The behaviour of cohesionless soils is known to be influenced by the method of reconstitution. It is generally accepted in the literature that different reconstitution methods produce samples of varying fabric and thus samples of varying behaviour. Very little evidence has been presented to validate this statement. The main aim of this is thesis is firstly to observe the fabric of in situ and reconstituted gold tailings samples and secondly to investigate the difference in behaviour between these samples at the same state. The investigation focused on testing in situ and reconstituted gold tailings samples obtained from 3 positions on a tailings dam; pond, middle beach and upper beach. Laboratory reconstitution methods included moist tamping and slurry deposition. Fabric analysis involved the use of SEM images to classify the observed differences in the fabric of the undisturbed and reconstituted gold tailings samples. A particle interaction model based on the observed fabric was postulated to explain the differences or similarities in behaviour. The scope of behaviour investigated included sedimentation, collapse and swell, consolidation and compressibility, creep, stiffness and shear behaviour. The fabric analysis indicates that differences in the fabric of undisturbed and reconstituted gold tailings samples are visible. Moist tamping produces an aggregated fabric while slurry deposition yields a homogeneous fabric similar to that of the undisturbed samples. Comparison of behaviour indicates that neither moist tamping nor slurry deposition can replicate the behaviour of the undisturbed sample fully. Consolidation and compression is a function of the fabric while friction angle is independent of the fabric. Available shear strength and liquifaction potential is also affected by the preparation method and the resulting fabric. / Thesis (PhD)--University of Pretoria, 2009. / Civil Engineering / PhD / Unrestricted

The aim of this study was to study the extraction of zinc from the mineral sphalerite, especially the leaching of concentrate recovered from the Rosh Pinah tailings by means of ferric chloride. To this end, the literature on zinc processing was surveyed and knowledgeable persons were consulted. The study also addressed the leaching kinetics of an upgrade Rosh Pinah tailings dam concentrate as well as those of a synthetic zinc sulphide in a ferric chloride medium. Valuable results were obtained, from the leaching of sphalerite concentrate in ferric chloride medium. An activation energy value of 45.82 kJ/mol was obtained, which compares well with what has been published in the literature. A chemical control model and a diffusion control model were applied to the data obtained. From neither of the models a straight-line relationship could be deduced over the leaching range. At t < 45 minutes it seems that the process is controlled by chemical reaction at the interface; at t > 45 minutes it seems that the process is controlled by diffusion through the product layer. If therefore seems that the rate-controlling step can be related to the process of diffusion through the product layer. The mixed control model proposed by Huang and Rowson, [1-(1-x)1/3+y/6[(1-x)1/3+1-2(1-x)2/3]=kMt, was applied to data obtained during this study. The resultant graphical fit was near perfect, indicating that sphalerite leached in ferric chloride follows a mixed control mechanism for the conditions reported in the study. An activation energy of 20.71 kJ/mol was determined for this model by using the following equation: / Dissertation (MSc)--University of Pretoria, 2006. / Chemistry / unrestricted

In the last couple of decades, geocell reinforced soil systems have been used in challenging new applications. Although the widely different application of cellular confinement systems demand a better understanding of the fundamental behaviour of the functioning of the cellular reinforced soil systems, surprisingly little research on the fundamental behaviour of the structures and the interaction of the components has been done. A research project has been initiated at the University of Pretoria and this thesis constitutes the first step in achieving an understanding in the functioning of geocell reinforced soil systems. This thesis is focused specifically on the geocell support pack I configuration. However, the research output is not limited to this configuration and may find wider application. The support packs were studied at a width to height ratio of 0.5. The fill material used in this study is classified gold tailings from the Witwatersrand Complex and the geocell membranes were manufactured from a thin (nominal thickness of 0.2 mm) High Density Polyethylene (HDPE) sheet. This study provides an understanding of the functioning of the geocell support pack by studying the constitutive behaviour of the fill and membrane material and their interaction, as well as the influence of multiple cells on the composite structures. The behaviour of the classified tailings material is interpreted in terms of Rowe's stress-dilatancy theory and a simple robust constitutive model for the material behaviour is developed. The stress-strain behaviour of the HDPE membranes is strain-rate-dependent and two simple mathematical models for the strain-rate-dependent stress-strain behaviour of the membranes are developed. An analytical calculation procedure for obtaining the stress-strain behaviour of the fill confined with a single geocell is developed with which some of the shortcomings of the previously presented theories are addressed. This procedure uses the models for the fill and membrane behaviour developed as part of this study. The interaction of adjacent cells in a multiple cell geocell structure, influences its behaviour. This thesis shows that, with exception of low axial strain levels, the efficiency of a structure consisting of multiple cells of a certain size is lower than a single cell structure with the same cell size and fill. These results are contrary to previously published opinion. A method for quantifying the efficiency of a multiple cell pack is also developed. / Thesis (PhD (Geotechnical Engineering))--University of Pretoria, 2006. / Civil Engineering / unrestricted

South Africa, as one of the world’s largest gold producing countries, also generates large amounts of tailings. These tailings are disposed in tailings dams, which pose great threat to the environment in the case of failure, in particular, liquefaction. In order to evaluate the potential of liquefaction, the void ratio of the tailings is required and is often impossible to obtain. Seismic methods allow an indirect method to estimate void ratio of in situ deposits of which tailings are examples of. Currently, the use of seismic methods to estimate void ratio of tailings rely on shear wave velocity – void ratio relationships derived for sands. It is thus uncertain whether this relationship holds for gold tailings, which is classified as a sandy silt or silt. The measurement of shear wave velocity of tailings is done in the laboratory using a triaxial apparatus modified to accommodate bender element. Shear wave velocities are measured using wide square pulses and continuous sinusoidal waves. The results show that there is a near linear relationship between void ratio and shear wave velocity normalized against effective stress. The position of this relationship lies below the previously published results for sands. Shear wave velocity of gold tailings is more sensitive to changes in effective stress than changes in void ratio or over-consolidation ratio. Furthermore, using phase sensitive detection of continuous waves, we can conclude that shear wave velocity of gold tailings is also frequency dependent. / Dissertation (MEng)--University of Pretoria, 2006. / Civil Engineering / MEng / Unrestricted

The disposal of fine-grained mining and industrial waste by formation of hydraulic-fill tailings dams is becoming a design and construction activity of increasing scale. In light of the increasing pressure on the mining industry to sustain stringent safety and environmental standards it is becoming more important to gain technical knowledge of the waste problem. The upper layers of the tailings residue dams are in the unsaturated state with the matric suction component contributing to the overall shear strength. The ability to incorporate the matric suction component in shear strength calculations is important to safe design. This research project investigates the use of the mid-plane suction probe to measure matric suction. The results obtained from the probe is used along with various tests to construct a complete soil-water characteristic curve for Mispah gold tailings as well as to investigate suction induced shear strength of drying tailings with depth. The tests were conducted on gold tailings from Vaal Operation’s Mispah tailings dam. The laboratory tests consisted of a trough test, to determine the soil-water characteristics of the gold tailing and also a drying box test that simulated the drying and desiccation of the gold tailings in the daywall. The project concluded that the mid-plane suction probe could be used with acceptable accuracy to determine soil suctions. The model for the prediction of the soil water characteristic curve, derived by Fredlund and Xing (1992), was used successfully to predict the complete soil water characteristics curve for Mispah gold tailings. The equation derived by Vanapalli et al. (1996) was successfully used to calculate both the normal and suction induced shear strength of gold mine tailings using either the volumetric water content from the extracted samples or from the soil water characteristic curve. / Dissertation (MEng (Geotechnical Engineering))--University of Pretoria, 2006. / Civil Engineering / unrestricted

A vast amount and variety of mine tailings are produced around the world each day. In the gold¬mining industry in South Africa the residue of crushed are is disposed of in large tailings or hydraulic fill dams. The outer walls of these dams are built up of layers of material, each of which is allowed to dry before the next layer is placed. In order to study the stability of these walls, the appropriate engineering properties of the tailings must be ascertained. Due to the construction technique used in tailings dam construction, the outer walls are in an unsaturated state, which also means that suctions are generated within the tailings. Various techniques exist to measure suction, most of which are indirect methods. The recent development of the mid-¬plane suction probe at the University of Pretoria created the opportunity of measuring suctions directly on desiccating samples of gold mine tailings. A test method has been developed from which soil mechanics parameters can be derived from suction measurements. The experimental programme consisted of a series of these newly developed tests on fine and coarse samples of gold mine tailings, as well as on different particle size ranges. The experimental results were used in the development of a new method of predicting the air-entry value, with only the grading of the tailings known. A new method of predicting the soil-water characteristic curve up to the air-entry value was also proposed. The results of the research showed that the tailings remain saturated up to the air-entry value. The clay, fine silt and medium silt sized tailings was found to be the controlling particle size ranges in the development of suctions. The vast amount of parameters and information gained through the use of the proposed test method clearly indicates its effectiveness in studying the performance and characteristics of a material drying from saturation. The results also indicated the effectiveness of the mid-plane suction probe for the direct measurement of suction. / Dissertation (M Eng (Geotechnical Engineering))--University of Pretoria, 2006. / Civil Engineering / unrestricted

South Africa, with its world leadership in the mining sector, and well-developed industrial sector, understandably has many tailings dams of various types. South Africa’s tailings dams are among the largest in the world in terms of delivered tailings tonnages, plan size and height. Obviously tailings disposal from the mining and industrial sectors in South Africa can have a major impact on the environment and the safety of human life if the dam design and tailings deposition process are not properly controlled. In South Africa there is a growing awareness of the importance of the environment and of the safety of the tailings dams. Catastrophes like the Merriespruit Gold Tailings dam failure in February 1994, where 17 people died and widespread devastation and environmental damage was caused, has sparked the renewal of research into tailings dam stability and safety. The rate of rise of tailings dams has an influence on the safety and stability of a tailings dam. If rate at which a tailings dam is built is too high, the dam may become unstable and be at risk of failure. There are many factors that control the rate of rise of tailings dams that are not very well understood. This research deals with sedimentation and desiccation of gold mine tailings. Sedimentation and desiccation are factors that influence the rate of rise. This research looked at how the gold mine tailings behave when sedimentation and desiccation occur. This was achieved through laboratory experiments, which consisted of column settling tests and drying box tests, and field tests. A model that predicts the behaviour of sedimentation and desiccation of tailings was also analysed. It was found that tailings sedimentation occurs very quickly. It was also found that suctions play an important role during the desiccation of the tailings. / Dissertation (MEng (Geotechnical Engineering))--University of Pretoria, 2007. / Civil Engineering / MEng / unrestricted

A geochemical study of the composition of natural sediments and contaminating mine tailings in Hastings and Alice Arms has been carried out. Apart from the geochemical investigation on the solid fraction, pore waters from six sediment cores have been analyzed to evaluate the diagenetic processes in the sediments of these two inlets. Differences in the mineralogy as well as in the chemical composition of the sediments were used to distinguish the natural sediments from contaminated sediments and pure tailings. In Alice Arm, two types of tailings could be differentiated with these methods. The first tailings type originated from the Kitsault Mo-deposit, which was mined in the past two decades by the B.C. Molybdenum Corporation and AMAX/Canada. These tailings are characterized by a number of features which make them distinguishable from natural sediments. The K-feldspar content of the tailings is significantly increased, mainly at the expense of plagioclase, which is the main characteristic for the mineralogical identification of this tailings type. The enhanced K-feldspar content is the cause for increased K and Rb values in the Mo-mine tailings. Another indicator specific to these recent tailings is an increased Mo content. The second tailings type is derived from an older mining operation in the Kitsault Valley, most likely the Dolly Varden Silver Mine. A specific indicator for these tailings is their high Ba content which is due to large amounts of barite. This mineral phase could be identified by X-ray diffraction methods in a heavy mineral fraction of the relevant sediment layers. Both tailings types show enrichment in their Pb, Zn and S concentrations, caused by an increased amount of metal-sulphides in the ore materials. In this area, these elements can therefore serve as a general indicator for the contamination of natural sediment with either tailings type. The interstitial water analyses indicated that the sediments in both inlets become reducing at a fairly shallow depth (10-15 cm), resulting in the mobilization of Mn, Fe and Mo from the solid phase. In the deeper parts of the cores, consumption of these metals could usually be observed which is likely due to precipitation of authigenic components. The dissolved Mo concentrations in the sediments contaminated with the modern tailings were much higher than in the natural sediments. In the pore water of the pure tailings the concentration reaches some 300 times that of the overlying water, which is the highest value ever reported for saline pore waters. These high Mo concentrations must support a flux of Mo from the sediment into the overlying water, and it is shown that such a flux could increase the inventory of naturally occurring dissolved Mo in the deep waters of Alice Arm by up to 4%. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

A geração de resíduos provocada pela atividade mineradora é revestida de considerável preocupação ambiental, tanto em função da área envolvida no depósito deste material, quanto pelos impactos causados por eventuais rupturas que possam a ocorrer nestes reservatórios. O método de disposição de resíduos, frequentemente utilizado pelas mineradoras, consiste no bombeamento do material por via úmida até os reservatórios de alteamento contidos através de diques ou barragens. Este processo pode tornar estas áreas suscetíveis à ocorrência de rupturas causadas por liquefação do material. Quando este tipo de evento acontece, tem-se um aumento repentino da poropressão, com consequente redução da resistência ao cisalhamento. A verificação do potencial de liquefação de resíduos de mineração é, portanto, imprescindível à prevenção de impactos ambientais, além de colaborar na execução de projetos geotécnicos mais seguros e econômicos. Neste trabalho são analisados três reservatórios distintos, sendo um composto por resíduo de mineração de ouro e os outros dois por resíduo de mineração de bauxita. Os resultados de ensaios realizados em campo (SCPTU/CPTU e SDMT) são utilizados na avaliação geotécnica dos resíduos, buscando-se verificar a compatibilidade com avaliações já realizadas através de ensaios de laboratório. O potencial de liquefação estática dos materiais é observado em laboratório para baixos níveis de tensões, demonstrando que os resíduos são suscetíveis à liquefação estática. Este comportamento é verificado também na interpretação de ensaios de campo, interpretados através de correlações de natureza semiempírica baseadas na combinação de uma medida representativa de pequenas deformações (módulo cisalhante) combinado a uma medida obtida à grandes deformações (resistência à penetração) que, combinadas, permitem a determinação do parâmetro de estado do material. A primeira proposta consistiu na definição de uma fronteira entre materiais de comportamento contrátil e dilatante no espaço G0/qc versus p’/pa. Esta proposta apresentou uma resposta adequada, entretanto, a concentração de todos os pontos referentes aos resíduos analisados, possivelmente suscetíveis ao fenômeno de liquefação estática, numa mesma região gráfica, somente foi possível no espaço G0/qc versus qc1. Neste espaço a separação entre materiais de comportamento dilatante e contrátil foi possível com a inserção de uma fronteira empírica. Este estudo demonstrou a boa sensibilidade dos parâmetros G0 e qc ao fenômeno de liquefação estática. A suscetibilidade à liquefação cíclica dos resíduos de mineração de ouro e bauxita também foi verificada através de correlações com resultados de ensaios de campo. Esta análise indicou a possibilidade de ocorrência do fenômeno para os mais baixos níveis de magnitude de sismo atuante. / Waste generation caused by mining activity emerges as an environmental concern, both because of the large area involved in deposits of this material, as well as the possible impacts caused by occasional failures that may occur in these deposits. The method of waste disposal, often used by mining companies, consists by pumping wet material in sequence until completion of the reservoirs contained by dikes or dams. This process makes these areas susceptible to the occurrence of the liquefaction failures. When this type of event happens there is a sudden increase in pore pressure with consequent reduction shear strength, which can result is risk of containment structures. Therefore, verification of liquefaction potential of these materials is essential in the prevention of environmental impacts. The present work analyzes three different reservoirs, one consisting of gold mining tailings and the other two of bauxite mining tailings. The results of field tests (SCPTU/ CPTU and SDMT) are used in geotechnical evaluation of tailings in order to verify the compatibility with evaluations already carried out through laboratory tests. The static liquefaction potential observed in laboratory at low levels of stresses is consistent with field assessment from in situ tests. Semiempirical correlations based on field tests are based on small strain measurements (shear modulus) combined with large strain measurements (penetration resistance), that are used to defined the state parameter of the material. The first proposal consisted in defining a boundary between materials of contractive and dilatant behavior in space G0/qc versus p’/pa. The proposal presented an appropriate response, however, the concentration of all analyzed points, possibly susceptible to static liquefaction phenomenon, in the same graphical region was only possible in space G0/qc versus qc1. In this space the separation between materials of contractive and dilatant behavior was possible with the inclusion of an empirical boundary. This study demonstrated the good sensitivity of the parameters G0 and qc to the static liquefaction phenomenon. The cyclic liquefaction susceptibility of the gold and bauxite mining tailings was also verified by correlation with field tests results. This analyzes indicated the possibility of occurrence of the phenomenon to the lowest levels of earthquake magnitude.

Iron has been an essential element to human development and iron-oxide deposits are known to host minerals that are labelled as critical raw materials (CRMs), especially in the EU. Therefore, ensuring a sustainable supply of CRMs require access to both primary and secondary sources of their host deposits such as iron oxides. Blötberget is an old mining site in central Sweden rich in both primary and secondary iron-oxide resources (i.e. tailings) from centuries-long mining activities. Thus, this thesis focused on this site, to (1) improve the image of its iron-oxide mineralisation under the historical tailings area through the extraction and processing of 2D data from a wider and sparse 3D dataset, (2) characterise the tailings in terms of geometry delineation and geomechanical property estimation by generating P-wave velocity models of the tailings, and (3) improve the interpretation of existing results in the area through 3D visualisations and comparison. Results from this thesis work suggest possible depth and lateral extensions of the mineralisation for few hundreds of metres beyond what was known previously in the area. It is believed that about 10 Mt of primary iron-oxide resources could arguably be present under the tailing area while the tailings contain an estimated 1 Mt of secondary iron-oxide resources. Also, this thesis work findings indicate that the historical tailings are approximately 10 -12 m thick, 650 m long, and 300 m wide, and has a Vp/Vs ratio between approximately 3-4, indicating a poor geomechanical strength. Additionally, the depth to bedrock in this area was estimated to be 50 m at its deepest parts, with a morphology indicative of complex geological occurrence. Therefore, it is concluded, based on these results, that Blötberget has a good potential to ensure the supply of both iron ore and its constituent CRMs. / Järn har varit ett viktigt grundämne för mänsklig utveckling och järnoxidavlagringar är kända för att innehålla mineral som är märkta som kritiska råmaterial (KRM), särskilt inom EU. Därför kräver säkerställandet av en hållbar tillgång till KRM tillgång till både primära och sekundära källor till deras värdfyndigheter, till exempel järnoxid. Blötberget är en gammal gruvplats i mellersta Sverige som är rik på både primära och sekundära järnoxidresurser (dvs. gruvavfall) från en lång gruvverksamhet. Således fokuserade denna avhandling att (1) förbättra karaktäriseringen av järnoxidmineralisering i det historiska gruvområdet genom utvinning och bearbetning av 2D-data från ett glest 3D-dataset, (2) karakterisering av gruvavfall för avgränsning av geometri och uppskattning av geomekaniska egenskaper genom att generera P-vågshastighetsmodeller för gruvavfallsområdet, och (3) förbättra tolkningen av befintliga resultat i området genom 3D-visualiseringar. Resultat från denna avhandling tyder på möjliga djup och laterala förlängningar av mineraliseringen om några hundratals meter bortom vad som tidigare var känt i området. Det antas att cirka 10 Mt primära järnoxidresurser finnas under avfallssområdet medan gruvavfallet innehåller uppskattningsvis 1 Mt sekundära järnoxidresurser. Dessutom visar denna avhandling att det historiska gruvavfallet är cirka 10-12 m tjockt, 650 m långt och 300 m brett och har ett Vp/Vs -förhållande mellan cirka 3-4, vilket indikerar en låg geomekanisk hållfasthet. Dessutom beräknades djupet till berggrunden i detta område vara 50 m vid dess djupaste delar, med en morfologi som indikerar komplex geologisk förekomst. Därför dras slutsatsen, baserat på dessa resultat, att Blötberget har en god potential att säkerställa leveransen av både järnmalm och dess ingående KRM