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In 2007, CDA published a set of technical bulletins to supplement Dam Safety Guidelines. The technical bulletins suggest methodologies and procedures for use by qualified professionals as they carry out dam analyses and safety assessments.
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Tailings are finely ground waste rock produced as a by-product of standard mining projects as well as some industrial and power plant operations. Tailings are conventionally impounded behind a dam that is raised perpetually insofar as operations continue, thus amassing large volumes of materials (sometimes including supernatant pond water) in the process. The failures of some tailings impoundments have triggered downstream mass movements that have caused human, economic and environmental impacts, thus inviting considerable public attention and scrutiny. Developing a detailed inventory of these tailings flows facilitates a better understanding of the magnitude-frequency statistics, preconditioning and trigger variables, breach-outflow processes and downstream runout behaviour. Upon screening over 350 historical waste impoundment failure incidents in pre-existing secondary datasets, we have developed a comprehensive global database of 63 tailings flows from 1928-2020 while following strict case selection criteria with the support of satellite imagery, digital elevation models (DEMs) and source literature. Using a novel runout zonation method, the satellite images and DEMs were analyzed on geographic information systems (GIS) platforms to independently estimate runout distances, inundation areas and travel path angles of tailings flows. Depending on data availability or quality, we also summarized the background information, impoundment conditions and geotechnical indices to provide site-specific context to case histories. The collated data is aimed to (i) broaden the scholarly understanding of tailings breach-runout behaviour, (ii) provide comprehensive documentation while assessing the limitations of data availability and/or quality in the public domain and (iii) establish a consistent framework for reporting various properties of tailings dam failures and tailings flows. Lastly, we note that the data should be treated with prudence. Tailings impoundments are highly variable depending on the locality, and site-specific conditions exert strong controls on post-breach behaviour. As such, it is recommended that our database be used purely as a basis for screening-level assessments, case analog comparisons and academic research. For site-specific prediction studies undertaken by practitioners, targeted field observations, laboratory investigations and numerical models are essential.
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Tailings storage facility (TSF) design has long been based on deterministic limits. By extension, the TSF owner accepts a Probability of Failure (PF) associated with these deterministic limits which are assessed against industry norms with respect to investigation/analysis and design assumptions related to the operation of the facility. If the Probability of Failure of a design that is derived in this way is taken as the likelihood related to the tolerable risk limit, it follows that the same, or a lower PF, should be maintained during operations. Examples of operational controls include pond management and inspections/monitoring. Upset conditions arise when operational controls are not being implemented. Therefore, by comparing the calculated PF of the TSF complying with the design assumptions and the PF for the same TSF in an upset condition, the required PF of operational controls can be estimated. This concept assists the TSF owner in determining what is required to safely operate the facility and communicate the geotechnical risk to all stakeholders. By extension, scenarios where a TSF owner cannot achieve the required PF of operational controls can be addressed with: 1. Greater rigor applied to operational controls. 2. Addition of more operational controls. 3. A change to the design assumptions, where the timing of the project allows. This method provides a measured approach to risk management in the design and operational phases, without a TSF owner having to quantify an acceptable risk tolerance. Instead, the design is based upon widely accepted practice and industry/business accepted safety, economic and environmental risk levels. Subsequently, the design PF can be calculated and then applied as a benchmark for operations. This approach serves to reduce uncertainty through alignment of the design and operation phases. The concept is explored for three different tailings storage methods: upstream raised TSF, downstream raised TSF, and impoundment by mine waste dumps, to estimate how sensitive each storage method is to the type and effectiveness of operational controls implemented by the dam owner.
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Tailings are the materials left over after the process of separating the valuable fraction of ore from the gangue. Tailings ponds are engineered structures created using dams, berms and natural features such as valleys, hillsides or depressions. The pumping of tailings slurry into a pond allows the sedimentation of solids from the water. Tailings ponds can be highly toxic because they are used to store harmful waste made from separating minerals from rocks or the slurry produced from tar sands mining. To minimise contamination of underlying groundwater, high-density polyethylene (HDPE) liners are used. These liners are prefabricated sheets that are welded onsite to form a continuous waterproofing membrane that prevents the migration of contaminated water into the environment. Despite their widespread application, HDPE liners have inherent performance limitations, such as leakages at the location of welds, UV resistance, maintenance and repair. This paper considers a new type of sprayable reactive membrane as a waterproofing structure. Permeability tests with the Rowe cell, chemical and durability tests (interaction with water and leachates at different temperatures, oxidation and UV resistance tests) and mechanical tests (tensile strength tests, elongation tests, puncture tests) were performed and compared with conventional HDPE membranes for tailing ponds. Results showed that the new sprayable membrane has good performance comparable with the conventional HDPE membrane and it can be a very attractive solution for tailings ponds liners
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One of the most critical issues when designing a slurry system is sedimentation of solid particles in pipelines and pumps. In pipelines, sedimentation will occur when the transportation velocity of a slurry through the pipe is below the deposition velocity. As soon as particles are settled, there is a considerable risk that, in time, a plug will be created which will block the pipeline completely. Settling of solids can, however, also be detrimental for piston diaphragm pumps; large and heavy solids may settle within the diaphragm housing, on top of the suction valves. This layer of solids will cause diaphragms to rupture. In addition, there is a risk that the settling particles may block the valve, causing pressure surges and further damage to the downstream equipment. In order to determine the settling behaviour of a slurry, costly and time-consuming loop tests need to be executed in specialised laboratories for which large quantities of solids are required. This test may also be an indication of the settling behaviour of solids within a piston diaphragm pump, but would not be very accurate, leaving risk of damage to diaphragms. Therefore, a simple, quick and inexpensive test (SE: sedimentation detection system with evaluation algorithm) was developed which indicates if a slurry is prone to settling or not, by determining how fast solids will settle within a diaphragm housing. For this test, just a few kilograms of solids are required, and the result of the test is known within a very short period of time. In principle, the test is based on the measurement of the speed at which particles settle on a scale; the faster the particles settle, the higher the risk of a settled pipeline and the higher the transportation velocity needs to be. This paper will describe the methodology of this test, its results and interpretation. Also, a technology will be presented which prevents settling of solids within the diaphragm housing of piston diaphragm pumps.
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Planning, operating, monitoring and closing a tailings storage facility (TSF) can present many challenges, especially in dynamic mining environments where site conditions vary spatially and with time. However, big impacts can be made at relatively small cost once the tailings management system, design and performance are well defined and understood. This paper presents various examples of initiatives aimed at achieving the design intent that have been adopted by Rio Tinto Iron Ore, which also reduce risks and improve tailings management performance. Examples presented include development and communication of short-term, long-term and life-of-facility deposition plans, implementation of simple deposition management tools, monitoring and managing slurry density, development and continual oversight of water balance models, and sound investment in water management infrastructure extending to safe performance in emergency situations. Regular governance was also implemented to provide assurance that these controls remain effective.
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Fluid fine tailings (FFT) management is one of the main challenges that oil sand developers continue to face. Syncrude Canada Ltd, independently or in collaboration with Canadas Oil Sands Innovation Alliance (COSIA) member companies, has developed various technologies to accelerate FFT dewatering to meet progressive mine closure and reclamation objectives. One of the technologies is FFT clay treatment that targets the problematic clays in FFT. The basis of this step-out technology is the use of a polymeric flocculant to enlarge the effective size of clays and a collector to change the clay surfaces from hydrophilic to hydrophobic. In this way, the treated FFT dewaters very fast. An effective, easy to use collector is key to the success of this technology. Collectors are chemical compounds added to FFT that change the clay hydrophobicity, promote aggregation of clay particles and assist in FFT dewatering. Theoretically, it is possible to directly use a cationic collector or a combination of a metal ion and an anionic collector to make the negatively charged FFT clays hydrophobic. Building on this concept, several process technology scenarios have been developed and tested. This paper demonstrates how fundamental research provides a simple and cost-effective method for screening collectors for operational FFT clay treatment.
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Tailings dam failures have and continue to cause large-scale devastation and environmental impacts. Historically these impacts have largely been predicted using Newtonian hydrodynamic modelling principles resulting in a general overestimation of potential consequences. However, since about 2014 the collective mining industry began developing complex tools to better predict the likely impacts of these failures. The industry has focused on leveraging the latest in computational flow dynamics modelling software and computational hardware to preform non-Newtonian tailings dam break assessments. However, as our tools become more sophisticated so does the requirement on input data. This paper discusses the past modelling approaches and the development of non-Newtonian tailings dam break models. The sensitivity of the flow behaviour is presented through four case studies, showing how this selection influences the outcomes and how previous approaches assuming Newtonian characteristics may present an overly conservative result. It is noted that additional knowledge and expertise will become available as non-Newtonian tailings dam break studies become the norm. In the interim, the uncertainty of these analysis needs to be analysed.
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?Mining using backfill methods has been utilized by many mines around the world. Tailings thickening, one of the ways to prepare backfill materials, has been studied worldwide and components of the process such as the thickening mechanism of the tailings tank and principles of selecting flocculants have already been worked out. The studies of hindered settling properties of tailings during this process have lagged which can restrict the precise control of tailings thickening and affect the backfill result. Using in-situ tailings from a mine, hindered and polydisperse settling experiments of tailing slurries with different concentrations and different particle size distributions have been launched to study and analyze the hindered settling features of tailing particles. The experimental results show that the R-square figure of the hindered settling rates of classified tailings between calculated values based on Richardson-Zaki model and experimental ones is over 0.87 proving the Richardson-Zaki model can be used to calculate and predict the hindered settling rates of classified tailings. Moreover, Selims theory can capture the main properties of the polydisperse settling process of the mix of sieved and silica tailings. The self-flocculation of fine particles in silica tailings has increased the hindering effect among particles, the experimental settling rates of silica tailings are less than those theoretical values calculated by Selim theory.
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?To explore the spatial strength distribution of backfill in the stope, a group of experiments in a large similar stope model was designed for simulating the consolidation of cemented tailings backfill (CTB) in a stope. The height of CTB in similar stope model was measured to analyse the flow and sedimentation characteristics. The unconfined compressive strength (UCS) test on specimens cored in the different position of CTB sample in similar stope model was conducted. Moreover, the particle size and cement content of CTB sample were tested to help to explain the mechanism. The results show that during the flow and sedimentation of filling slurry in the model, inconsistency of the particle size and cement content leads to the inconsistency of strength. In the flow direction (horizontal direction), the median particle size of CTB first increases and then decreases, the cement content of CTB decreases slowly and then increases sharply, and the strength of CTB first decreases and then rises. In the sedimentation direction (vertical direction), the cement content of CTB decreases with the increase of depth, while the strength of CTB increases with the increase of depth. The strength is affected by the interaction between particle size and cement content, and the higher cement content of CTB does not translate into higher strength. The results provide a theoretical basis for improving the quality of CTB and optimizing the design.
