We use handpicking in separating stones from rice and dal. We use washing methods to separate dust from rice, dal, vegetables, fruits etc.
Hand picking: The colour and size of impurities is different from rice or dal. So we can easily separate them by hand picking. In the same way if the ore particles and the impurities are in different sizes, colour etc., we can see this hand picking method to separate ore from impurities.
Washing : Less density particles like dust is separated from more density particles like rice, vegetables etc., by washing. In the same way ore particles are crushed and kept on a slopy surface. They are washed with controlled flow of water. Less densitive impurities are carried away by water flow, leaving the more densitive ore particles behind.