APPLICATION OF EQUILIBRIUM STATE RHEOLOGICAL DATA IN THE RED MUD DISPOSAL PROCESS

Accurate prediction of transport energy requirements for a non-Newtonian material involves overcoming a number of inherent problems. For a complex thixotropic material such as bauxite tailings (red mud), the major problem is a result of the difficulty in obtaining rheometric parameters which are representative of the structural state of the material in the pipeline.

The rheological behaviour of a suspension is generally summarised by the construction of a flow curve relating the shear stress to the shear rate. The present study identifies significant time dependent characteristics of the flow curve and outlines a method for simplifying pipeline design. The results obtained suggest that the yield stress at the pipeline conditions, as measured by the simple slump test (Pashias et al, 1996) and a single flow curve at any structural state can be used to calculate the shear stress, hence pumping energy, at the shear rate of interest.

Red mud rheology is dependent on shear and compression history, elapsed time since shearing and the dose and method of flocculant addition. Although the viscosity is a function of all of these factors, it also varies with shear rate for non-Newtonian slurries such as red mud. The yield stress however, is a singular point for each curve that also reflects the material’s history and additives used. As such, it is proposed that the yield stress is a unique parameter, which may be used to eliminate the need for quantification of slurry history.

The proposed prediction method is applied to a wide range of pipeline data and good agreement with measured pipeline data is obtained.