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J o u r n a l P a p e r Introduction The minerals processing industry is under continuous pressure from environmental, legal and financial quarters to use less water, and designers are obliged to consider the option of operating at higher concentration. As the concentration of fine particle mineral processing slurries increases, viscous stresses also increase, and inevitably become nonNewtonian in nature. For some years, the Flow Process Research Centre (FPRC) at the Cape Peninsula University of Technology has been researching the behaviour of high concentration non-Newtonian slurries in pipes, valves and fittings, pumps and launders, and these will form the focus of the paper. The aim of this paper is to highlight the important practical aspects of these fundamental issues, and their implications for design for slurry handling. In particular, the objective is to present the principal conceptual issues that underpin sound design. The full detail of the design process for handling slurries is an extensive topic, beyond the scope of this paper, and the reader is referred to sources dealing directly with these for more detail 1 . The important point to make at the outset is that the foundation of sound design for slurry handling does not revolve around the task of choosing or producing special materials and plant-although these are often required. The foundation lies rather in having a good understanding of the slurry environment 1,2 , which is the basis of this paper and our work at the FPRC. Rheological characterization Slurry rheology (viscous character) is a dynamic property of microstructure 3 . When the slurry is stationary, the attractive forces between particles or agglomerates form a three-dimensional structure, which extends to the walls of the container. The shear stress required to rupture this structure and initiate flow, is called the yield stress. Below this stress, the material behaves like an elastic solid. As shear stresses and shear rates increase, the agglomerates gradually reorientate and disintegrate, resulting in a decrease in the viscosity of the material. This process is known as shear thinning. At very high shear stresses and shear rates, the reorientation and disintegration process reaches equilibrium, and the viscosity becomes constant. Although this portrayal of the relationship between viscosity and microstructure is idealized, it is useful for engineering purposes. The simplest steady state, time independent rheological model, which can accommodate the behaviour described, above is the Bingham plastic model. This model can be formulated in terms of shear stress τ; where τ y is the yield stress, K is the plastic viscosity and γ · is the shear rate or velocity gradient. The two terms on the right-hand side of Equation 2 will be equal when 3 . [3] Plant design for slurry handling by P. Slatter* Synopsis The key issue when designing plants for slurry handling, is understanding the slurry environment. Pressure to use less water and operate at higher concentrations directly affects slurry flow behaviour. Using the Bingham plastic rheological model, the impact that slurry rheology has on transitional pipe flow, particle settling in laminar shear flow, losses in valves and fittings, centrifugal pump derating and launder flow are presented