The mining industry is an important component of the Canadian economy. The principal waste material from this industry is tailings. Numerous failures of tailings dams have caused loss of life and serious pollution problems. This thesis relates to the broad scale investigation and development of improved methods for tailings disposal. A systematic morphology has been developed which provides an effective approach to the overall problem for long-term planning and design. Improved design and construction techniques are advanced for the hydraulic construction of tailings dams with mobile hydrocyclones. The new design incorporates a sealed structure to improve the structural quality and safety of the dam by reducing and maintaining the porewater pressure at zero or negative values over the long-term period. Significant economic benefits are also attainable with the new design techniques. Economic advantages and structural considerations are presented for the system to decant effluent from the tailings basin. Special instrumentation has been designed, developed, and tested which will facilitate the evaluation of the material shear strength for this specific type of tailings dam.

The purpose of this thesis was to investigate the potential ability of nano-scale zerovalent iron (nZVI) to remediate multiple metal contaminants, specifically in the context of mine tailings. The project began by adopting techniques reported on by investigators researching the remediation effectiveness on metal contaminants of nZVI within the framework of civil engineering applications, such as groundwater treatment (Karabelli et al, 2008). This phase of the project saw the treatment of laboratory prepared samples of copper contaminated waters (at 10, 30, 50 and 100 ppm) by the addition of unstabilized nZVI. Results showed that all but the 100 ppm samples were effectively cleared of nearly all metal contamination following treatment additions of 1 mL nZVI to 50 mL of sample water. The second phase of the project sought to expand on this success by subjecting laboratory prepared water samples containing multiple metal contaminants to the same dose on nZVI. A collection of metal contaminants, known as the Arctic Suite, containing arsenic, cadmium, cobalt, chromium, nickel, lead and zinc, was made up as contaminated waters (at 1, 3, 5, and 10 ppm concentrations) and was tested for nZVI remediation. Results showed that only the 10 ppm samples were not effectively remediated and furthermore showed preferential treatment of arsenic, chromium and lead instead of an even distribution of treatment amongst all metal contaminants present. The final phase of the project saw the testing of contaminated waters produced from five mine tailings, acquired from separate sources, by the same dose of nZVI as in the first two phases of the project. Results showed that where contaminant metals were present some remediation effect did occur. However, an inability to produce highly contaminated leachates from the mine tailings meant that no trends in nZVI remediation effectiveness could be determined with any certainty. / Thesis (Master, Mining Engineering) -- Queen's University, 2011-09-01 11:04:28.869

Historic mine tailings pose a significant health risk to surrounding ecosystems and communities because of high residual concentrations of contaminant metals. The initial tailings mineral assemblage, metal sulfides, silicates, and carbonates are unstable at earth surface conditions and undergo oxidative and proton-promoted weathering. The weathering of metal sulfides generally produces acid that, if not balanced by protonconsuming dissolution of silicates and carbonates, leads to progressive acidification. The Klondyke State Superfund Site in Graham County, Arizona contains high concentrations of Pb (up to 13 g kg⁻¹) and Zn (up to 6 g kg⁻¹), and remains unvegetated 50 years after mining cessation. Field-scale investigation revealed a wide range of pH (2.5-8.0) and plant-available (DTPA-extractable) metals in the near surface of the tailings pile. Four samples were chosen for in-depth characterization ranging in pH, as denoted by subscript, from 2.6 to 5.4. The mineral transformations occurring in these four samples were investigated using a variety of techniques and the data indicated an increase in tailings weathering extent with increasing acidification (decreasing pH). Lead speciation, studied by a combination of chemical sequential extraction and X-ray absorption fine structure (XAFS) spectroscopy, was found to vary with tailings depth. The principle lead-bearing mineral was plumbojarosite (PbFe₆(SO₄)₄(OH)₁₂), with smaller amounts of anglesite (PbSO₄) and lead-sorbed iron-oxide. Anglesite, the most bioavailable mineral form of Pb in the tailings, was found to accumulate at the tailings surface, which has important implications for health risks. Total Zn content decreased by an order of magnitude (from 6 to 0.4 g kg⁻¹) and showed a change in molecular speciation with decreasing pH. Zinc-rich phyllosilicates and Zn-containing manganese oxides predominate at high pH, whereas low pH samples contained principally Zn-sorbed iron oxides. One of the overarching goals of the project is to remediate the Klondyke site using phytostabilization to keep contaminant metals from eroding offsite either by wind or water transport mechanisms. However, the impacts of plant growth on metal bonding environment are unknown. To address that gap in knowledge, we have developed a technique for the study of root-microbe-mineral-metal interactions that occur in the rhizosphere, the volume of soil surrounding, and affected by, plant roots. This technique involves the conjunctive use of fluorescence in-situ hybridization, X-ray fluorescence elemental mapping, XAFS and Raman micro-spectroscopies, and electron microscopy on single roots. Manganese and iron root plaques collocalized with elevated Pb, Zn, and Cr demonstrate that the rhizosphere can affect metal speciation. Metal speciation is an important factor in determining metal bioavailability, and thus is critical for understanding the health risk associated with mine tailings. The results of this research provides site-specific information about Pb and Zn speciation, which will be used to evaluate the effectiveness of site remediation within the context of metal toxicity.

Phytostabilization is a remediation technology that uses plants for in-situ stabilization of contamination in soils and mine tailings. The objective of this study was to identify native plant species with potential for phytostabilization of the abandoned mine tailings in Nacozari, Sonora in northern Mexico. A flora of 42 species in 16 families of angiosperms was recorded on the tailings site and the abundance of the most common perennial species was estimated. Four of the five abundant perennial species showed evidence of regeneration: the ability to reproduce and establish new seedlings. A comparison of selected physicochemical properties of the tailings in vegetated patches with adjacent barren areas suggests that pH, electrical conductivity, texture, and concentration of potentially toxic elements do not limit plant distribution. For the most abundant species, the accumulation factor for most metals was <1, with the exception of Zn in two species. A short-term experiment on adaptation revealed limited evidence for the formation of local ecotypes in Prosopis velutina and Amaranthus watsonii . Overall, the results of this study indicate that five native plant species might have potential for phytostabilization of the Nacozari tailings and that seed could be collected locally to revegetate the site. More broadly, this study provides a methodology that can be used to identify native plants and evaluate their phytostabilization potential for similar mine tailings.

Erosion on the slopes of mine tailings represents one of the most important environmental problems arising from the disposal of mine tailings. Tailings dam erosion is the main source of pollution that contaminates agricultural land and streams around mining areas. There is an urgent need to reduce erosion of the slopes of mine tailings in-order to limit further devastation of natural ecology. The present study investigates the possible use of cement to reduce erosion of the slopes of mine tailings dams. The pinhole erosion test was used to measure erodibility of tailings stabilized with cement. The strength properties of cement-stabilized tailings have been evaluated by the unconfined compression test. Conbex and ordinary Portland cement have been used for tailings stabilization, with contents of 0, 3, 5, 7, and 10% by mass. It has been established that cement can be used to reduce erosion of the slopes of mine tailings dams. At least 3% by mass cement is required to produce zero erosion loss. The resistance of tailings to erosion can be enhanced by increasing compaction density, curing period and cement content. Ordinary Portland cement produced higher strengths and erosion resistance than Conbex, although Conbex may be useful for stabilizing fine tailings. Cement-stabilized tailings could be used to make bricks and rubble for use in reducing erosion of the slopes of mine tailings dams. As little as 10% of cement is necessary to produce unconfined compressive strengths of 1600- 2600 kPa.

Modified cellulase enzyme assay methods were developed to determine the potential of using enzyme activities to evaluate the decomposition of organic matter in carbon amended mine tailings systems. Cellulase assays are commonly performed in soil science applications, industrial production and bio-energy research to determine organic matter response to physical, chemical or temporal variation but, they have not been applied in a mine waste environment. Heavy metal content is considered to be a potential inhibitor to cellulase enzyme activity. Using samples collected from Greens Creek Mine in Juneau, Alaska, USA, the modified assay was evaluated to develop a method that provided reproducible results. It was determined that a sample mass of three grams is sufficient to provide consistent enzyme measurements. Each sample location was characterized by four replicates to ensure statistically representative data. Matrix interferences were determined to be inconsequential in this system. Despite the low organic content amended to the tailings, heavy metal content and potentially low enzyme activity, the modified enzyme assay method provided reproducible enzyme measurements. Following the development of the cellulase assays, spatial and temporal variations in cellulase enzymes were investigated from carbon amended tailings samples collected at the Greens Creek Mine. Six test cells, containing a mixture of tailings and a combination of peat, spent brewery grain and/or municipal biosolids were sampled in the fall of 2005, 2007 and 2009. Exo-(1,4)-β-D-glucanase (EC 3.2.1.91), Endo-(1,4)-β-D-glucanase (EC 3.2.1.4) and β-glucosidase (EC 3.2.1.21) enzymes were assayed from core sections at five different depths. Enzyme activities were compared to sulfate reducing and acid producing bacterial enumerations, sulfide trends and carbon content. General trends were consistent between enzyme activity and SRB enumerations. The range of total carbon values fell between 3 and 5 wt % in each test cell while the average inorganic carbon content was 3.5 wt %. The range of organic carbon content was between 0.2 and 1.2 wt %. Total, inorganic and organic carbon values were more characteristic of test cell carbon distribution. Cellulase enzyme assays provide valuable information regarding the degradation of cellulose and hemi-cellulose. This study demonstrates that enzymes can be monitored in a tailings environment and that enzyme assays conducted for monitoring purposes may be a useful practice to indicate the sustained or declining performance of organic matter in a carbon amended remedial system.

Acid Mine Drainage (AMD) is characterized by high metal concentrations and an extremely low pH, primarily generated by the microbial oxidation of iron sulfides from mine tailings. Research on the microbial AMD community has largely focused on Bacteria, while little information is known about the Archaeal and Eukaryote members or the seasonal patterns within the communities. Here I examined the Bacterial, Archaeal, and eukaryotic AMD seasonal microbial community, using direct sequencing techniques on AMD samples from the Copper Cliff Tailings AMD site in Sudbury, Ontario, Canada. I found large variation in the community profile and species composition between sampling times of both the Bacterial and Eukaryote communities, suggesting a dynamic community, both between and within seasons. Bacterial diversity was highest during the winter, with Acidithiobacillus dominating, while during the summer, Acidiphilium was the dominant genus. The winter Eukaryote community was dominated by classes of algae and fungi, while the majority of summer sequencing could not be classified to the class level. Few reads were obtained for the Archaeal domain, with low and similar biodiversity between seasons. Overall, the AMD community variation and abundance were found to largely correlate with drainage water and seasonal temperature.

The existence of small-scale gold mining in Nova Scotia between 1868 and 1942 has resulted in many high arsenic (As) tailings areas in the province, some of which are near rural/urban areas and are used for recreational activities such as dirt bike racing and all-terrain vehicle (ATV) riding. Because of the natural association of As with gold ore in the Meguma Terrane, processing of ore has resulted in As-rich mine waste that contains up to 2500 times more As than the Canadian soil quality guideline of 12 mg/kg. These high As concentrations in combination with the recreational use of these sites creates a risk of human exposure. The objective of this work was to investigate the effects of different cover options that might be used to mitigate the risk of human exposure. Four tailings samples were selected to represent the geochemical variability from two tailings areas: Montague gold mines and Goldenville. These samples were characterized and subjected to 29 weeks of column testing, in which each sample was leached with three different input solutions including synthetic rainwater (to simulate uncovered tailings exposed to natural acid rain), synthetic rainwater equilibrated with calcium carbonate (to simulate rainwater percolation through a crushed limestone cover), and a dilute organic acid solution (to simulate a vegetative cover). Results of acid base accounting (ABA) tests indicate that samples have the potential to generate acid in the future (ratio of neutralization potential to acid potential is less than 2), though surface water at the sites is currently circum-neutral. Acidic paste pH values (2.9) from a sample of As-rich hardpan indicate that a small volume of tailings at Montague are currently generating acid. Results of column testing indicate that the cover types simulated by the input solutions had less of an effect on the out-flowing leachate chemistry than did the small volume of secondary As phases in each sample (scorodite, yukonite, hydrous ferric arsenate and hydrous ferric oxides). For the majority of sample types, columns leached with an organic acid solution reported higher leachate As concentrations than were reported from columns leached with either the rainwater or carbonate-rainwater solutions. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2010-10-27 14:26:06.13

Revegetation is employed to mitigate the spread of mine tailings in the environment by ameliorating tailings with organics to promote plant cover. Revegetation has proven to be successful in establishing plant cover, but the long-term effects are largely unknown. A field study was conducted to evaluate the success of four artificially revegetated tailings from Manitoba by comparing plant cover and diversity. Central Manitoba, Flin Flon, and Thompson had moderate cover while cover was low in Lynn Lake. All four sites had low diversity and were composed of early-successional species. The results suggest that while current revegetation methods promote plant growth on tailings, it is currently difficult to determine if and how the vegetation will progress from a grass-legume community to a boreal forest. In addition, while various amounts of effort were invested into each site, the results indicate the degree of remediation does not affect overall success.

Revegetation is employed to mitigate the spread of mine tailings in the environment by ameliorating tailings with organics to promote plant cover. Revegetation has proven to be successful in establishing plant cover, but the long-term effects are largely unknown. A field study was conducted to evaluate the success of four artificially revegetated tailings from Manitoba by comparing plant cover and diversity. Central Manitoba, Flin Flon, and Thompson had moderate cover while cover was low in Lynn Lake. All four sites had low diversity and were composed of early-successional species. The results suggest that while current revegetation methods promote plant growth on tailings, it is currently difficult to determine if and how the vegetation will progress from a grass-legume community to a boreal forest. In addition, while various amounts of effort were invested into each site, the results indicate the degree of remediation does not affect overall success.