The grinding circuit at the Sweetwater Mill consists of an 18 x 6 Koppers semi-autogenous grinding mill (shown) in a closed loop with one of two 26 inch Krebs hydro-cyclones. The grinding circuit flowsheet can be viewed as a *.dwf file in AutoDesk's ExpressViewer. Other uranium mills use other grinding arrangements including a crusher (Ambrosia Lake Mill), rod mills and ball mills. The term semi-autogenous means that the ore acts to a certain extent as its own grinding media. The flow through the circuit is fresh ore fed onto the conveyor and scrubbed to a +10 to -20 mesh in the mill with the aid of 3 - 4 inch in diameter steel grinding balls. The scrubbing action takes place inside the mill with the lifting action of the sag mill as it rotates at 13 rpm. The design rate of flow of the mill is 137 dry tons per hour or 152 tons per hour (wet). The ore is mixed with the cyclone underflow and makeup water as it enters the sag mill. Ground ore leaves the sag mill at a design density of 70% solids and a maximum size of 1/2 inch. The maximum discharge size is determined by the size of the mill discharge grates. Undersized ground ore leaving the sag mill and cyclones enters the leach tanks .