The influence of inert particles on liq./solid mass transfer is studied in fluidized beds by using a binary-mixt. of solids of differing size and d. The addn. of inert particles of higher d. and smaller diam., e.g. glass beads, exerts remarkable effects on mass transfer coeffs. in comparison to that of mono-component active particles at the same liq. velocity. The extent of the effect on liq.-solid mass transfer coeffs. increases with an increasing fraction of the small inert particles in the mixt. The liq.-solid mass transfer coeffs. for binary-mixts. are well correlated in terms of dimensionless groups and the voidage parameter. [on SciFinder (R)]