PURPOSE: To enable the reconditioning and recycling of used green sand by drying and calcining the green sand to evaporate org. matter, then mechanically separating clay and further reacting the green sand with an aq. acid soln. to free the clay.

CONSTITUTION: The used green sand regulated in grain sizes is sent to a drying/sizing device 6 where the moisture is reduced to zero and the clay is made to soar up from a sand bed 8. The separated sand is sent from a hopper 10 to a fluidized bed type thermal calcining machine 14 where the temp. of the sand is elevated and an org. binder is removed. The calcined sand is dropped onto a cooling/separating device 30 to separate the clay. The sand is then released into a bombardment chamber 38 where the bonding of the sand and the clay is destroyed. The sand from which the clay particles are removed is transferred to a surge hopper, is metered and is sent to a mixer 48. Simultaneously the aq. acid soln. is poured by a metering pump 50 into the same and is mixed therewith, by which the clay particles are separated. The sand regulated in pH is fluidized in the drying/sizing device 56 to have clay particles captured in an air passage pipe 60. As a result, the dry sand which does not contain the clay and is regulated in the pH is obtd.