholing.


The spiral inner blade improves mud bed residence time distribution as it cuts off short circuiting and eliminates dead zones. The spiral design steadily pulls more material along the floor, so mud bed distribution is much more even, effectively eliminating the ratholing effect.


This innovation has a side benefit of reducing the torque requirements dramatically. The spiral rake blade combines with a low-drag rake arm that has proven critical to discharging high underflow densities while allowing for easy operation and control. And because the spiral rake assembly produces a denser material in the thickener, less water is lost in the tailings, allowing more water to be recycled back into the plant. 


Improved efficiency on high-tonnage thickeners

The spiral design of our thickener rake arm assembly offers a number of unique benefits that traditional rake arms cannot provide. By delivering a consistent, low-torque action in the high-density underflow, the spiral rake arm reduces power peaks and valleys, and reduces the ratholing that conventional straight rake arms can create.

Increased raking capacity
Improved raking power at a lower torque ensures the mining thickener rake arm will better manage underflow densities and mud bed residence time for improved discharge material. 
Reduced ratholing
The spiral design moves material evenly and steadily along the thickener floor for more consistent mud bed distribution, cutting off ratholing. 
Improved mud bed residence time
The spiral inner blade improves mud bed residence time distribution by cutting off short circuiting and eliminating dead zones. This allows the underflow to properly thicken prior to discharge. 
Reduced energy and water consumption
The combined advantages of reduced torque and the spiral rake blades’ steady and consistent action in the mud bed (improving underflow density and clarified overflow) result in overall lower energy consumption and increased water reclamation. 
Reduced maintenance
By lowering overall torque while effectively moving solids, the spiral rake assembly improves the life of the rake arms and the drive motor. Steadier contact with the underflow reduces wear on components. 
Mud bed raking pattern of the FLSmidth spiral rake blade for thickeners.

Spiral rake assembly

Conventional rakes do not provide enough raking capacity to move mud evenly to the outlet. Instead, the low-density material ratholes, flowing directly toward the outlet without optimal time in the thickener. The spiral rake blade achieves an even residence time, as well as overall higher underflow density, as compared to a traditional rake arm. Longer time is better for thickening – up 0 to 2 hrs for low density, where 3 to 8 hours is ideal for even distribution and higher density.

Ratholing occurs when lower-viscosity material flows out too quickly due to uneven distribution.

Thickeners work on the operating principles of gravity and particle interactions, with solids settling downwards and liquids rising to the top as they separate. The design of the thickener focuses on providing a high-density underflow while maintaining an acceptable overflow clarity. 

To that end, our spiral rake arm and blade assembly increases residence time for solids in the mud bed, which creates higher underflow density, as compared to a traditional rake arm. By producing denser material in the thickener underflow, less water is lost in the tailings and instead is recycled back into the plant. 

We build our spiral rake assembly for thickeners in a high-strength tubular construction that in and of itself will enable an increase in underflow density of 2 to 3 wt%, compared with traditional box-truss construction. It is ruggedly dependable and intuitively designed for long life and continually impactful results in your mining tailings management efforts. 

We design and build all of our energy- and water-saving thickener units and components to provide the most economical and reliable solution for your processes. All of our thickener products are backed by more than 100 years of experience in engineering and manufacturing, ensuring you the best thickener fit for your unique plant requirements. 

FLS_thickener_spiral rake blade

An eye towards the future

With more than a century of experience in mining tailings management, we have high-tonnage thickener installations in more applications across the world than any of our competitors. The success of your operation is too important to trust to just anyone, and we understand your unique needs for sustainable mining. That’s why our thickeners are built with your specific operation in mind. We’ll work closely with you to ensure proper installation and correct maintenance. 

We are your partner, not just your supplier

Get in touch and benefit from our decades of operational expertise.

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