One design heuristic used to determine the just suspended speed, N-js, for mixed slurries assumes that the mixture N-js is dominated by the particle phase with the maximum N-js. This approach does not incorporate the effect of the second solid phase. Two new models are proposed to predict the mixture N-js: the power model and the momentum model. These models determine the mixture N-js using the sum of the power or the sum of the momentum required to suspend the individual solid phases. The models were tested using experimental data for two impellers, a Lightnin A310 impeller and a 45 degrees pitched-blade turbine. A range of off-bottom clearances, and six mixtures of solids up to 27 wt% solids loading completed the data set. The power model accurately predicts mixture N-js for both impellers over the full range of clearances and up to 27 wt% mixtures. (c) 2012 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.