<p> The mining and milling activities associated with extraction of metals directly generates waste in the form of mine tailings. This material is one of the largest sources of heavy metal contamination via water, air, flora, and fauna in the world. The re-use of this waste as an input to a construction material such as concrete could lead to a preventive method of reducing the environmental impact. This method of encapsulation of heavy metals has been applied to paste backfill; however, the compressive strength requirements are much lower compared to the ASTM standards for structural concrete. The objectives of this study were: (a) to examine the feasibility of maintaining the structural integrity of concrete, with compressive strength of 4,000 psi or greater with a slump of 3-4 inches, when using mine tailings as a fine aggregate, (b) investigate the ability of this material to encapsulate heavy metals, sulfates, and acid.</p><p> The waste material, collected from the Pride of the West mill in Silverton, CO, was first physically and chemically characterized. After performing batch leach extraction tests, the raw mine tailing leachate contained heavy metal concentrations above conservative regulatory limits. Then, the optimal tailing to fine aggregate ratio was investigated. It was found that the compressive strength was comparable to control samples made with aggregate and the concentration of heavy metals found in the leachate were consistently low when the ratio varied below 50%. Therefore, the ASTM standard for the minimum allowable fineness modulus was used to obtain in maximum amount of mine tailings allotted in the concrete mixture.</p><p> To examine whether metals could be leached from the concrete-tails mix, three extraction fluids varying in pH were used to accelerate the weathering process. The metals of concern were shown to have been thoroughly encapsulated in the concrete matrix, with a 2-4 log encapsulation capacity when compared to the metals leached from the raw tailings. Finally, a strength development experiment was conducted to observed changes over time. It was found that the specimens that contained mine tailings maintained comparable compressive strengths as the controls cylinders, above the minimum compressive strength requirements for structural concrete.</p>

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4676. Adviser: G. Fernandez. Includes bibliographical references (leaves 254-260) Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2006. / Source: Dissertation Abstracts International, Volume: 67-11, Section: B, page: 6596. Advisers: Jamshid Ghaboussi; Youssef Hashash. Includes bibliographical references (leaves 120-122) Available on microfilm from Pro Quest Information and Learning.

<p>The flow of thickened mine tailings within a tailings storage facility is a complex interaction between unconstrained viscoplastic free surface flow and possible coarse particle settling within the flow depth. The broad focus of this work is developing a robust framework for modelling tailings beach flows. Modelling tailings flow evolution in three dimensions within a storage facility will ultimately provide greater understanding of beach slope formation, as well as the ability to optimize deposition sequencing. This thesis focuses on the first step of developing a tailings model considering the transport and settling of mono-sized coarse particles within two dimensional (length and depth) laminar viscoplastic carrier fluid sheet flow. The 2D model consists of a semi-implicit finite difference shallow water sheet flow model for predicting the viscoplastic flow depth and discharge down the beach. The coarse particle transport and hindered settling within the flow are predicted using a scalar transport model. The scalar transport and shallow water flow model are coupled together using coarse particle rheology augmentation. Two key novel advancements were made through the model development. The first is coupling the coarse particle rheology augmentation within the free surface flow to the coarse particle hindered settling behavior with depth. This coupling allows for the rheology augmentation due to the coarse solid fraction to be incorporated seamlessly into both the fluid flow solver and the particle settling model. The second advancement is expanding the rheology augmentation and hindered settling coupling to particle flows beyond the Stoke?s flow regime. Ultimately, the 2D model results are compared against Spelay?s (2007) laminar settling experimental measurements for oil sand thickened tailings (TT) and composite tailings (CT) slurries, along with Spelay?s 1D settling model. The 2D model provides improved prediction of the particle concentration profiles within the fluid flow compared to the 1D model. The 2D model is also able to predict the increase in flow depth due to the particle accumulation on the bed, as well as the downslope particle transport and settling behavior.