Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliographical references.

Thesis (Ph.D.) - University of Queensland, 2006. / Includes bibliography.

Centrifuged fine tailings (CFT) technology was developed to reduce volumes of fluid fine tailings (FFT) stored in tailings ponds at oil sands mines. Increasing FFT inventories in tailings ponds results from slow settlement of clay minerals suspended in oil sands process-affected water (OSPW). High sodium (Na) concentrations in OSPW increase the electrical double layer (EDL) thickness at clay-mineral surfaces, which hinders aggregation and, therefore, settlement. Production of CFT involves dredging FFT from tailings ponds, amending with polyacrylamide and gypsum, and decanter centrifuging. This process promotes aggregation and flocculation, and decreases gravimetric water content from approximately 70 to 55 % (w/w). The resulting CFT is deposited in thin lifts (< 2 m) into sub-aerial containment areas to facilitate further dewatering via freeze-thaw cycling. This research was focused on characterizing the biogeochemical conditions and processes within the CFT deposits. These deposits remain tension-saturated and, similar to tailings ponds, anaerobic redox processes including iron (Fe) reduction, sulfate (SO4) reduction, and methanogenesis likely dominate. The geochemistry, mineralogy, and microbiology of core samples from two field-scale test deposits and two full-scale production deposits were examined. Results were compared with previously published data from FFT deposits to assess impacts of chemical amendments on biogeochemical processes within CFT deposits. Pore-water chemistry within the CFT deposits is affected by evaporative concentration of dissolved ions, which leads to high concentrations of salts (Na, 3000 mg L-1; Cl, 1500 mg L-1; SO4, 5000 mg L-1) and naphthenic acids (NAs 150 mg L-1) near the surface (< 0.3 m) of these deposits. Increases in concentrations of conservative ions (i.e., Cl) indicated that 30 to 40 % of pore water was lost to evaporation at a depth of 0.1 m below surface. Results also suggest that microbially-mediated Fe reduction, SO4 reduction, and methanogenesis are dominant redox processes within the CFT deposits. Microbes related to genera known to use these terminal electron acceptors were identified by high-throughput DNA sequencing data. Increases in dissolved Fe and H2S with depth were also indicative of Fe and SO4 reduction, respectively. These results provide the first insight into biogeochemical conditions and processes within oil sands CFT deposits.

Metals are ubiquitous and naturally occurring; however, anthropogenic activities have elevated metal concentrations in river sediments above what would be expected naturally. One of the primary anthropogenic sources of metals in freshwater is contamination by mine tailings, a toxic slurry of waste rock and chemicals left over after ore minerals or coal extraction. Mining waste is most often stored in retention ponds, which sometimes leak or fail. One of the worst mine tailings disasters on record occurred on the Tisza River of Central Europe in the winter of 2000, releasing over 240,000 tons of mine tailings laced with metals into the natural environment. Elevated metals in freshwater can negatively affect fish and other aquatic organisms, raising concerns as to the long-term ecological consequences of the spill. Therefore, the objectives of this dissertation were to describe the ecological implications of metals pollution from mining on freshwater systems through an empirical case study of the Tisza River combined with controlled laboratory experiments of chronic cadmium exposure on a model species, channel catfish (Ictalurus punctatus). Specific research questions discussed in the following chapters include: (1.) What is the current distribution of metals in the lower Tisza River Basin and are metals transported from the main channel to floodplain habitats?; (2.) Is there evidence for bioaccumulation and/or trophic transfer of metals to fish in the Tisza?; (3.) What are angler’s perceptions and fish consumption risks in the lower Tisza river basin?; and (4.) What are the effects of sub-lethal exposure to cadmium on growth, development, metabolism, and stress response in a model fish species? The case study of the Tisza River Basin was conducted during early summer in 2013 and 2014. Water, sediment, and fish were collected from the Tisza River as well oxbow lakes along the lower basin. Samples were screened for metals via GF-AAS following standard methods. Additionally, we conducted interviews at each sampling location to determine fish consumption habits. Controlled laboratory exposures were conducted during summer of 2015. Eggs of channel catfish (Ictalurus punctatus) were fertilized in treatment water and raised to 6 month old fingerlings. Treatments of cadmium included concentrations of 0.5 µg L-1 (control), 2 L-1 (low) and 6 L-1 (high), with endpoints of growth, development, cellular stress, metabolism, and general stress response. Results indicate that lakes with the greatest connectivity trended toward elevated metals; however, chlorophyll a concentrations decreased suggesting dilution of nutrients from surrounding agriculture. River connectivity therefore increases ecosystem health of floodplain lakes by ameliorating eutrophication, but as a trade-off with potential contamination of metals. This may have implications for management strategies in the basin as fish from the oxbow lakes also trended toward higher concentrations of metals compared to the river main stem. Although we did not detect any indication that metals are biomagnifying through the fish community, fish are clearly taking up contaminants from the water and sediment. Additionally, although fish fillets generally fell below human consumption guidelines, surveys collected at field sites indicate disparities between health risks and perceptions of those risks. For example, many people believe that fish from the oxbow lakes present a lower risk for metals than the river main stem, converse to our findings. Exposure of channel catfish to cadmium concentrations similar to those observed in the Tisza Basin indicate that negative physiological effects, such as altered carbohydrate metabolism and subsequently growth, can occur in fish at muscle concentrations below consumption guidelines. Although cadmium in Tisza fish fillets were lower than expected, metals may still be problematic for the basin as they may disproportionately affect early life stages of fish. This could skew life histories of exposed populations compared to unaffected fish, potentially reducing growth rates, size at maturity, reproductive output, and lifespan; indicating the need for more paired field and laboratory assessments of chronic metals exposure.

Esta dissertação é uma contribuição, através de uma pesquisa bibliográfica, sobre o tema instrumentação e monitoramento em empreendimentos de barragens de rejeitos da mineração. Nesta pesquisa apresentam-se os objetivos básicos da instrumentação de barragens e suas características técnicas, metodologia construtiva das barragens de rejeitos e seu monitoramento através de auscultação da instrumentação. Como limitação do trabalho, devido à variedade de instrumentos que podem ser instalados em uma barragem, buscou-se pesquisar os instrumentos de medição de deslocamentos e controle de fluxo percolante, sendo os mais utilizados em barragens de terra e rejeitos. Justifica-se este tema motivado pelos últimos acidentes ocorridos em barragens de contenção de rejeitos, enfatizando a importância e a necessidade permanente da melhoria das condições de segurança e monitoramento das barragens brasileiras. Estes acidentes causam danos à população do entorno da barragem, econômicos ao empreendedor e ambientais. Como resultado obtido nesta pesquisa pode-se concluir que propiciou conhecimento atualizado ao meio técnico nacional de barragens. / This dissertation is a contribution, through a bibliographical research, on the subject of instrumentation and monitoring in enterprises of tailings dams. This research presents the basic objectives of the instrumentation of dams, their technical characteristics, the construction methodology of tailings dams and their monitoring through auscultation of the instrumentation. Due to the variety of instruments that can be installed in a dam, this work was limited to the analysis of two segments, instruments of measurement displacements and those for controlling percolation flow, which are the most commonly used in earth and tailings dams. This study is justified due to recent accidents occurring in tailings dams, which stress the importance and the permanent necessity of the improvement in security and monitoring conditions of Brazilian dams. These accidents cause social, economic and environmental damages to the enterprise. As a result of this research it can be concluded that it contributed with up-to-date knowledge to the national technical dam sector.

Mine tailings pose a health risk for populations and ecosystems in the Southwest; this is why effective, and low-cost solutions for the long term are needed. This work is groundbreaking since little information is available with regards to applying greenhouse studies of phytostabilization to the field for mine tailing remediation. Mine tailings from Iron King Mine and Humboldt Smelter Superfund (IKMHSS) site can be considered one of the worst scenarios due to the extreme conditions which prevent the growth of a vegetation cap. The high concentration of metals, such as arsenic and lead, highly acidic, lack of the nutrients carbon and nitrogen in the soil structure, and low microbial communities are factors that negatively affect plant growth. This project provides practical field-scale applications for the use of phytostabilization, which uses plants to create a vegetation cap that stabilizes metals in the root zone while preventing wind and water erosion in mine tailings. The project is divided into three main studies: (1) the assessment of the translation of successful greenhouse results to the field of phytostabilization using compost-assisted direct planting. This includes the use of different rates of compost as an amendment and different desert native plant species in addition to some potential parameters that could be used as indicators of a successful modification of biochemical and physical environment from a disturbed soil towards a more healthy soil when compost assisted direct planting phytostabilization is used; (2) the second study aims to evaluate the effect of the phytostabilization strategy on reducing windborne transport of particle and metal(loids) following the establishment of the vegetation cap. The results indicate that the vegetation resulted from direct planting decreases dust emissions from IKMHSS mine tailings; and (3) the third study focuses on one of the most important requirements for phytostabilization application in the field, the performance of the different plant species selected from the greenhouse studies. This performance was evaluated as the metal accumulation in aerial plant tissue based on metal concentration guidelines from the National Research Council as well as changes in the composition of plant species and canopy cover with time. The results derived from the translation of compost–assisted direct plating based on successful greenhouse results are showing the capacity of this technology on a field scale by maintaining a canopy cover over time that decreases mobilization by not hyper-accumulating metals in the aerial tissue and by preventing windborne particle dispersion with the potential of disrupting contamination pathways.

Particulate and dissolved forms of arsenic and heavy metals are released from legacy mine tailings, particularly in (semi-) arid environments where tailings remain barren of vegetation and therefore highly susceptible to erosion. This leads to contamination of adjacent ecosystems and increased risk to public health. Establishment of a vegetative cap using amendments, such as composted organic matter to enhance plant growth, may be employed to reduce both physical erosion and leaching, but the impacts of such practices on molecular-scale mechanisms controlling metal(loid) speciation and lability remain poorly understood. Here we report on subsurface biogeochemical transformations of metal(loid)s in a phytostabilization field study at a Superfund site in Arizona, USA, where a legacy pyritic tailings (4,000 mg kg^-1 As, 2,438 mg kg^-1 Pb, 6,142 mg kg^-1 Zn, 13.25% Fe, and 11.71% S, averages for the top 0.5 m) has undergone oxidation in the top 1 m. Tailings were amended in the top 20 cm with 10%, 15%, and 20% composted organic matter by mass and seeded with native halotolerant plant species. All field treatments and the uncomposted control received irrigation of 0.36 ± 0.03 mm y^-1 in addition to 0.25 ± 0.16 mm y^-1 of precipitation, resulting in water input of 144% the annual precipitation rate. The field trial incorporated four annual samplings from 2010 – 2013. Sampling consisted of a single core of 90 cm in length and 2.54 cm in diameter collected from each field plot that was subsequently sectioned into 20 cm depth increments for analysis by synchrotron Fe and As X-ray absorption spectroscopy (XAS) coupled with quantitative chemical extraction methods. Subsurface stabilization of arsenic by Prosopis juliflora (mesquite) was investigated by bulk and micro synchrotron XAS and multiple-energy microscale fluorescence mapping combined with chemical digestion of plant samples following 1, 2, and 3 months of growth in greenhouse microcosms as well as 14 and 36 months of growth at the field site. Results indicate persistence of oxidizing conditions following compost amendment in surface tailings despite addition of organic matter, development of heterotrophic microbial communities and irrigation of a poorly draining medium. Compost amendment of 20% corresponded with evidence of higher oxidative pyrite weathering activity at 40-60 cm depth during phytostabilization compared to treatments of 0% or 10% compost for which the highest oxidative pyrite weathering activity was observed closer to the surface at 20-40 cm depth.. Despite observed downward transport of As, Fe, Zn, Mn, Pb, Ni, Cu, Cr, V, and Co during phytostabilization, ≥ 75% of total As was found to be attenuated by ferrihydrite in surface depths. Attenuation of Mn, Co, and Ni was observed below 40 depth by tailings receiving compost amendment relative to the irrigated control. Root associated As(V) was immobilized on the root epidermis bound to ferric sulfate precipitates and within root vacuoles as trivalent As(III)-thiol complexes. Rhizoplane associated ferric sulfate phases were dissimilar from the bulk tailings mineralogy shown by XAS and exhibited a high capacity to scavenge As(V) with As:Fe ratios 2x higher than the compost amended growth medium, indicating a root surface mechanism for their formation or accumulation. Results indicate that arsenate attenuation in semi-arid mine tailings during phytostabilization greatly depends on the presence of high concentrations of Fe(III) (oxyhydr)oxide minerals with a high capacity for arsenic adsorption.

Legacy mine sites are of concern due to their prevalence and associated environmental and human health risks. The United States Bureau of Land Management estimates as many as 500,000 abandoned mine sites in the US (BLM, 2017). Sites requiring costly management and long-term response to the environmental hazardous risks can be designated to a National Priority List (NPL) by the Environmental Protection Agency (EPA) under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) (EPA, 2017). One such site, located in Central Arizona, is the Iron King Mine Humboldt Smelter Superfund Site (IKMHSSS). The site was designated to the NPL in 2008 due to concerns regarding the size of the tailing pile, the proximity of contaminated materials to the town of Dewey-Humboldt and waterways, and the dangerous concentrations of arsenic (As) and lead (Pb) of the tailings (EPA, 2017). Remediation efforts have been ongoing since the designation of the site to the NPL, including sampling, yard soil removal, and distribution of information to the local community regarding risks from the site. The University of Arizona Superfund Research Program (UA SRP) has conducted greenhouse and phytostabilization studies of the site in an attempt to understand the processes and mechanisms employed to stabilize the tailings materials as well as reduce dust emissions from the tailings to the town of Dewey-Humboldt (Gil-Loaiza et al., 2016). This effort has successfully demonstrated a reduction of dust emissions (Sáez, 2016), however chemical changes to the tailings due to phytostabilization are the focus of this research. This work attempts to ascertain whether adverse effects from the method of phytostabilization are observed in the pore waters of the tailing material, in particular the potential for contamination of water sources by mobilized As through chemical or microbiological means. Recent studies have proposed potential mechanisms that can promote mobilization of As by dissolved organic matter (DOM) (Mladenov et al., 2015). Heterotrophic microbial respiration under O2 limited conditions can cause the reduction of Fe3+ to Fe2+, enhancing desorption or dissolution of As from Fe containing minerals (Hasan et al., 2007). Additionally, DOM competes with As for sorption sites at mineral surfaces (Grafe et al., 2002). In this study, batch and column experiments were used to investigate the mechanisms of sequestration and release of As in compost amended mine tailings. Mine tailings were reacted in triplicate in the presence and absence of DOM using plain tailings and radiated tailings for microbiological control and under anoxic and oxic conditions at timescales from ranging from 3 to 900 hours for batch experiments and 1 to 900 pore volumes in column experiments. The highest As release to pore waters was observed under anoxic conditions in the presence of DOM both with microbial activity inhibited and uninhibited through 60Co gamma irradiation after 3 and 910 h of reaction. The release of As from batch experiments was lowest in the control treatment with no DOM added to tailings in both anoxic and oxic treatments after 24 h. Column flow-through experiments were also carried out to better understand the kinetic biogeochemistry of the tailings interacting with DOM. Columns were completed under suboxic conditions to best mimic field scenarios. To test the effect of microbes, control tailing samples were sterilized by 60Co gamma irradiation prior to flowing DOM. Pore volumes (PV) were collected using fractionation equipment from 1 to 900 PVs. The release of As was highest in the presence of DOM after approximately 40 PVs when As release began increasing to its maximum release of 50 μmol l-1. No significant difference between irradiated and non-irradiated tailings was observed in either irradiated or non-irradiated tailings. Lowest release of As to effluent solutions was in the absence of DOM. These results were consistent with the findings from batch experiments. Batch and column experiments show that DOM influences the mobilization of As from mine tailings, and demonstrates the potential risk to proximal ground water resources in the absence of attenuation processes between the oxidized tailings and groundwater.

Philosophiae Doctor - PhD / In Africa as well as in the world, South Africa plays an important role in the mining industry which dates back almost 120 years. Mining activities in South Africa mainly take place in Gauteng Province. Every year millions of tons of rocks are taken from underground, milled and processed to extract gold. Uranium is one of the minerals which is mined as a by-product of gold. The uranium bearing tailings are then placed on large dumps which are usually one or more kilometres in diameter in the environment. There are approximately 250 gold mine tailings dumps covering a total area of about 7000 ha. These gold mine tailings dumps contain considerable amounts of radium (226Ra) and have therefore been identified as large sources of radon (222Rn). Radon release from these tailings dumps pose health concerns for the surrounding communities. This study reports on the 222Rn soil-gas concentrations and exhalations measurements which were conducted at a non-operational mine dump (Kloof) which belongs to Carletonville Gold Field, Witwatersrand, South Africa. Radon soil-gas concentrations were measured using a continuous radon monitor (the Durridge RAD7). The radon soil gas concentration levels were measured at depths starting from 30 cm below ground/air interface up to 110 cm at intervals of 20 cm. These radon soil-gas measurements were performed at five different spots on the mine dump. The concentrations recorded ranged from to kBq.m-3. Furthermore, thirty four soil samples were taken from these spots for laboratory-based measurement. The soil samples were collected in the depth range 0-30 cm and measured using the low-background Hyper Pure Germanium (HPGe) -ray detector available at the Environmental Radioactivity Laboratory (ERL), iThemba LABS, Western Cape Province. The weighted average activity concentrations in the soils samples were Bq.kg-1, Bq.kg-1 and Bq.kg-1 for 238U, 40K and 232Th, respectively. 1 26 23 472 7 308 5 2551 18 The activity concentration of 40K and the decay series of 238U and 232Th for the top 30 cm of the accessible parts of the mine dump were measured using the MEDUSA (Multi-Element Detector for Underwater Sediment Activity) -ray detection system which was mounted on the front of a 44 vehicle, 0.6 m off the ground. The spectra acquired by the MEDUSA system were analysed and the activity concentrations were extracted using the Full Spectrum Analysis approach. The average activity concentrations obtained were 25975 Bq.kg-1 for 40K, 30940 Bq.kg-1 for 238U series and 185Bq.kg-1 for 232Th series for 2002 survey while 26075 Bq.kg-1 for 40K, 31040 Bq.kg-1 for 238U series and 20 5 Bq.kg-1 for 232Th series were recorded for 2010 survey. Moreover, a novel technique by means of the MEDUSA -ray detection system was utilised to map radon exhalation from the Kloof mine dump. In this technique the 214Bi concentration in the top 30 cm of the dump, which is used as a proxy for the 238U or 226Ra concentration, is measured even though there is not secular equilibrium between the radium and bismuth because radon has escaped. The actual activity concentrations of 40K and 226Ra are obtained from soil samples which were collected, sealed and measured in the laboratory settings after attaining secular equilibrium since radon gas does not escape. By comparing the ratios of the activity concentrations of the 214Bi obtained in the field using the MEDUSA -ray detector system to the activity concentrations of the 214Bi obtained in the laboratory using the HPGe -ray detector system yields a reasonable radon exhalation for a particular location in the mine dump. In this case it is assumed that the 40K and 232Th series activity concentrations are not or hardly affected by radon exhalation. By applying this new technique an average normalised radon flux of 0.120.02 and 0.120.02 Bq.m-2.s-1 were obtained for 2002 and 2010 surveys, respectively. The electrets and the IAEA standard formula were also utilised to calculated radon fluxes yielding 0.060.02 and 0.120.02 Bq.m-2.s-1 respectively.

Please read the abstract in the section 00front of this document / Thesis (PhD (Civil Engineering))--University of Pretoria, 2007. / Civil Engineering / unrestricted