Slurry Bed Level Sensing Built for the Impossible!

Thickener Optimization Through Continuous Bed and Hindered Layer Monitoring

Efficient thickener operation is critical to the performance of modern mineral processing plants. Whether processing iron ore, copper, gold, lithium, coal, alumina, phosphate, mineral sands, or other commodities, operators rely on thickeners to maximize water recovery, improve underflow density, reduce reagent consumption, and maintain stable downstream processes.

Despite advances in thickener design, many operations continue to run below their optimum performance due to limited visibility of the internal settling process. Operators often rely on indirect indicators such as rake torque, underflow density, overflow clarity, or manual sampling. While useful, these measurements do not always provide a complete picture of what is occurring inside the thickener. The key to improved thickener performance is understanding and controlling the relationship between the compact bed and the hindered settling layer. Understanding Thickener Settling Zones Inside a thickener, solids naturally separate into distinct layers according to density. The dense compacted bed forms at the bottom of the thickener and represents the highest solids concentration. Above this lies the hindered settling layer, where particles remain suspended while continuing to settle. Above the hindered layer is the clarified liquid zone, which overflows through the launders for reuse within the plant.

The position and movement of these layers provide valuable insight into thickener performance. Changes in feed characteristics, ore mineralogy, throughput, reagent dosage, particle size distribution, or process upsets can all influence the behaviour of the settling zones.

By continuously monitoring both the compact bed level and the hindered layer interface, operators gain real-time visibility into thickener performance and can respond before process conditions deteriorate.

Improving Underflow Density and Water Recovery

Many thickeners operate with conservative bed levels to avoid the risk of bogging, excessive torque, or process instability. However, operating with a compact bed level that is too low often reduces achievable underflow density and increases the amount of water reporting to tailings storage facilities.

Maintaining the compact bed at an optimized operating position allows higher-density underflow to be produced while reducing water losses to tailings. This improves water recovery, reduces pumping costs, lowers tailings storage requirements, and increases overall process efficiency.

Continuous bed level monitoring also provides valuable feedback for controlling underflow pumps, allowing automated operation based on actual thickener conditions rather than operator judgement alone.

Optimizing Flocculant Dosing

Flocculant performance has a major influence on thickener efficiency. Under-dosing can result in poor settling, elevated suspended solids, and reduced overflow clarity. Over-dosing can increase operating costs and may even negatively affect compaction performance.

Monitoring the relationship between the hindered layer and compact bed provides a powerful method of evaluating settling efficiency. Under stable conditions, the compact bed and hindered layer generally move together. When settling conditions begin to deteriorate, the hindered layer rises while the compact bed falls, indicating that solids are no longer consolidating effectively. This early warning allows operators to adjust flocculant dosing before significant process disruption occurs.

The information can also be integrated directly into automatic control systems, providing an additional feedback loop to optimize reagent consumption and maintain stable thickener operation.

Managing Variable Ore Characteristics

Modern mineral processing facilities frequently process material from multiple ore bodies, stockpiles, or mining areas. Each material may exhibit different settling characteristics and require different flocculant requirements.

Changes in feed composition often manifest first within the settling zones of the thickener. Continuous monitoring of the compact bed and hindered layer allows process engineers to identify these changes in real time and adjust operating conditions accordingly. This capability becomes particularly valuable in CCD circuits, tailings thickeners, and concentrate thickeners where stable performance is essential for downstream recovery processes.

From Monitoring to Process Control

Traditional instrumentation often provides only monitoring information. Advanced sonar technology enables thickener measurements to be used directly for process control.

Real-time bed level measurements can be incorporated into underflow pump control strategies, while hindered layer measurements can provide supplementary feedback for flocculant dosing systems. Together with density transmitters, rake torque measurements, and overflow clarity monitoring, a comprehensive thickener control strategy can be developed.The result is improved process stability, reduced operator intervention, lower reagent consumption, improved water recovery, and more consistent underflow density.

Sonar Technology for Thickener Applications HAWK's ORCA Sonar Level Transmitter is specifically designed for difficult slurry and thickener applications. The high-powered sonar system is capable of penetrating suspended solids and identifying multiple density interfaces within the thickener, including both the compact bed and hindered settling layer. This provides operators with continuous visibility of the internal settling process and allows real-time optimization of thickener performance across a wide range of applications, including tailings thickeners, CCD circuits, concentrate thickeners, water recovery systems, and clarification processes. By transforming internal thickener conditions into actionable process information, ORCA Sonar enables mining operations to maximize throughput, improve water recovery, reduce operating costs, and achieve more consistent process performance.

For nearly 30 years HAWK has developed a unique range of Slurry Level Technologies to solve the most difficult level applications for which competitors struggle to provide solutions. HAWK’s technological advances in Sonar design provide much higher power on signal propagation through challenging liquid and settling media. A blend of exceptional transducer design and advanced signal processing with automatic control allows HAWK to work on almost every level measurement application.