The mass transfer rate in fluidized beds of inert particles (FIB) is shown to be dependent on the electrolyte flow velocity and the intensity of particle collisions with the electrode. The influence of particle size and density on the ratio of the magnitude of these two influences on the mass transfer rate in a FIB was studied. Use of particle materials of varying density in an FIB permits variation of the two effects. The influence of collision currents prevails in FIBs of low density materials, and the influence of interstitial velocity is dominant in beds of high density material. The ratio of these factors also depends on the size of particles of the same density. With smaller particle size the influence of collision currents is greater. Smoothing of mass transfer maxima in beds of particles both of small and high density is explained. The results establish a basis for the selection of FIB materials for electrochemical processes.