Thickener

What is a thickener?

A thickener is usually the first stage of dewatering for concentrates and tailings. It is a large, often circular tank into which slurry is fed through a central feedwell. Solids settle to the bottom, where slowly rotating rakes move them to a central outlet. The dense slurry drawn off there is the underflow. Clear water rises and spills over a launder around the rim as the overflow.

What thickeners do

• Recover water. Overflow water is returned to the plant, which is critical where water is scarce.
• Increase solids density. A denser underflow is easier to filter, safer to store as tailings, and cheaper to pump over short distances.
• Clarify water, producing overflow clean enough for reuse.

Types of thickeners

• Conventional thickeners, large and slow.
• High-rate thickeners, which use efficient flocculant dosing and feedwell design to achieve more throughput in a smaller tank.
• High-density and paste thickeners, which produce very dense underflows, used for thickened or paste tailings.

What affects thickener performance

• Flocculation. Most thickeners rely on flocculants, polymers that bind fine particles into larger flocs that settle faster. Dosage and mixing are critical.
• Particle size and mineralogy. Fine particles and clays settle slowly and can cloud the overflow.
• Slurry chemistry. pH, dissolved salts and residual flotation reagents affect how particles aggregate.
• Feed rate. Overloading a thickener reduces underflow density and overflow clarity.

Performance is tracked by underflow density, often as percent solids, and overflow clarity, often measured as turbidity.

Frequently asked questions