Tailings dewatering and disposal is a challenge that Finnish-listed technology company Outotec has sought to address by introducing the Outotec 2nd Generation Paste Thickener, which is able to maximise underflow density regardless of challenging mineralogy and tailings feed rate variation.
The paste thickener enables consistent and efficient dewatering performance. Its consistent performance and high underflow density maximises beaching angle in the tailings storage facility to provide safer operations and enhanced life span.
Outotec 2nd Generation Paste Thickener product manager Simon Courtenay explains that the new paste thickener enables ease of operation and reliability for applications requiring a high degree of dewatering, specifically, minerals tailings, mine backfill, and pre-leach and charge-coupled device circuits.
The technology is customised to address each operation’s unique drivers, including environmental concerns, water recovery, regulatory requirements, tailings management, and land limitations.
Improved by Performance
“Outotec has a long history of developing paste thickeners as well as the design and delivery of large-scale paste thickening projects,” says Courtenay, adding that this has enabled the company’s deep understanding of the key aspects of high-density thickeners, including effective flocculation, dewatering, raking, prevention of rotating mud beds, process control, and the discharge of thickened solids.
He points to a case involving the deployment of Outotec paste thickener technology – including a full-scale paste tailings plant and Outotec ACT Thickener Optimiser system – at Norwegian fertiliser company Yara’s Siilinjärvi apatite mine, in Finland.
Courtenay explains that Siilinjärvi’s plant generates around 10-million tons of tailings a year and, owing to the Outotec ACT Thickener Optimiser, the paste thickeners can consistently run with a high and stable underflow solids content of 66% to 68%.
This results in average beach slope angles of 3.5 ºC in the tailings disposal area, which assists in extending the tailings storage facility’s life. The Outotec system has also enabled a 10% to 20% reduction in flocculant costs.
The new 2nd Generation Paste Thickener builds on the ACT Thickener Optimiser’s proven performance with several new and innovative features.
Vertical load monitoring with the Smart Rake Lift system means the thickener is one of the only systems in the world that can detect early formation of rotating beds, allowing for early counteraction.
The system also monitors and actively adjusts the individual hydraulic cylinders to maintain alignment of the rake mechanism, Courtenay explains.
Incorporating vertical load sensing with plant process data in the ACT Thickener Optimiser control system means that the solids inventory within the tank can be maintained to ensure improved overall thickener performance.
In addition to mechanical improvements, process control has been further developed to stabilise and optimise the performance of the paste thickener.
Courtenay highlights that, the ACT Thickener Optimiser uses a multivariable controller to manage process changes, as well as the associated delays in the response time of the thickener, which can be challenging for traditional control systems.
It can also be configured to manage the effects of variable feed types to ensure optimum performance.
Courtenay adds that the system’s short installation and configuration time is coupled with ongoing services to ensure a practical yet flexible long-term control solution.
Design Specifications
“Our application-specific design of the thickener begins with the use of methods such as discrete element modelling to understand solid particle movement within the thickener, computational fluid dynamics for feed system design and finite element analysis for structural steel design.”
Courtenay adds that the paste thickening solutions are also designed with ease of maintenance in mind, pointing to the skid-mounted hydraulic power unit enabling centralised connection of hydraulic hosing from the rake lift cylinders and drive unit.
Other key design features include low profile rakes with tie-cable load sharing that reduces rake drive torque requirements, as well as rake blades supported by thixoposts to move the rake arm away from the highest density thickened solids.
The thickener also has high sidewall and steep tank floor slope for more efficient dewatering of flocculated solids and compaction of the bed. It also enables better transport of the solids inward toward the tank discharge point.
The system’s high installed drive torque facilitates the rake blade’s movement through beds of thickened solids with high yield stress and viscosity.
The thickener also has feed systems with break tanks which can be used as required for different thickener feed situations. This includes Outotec’s patented Vane Feedwell, and break tanks inside the thickener perimeter which saves on site space, Courtenay notes.
Plant Life Cycle Support
Beyond the technology and equipment, Outotec also provides complete solutions for thickening needs to help ensure operational reliability, Courtenay states.
“We can also support customers with ongoing operation and maintenance services after plant commissioning,” he concludes.