Firstly, mineral liquid is mixed uniformly and then carried into thickener. Secondly, by the action of cohesive and gravitational force, the majority of overflows are overflowed through the overflow groove. The minority of overflows form small cyclone inside the settling area and subsequently are compressed in the compressive area. As a result, granules are compressed by gravity and then fall down, while clear liquid moves upward. Finally, concentrations are discharged from the lower underflow tube.