Despite the importance for the process industry of solid-liquid mixing operations involving viscous liquids and high solids concentrations, most of the reported results have been obtained in the turbulent regime with low solids loadings. In this work, the suspension of non-dilute concentrations of spherical particles in viscous liquids is investigated through the determination of the just-suspended speed N-js, the homogenization speed N-H and the homogenization time t(H). The pitched blade turbine, which is a common and suitable agitator for the suspension of solids in the turbulent regime, is chosen. N-js is obtained using the pressure gauge technique, and N-H and t(H) via electrical resistance tomography. The impact of the particle diameter d(p), the solids mass concentration X-w, the liquid viscosity mu, and the impeller diameter D and off-bottom clearance C are assessed. In particular, the effect of d(p) and mu on N-js are observed to be in contradiction with the Zwietering correlation, which was derived in the turbulent regime. This is attributed to the hydrodynamics and mechanisms prevailing in the laminar and early transitional regimes, which are similar to those for the erosion of a particle bed. This also explains the discrepancies between our experimental values and the values of N-js predicted by the Zwietering correlation. Also, increasing X-w affects N-js in a more complex manner than what is predicted by this correlation. Finally, our results indicate that particle bed erosion is the dominating phenomenon to consider both to suspend the particles and achieve a uniform suspension in the tank. (C) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.