PURPOSE:To restore the fire resistance of chromite sand by bringing the recovered sand into contact with a grindstone rotating at a high speed. CONSTITUTION:Chromite sand is introduced from an entrance opening 38 of a hopper 40 onto the bottom part 10a of a casing thereof. A motor 34 is energized to rotate a rotary grindstone 18 in the direction B at a high speed and a rotary drum 14 in the direction A at a lower speed, whereby the chromite sand collected on the casing bottom 10a is picked up by lifting blades 24 of the rotary drum 14 and delivered into each space S thereof through slits 22 and whereby the chromite sand C is dropped onto the grindstone 18 rotating at a high speed. This improves the fire resistance of the chromite sand.
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