Effect of shear on concentrated hydrous ferric floc rheology

The primary interest of this work is to determine the effect of continuous shear, variable shear rate, and shear history on concentrated hydrous ferric floe rheology. The floe suspensions are strongly shear degrading with the behaviour being adequately described by a power law model. This is supported by images of the floe particles, which indicate a breakdown in floe structure, with the release of water and formation of smaller particles, after the application of shear. A shear rate sweep of the sample produces a hysteresis loop due to the time dependency of the samples. Higher shear rates are shown to destroy more structure, resulting in an overall decrease in floe viscosity. This is irreversible, and occurs due to a breakdown in floe structure to release trapped water and produce smaller floe particles. Shear also causes an instantaneous reduction in viscosity. This effect is instantaneously recoverable, and is due to a decrease in floe particle aggregation. Floc behaviour within the shear rate range 20-250 s(-1) is also adequately modelled by the Sisko model. (C) 2004 Elsevier Ltd. All rights reserved.