Master of Science in Engineering - Engineering / The most significant benefit of co-disposal of tailings based on the “Paste and Thickened Tailings Disposal” concept is the improved ability to “design” the properties of the co-disposed tailings material to suit the surrounding environment. The overall aim of this study was to gain a better understanding of the relationship between the key slurry material characteristics and the flow behaviour of co-disposed tailings upon deposition, for the case of montmorillonite clay-based kimberlite tailings. A fundamental understanding of this relationship will enable the successful manipulation and exploitation of the co-disposed tailings rheology for optimal tailings disposal and the minimisation of associated financial, environmental and social risks. The key material characteristics selected for investigation were the vehicle solids concentration, suspension pH and vehicle to load ratio. The yield stress was selected as the key rheological property representing both the vehicle component rheology and co-disposed tailings rheology. Two yield stress measurement techniques were used, namely (1) direct yield stress measurement with the vane method and (2) indirect yield stress measurement with the slump test method. The correlation between these two methods was investigated as a secondary objective of this study. It was concluded that the suspension pH strongly influences the degree of microscopic particle interaction of the vehicle component and that manipulation of the suspension pH could move the material between interactive and noninteractive states. It was further concluded that increasing load mass percentage leads to a significant increase in the co-disposed material yield stress. It is believed that the load component mainly affects the co-disposed material yield stress through its contribution to the total solids concentration, which in turn results in an exponential increase in the material yield stress. The findings of this study showed remarkable flexibility in the manipulation of the various input parameters to produce the same yield stress value. It is therefore now possible to maintain a constant yield stress value as required by the environmental depositional requirements through various combinations of the input parameters and so keep the integrity of the deposition site intact. The correlation obtained in this study between the vane and slump test yield stress measurement techniques was fairly poor. The slump test only provided an accurate prediction of the yield stress when the material was in a highly interactive state. It is recommended that future research focuses on the thixotropic nature of the vehicle component as a function of suspension pH, the accuracy of the correlation between the vane and slump measured yield stress and the effect of the load on the bulk rheology of the co-disposed material.

In South Africa, being the second largest global coal exporter, coal mining plays a pivotal role in the growth of our economy, as well as supplying our nation’s ever increasing electricity needs; while also accounting for more than 10% of the 20 x 109 m3 water used annually in the country. Coal mining may thus be classified as a large-scale water user; known to inevitably generate wastewater [acid mine drainage (AMD)] and other waste material, including fly ash (FA). Current and conventional AMD treatment technologies include precipitation–aggregation (coagulation/flocculation) – settling as hydroxides or insoluble salts. The process stream resulting from these precipitation processes is still highly saline, therefore has to undergo secondary treatment. The best available desalination techniques include reverse osmosis (RO), electro dialysis (ED), ion exchange and evaporation. All available treatment methods associated with raw AMD and its derived process stream fall prey to numerous drawbacks. The result is that treatment is just as costly as the actual coal extraction. In addition, remediation only slows the problem down, while also having a short lifespan. Research conducted into converting fly ash, an otherwise waste material, into a marketable commodity has shown that direct mixing of known ratios of FA with AMD to a pre-determined pH, erves a dual purpose: the two wastes (AMD and FA) could be neutralized and produced a much cleaner water (secondary co-disposal [FA/AMD]-process water), broadly comparable to the process water derived from precipitation-aggregation treated AMD. The collected post process solid residues on the other hand, could be used for production of high capacity ion exchange material (e.g. zeolite A, faujasite, zeolite P, etc.). The produced ion exchange material can subsequently be utilized for the attenuation of metal species in neutralized FA/AMDprocess waters. / Magister Scientiae - MSc