Classification by decantation

The fraction of particles of this size still in suspension will be  

If the suspension is made up to its original volume, re-dispersed and a second fraction removed after a further time t, a further fraction of particles of size xD will be removed where  

The effect of the ratio h2/h ) is small over a wide range compared with x hence there is little to be gained from making hj - h ) very small with consequent risk of disturbing the solids which have settled out. 

For example, if (h2/h ) is reduced from 0.9 to 0.8, the number of decantings to achieve the same separation will increase from nto m where (Table 5.3)  

Richards, J.C. (1966), The efficiency of classifiers, BCURA Monthly Bull. 30(4), 251 

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