PURPOSE: To efficiency separate Na from Ca by centrifugally separating sludge contg. Na, Ca and their oxide.

CONSTITUTION: The sludge generally consisting of 70% Na, 20% Ca and 10% hybrid oxide (consisting mainly of Na2O) is housed into a wire net cage made of stainless steel having meshes of preferably 25 to 125 micrometers. Next, the wire net cage contg. the sludge is immersed into an oil bath kept preferably at 110 to 200°C. The wire net cage is rotated preferably at a rotating speed of 600 to 300 r.p.m. The Na is taken as many pieces of discrete particles to the outside of the cage through the meshes of the wire net by the centrifugal force to be applied on the sludge. These particles are gathered at the bottom of the oil bath and are recovered. After the Na is separated from the sludge, the Ca is separated from the residual components remaining thereafter.