The present invention concerns an apparatus for treating and cooling foundry molding sand, comprising a mixing container and a mixing tool rotatable about a drive shaft, wherein there is provided an air feed for the feed of air into the container interior. To provide an improved apparatus with which a more uniform fluidized layer is produced as far as possible over the entire cross-section of the mixing container, wherein moreover the proportion of the solid particles entrained with the gas flow is to be reduced, it is proposed according to the invention that the mixing tool has at least two mixing vanes spaced from each other in the vertical direction and at least one mixing vane has a mixer blade with a surface which is inclined relative to the horizontal.