In recent years, emissions of hydrogen cyanide from metallurgical operations have received renewed attention by legislative bodies, leading to the need for a reliable quantification method for HCN volatilisation. Subsequently, the purpose of this project, launched by Anglogold Ashanti Ltd. and in collaboration with MINTEK and the University of Pretoria, was to develop a prediction model for cyanide volatilisation from plant operations and tailings storage facilities in South Africa. The study was done in four stages, the first being a laboratory study of the equilibrium behaviour of hydrogen cyanide. Henry’s Law constant (kH) was determined at different solution cyanide concentrations, salinities and temperatures. A value for kH was established at 0.082 atm.L/mol, which was found to be independent on the solution cyanide concentration between 10 and 200 ppm cyanide. In addition, the effect of temperature on kH was found to be negligible at solution temperatures between 20 and 35ºC. It was also concluded that high salinities increase kH and promote volatilisation, but this effect was negligible at the typical salinity levels found in South African process water. The second stage entailed a detailed study of the mass transfer coefficient, KOL, for hydrogen cyanide from cyanide solutions and pulp mixtures, both in the laboratory and on-site. It followed from this investigation that the most important parameters affecting KOL are the HCN (aq) concentration in the liquid, the wind velocity across the solution or pulp surface, expressed in terms of a Roughness Reynolds number, Re*, and the moisture content, or solid to liquid ratio, of the pulp. Furthermore, it was concluded that KOL is highly sensitive to HCN (aq) concentrations at low concentrations, while it becomes rather insensitive to HCN (aq) at concentrations above 20 ppm HCN (aq) . The data generated by the laboratory and on-site test work was incorporated into the development of an empirical prediction model, based on the Roughness Reynolds number (Re*), moisture content (M), and aqueous cyanide concentration (HCN(aq) ) which may be described by the following equation: KOL= <font face="symbol">a</font> Re*b Mc HCN(aq)d + e The model coefficients were subsequently determined for application of the model to leach tanks, adsorption tanks, tailing storage facility surfaces and return water dams. The calculated model predictions for KOL were in excellent agreement with the measured test work data. Finally, the prediction model was validated at the leach and adsorption sections of a selected gold plant and a selected tailings storage facility. The model predicted that 9% of the cyanide lost in the leach and adsorption section could be attributed to HCN volatilisation. As for the tailings storage facility, the model assigned 63% of the cyanide lost from the tailings storage facility to HCN volatilisation, of which 95% occurred from the area on the tailings dam surface covered in a thin liquid film. It is recommended that the current methods available for the determination of HCN (aq) be further improved, due to the sensitivity of the model to the input value of the HCN (aq) concentration, in order to ensure that reliable predictions are made. It is also suggested that additional validation work be done in order to establish the generic applicability of the model to different sites. / Dissertation (MEng(Metallurgical))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

Contaminant release and transport in platinum tailings are poorly studied in literature. This study serves to characterise these processes. The tailings facility is located in Steelpoort, Mpumalanga, South Africa on Critical Zone rocks of the Rustenburg Layered Suite in The Bushveld Igneous Complex. Tailings material samples were collected by hand auger- and direct push probe drilling at specific locations to represent the different materials present in the tailings facility. Water samples were collected from monitoring boreholes as well as the Steelpoort River. The samples were analysed using XRD, XRF, ABA, NAG, Reflected Light Microscopy, Acid Leaching Tests and ICP scans. Using the collected data, a geochemical model was constructed for the interpretation of mineral phase dissolution and to trace the mineral phases releasing contaminants. Analysis-, test- and modelling results showed that alteration mineral phases formed within ten years in the tailings material and that the existing alteration phases viz. talc and chlorite, as well as sulphides, are the major contributors of contaminants. Elevated pH values as well as major cation and anion concentrations were found in the fluid discharging from the tailings as well as the in groundwater, with little to no heavy metals, which were traced directly to the chromite phase. This suggests that platinum tailings do not contribute to heavy metal contamination or acid rock drainage but may increase aquifer salinity and alkalinity. The flow through the tailings, underlying vadose zone and fractured rock aquifer was characterised using permeameter- and pumping tests. From the data collected, an unsaturated flow model was developed to characterise the flow through the tailings. From the model, discharge from the tailings was calculated to take place at 0.7m per decade into the underlying vadose zone with fracture flow in the aquifer ranging from 0.46-0.026m/d, as calculated from pumping test results. Contaminant migration into the Steelpoort River is possibly inhibited by the Dwarsriver Fault, based on the chemical data and hydraulic conductivities calculated. Therefore, groundwater is considered to be the major receptor in the system and groundwater users may be negatively impacted by increasing groundwater salinity and major ion concentrations. / Dissertation (MSc)--University of Pretoria, 2013. / Geology / unrestricted

Underground mining produces a huge amount of voids and an even larger quantity of mine waste. Overlooking these voids could lead to the possibility of ground subsidence, as well as safety issues during mining operation; while ignoring the waste, could cause environmental pollution and significant suffering. One solution to remedy both (the voids and the waste) is cemented paste backfill (CPB), which is gaining increased recognition in both the mining industry and academic research. Transforming tailings into cemented paste, and transporting this back to underground stopes, not only negates these safety issues to a large degree, but also makes it possible to put waste to good use.However, most studies involving CPB have been conducted at temperatures above 0°C; knowledge of CPB in sub-zero environments is still lacking. For this reason, this thesis investigates the mechanical behaviour of CPB in a the latter type of environment.Uniaxial compressive strength tests were carried out on a series of frozen CPB (FCPB) samples to evaluate the mechanical behaviour (e.g. compressive strengths, geotechnical features, and the stress-strain relationships) of FCPB. It has been discovered in this thesis that FCPB exhibits remarkable strength compared to CPB and, has a great resemblance to frozen soil. Factors which may affect the behaviour of FCPB were thoroughly examined. Binder contents and types were found to be irrelevant; water content, in contrast, plays a dominant role, with an optimum value of around 26% by weight. Sulphate was confirmed to have an adverse effect on the strength of FCPB due to the increasing unfrozen water content and the formation of legible ice lenses. Hydraulic conductivity tests, scanning electron microscope observations, thermal gravimetric analyses, and mercury intrusion porosimetry were also performed as subsidiary experiments to understand the geotechnical features of FCPB. This information will be of significant value for numerous practical applications.

One of the most novel technologies developed in the past few decades is to convert mine wastes into cemented construction materials, otherwise known as cemented tailings backfill (CTB). CTB is an engineered mixture of tailings (waste aggregates), water and hydraulic binders. It is extensively used worldwide to stabilize underground cavities created by mining operations and maximize the recovery of ore from pillars. Moreover, the application of CTB is also an environmentally friendly means of disposing potential acid generating tailings underground. During and after its placement into underground mine excavations or stopes, complex multiphysics processes (including thermal, T, hydraulic, H, mechanical, M, and chemical, C, processes) take place in the CTB mass and thus control its behavior and performance. With the interaction of the multiphysics processes, the field variables (temperature, pore water pressure, stress and strain) and geotechnical properties of CTB undergo substantial changes. Therefore, the prediction of the field performance of CTB structures during their life time, which has great practical importance, must incorporate these THMC processes. Moreover, the self-weight effect, water drainage through barricades, thermal expansion and chemical shrinkage can contribute to the volumetric deformation of CTB. Consequently, CTB exhibits unique consolidation behavior compared to conventional geomaterials (e.g., soil). Furthermore, the consolidation processes can result in relative displacement between the rock mass and CTB. The resultant rock mass/CTB interface resistance can reduce the effects of the overburden pressure or the vertical stress (i.e., arching effect). Hence, a full understanding, through multiphysics modeling and simulation of CTB behaviors, is crucial to reliably assess and predict the performance of CTB structures. Yet, there are currently no models or tools to predict the fully coupled multiphysics behavior of CTB. In this Ph.D. study, a series of mathematical models which include an evolutive elastoplastic model, a fully coupled THMC model, a multiphysics model of consolidation behavior and a multiphysics model of the interaction between the rock mass/CTB interface are developed and validated. There is excellent agreement between the modeled results and experimental and/or in-situ monitored data, which proves the accuracy and predictive ability of the developed models. Furthermore, the validated multiphysics models are applied to a series of engineering issues, which are relevant for the field design of CTB structures, to investigate the self-desiccation process, consolidation behavior of CTB structures as well as to assess the pressure on barricades and the strength development in CTB structures. The obtained results show that CTB has different behaviors and performances under different backfilling conditions and design strategies, and the developed multiphysics models can accurately model CTB field behavior. Therefore, the research conducted in this Ph.D. study provides useful tools and technical information for the optimal design of CTB structures.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / Mining in Peru has existed for several decades, and for several years, there has been no proper environmental management of the impact of this activity on the environment and society in general, whether it be gas emissions, the presence of acidic water, or the generation of mining tailings. One of the most prominent examples involve mine tailings; these are by-products of mining processing plants and are stored in a dam known as a tailings dam. Like any extraction activity, mining generates large amounts of waste material that could become potential risks to the environment and society. Using hydraulic fills, the mine tailings contained in tailings dams could be reused. These fills seek to decrease the volume of stored tailings to prevent any future dam collapses, as observed in Brazil with the Vale mining company, where its tailings dam collapsed and caused more than 200 deaths.

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado. / Based on the review of different research studies, we could assess that, due to their unique biological features, microbes, specifically bacteria, could be used to repair damaged soils with heavy metal and toxic compound contents. Furthermore, these microorganisms are metabolically capable to oxidize cyanide and its by-products to generate less-toxic compounds at the end of the process. This research proposal seeks to improve conventional mine closure designs, thus counteracting their negative short-term, medium-term, and long-term after-effects to the environment. The proposed technique as a solution, therefore, is microbial remediation, using pseudomonas fluorescens bacteria to oxidize this compound to non-toxic components. It will ensure operational continuity for the deposits and, in turn, the sustainability of the entire mining industry.

A project report submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Science in Engineering. / The project report deals with the relationship between the undrained shear strength and the moisture content of Red Berea sand tailings. The tailings were obtained from the Red Berea sand dunes near Richards Bay, Kwa-Zulu Natal, South Africa. The geology of the area consists of Miocene deposits of red clayey sand, classified as Berea Formation. A method for determining stability of a tailings dam for Red Berea sand tailings, was investigated. The general method of using the degree of saturation of the tailings to specify the rate of rise, is not applicable to this type of tailings. It was found that a relationship exists between the undrained shear strength of the tailings, and the moisture content. The moisture content can easily be measured and the undrained shear strength can then be calculated. The calculated undrained shear strength can be used in a total stress analysis to determine a factor of safety against failure. This project report consists of a discussion of the literature, which was used as the basis for the assumptions made, as well as a description of the tests performed to prove the above-mentioned relationship. Test results are given, interpreted and used in an illustrative example of a stability analysis. / Andrew Chakane 2020

Student Number : 9612464Y - MSc dissertation - School of Mining Engineering - Faculty of Engineering and the Built Environment / This study was conducted at the West Rand Region, part of South African-based AngloGold operations. The study assesses the impacts of gold mining on the water quality and the change in landuse resulting from the mining activities on the West Rand Region. This was achieved by collecting historical data relating to the tailings dams and both surface and groundwater qualities between 1998 and 2003. The landuse information was gathered from the topographic map of Carltonville and remotely sensed data in the form of aerial photographs, landsat data and ASTER images. The data was analysed in a GIS ILWIS. The sizes of the tailings dams have not changed significantly during the study period. The size of the plantation also shows a decreasing trend due to pollution from the tailings dams. The area surrounding the Anglo Gold mining operations is sparsely-vegetated due to both poor soils and the impacts of mining activities. The surface water quality is poor and this water has negative impacts on the environment following accidental discharges and has potential negative impacts from seepage through the unlined dams. The quality of the groundwater is generally good with the exceptions of BH 18, MBH 8, MBH 5 and MBH 3 whose pollution arises from North mine tailings dams and North boundary dam. MBH 5 shows an improvement in water quality over time. The potential generation of AMD from the tailings dams is inhibited by the neutral pH of the tailings. In order to improve the environment in the West Rand Region and to prevent further pollution, planting of indigenous trees to make up for shrinking plantation and lining of the dams be undertaken. Stricter maintenance and monitoring of both the sewage plants and the dams be implemented to avoid accidental discharges of poor quality water into the environment. A study to accurately quantify the groundwater pollution arising from both the tailings dams and other surface water bodies should be undertaken.

<p>Surface mining of Alberta’s oil sands has led to significant land disturbance, making reclamation and sustainable development of this resource one of the largest challenges facing the industry today. Syncrude Canada Ltd. has developed an innovative technique to reclaim composite tailings (CT) through constructed wetland landscapes and is currently investigating the viability of a pilot-scale freshwater fen built over sandcapped CT. Unpredicted by abiotic geochemical modelling of CT behaviour, a minor episode of hydrogen sulfide (H₂S) gas release was encountered during the initial stages of fen construction indicating microbial activity was likely involved in H₂S generation within CT. This thesis investigates the S geochemistry of CT with depth and employed 454 pyrosequencing and functional enrichments to characterize the associated microbial communities in the first S biogeochemical study of oil sands CT. Porewater H₂S was detected extensively throughout the deposit with background levels ranging from 14 – 23 µM and a maximum of 301.5 µM detected at 22-24 m of depth. Reduced Fe (Fe²⁺) was also detected, but confined within surficial depths sampled, ranging from 1.2 – 38.5 µM. Mass balance calculations identify that the Fe²⁺ generated within the surficial zone of the CT deposit is sufficient to effectively sequester ambient concentrations H₂S generated in this deposit through FeS precipitates. Results identifying (1) distinct zones of porewater Fe²⁺ and H₂S, (2) co-occurrence of the highest [H₂S] and lowest dissolved organic C (DOC) at 22-24 m consistent with heterotrophic sulfate reducing bacteria (SRB) activity, and (3) the presence of mixed valence Fe biomineral, magnetite, throughout the deposit, are all consistent with microbially-mediated Fe and S cycling occurring within this CT deposit. The cultivation independent identification of several known iron reducing bacteria (IRB) and SRB within CT microbial communities, in conjunction with observed positive growth of IRB and SRB functional metabolic enrichments, demonstrates widespread capacity for microbial Fe and S activity throughout the CT deposit. Metagenomic characterization of CT microbial communities revealed high diversity (over 20 phyla) over the 5 depths examined. Multivariate statistical analyses (Unifrac) revealed that bacterial community composition and structure was driven by changed in DOC, ORP and salinity and that structuring corresponded with a surficial zone of Fe³⁺ reduction and an underlying zone of SO₄^2- reduction. Despite the high organic carbon (OC) content of oil sands tailings, much of that C is not considered to be labile and accessible to microbes. Based on the results of this thesis, CT SRB appear to have a greater ability than IRB to utilize recalcitrant OC (e.g. bitumen, naphthenic acids) given the widespread occurrence of porewater [H₂S] and surficially restricted [Fe²⁺] despite accessible pools of Fe³⁺ and OC with depth. This enhanced understanding of biogeochemical S cycling within CT newly establishes the importance of microbial activity in these processes, identifying the need to incorporate microbially based understanding into on-going development of reclamation strategies in order to manage these waste materials effectively.</p> / Master of Science (MSc)

As the world moves towards more green technology and energy-resources, the need for rare earth elements (REE) has increased rapidly. A potential secondary resource for REE’s are mine tailings, and a technique to estimate the thickness of a tailing is the horizontal-to-vertical spectral ratio (HVSR) method. In this project, the depth of a mine-tailing along a profile in Blötberget was estimated using this method. The HVSR method is a non-invasive environmentally friendly seismic method which utilizes ambient noise of the Earth. The method uses seismic sensors consisting of 3 components, which measures ground motion in three directions. The acquired data was processed in the Geopsy software, where certain parameters, such as filtering and window selection, are set to make the most satisfactory results. The Geopsy software provides the user HVSRs for the selected windows. This ratio makes up a curve in the frequency domain, where a fundamental resonant frequency can be derived. The fundamental frequency is determined as the sharp, lowest-frequency peak in the data in case of a strong velocity contrast. This fundamental frequency must fulfil certain criteria to be considered reliable. When the fundamental resonant frequencies could be determined reliable, they were mathematically calculated into the thickness of the tailing by a simple mathematical formula in Excel, using the shear-wave velocity of the overlying layer and the fundamental frequency. The elevation at the location of each sensor and the thickness of the contrasting interface is used to provide a 2-D depth of the mine-tailing. This profile was compared to radiomagnetotelluric measurements. Although the measurement locations were not coinciding reasonable results were obtained.