Geotechnical Evaluation of Mine Tailings for Improved Dewatering

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Mining operations generate large volumes of tailings (colloidal suspension in process water) presenting significant challenges throughout their lifecycle. From design to reclamation of containment facilities, the geotechnical properties of the tailings are influenced by ore geology, chemical extraction, slurry disposal, and ambient climate. The slow settling rate of the fine-grained tailings and the highly contaminated liquid in the ponds requires that the containment structures be carefully managed for decades. The resulting low sediment volume reduces the storage capacity of an impoundment to accommodate the new tailings inventory at a mine site. To minimize its environmental footprint, the mining industry proactively modifies its waste management practices. The recent shift from conventional waste handling is to produce tailings streams with the bulk of the processing water removed and recycled back for extraction. The applicant's research program supports this paradigm change by developing a geotechnical engineering framework (based on scientific rationale) for improved tailings dewatering. The basic concepts of flow through porous media during volume change will be investigated in light of micromechanics and microstructure under both saturated and unsaturated conditions. The short-term (within the next five years) objectives are to devise polymer-modified tailings with improved compression rheology and to assess tailings dewatering under large-strain consolidation and evaporative desiccation. Specialized laboratory investigation techniques and numerical modeling approaches will be adopted to capture the unique features of colloidal slurries, namely: electrochemical interactions, polymeric flocculation, large strains, and evolving microstructure. This novel approach is an extension to the field of geotechnical engineering that generally deals with load-deformation based analyses by assuming that earthen materials are inert. Such a fundamental understanding of tailings dewatering will be critical in developing sustainable (cost effective, environmentally friendly, and socially viable) strategies for water and energy management during operation, closure, and reclamation of new and existing mines. The proposed research methods (developed for mine tailings) can be applied to drilling muds, dredged materials, slurry walls, and marine deposits. Likewise, the expected technological and socio-economic benefits of tailings amelioration to the mining industry include reduced water consumption during ore beneficiation, enhanced reclamation of process water, reduced chemical pollutants in tailings, and increased storage capacity in containment facilities. Finally, the training of highly qualified professionals will be particularly beneficial for the mining industry with respect to both economic development and environmental compliance.