In mineral processing, thickeners are used to continuously remove water from slurries. The feed enters a central well, where particles flocculate and begin to settle, forming distinct layers: a clear liquid zone at the top, a transition zone in the middle, and a compression zone at the bottom. Rotating rakes move the settled solids toward a central underflow cone, producing a dense discharge typically containing 55–75% solids. Meanwhile, the clarified liquid overflows at the edges through peripheral launders(How a Thickener Works – 911Metallurgist, 2016).
Underflow density is influenced by several key operating variables. Feed rate and particle size distribution are especially important—higher throughput or feeds with a high proportion of fines or clays tend to produce a more dilute underflow. To compensate, operators may reduce pump rates to build up an adequate bed mass (typically about 0.5–2 m above the rakes) and add flocculants (around 20–100 g per tonne of solids) to improve settling(Thickener Underflow Density Control, n.d.).
Maintaining the right balance between bed depth, rake speed (generally 0.1–0.3 RPM), and torque is essential to prevent equipment overload or stalling. Pressure sensors help maintain an optimal bed depth of about 1–1.5 m, while automated controls adjust underflow pumping to keep the system stable.
