Student Number : 0418755N - MSc (Eng) dissertation - School of Civil and Environmental Engineering - Faculty of Engineering and the Built Environment / Environmental impacts from tailings impoundments differ according to their mineral constituents. Erosion is one of the processes that aggravate the environmental impacts from tailings due to the transportation of particles, and knowing the susceptibility mechanisms of those tailings particles for erosion will provide understanding of how to prevent impacts arising from erosion. Laboratory pinhole erosion tests were used to determine the susceptibility of tailings particles to erosion. Compacted tailings samples were used, as compaction is an important parameter of erosion susceptibility. The study entails investigation of factors that affect erosion from the slopes of tailings deposits in order to evaluate mitigation measures. The results could help to provide more effective methods to reduce gully formation and enhance environmental protection. It is advisable to prevent environmental impacts at the source, before they become detrimental and costly to mitigate.

A Research Report submitted in partial fulfilment of the requirements for the degree of Master of Science in Engineering (Mining) to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa, July 2017 / The project investigated the application of geostatistical techniques in evaluating a mechanically deposited platinum tailings resource. The project was undertaken on one of the Anglo American Platinum tailings dams, the identity of which cannot be revealed, due to the agreement in place or permission given. Remnant unrecovered minerals of economic potential still exist in tailings dams. These unrecovered minerals have influenced several mining companies to turn their attention to the economic potential that still exists in tailings, making them a key strategic component of their resources and reserves. Geostatistics has been developed and thoroughly tested or improved to address challenges experienced in estimating in situ geological ore bodies. The main aim of this Research Project is to test whether these fundamental principles and theories of geostatistics are relevant and appropriate in evaluating man-made ore bodies, such as a Platinum tailings dam, without any significant changes needed on the underlying principles or estimation algorithms. The findings on the Case Study tailings resource can be applied in the evaluation of other tailings dams, as well as any other man-made structures such as low grade rock dumps, muck piles, with related characteristics. A standard approach (methodology) was followed to evaluate the Case Study tailings resource. Drilling and sampling was conducted through sonic drilling. It is a dry drilling technique that is suitable for sampling unconsolidated particles such as tailings. Thereafter, 2 samples were sent to the laboratory to establish grade (concentration) of Platinum Group Metals (Platinum, Palladium and Rhodium), Gold and Base Metals (Copper and Nickel). Density was also measured, and comprehensively analysed as part of variables of interest in this research. Statistical analyses were performed on all variables of interest contained in the dam: which are Platinum (Pt), Palladium (Pd), Gold (Au), 3E (two PGMs plus Gold), Copper (Cu), Nickel (Ni) and Density. The underlying statistical distributions of all metals and density were found to be non-symmetrical and slightly positive skewed. The skewness of the distributions was established to be marginal. Differences between raw data (untransformed) averages and the log-normal estimates were analysed and found to be insignificant. As such Ordinary Kriging of untransformed data was concluded to be the appropriate geostatistical technique for Case Study tailings resource. Analysis of mineralisation continuity (variography), a pre-requisite for geostatistical techniques such as Ordinary Kriging applied on the case study tailings resource, was also performed. Reasonable and sufficient mineralisation continuity was established to exist in the Case Study tailings resource. Although characterised by high nugget effect, these spatial correlations were established to be continuous with ranges of influence well beyond 450 m in all variables. Anisotropic variograms were modelled for all variables and are comprised of nested structures with two to three spherical models. Resource estimation was conducted through Ordinary Kriging in Datamine. All the seven variables were successfully interpolated into each cell of the 5m x 5m x 5m block model. Rigorous validation of the resource model was performed to establish the quality and reliability of the estimation carried out. Estimated resource model was analysed against the original borehole data, through comparison of grade profiles, statistical analysis, QQ Plots and histograms. The grade profile was recognised to be similar between boreholes (5 m composites) and the adjacent cells that have been estimated. Furthermore, statistical analyses revealed minimal differences between means of the estimated model and the original borehole data: the highest difference being 1.7% realised on 3E, followed by 1.1% on Density and Gold (Au). The rest of the variables (Pt, Pd, Cu, and Ni) have differences that are below 1%. 3 QQ plots and histogram were plotted from resource model with 5m x 5m x 5m cells and 5 m composited boreholes. Although these data sets are of different (slightly incompatible) supports, the intended purpose of comparing distributions was achieved. QQ plots and histograms revealed approximately identical shaped distributions of the two data sets, with some minor deviations noticeable in graphs of only two variables (Au and Density) that are underlain by two populations. The validation process carried out gave a compelling assurance on the quality and reliability of the resource model produced. The Case Study tailings resource therefore is successfully estimated by Ordinary Kriging. The results achieved on the Case Study tailings dam has successfully proved that geostatistical principles and theories can confidently be applied, in their current form or understanding, to any man-made tailings resource / CK2018

A presente pesquisa faz uma avaliação da influenciado regime de fluxo na estabilidade de uma barragem construída pela disposição hidráulica de rejeitos. Usualmente, essas estruturas são avaliadas com modelos de equilíbrio limite adotando-se, de modo simplificado, uma superfície freática em um regime hidrostático. No entanto, em casos em que a condutividade hidráulica da fundação ou de camadas na base do aterro é relevante em relação à dos rejeitos, o fluxo se torna verticalizado e o gradiente significativo, portanto, a premissa de regime hidrostático se torna não válida. Com o objetivo de avaliar a influência desses fatores, foram realizadas análises numéricas, simulando condições de fluxo e seus reflexos nos fatores de segurança. Ademais, foi desenvolvida uma extensa análise de dados e cálculos no estudo de caso de uma barragem, com expectativa de ampliar a vida útil de uma Planta de beneficiamento de minério de ferro. Ao se incorporar a real distribuição de pressões neutras, medidas na barragem, concluiu-se que o seu Fator de Segurança era cerca de 20% maior do que o obtido em cálculos simplificados, que desconsideram o regime de fluxo descendente, admitido, por hipótese, na barragem em estudo. Alguns comentários quanto à segurança à liquefação foram feitos, exceto a liquefação dinâmica, que foge do escopo desse trabalho. / The present research evaluates the influence of the foundations permeability in the scheme of flow and in the stability of a dam built through the hydraulic tailings disposal. Usually, these structures are evaluated with models of equilibrium limit, considering, in a simplified way, a phreatic surface in a hydrostatic scheme. However, in cases in which the foundations hydraulic conductivity is relevant when related to the tailings, the flow becomes verticalized and the gradient becomes significant. Therefore, the hydrostatic scheme premise becomes not valid. With the purpose of evaluating the influence of these factors, numerical analysis were made, simulating flow conditions and their influence in the factor of safety. Moreover, an extensive data and calculations analysis was developed in the case study of a dam, with the expectation of increasing the lifetime of an ore mining beneficiation plan. When incorporating the actual distribution of porepressure, measured at the dam, it was concluded that the safety factor of the dam was about 20% higher than that obtained for simplified calculations, that disregard the downward flow regime, admitted in the dam under study. Some comments about the safety of liquefaction were made, except the dynamic liquefaction, beyond the scope of this work.

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.

A presente pesquisa faz uma avaliação da influenciado regime de fluxo na estabilidade de uma barragem construída pela disposição hidráulica de rejeitos. Usualmente, essas estruturas são avaliadas com modelos de equilíbrio limite adotando-se, de modo simplificado, uma superfície freática em um regime hidrostático. No entanto, em casos em que a condutividade hidráulica da fundação ou de camadas na base do aterro é relevante em relação à dos rejeitos, o fluxo se torna verticalizado e o gradiente significativo, portanto, a premissa de regime hidrostático se torna não válida. Com o objetivo de avaliar a influência desses fatores, foram realizadas análises numéricas, simulando condições de fluxo e seus reflexos nos fatores de segurança. Ademais, foi desenvolvida uma extensa análise de dados e cálculos no estudo de caso de uma barragem, com expectativa de ampliar a vida útil de uma Planta de beneficiamento de minério de ferro. Ao se incorporar a real distribuição de pressões neutras, medidas na barragem, concluiu-se que o seu Fator de Segurança era cerca de 20% maior do que o obtido em cálculos simplificados, que desconsideram o regime de fluxo descendente, admitido, por hipótese, na barragem em estudo. Alguns comentários quanto à segurança à liquefação foram feitos, exceto a liquefação dinâmica, que foge do escopo desse trabalho. / The present research evaluates the influence of the foundations permeability in the scheme of flow and in the stability of a dam built through the hydraulic tailings disposal. Usually, these structures are evaluated with models of equilibrium limit, considering, in a simplified way, a phreatic surface in a hydrostatic scheme. However, in cases in which the foundations hydraulic conductivity is relevant when related to the tailings, the flow becomes verticalized and the gradient becomes significant. Therefore, the hydrostatic scheme premise becomes not valid. With the purpose of evaluating the influence of these factors, numerical analysis were made, simulating flow conditions and their influence in the factor of safety. Moreover, an extensive data and calculations analysis was developed in the case study of a dam, with the expectation of increasing the lifetime of an ore mining beneficiation plan. When incorporating the actual distribution of porepressure, measured at the dam, it was concluded that the safety factor of the dam was about 20% higher than that obtained for simplified calculations, that disregard the downward flow regime, admitted in the dam under study. Some comments about the safety of liquefaction were made, except the dynamic liquefaction, beyond the scope of this work.

A research report submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the Degree of Master of Science by Coursework and Research Report. Johannesburg, March 2016. / A vegetation survey was carried out in July 2014 on the substrates of 5 tailings dams by selecting 10 sampling sites which were previously used as sampling plots during the 1996/97 survey of Weiersbye et al. (2006). At each sampling site a 100m transect horizontally across the substrate and covering all levels of the tailings dam from the flat top to the toe paddock was established. Each transect was surveyed for the frequency of the species occurring and these were categorized based on their mode of colonization (natural, intentionally introduced and persisting) while tailings were collected by digging approximately 20cm into the ground for soil sample collection per substrate. The recorded species were then divided using Raunkier’s classification categories into growth forms and a comparison was done between the two surveys (2014 versus 1996/7) to identify the species that were lost, those that were still persisting and the new ones that had colonized over time. A total of 51 species (over 15ha) in 36 genera within 14 families were recorded on the tailings dams, compared to 168 species (over 765ha), 98 genera and 59 families found in the previous study. Families with the most species in 2014 were similar to those of the 1996/97 survey, following the dominance order of Poaceae >Asteraceae >Fabaceae >Anacardiaceae, with the percentage frequency of grasses (Poaceae) noted to have almost doubled over this period. Compared to 6 species common across the substrates in the previous study, the later survey recorded 12 common species (6 of the species occurring on all substrates) but overall both studies found vegetation cover to be high (above 65%) on flat tops and berms with species richness being high on the toe paddock>slopes>tops and berms and substrates susceptible to low nutritional (N,P,K,C) value. Indigenous plant species (54.9%) were dominating the tailing dams and were mostly perennials (82.3%) that were naturally colonizing and persisting (72.5%) on the tailings dams (similar to the 1996/97 survey), while alien (45.1%) plant species comprised annuals/biennials (17.7%) that were intentionally introduced (27.5%) prior to the 1996/97 survey by contractors. The ceased ameliorative initiatives since the first survey are believed to have significantly contributed to a decrease in herbaceous species richness, which formed the majority of the introduced species in the former survey (58.8% compared to 29.4%) as they depended on the supplementary additions of fertilizers and lime. Approximately 117 species, 62 genera and 45 families (including Chenopodiaceae, which was dominant) were lost over the 17 years period, the majority of these were introduced prior to the 1996/97 vegetation survey, while only Ficus sp. was the only new species colonizing apart from the increase noted in alien species (some invasive in nature). The decrease in species richness has encouraged woody and semi-woody (35.3%) and grasses (35.3%) to dominate the slimes reaffirming their potential as temporal and long term rehabilitation species that have developed physiological tolerance to acidic conditions, salinity and heavy metal pollution. In conclusion, this study has identified the species that can be used for phytoremediation to provide long terms solutions for dust, air and water pollution and soil erosion suppression for rehabilitation of these contaminated lands (Appendix 8). The survey also helps to identify species that are able to naturally colonize and persist on the tailings dams without supplements, making them ideal economic species to use for rehabilitation. Results also highlight the negative impacts of the lack of ameliorative supplementations, which in turn affects the floristic composition and structure on these tailings dams over time. Keywords: Aerial cover, Macronutrients, Tailings dams, Species richness, Tailings Storage Facilities (TSFs) and Vegetation survey / LG2017

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, in fulfilment of the requirements of the degree of Doctor of Philosophy in Engineering / The thesis describes the determination of the steady state line for the Merriespruit gold and Bafokeng platinum tailings by means of triaxial undrained compression tests. It shows that there are numerous steady state lines for the above mentioned tailings products and thatthe location oftheirsteady state lines in void ratio- mean confining effective stress space is influenced by the percentage fines (particles smaller than 0.075mm) present in the tailings, among other factors. As the percentage fines increases so the steady state line for the particular material shifts downwards in void ratio- mean confining effective stress space. The difficulty of defining a unique steady state line for a particular fines content tailings, due to errors in measurement of initial size, mass, etc. and changes in void ratio due to flooding, saturation and consolidation of the moist tamped triaxial test samples is illustrated and it is recommended that error bands be assigned to the steady state lines. The steady state lines determined for the Merriespruit gold tailings and the concepts of liquefaction are combined with evidence obtained from the post failure investigation into the Merriespruit flow slide failure to prove the premise that the flow slide was as a result of static liquefaction failure of the tailings. It is also illustrated that the notion of using a single steady state line to evaluate the liquefaction susceptibility of a tailings dam is insufficient due to the particle size distribution of the tailings varying along the beach length of the tailings dam and the location of the steady state line being influenced by the percentage fines content. Flume modelling using the Merriespruit gold tailings were carried to obtain a qualitative understanding of the behaviour of flow slides. Comparisons between the flume model tests and the Merriespruit flow slide (prototype) showed that it is difficult to obtain a correlation between the two due to the influence of scale, different dominating forces in the model and prototype and the inherent variability associated with such geotechnical phenomena- particularly in the preparation and deposition of the tailings in the flume model. Keywords: liquefaction, steady state line, flow slide, failure, flume modelling, Merriespruit, Bafokeng, gold, platinum, tailings / AC 2018

Tailings (mining waste) disposal is a significant consideration for the mining industry, with the majority of the ore processed in most mining operations ending up as tailings. This creates large volumes of tailings, which must be handled and stored responsibly to avoid potential environmental catastrophes. The most common form of tailings storage facility is the impoundment, where tailings are contained within a basin, with beaches forming around the perimeter of the impoundment and a pond standing in the middle. A relatively new method of tailings storage is to create a 'stack', whereby the tailings solids form a large heap, with the discharge of tailings slurry from the apex of the heap. It is of significant value for mine operators and tailings engineers to be able to predict the shape of the beach that forms in either of these disposal scenarios. The key to being able to do this relies on a method of prediction of the beach slope. The aim of this work is to develop a method of tailings beach slope prediction for tailings slurries that are sub-aerially discharged from a pipe. In this thesis a literature review is undertaken, investigating existing methods for the prediction of tailings beach slopes. These methods are validated against relevant industrial and experimental data. Two separate phases of experimental work have taken place in an effort to investigate tailings deposition behaviour, one at mine sites and the other in a laboratory on a small scale. Three new tailings beach slope prediction models are presented; a simple empirical model enabling quick approximate predictions; an a priori tailings beach slope prediction model based on existing theories of open channel flow, sediment transport and rheology, which is more powerful due to the greater degree of theory in its foundation; and a new semi-empirical model that shares some of the theoretical aspects of the a priori model but offers better predictions due to its empirical calibration to the experimental data. The experimental results, along with 3 other independently collected sets of relevant industrial and experimental data, are used to validate the beach slope prediction models found in the literature, as well as the new beach slope models presented in this thesis. Statistical evaluation of the performance of all of these models is presented to enable comparison. Finally, a new beach shape model is presented for the three dimensional geometric forecasting of the beach surface of a tailings stack. Historic tailings discharge data is run through the beach shape model, and the shapes predicted by the model are compared with aerial survey data of a real tailings stack for validation of the shape model. This work not only presents a new method of tailings stack shape prediction, but also a plausible theory for explaining the concavity of tailings beaches. The stack shape model also has the potential to be developed further for the three dimensional modelling of tailings beaches formed in other types of storage facilities, such as impoundments or valleys.

Uranium mill tailings from the Ranger mine, located in the Alligator Rivers Region of the Northern Territory, Australia, were examined to assess the effects of weathering and diagenesis on their long-term geochemical stability. Run of mill uranium tailings are a complex heterogeneous mixture of lithogenic ( primary gangue minerals and weathering products ) and secondary ( components that form during milling ) minerals, residual process chemicals and biogenic ( products of biological activity ) phases. Following transfer to the tailings storage facility, post depositional reactions alter the mineralogical and hydrochemical characteristics of the tailings solids and pore waters in accordance with weathering and diagenetic processes. In this thesis, a detailed examination of tailings cores and pore waters, kinetic column test work and geochemical modelling was combined with results from earlier studies to examine the key processes governing the geochemical stability of the Ranger tailings. Conclusions drawn from the work clearly demonstrates that the solid state speciation and mobility of metals and radionuclides in the tailings pile are governed by the processes of oxidative dissolution of sulfide minerals, weathering of phyllosilicates and organic matter diagenesis. The processes are spatially dependent, evolve over time and are influenced by the following key factors : 1. Tailings water content or degree of saturation ; 2. The nature and content of organic matter in the tailings ; 3. Redox potential of the tailings solid - pore water interface ; and 4. The specific reactivity of precursor minerals ( primary / secondary ) from the milling process and pore water solutes. Combined, these processes lead to the formation of authigenic minerals, which control the solubility of pore water constituents. These mechanisms will also have a profound impact on the long-term geochemical stability of the tailings pile and, as such, will need to be taken into account in the design, management and closure of the final tailings repositories at the Ranger site. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2004.

<p>Mine tailings can be rich in sulphide minerals and may form acid mine drainage (AMD) through reaction with atmospheric oxygen and water. AMD contains elevated levels of metals and arsenic (As) that could be harmful to animals and plants. An oxygen-consuming layer of organic material and plants on top of water-covered tailings would probably reduce oxygen penetration into the tailings and thus reduce the formation of AMD. However, wetland plants have the ability to release oxygen through the roots and could thereby increase the solubility of metals and As. These elements are released into the drainage water, taken up and accumulated in the plant roots, or translocated to the shoots. </p><p>The aim was to examine the effects of plant establishment on water-covered mine tailings by answering following questions: A) Is plant establishment on water-covered mine tailings possible? B) What are the metal and As uptake and translocation properties of these plants? C) How do plants affect metal and As release from mine tailings, and which are the mechanisms involved?</p><p><i>Carex rostrata Stokes, Eriophorum angustifolium</i> Honck., <i>E. scheuchzeri</i> Hoppe, <i>Phragmites australis</i> (Cav.) Steud., <i>Salix phylicifolia</i> L. and <i>S. borealis</i> Fr. were used as test plants. Influences of plants on the release of As, Cd, Cu, Pb, Zn and in some cases Fe in the drainage water, and plant element uptake were studied in greenhouse experiments and in the field. </p><p>The results obtained demonstrate that plant establishment are possible on water-covered unweathered mine tailings, and a suitable amendment was found to be sewage sludge. On acidic, weathered tailings, a pH increasing substance such as ashes should be added to improve plant establishment. The metal and As concentrations of the plant tissue were found to be generally higher in roots than in shoots. The uptake was dependent on the metal and As concentrations of the tailings and the release of organic acids from plant roots may have influenced the uptake. The metal release from tailings into the drainage water caused by<i> E. angustifolium </i>was found to depend greatly on the age and chemical properties of the tailings. However, no effects of <i>E. angustifolium </i>on As release was found. Water from old sulphide-, metal- and As-rich tailings with low buffering capacity were positively affected by <i>E. angustifolium </i>by causing higher pH and lower metal concentrations. In tailings with relatively low sulphide, metal and As contents combined with a low buffering capacity, plants had the opposite impact, i.e. a reduction in pH and elevated metal levels of the drainage water. The total release of metal and As from the tailings, i.e. drainage water together with the contents in shoots and roots, was found to be similar for <i>C. rostrata</i>, <i>E. angustifolium </i>and <i>P. australis</i>, except for Fe and As, where the release was highest for <i>P. australis</i>. The differences in metal and As release from mine tailings were mainly found to be due to the release of O₂from the roots, which changes the redox potential. Release of organic acids from the roots slightly decreased the pH, although did not have any particular influence on the release of metal and As. </p><p>In conclusion, as shown here, phytostabilisation may be a successful technique for remediation of mine tailings with high element and sulphide levels, and low buffering capacity.</p>