Rheology and sedimentation velocity of alkaline suspensions of hematite particles at elevated temperature

International audience; This study aims to characterize the sedimentation velocity and the rheology of suspensions of hematite particles suspended in strongly alkaline media at 100 and 110 degrees C, as done for an alternative electrochemical process in development for iron production by direct electrode reduction of hematite. Considering the medium used in the process, i.e. 12% (v/v) suspension of hematite particles in 50% sodium hydroxide aqueous, the sedimentation velocity of hematite particle at 110 degrees C is 0.010 mm/s, which is very slow because the average size of the solid particles is around 10 mu m and the significant collisions and inter-actions occuring between the particles in the concentrated suspension. Two geometries were used to characterize the theological behavior of the apparent viscosity of the suspension of 12% (v/v) (i.e. 33 wt%) at 100 degrees C: a conventional Couette geometry and a helical ribbon mixer. The suspension was found shear thinning in the range of shear rate studied. The rheological behavior of the suspension can be described by a power-law model. The apparent viscosity of the hematite suspension estimated at a shear rate between 0.5 and 10 s(-1) is between 100 and 20 mPa s for the two geometries. The apparent viscosity calculated from the terminal velocity of 10 mu m particles is of the same order of magnitude of the results obtained with the two rheometer configurations. The effect of the particle concentration on the sedimentation velocity and viscosity of the hematite suspensions was also studied.