FINLAND – Tailings dewatering and disposal is a challenge that every mining operation has to deal with. The Outotec 2nd Generation Paste Thickener is designed to maximize underflow density regardless of challenging mineralogy and tailings feed rate variation. It enables consistent and efficient dewatering performance – even with changing process conditions. Through consistent performance and high underflow density, the 2nd Generation Outotec Paste Thickener maximizes beaching angle in the tailings storage facility to provide safer operations and maximized lifespan.
Outotec 2nd Generation Paste Thickener in operation at Yara Siilinjärvi apatite mine in Finland. Courtesy of Outotec.
The new paste thickener provides ease of operation and reliability for applications requiring a high degree of dewatering, such as minerals tailings, mine backfill, and pre-leach and CCD circuits. The technology is customized to address each operation’s unique drivers, which can include environmental concerns, water recovery, regulatory requirements, tailings management, or limitations on available land space.
Unique improvements based on proven performance
Outotec has a long history of developing paste thickeners as well as the design and delivery of large-scale paste thickening projects. This has given us a 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.
“One such case was the deployment of Outotec paste thickener technology – including a full-scale paste tailings plant and Outotec ACT Thickener Optimizer system – at Yara’s Siilinjärvi apatite mine in Finland,” explains Simon Courtenay, Product Manager for the Outotec 2nd Generation Paste Thickener. “The plant generates around 10 million tons of tailings a year and thanks to the Outotec ACT Thickener Optimizer, the paste thickeners can consistently run with a high and stable underflow solids content of 66-68%, regardless of challenging mineralogy and tailings feed-rate variation. This results in average beach slope angles of 3.5 degrees (6.1%) in the tailings disposal area, helping to extend its lifespan. The system has also enabled a 10-20% reduction in flocculant costs.”
The new 2nd Generation Paste Thickener builds on this proven performance with a range of innovative new features. For example, vertical load monitoring with the Smart Rake Lift system means the Outotec Paste Thickener is one of the only systems in the world that can detect early formation of rotating beds, enabling counteractions to be taken early. The system also monitors and actively adjusts the individual hydraulic cylinders to maintain alignment of the rake mechanism. Incorporating vertical load sensing with plant process data in the Outotec ACT Thickener Optimizer control system means that the solids inventory within the tank can be maintained to ensure a consistent underflow density, stable process, and improved overall thickener performance.
In addition to mechanical improvements, process control has been further developed to stabilize and optimize the performance of the paste thickener. Outotec’s ACT Thickener Optimizer utilizes a multivariable controller to manage process changes and the associated delays in the response time of the thickener that can be challenging for traditional control systems. It can also be configured to manage the effects of variable feed types to ensure optimum performance despite changing inputs to the process. Short installation and configuration time of the system is coupled with on-going services to ensure a practical yet flexible long term control solution.
Better by design
Our application-specific design of the thickener begins with the use of methods such as discrete element modeling (DEM) to understand solid particle movement within the thickener, computational fluid dynamics (CFD) for feed system design and finite element analysis (FEA) for structural steel design. Our paste thickening solutions are also designed with ease of maintenance in mind, with a skid-mounted hydraulic power unit for centralized 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 minimize rake drive torque requirements
- Rake blades supported by thixoposts to move the rake arm away from the highest density thickened solids
- High sidewall and steep tank floor slope for more efficient dewatering of flocculated solids and compaction of the bed, as well as better transport of the solids inward toward the tank discharge point
- High installed drive torque to move the rake blades through beds of thickened solids with high yield stress and viscosity
- Feed systems with break tanks when required for different thickener feed situations, including our patented Vane Feedwell, and break tanks inside the thickener perimeter to save on site layout space
Support for the entire plant lifecycle
Beyond technology and equipment, Outotec provides complete solutions for thickening needs. Proven design features and process guarantees, combined with lifecycle service support, help ensure operational reliability. We can also support customers with ongoing operation and maintenance services after plant commissioning.