The paper shows how the equations developed for modeling the fluidization process of two-solid mixtures, originally tested on mixtures of spherical particles, can successfully be extended to segregating fluidization of beds of irregular solids. The influence of particle shape on bed voidage at varying component concentration is analysed and it is demonstrated, in particular, that the relationship that calculates the final fluidization velocity of any binary mixture maintains its predictive ability also for solids of practical interest like in the case of beds of biomass and inert particles. As regards the mixtures of olive pits and sand addressed in this study, that makes possible a comparison among the mixing states of these systems at varying average size of the inert component, each at its own u(ff), a fluid dynamic condition at which the equilibrium between the mixing and segregation tendencies in the dense phase of the bed is fully developed. In this way, an appropriate choice of the particle size of the inert material can be made for the purpose of promoting component mixing and even biomass distribution along the bed height. (C) 2019 Elsevier B.V. All rights reserved.