Rheology of slurries and environmental impacts in the mining industry

The world's resource industries are the largest producers of waste. Much of this waste is produced as a fine particle slurry, which is pumped to a storage area, generally at a low concentration, where it behaves like a Newtonian fluid. Simply removing, reusing, and recycling water from the slurry represents a step toward a more sustainable practice in this industry. As the concentration of such a slurry is increased as a result of dewatering, the materials exhibit non-Newtonian behavior, which is characterized by shear thinning, a yield stress, and in some instances thixotropic behavior. Such high-concentration, nonideal (dirty) suspensions in the resource industries have meant that new rheological methods and techniques have been needed to measure and interpret the basic flow properties. Also, some older empirical techniques have needed to be modified and interpreted in a more fundamental way so that the results could be used in design. This article reviews these techniques and illustrates how the industry itself has motivated their development. Understanding and exploiting this rheology has resulted in dramatic improvement in the waste-disposal strategy for some industries, but many have failed to embrace the available technology. The reasons for this are discussed. The article concludes that a greater positive change in waste-management practice will occur in the future, motivated by several factors, including public perception, tighter regulation, and perhaps even commonsense life cycle accounting.