<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.

The objective of this dissertation is to develop a ballast quality evaluation computer model based on the relations among the ballast particle characteristics and ballast performance. Much effort has been given in the past to seek suitable criteria for ballast material selection considering ballast performance and maintenance costs. But the selection of ballast material has appeared to be based on limited information without full regard to the effect of ballast particle characteristics on the ability of ballast to fulfill its functions in track. This will result in some misjudgments in the ballast material selection. The developed model can quantify the ballast suitability with a ballast quality index which has taken the basic ballast particle characteristics and the main ballast field functions into consideration. The basic ballast particle characteristics included are shape, angularity, surface texture, gradation, and specific gravity. The main ballast field functions for track are providing resistance forces, resiliency, void storage, drainage, and facilitating maintenance. The ballast particle characteristics are numerically related to the ballast field functions based on available data from field and laboratory tests on granular materials and some assumptions. Weighting factors are used to represent the relative importance of the basic ballast particle characteristics to each ballast function and then the relative importance of the main ballast functions to the overall ballast field performance. The developed model is evaluated using the ballast field data related to the track performance. The verification results show that the developed ballast quality index can reflect the ballast quality.

<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.

Acid Mine Drainage (AMD) is a consequence of mining activity; it results from bacterial and chemical oxidation of pyrite and other sulfide minerals in waste rock and tailings. AMD is characterized by low pH, and elevated sulfate, iron and often heavy metal concentrations that cause severe damage to the environment. Microorganisms indigenous to highly acidic environments are very diverse and include microorganisms capable of generating alkalinity. The objective of this research was to investigate the biological attenuation of AMD in Davis Mine, an abandoned pyrite mine in Western Massachusetts. The main focus was to evaluate the effects of dissimilatory iron reducing bacteria (DIRB) and sulfate-reducing bacteria (SRB) on the geochemistry of Davis Mine using in situ (ISM) and laboratory (LBM) microcosms. Evidence of ongoing microbial activity was indicated by geochemical changes observed only in live LBMs: increase in concentration of ferrous iron over time, the development of reducing conditions, increase in pH and the development of black precipitates. Data showed that indigenous bacteria change the water chemistry and mineral composition favoring the natural attenuation of the site. However, the results from this study were not sufficient to confirm whether or not SRB or DIRB were metabolically active. The LBM experiments showed that in a closed system and under favorable environmental conditions (temperature, Eh, pH) biological reduction was one of the main mechanisms for the remediation of AMD. Indigenous bacteria were capable of remediating AMD without the addition of an external carbon source, and attenuation rates increased with the addition of glycerol, nitrogen and phosphorous. A program for aqueous geochemical calculations, PHREEQC, confirmed the precipitation of some minerals from the water geochemistry resulting from the microbial activity. Due to hydrological problems in the ISM, it was not possible to obtain in situ rates of degradation. The ISM was affected by the introduction of water with different chemical characteristics. The in situ experiments showed that groundwater transport and diffusion played an important role in the groundwater chemistry. Further in situ experiments are needed to account for environmental factors such as soil pore diameter, temperature, groundwater flow and geochemical processes, availability of electron donor and nutrients in order to determine the rate of microbial activities.