This process, tried at Marion, Ky., is somewhat different from the other flotation processes, inasmuch as no acid is used in the bath, the latter being, on the contrary, basic, being in fact a very dilute solution of aluminium sulphate. Moreover, instead of being performed in deep vats, as in the case of the acid-flotation process (wherein the depth of the vat has been found to be a rather important consideration), the basic flotation process is performed in shallow pans, in which mechanical stirrers are operated. Besides the trials at Marion, some experiments with the Sanders process have been made by the Tennessee Zinc Company at Straight Creek, Tenn. The Kelly mine, near Magdalena, N.M., was equipped with a loo-ton plant.

The apparatus (Fig. 53) consists of a vat, preferably round, with a feed-hopper leading below the normal liquid surface. A solution-inlet pipe is placed either in the vat or in the hopper, depending on the ore to be treated. A vertical shaft in the centre of the vat rotates an agitator, the blades of which are arranged to impart a whirling motion to the solution. This whirling motion is designed to assist in raising the valuable mineral particles to the centre of the vat, and to cause a slight cavitation at the centre of the surface, which causes the particles which have been elevated to pass at once to the overflow pipe. The tailing is discharged through a pipe in the centre of the bottom of the vat. A steam-pipe is used on the bottom of the vat to keep the solution at an even temperature.