How do I obtain iodine crystals from solid mixtures of iodine and sand?
Iodine crystals can be separated from sand by sublimation. Solid iodine undergoes sublimation to form purple iodine gas at room temperature. This process can be accelerated by gentle heating while keeping the temperature below the melting point of iodine, 113 degrees C. Sand has a very high melting point and won't be affected by the heating.
This is best done in a flask with a one-hold rubber stopper that's connected to an empty flask by a rubber hose. The iodine vapors will deposit as a solid onto a cold surface, so put the empty flask in an ice bath.
Make sure the vapors can't escape so you can collect as much solid iodine as possible. Another reason for containing the vapors is that iodine gas, like fluorine, chlorine and bromine gases, is poisonous.