High-Density Thickeners

High-Density Thickeners can come as either elevated or on-ground tanks according to industry preference. Likewise, the tank structure is available in a number of material choices, such as steel, concrete or FRP. 

 They are commonly characterized by:

• Having a higher sidewall tank (to provide enhanced compression effects)
• A steeper floor slope to assist in moving solids to the discharge area
• A low profile rake structure combined with pickets to enhance the bed dewatering
• A rake drive suitable for underflow mud with a yield stress of 50-150 Pa
• Producing underflow mud capable of being pumped with the McLanahan M3H centrifugal Slurry Pump

How High-Density Thickeners Work

High-Density Thickeners separate liquids from solids using gravity settling. A key requirement is to contact the solids with added chemicals under the right shear conditions for building large floccules. The efficiency of flocculation contributes to an enhanced settling rate. Once settled in the bottom of the tank, the deep mud bed is further dewatered by the use of pickets attached to the rake arms. Thickeners are operated and controlled by a touchscreen programmable logic controller system. Operating logic allows for the customization of the unit for plant needs, including the ability for the Thickener to shut down without an operator being present during extended hours of operation. The hydraulic drive gives an accurate sense of torque on the rakes. At high-torque conditions, a rake lift will activate to draw the rakes up from the mud. The system then steps the rake down, monitoring torque on the way.

High-Density Thickeners are found in many applications such as:

• In the feed preparation to a subsequent filtration stage. Filters are most efficiently sized with a higher solids concentration but not too high such that the flow properties into the filter are inhibited. This enables the designer to take advantage of the lower operating costs of gravity separation provided by thickener before requiring the higher driven force (and higher cost) of a vacuum or pressure filter.
• Where there is value in improving water recovery in a tailings application but insufficient justification for a full paste system.
• In a counter-current wash system where the higher underflow densities may reduce the number of stages required or reduce the volume of wash water required.