Enhancing Design of Water Balance Cover Systems Composed of Mixed Mine-Waste Materials

Colorado State University, Fort Collins CO

Investigators

Abstract

The objective of this project is to create an innovative design approach for water balance cover systems composed of mixed mine waste materials (i.e., waste rock and tailings). Water balance covers are designed to minimize the ingress of precipitation and oxygen into underlying waste via moisture retention within earthen materials used in the cover system. These earthen materials must also provide the necessary resistance against slope failure and erosion. Challenges to the design of water balance cover systems composed of mixed mine waste include limited knowledge on (i) mine waste mixing methods, (ii) mine waste characteristic effects on engineering properties, and (iii) techniques to scale-up processes from the laboratory to the field. This project will enhance assessment and design of using mixed mine waste materials in water balance covers to expedite adoption in practice and promote sustainable mine closure. Findings from the project will be relevant to mine owners and engineers worldwide, and have the potential to enhance environmental sustainability and land stewardship throughout our global society. The project will include an academia-industry partnership between Colorado State University and the Tailings and Mine Waste Conference Committee to create collaborations between academicians, students, consultants, and industry personnel. These collaborations will enhance research and education activities of the project. The research objectives for this project include the following: (i) evaluate mixing techniques to create homogenized materials from mine waste rock and tailings; (ii) understand the effects of mixture ratio (i.e., mass of waste rock to mass of tailings) and tailings composition on moisture retention and shear strength of mixed mine waste; and (iii) establish proof-of-concept via up-scaling technology from the laboratory to the field. An innovative discrete element method and computational fluid dynamics model will be used to simulate mixing behavior of mine waste in laboratory experiments and to design a mixture process for field-scale implementation. Additional laboratory experiments will focus on moisture retention and shear strength behavior of mixed mine waste. The coupled experimental and numerical efforts will lead to an experimentally-validated numerical model that integrates non-Newtonian flow mechanics and is capable of predicting mixing behavior of dissimilar geomaterials. The shear strength and moisture retention experiments will lead to empirical tools to predict engineering properties of mixed mine waste as a function of mixture ratio and mine waste composition. The field-scale experiment will close-the-loop between laboratory research and field-scale feasibility and provide rationale for evaluating the overarching hypothesis that water balance covers composed of mixed mine waste can be designed via numerical simulations of the mixing process and mechanistic understanding of the effects of mine waste properties and mixture ratio on shear strength and moisture retention.