The rotary drum filter consists of a drum on which a filter cloth is tightened with a metal wire. The drum is in a basin. Inside the drum a suction draws sludge from the basin through the filter cloth as the drum rotates in the basin. The concentrate sticks to the cloth and rises upward on the rotating drum, drying on the way. Once concentrate reaches the far side of the drum, the pressure is reversed and the “sludge cake” comes off the surface.

The rotary drum filter was first patented as early as 1872. The rotary drum filter has been used in both the old concentration plant and the Keretti concentration plant. In the old mine, the concentration plant started operating with rotary drum filters, but they were found to be ineffective and were replaced by disk filters.