Upstream Tailings Dam - Liquefaction

The collapse of Dam I, tailings dam, at Vale S.A.’s (“Vale”) of the Córrego do Feijão Iron Ore Mine in Brazil was an accident that caused over 270 casualties and made irreparable damage to the surrounding environment. The exact reason for the failure is not known however, liquefaction was suspected to be the most influencing factor in the failure. Liquefaction failure of impoundment is increasing concern in the mining community and especially mine planners who will have to design and build the tailings dam. Different design methods are available with varied degree of challenges. Upstream construction methods, as one of the tailings dam types, is more susceptible to liquefaction. To investigate the effect of tailings on the impoundments, the research effort in this report determined four scenarios that affected the impoundment. Slide2, a two dimensional limit equilibrium based program was used to analyze four parametric conditions for predicting the failure of the impoundment. Each scenario represents a unique case where number of external and internal factors simulated the field condition. In addition to the safety factor, regression analysis was conducted to predict the future Factor of Safety by varying parameters such as cohesion, relative density, and friction angle. Analysis of the given scenarios showed significant sections of the dam stressed due to the weight of the tailings with high internal water level

Geochemistry, Mineralogy and Microbiology of Molybdenum in Mining-Affected Environments

This is the final version of the article. Available from MDPI via the DOI in this record.Molybdenum is an essential element for life, with growing production due to a constantly expanding variety of industrial applications. The potentially harmful effects of Mo on the environment, and on human and ecosystem health, require knowledge of Mo behavior in mining-affected environments. Mo is usually present in trace amounts in ore deposits, but mining exploitation can lead to wastes with very high Mo concentrations (up to 4000 mg/kg Mo for tailings), as well as soil, sediments and water contamination in surrounding areas. In mine wastes, molybdenum is liberated from sulfide mineral oxidation and can be sorbed onto secondary Fe(III)-minerals surfaces (jarosite, schwertmannite, ferrihydrite) at moderately acidic waters, or taken up in secondary minerals such as powellite and wulfenite at neutral to alkaline pH. To date, no Mo-metabolising bacteria have been isolated from mine wastes. However, laboratory and in-situ experiments in other types of contaminated land have suggested that several Mo-reducing and -oxidising bacteria may be involved in the cycling of Mo in and from mine wastes, with good potential for bioremediation. Overall, a general lack of data is highlighted, emphasizing the need for further research on the contamination, geochemistry, bio-availability and microbial cycling of Mo in mining-affected environments to improve environmental management and remediation actions.Francesca Frascoli was supported by an Erasmus+ traineeship studentship EQF level 7

Mineral reactivity in sulphide mine wastes: influence of mineralogy and grain size on metal release

The aqueous oxidation of sulphide minerals leads to the generation of acid mine drainage (AMD), one of the main causes of water pollution worldwide. Mineral reactivity is greatly enhanced as a result of extraction and processes such as blasting, crushing, and grinding that increase rock surface area. The exposition of sulphide mine wastes to atmospheric conditions enhances AMD generation. However, a large number of processes and factors (e.g., pH, redox conditions, aqueous and surface complexation reactions) may control the mobility of elements in solution. In particular, the formation of soluble secondary minerals may act as transient storage of metals and acidity during AMD generation, leading however to their release upon rainfalls. To study the influence of mineralogy and grain size on the metal release from a variety of sulphide mine wastes collected in the Iberian Pyrite Belt, different grain size samples were treated with distilled water (S:L ratio 1:10) for 24 h simulating rainfall weathering. Results reveal that grain size plays a major role on metal mobility from sulphide mine wastes. However, mineralogical and geochemical evidence points at the partitioning of highly soluble secondary minerals among grain size fractions as the key factor controlling the metal release rate from these wastes. The results obtained show the importance of grain size on the reliability of the different leaching test procedures, and thus encourage standardizing these procedures worldwide.The authors thank two anonymous reviewers for helpful comments that clearly improved the quality of the manuscript, and Associate Editor Encarnación Ruiz-Agudo and Chief Editor Carlos Rodriguez-Navarro for their handling. This work was supported by the Spanish Ministry of Economic and Competitiveness through the projects CGL2016-78783-C2-1-R (SCYRE) and ERAMIN PCIN2015-242. C.R. Cánovas was funded by the Talent Consolidation Program of the University of Huelva. MD Basallote also thanks the Spanish Ministry of Economy and Competitiveness for the Postdoctoral Fellowship granted under application reference FJCI-2015-24765

Inter-Code Comparison of Variably Saturated Fluid Flow and Prediction of Percolation through a Tailings Impoundment in Southeast Nevada, USA.

Hypothetical infiltration columns were simulated to evaluate the performance of 6 different modeling codes (HYDRUS 1D, HYDRUS 2D/3D, HELP, SV FLUX, UNSAT-H, and VS2D) at simulating near ground surface water balance processes occurring at mine process components (e.g. tailings pile or heap leach pile) under a simplistic scenario. Model results suggest that various codes for unsaturated flow arrive at similar solutions for identical models of well-defined problems. A literature review of several previous model comparison studies was conducted in order to provide insight into considerations for more complicated and realistic modeling scenarios. Unsaturated zone hydrologic modeling, field investigations, and laboratory analysis were conducted for a legacy tailings impoundment in Caselton, Lincoln County, Nevada to assess the potential for percolation of meteoric water through the tailings material. Field investigations consisted of field-saturated hydraulic conductivity testing, in-situ density measurement, and collection of tailings samples for laboratory analysis. Laboratory analysis included determination of field moisture content, bulk (dry) density, and water retention curve measurement by hanging column, pressure plate, and chilled mirror hygrometer methods. Hydrologic models of the tailings were performed using a variety of conceptual models, hydraulic property models, finite element discretizations, temporal boundary condition data resolutions, tailings hydraulic property descriptions, and lower boundary conditions. Numerical, mechanistic hydrologic flow models predict percolation rates ranging from 51 - 0 mm/yr. through the tailings, while previous efforts utilizing non-mechanistic water balance models predict a rate of 3.2 mm/yr., suggesting that significant variability exists in the model results depending on model approach and assumptions. Some simulations utilizing more complex and physically representative models resulted in higher percolation rates than the HELP simulation, which is counter to common assumptions of overprediction of drainage for simple water balance approaches

Examination of the seepage face boundary condition in subsurface and coupled surface/subsurface hydrological models

A seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions, water table fluctuations, and flow patterns. Its handling in hydrological models, especially under complex conditions such as heterogeneity and coupled surface/subsurface flow, has not been extensively studied. In this paper, we compare the treatment of the seepage face as a static (Dirichlet) versus dynamic boundary condition, we assess its resolution under conditions of layered heterogeneity, we examine its interaction with a catchment outlet boundary, and we investigate the effects of surface/subsurface exchanges on seepage faces forming at the land surface. The analyses are carried out with an integrated catchment hydrological model. Numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the Landscape Evolution Observatory. The results show that the static boundary condition is not always an adequate stand-in for a dynamic seepage face boundary condition, especially under conditions of high rainfall, steep slope, or heterogeneity; that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic; that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role; and that seepage faces at the land surface are not always controlled by subsurface flow. The paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way, is applicable to unstructured grids, and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models

A Numerical Investigation of the Seismic Response of Tailings Impoundments Reinforced with Waste Rock Inclusions

RÉSUMÉ La fréquence de rupture des digues de parcs à résidus miniers est beaucoup plus élevée, par un facteur de 10, que celle des ouvrages de retenue d’eau conventionnels, avec 2 à 3 événements majeurs se produisant annuellement surtout le monde. Une des conséquences de ces ruptures (avec brèche) est l’écoulement de résidus liquéfié. Ces écoulements (ou épanchements) sont responsables de pertes de vie, de dommages à l’environnement et de coûts financiers considérables; ils représentent à cet égard un des principaux risques liés aux opérations minières. Les résidus miniers produits par les mines en roches dures sont particulièrement susceptibles à la liquéfaction (i.e. un perte quasi-complète de résistance due à un chargement dynamique ou statique), pouvant alors causer une rupture (p. ex. durant un séisme) ou être une conséquence de la rupture (p. ex. suite à une défaillance de la fondation qui réduit le confinement). Aubertin et al. (2002b) ont proposé d’ajouter des inclusions de roches stériles dans les parcs à résidus, conjointement avec la déposition des rejets de concentrateur, afin d’améliorer leur performance environnementale et géotechnique. La roche stérile est ainsi placée de façon à créer des inclusions continues le long des orientations prédéfinies dans le parc. Il a alors été postulé que ces inclusions pourraient induire divers bénéfices, notamment en accélérant la consolidation des résidus et en agissant comme renforcement pour mieux résister aux sollicitations statiques et sismiques.----------ABSTRACT The rate of failure of tailings impoundments is much larger, by a factor of about 10, than that of conventional water retention dams, occurring at a rate of about 2 to 3 per year worldwide. A primary consequence of the failure of a tailings impoundment is the flow of liquefied tailings. Such flows have been responsible for considerable loss of life, environmental damages and economic costs and represent one of the major risks associated with mining. Tailings, specifically those from hard rock mines, are particularly susceptible to liquefaction (a significant loss of shear strength) that can cause failure of the retention dyke and the release of liquefied tailings. Tailings liquefaction can be induced in dynamic loads, such as earthquakes, or static loads, such as dyke raising, erosion (loss of confining stress) or foundation movement. Aubertin et al. (2002b) considered placing waste rock in tailings impoundments in tandem with tailings deposition to improve the environmental and geotechnical performance of the impoundments. The waste rock would be placed to create relatively narrow, continuous inclusions along planned routes in the impoundment. It was postulated that these waste rock inclusions would provide a number of benefits, particularly by accelerating the consolidation of the tailings and acting to reinforce the impoundment with respect to static and seismic loads

An integrated approach to AMD mitigation through sulfide removal from tailings

Includes bibliographical references (leaves 67-73).The formation of acid mine drainage (AMD) from the microbial oxidation of sulfides in mineral waste deposits is one of the major challenges facing the mining industry worldwide. Growing environmental awareness and subsequent changes in legislation has focused research in addressing the prevention of pollution by AMD. Current waste management approaches focus on deposition techniques to control AMD formation and on remediation. However, these approaches do not remove the risk of AMD generationand are yet to be proven effective in mitigating long-term acid generating potential. Incompliance with the principles of pollution prevention, addressing waste at its source,the aim of this work is to remove the risk of AMD generation by focusing on theremoval of sulfides from potentially acid generating tailings prior to disposal

The use of waste rock inclusions to control the effects of liquefaction in tailings impoundments

Objectives -- Scope and content of this thesis -- The sate of the knowledge and practice -- Hard rock mine waste and tailings impoundments -- Liquefaction -- Evaluation of the potential for liquefaction -- The liquefaction of hard rock tailings -- Methods of controlling liquefaction and its effects -- The use of waste rock inclusions in tailings impoundments -- Modeling liquefaction and its effects -- Evaluation of the stability of tailings impoundments -- Remarks -- Geotechnical study of a tailings impoundment -- Introduction -- Document review -- Geologic conditions -- Field exploration -- Laboratory testing -- Site conditions -- Characterization of the tailings -- Stability evaluation criteria and assumed earthquake loads -- Liquefaction evaluation -- Preliminary stability evaluation of the representative tailings impoundment -- Remarks on the geotechnical study -- Preliminary numerical analysis of the dynamic behavior of the tailings -- System of analysis -- Numerical modeling of the CDSS testing -- Numerical evaluation of the liquefaction potential of the tailings -- Remarks on the preliminary numerical modeling -- Numerical analysis of the representative tailings impoundment -- Method of analysis -- Model geometry, material properties and boundary conditions -- Static conditions -- Dynamic analyses -- Comparison of the Dynamic response of the tailings with the level ground analyses -- Comparison of the dynamic response of the representative impoundment with the analytical stability evaluation -- Remarks on the numerical analyses of the representative impoundment -- Evaluation of the use of waste rock inclusions -- Earthquake loadings -- Conceptual tailings impoundment -- Analysis and evaluation of the conceptual impoundment -- Discussions on liquefaction and stability -- Remarks on the evaluation of waste rock inclusions -- Parametric evaluation and discussion -- Parametric evaluation of the conventional impoundment -- Parametric evaluations of the reinforced impoundment -- Remarks on the parametric evaluations -- Conclusions and recommendations

Modeling of tailings flow following a dam breach using smoothed particles hydrodynamics

Choosing impoundments as the method of tailings disposal for mining processes necessitates the construction of tailings dams. As various types of chemicals remaining from the mining processes are retained in the pond behind a tailings dam, a dam failure may result in environmental damages in addition to threatening lives. Therefore, the distribution and distance to which tailings would travel in the case of a dam failure is important to determine the amount of potential damage. The aim of this research was to study the feasibility of modeling tailings following a dam breach based on the available data in the literature and reach the same distribution and travelling distance of the tailings as in the physical incidents. The numerical tool chosen for this research would simulate tailings as a Non-Newtonian fluid using a Smoothed Particle Hydrodynamics (SPH) method. To calibrate the simulation tool a series of flume tests on two different tailings pastes from two different operation stages of Bulyanhulu gold mine (Tanzania) was modeled. The flume was created in the simulation tool and more than so simulations were run to calibrate the simulation tool. Through these tests the effects of changes in the values assigned to parameters related to tailings and their environment on the model were studied. Practical application of the model was performed by using a digital elevation model (DEM) of the areas of two reported tailings dam failures in the simulation tool and repeatedly running tests with changes in the values for the terrain and tailings parameters to compare the results with the literature reported distribution of tailings outflow