Simulations of solidliquid flow in an agitated tank have been performed. The simulations fully resolve the mildly turbulent liquid flow (Re approximate to 2000) in the tank, and the spherical solid particles suspended in the liquid. Full resolution of the particles sets the grid spacing and thereby limits the tank size and the number of particles (up to 3600 in this article) that are computationally affordable. The solids volume fraction is some 8%. The lattice-Boltzmann method has been used to solve the flow dynamics; the particles move under the influence of resolved hydrodynamic forces, unresolved lubrication forces, net gravity, and collisions (with other particles, the tank wall, and the impeller). We show the start-up of the suspension process, demonstrate its dependency on a Shields number (that we interpret in terms of the Zwietering correlation) and show the impact of polydispersity on the suspension process. (c) 2012 American Institute of Chemical Engineers AIChE J, 58: 32663278, 2012