The classification determines which parts of the sludge are fine enough to continue in the process and which need to be returned to the mill for further grinding. The classification is based either on centrifugal force or the time in which smaller pieces of ore sink in the sludge.

You can see three different classifiers in the exhibition. The screw classifier and the rake classifier are based on the sinking speed of the pieces of ore and the hydrocyclone classifier operates by centrifugal force.