Gravity separation and Ore Beneficiation Oct12

Gravity separation and Ore Beneficiation...

Gravity separation and Ore Beneficiation Gravity separation is the oldest known ore beneficiation technique and is practiced extensively in ‘Nature’. Earliest recorded human use of gravity separation was recovery of gold by panning from the Upper Nile by ancient Egyptians, dating back to 1900 BCE. Gravity separation is a physical process which consists of the separation of different mineral types in the ore from one another based on differences in their specific gravities using the force of gravity, which can be influenced by one or more of other forces such as centrifugal force, resistance to motion by a fluid (e.g. air, water) etc. Hence, besides gravity, other factors, such as size, shape etc., also have an influence on the relative motion and thus in the separation. The effect of centrifugal action on the gravity force is given at Fig 1. It can be seen that as the gravity force increases, settling velocity of smaller particles becomes higher. Fig 1 Effect of centrifugal force on gravity force Separation of the ore particle by gravity is dependent on two factors namely (i) settling rate of the particles, and (ii) difference in specific gravity when compared against the medium in which they are being separated, this gives differential settling rate and has been termed the ‘concentration criteria’.Settling rate of a particle is dictated by ‘Stoke law’ and is equal to kd2g(Ds-Df), where k is a constant, d is particle diameter, g is force of gravity, and Ds is the specific gravity of solid and Df is the specific gravity of the fluid medium. The ‘concentration criteria’ (CC) gives an idea of the amenability of separation of two ore particles and can be expressed by (Dh-Df)/(Dg-Df) where Dh is the specific  gravity of heavier component of the ore,...