Water and Wastewater Treatment and Management · Water Treatment · 1 mark · Numerical answer
Clay particles of diameter 75 µm and specific gravity2.65 settle twice as fast as metal particles of specific gravity8. Under discrete laminar settling, find metal diameter in integer µm.
Stokes velocity is proportional to $(\rho_p-\rho_w)d^2$. Therefore $1.65(75)^2=2(7)d_m^2$. Solving gives $d_m=75\sqrt{1.65/14}=25.7474$ µm, rounded **26 µm**. The density difference from water, rather than particle density alone, is needed.
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