A thickener is a solid-liquid separation device based on the principle of gravity sedimentation. Typically, it consists of a shallow cylindrical tank with a conical bottom, constructed using structural materials such as concrete, wood, or welded metal plates. It is capable of concentrating mineral slurries with a solids content of 10%–20%-via gravity sedimentation-into a thickened underflow slurry with a solids content of 45%–55%. A rake mechanism, installed within the thickener and rotating at a slow speed (1/3 to 1/5 rpm), facilitates the discharge of this thickened underflow slurry through an outlet located at the bottom of the tank.
The upper section of the thickener yields a relatively clear liquid (known as the overflow), which is discharged through an annular launder located at the top.
Thickeners are widely utilized in production environments requiring solid-liquid enrichment and separation-such as hydrometallurgy operations, mineral processing plants, and chemical factories-and typically range in diameter from 3 to 100 meters, with depths ranging from 2 to 4 meters.
In a central-drive thickener, the tank bottom features a gently sloping conical shape, with an inclination angle of 6° to 12° relative to the horizontal plane. The rake mechanism comprises rake arms, rake blades (teeth), and reinforcing tie rods; the two radially arranged rake arms are positioned perpendicular to each other, forming a cross shape, while the rake blades are mounted on the arms at an angle of approximately 30°. To enhance efficiency, some mineral processing plants have implemented technical upgrades; for instance, the Nanfen Mineral Processing Plant employs gamma-ray density measurement to control the concentration of the underflow slurry. Similarly, Henan Luoyang Luanchuan Molybdenum Co., Ltd. increased its processing capacity by 8%–10% by modifying its feeding method to introduce the slurry directly into the high-density zone and by incorporating an agitation device. Deep-cone thickeners can be dosed with flocculants to further increase both the underflow concentration and the processing capacity. As a core thickening unit, thickeners have been successfully deployed in Phase I of the 2-million-ton-per-year potassium chloride project at the Kouilou Potash Mine in the Republic of the Congo.
