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Conventional mineral waste disposal involves pumping dilute concentration suspensions of tailings to large catchment areas, where the solids settle to form a consolidated base while the excess water is evaporated. Unfortunately, this often takes years, if ever, to occur, and the interim period poses a severe threat to the surrounding countryside and water table. A worldwide movement to increase the concentration of these tailings to pastes for disposal above and below ground, obviating some of these issues, has led to the development of new technologies. Increasing the solids concentrations invariably produces non-Newtonian effects that can mask the underlying nature of the suspension mechanics, resulting in the use of poor pipeline and disposal methods. Combining rheological characterization and analysis with non-Newtonian suspension fluid mechanics provides insight into these flows, both laminar and turbulent. These findings provide the necessary basis for successful engineering designs.

A significant development during the evolution of thickened tailings and paste technology has been the increased understanding of the importance of rheology for both design and operation of thickened tailings and paste systems. It is now well accepted that dewatering, pipeline transport and deposition processes are all rheology governed and that the more the rheology is understood, and in some cases manipulated, the more successful the operation will be. This increased knowledge and adoption of rheology has led to a paradigm shift where tailings are engineered to suit the environment rather than engineering the environment to suit the tailings. In the early to mid 1970s when Eli Robinsky first introduced the concept of thickened tailings disposal, the systems were based primarily on empirical flume tests. Since that time, numerous advances in measurement techniques have facilitated the understanding of the influence of variables such as particle size distribution and shape, shear effects (rate and time of shear) and mineralogy on the rheology of tailings. Compressional rheology has also emerged as a whole new area of interest. This progress, coupled with advances in understanding the interrelationship between surface chemistry and rheology, has highlighted methods of exploiting and/or manipulating the dewatering, flow and depositional properties of tailings and backfill. As flocculant and other additive technologies advance, we may begin to see more complex rheological phenomena and new measurement techniques may need to be adopted or developed for a fuller understanding and exploitation of slurry and paste rheology. The paper examines the driving issues faced in the past, now and likely in the future, the testwork that has been developed and its applicability or limitations and how this has progressed thickened tailings and paste technology.

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The shift from pumping low-concentration Newtonian fluid tailings suspensions to disposal to the production of non-Newtonian paste and thickened tailings has meant that the minerals and energy industries have had to learn how to handle (dewater, pump, and deposit) non-Newtonian materials. Such high concentration, non-ideal (dirty) suspensions has meant that new rheological methods and techniques were needed for both shear and compression to measure and interpret the basic flow properties of paste and thickened tailings. Also, some older empirical techniques needed to be modified and interpreted in a more fundamental way so that the results could be used in design. The paper reviews these rheological techniques and illustrates how the industry itself has motivated their development.