ANS:B - sedimentation

Dorr thickener is an equipment used for sedimentation. A Dorr thickener, also known as a continuous thickener, is a type of sedimentation equipment used to increase the concentration of solids in a liquid/solids mixture by sedimentation. It operates on the principle of gravity sedimentation, where particles settle under the influence of gravity. In a Dorr thickener, the liquid/solids mixture is fed into a large tank, known as a thickener tank, where it is allowed to settle. The solid particles settle to the bottom of the tank, forming a thickened slurry, while the clarified liquid overflows from the top of the tank. The settled solids are then removed from the bottom of the tank using a rake mechanism or similar device. Dorr thickeners are commonly used in mineral processing, wastewater treatment, and other industries where the separation and concentration of solids from liquids are required. They are particularly effective for large-scale applications where high throughput and efficiency are needed.