Adry mixture of kno3 and sand could be separated by

Place the mixture in hot water and stir well. 
The KNO3 is very soluble in hot water. 
Use a fine filter paper and filter off the sand. 
The sand will be separated from the KNO3 solution. 
The water can now be evaporated from the solution by further, gentle heating leaving the solid in the container.

Particle exchange energy though elastic collision , hope this .