Motor drives impeller to rotate slowly through transmission mechanism---triangle belt, speed reducer and gear reducer. With impeller rotating slowly, sand is grinding with each other when it is taken from feeder tank to washing tank, and this could help to remove the impurity covered on the sand surface. Meanwhile, it also destroys the vapor layer covered on the sand surface in order to get dewatered. On the other hand, fast flowing water could help to take impurity and other low-density material away through outlet of washing tank. The rotating impeller takes clean sand out of outlet of discharger tank.