Industrial applications of solid-liquid mixing generally comprise of high solids loadings with a wide range of large particles. Since the required power for the mixing of highly concentrated slurries is extremely high, it is critical to accurately assess the just-suspended impeller speed, power number as well as the degree of homogeneity. The major objective of this study was to analyze the suspension of large solid particles in highly concentrated slurries. Design of experiment (Box-Behnken Model) was used for the response surface methodology (RSM) analysis. Electrical resistance tomography (ERT) was employed to measure the extent of homogeneity in a slurry reactor. The effects of different variables such as impeller type (PBT, PF3, and A310 impellers), impeller clearance (from 0.050 to 0.133 m), solids loading (30 <= x (wt%) <= 55), and particle size (753, 2900, and 5000 mu m) were investigated on the performance of the solid-liquid mixing operation. The collected data revealed that the average Zwietering solids loading exponent increased from n=0.13 at low solids concentrations (5 < x (wt%) <= 20) to n = 0.38 for the high solids loadings (30 <= x (wt%) <= 55). It was found that in a slurry reactor the particle size, solids loading, and their interaction had a significant impact on the just-suspended impeller speed for the highly concentrated slurries of large particles. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.