Application of rheology to the post-deposition behaviour of tailings is important for the design of the slope of the impoundment, control of layering for purposes of strength enhancement through desiccation, properly describing the mixing of different tailings streams and for dam breach consequence analysis.This paper aims to advance the understanding of tailings rheology in the post-deposition context to aid all of these applications.Firstly, thixotropy and its quantitative implications for beach slope and layer geometry are explored using a simple treatment.Secondly, method dependency in yield stress measurement is discussed, along with how such uncertainty can be practically handled by considering the appropriate stress path and timescale for a particular application.Finally, numerical simulation using a thixotropic rheology of channel flow down a beach and runout from a dam breach experiment, conducted in a centrifuge, is used to highlight the utility of advanced rheology to such problems.The paper uses data collected from published work on both hard rock and oil sands tailings over the last 15 years.
In the digital era, the mining industry benefits from powerful tools that can help to optimise underground backfilling operations and to increase overall safety.Indeed, with current progress in artificial intelligence (AI), machine learning (ML) creates state-of-the-art techniques in the mining sector that could significantly improve the productivity and efficiency of mining operations.The purpose of this study is to apply ML algorithms, including the gradient boosting regressor (GBR), the XGBoost regressor (XGBR), and the support vector regressor (SVR) to predict the uniaxial compressive strength (UCS) of cemented paste backfill (CPB).A total of 1,587 UCS data were used to train the ML algorithms, considering different variables such as the types of tailings, binder and their proportion, solid mass concentration, slump height, water quality, and curing time.The raw data were pre-processed before training the models, as well as their hyperparameters tuning was made by a random search method followed by 4-fold cross-validation.The prediction results show that the GBR algorithm is the most powerful one which has a coefficient of correlation (R) between predicted and experimental values equal to 0.99 and a root-mean-square error (RMSE) equal to 0.16.This prediction is validated through new-lab prepared CPB specimens.
The conventional method of segregated disposal of tailings and waste rock is associated with several environmental problems, especially acid rock drainage (ARD) which is a challenging and crucial issue.Previous studies have shown that mixing tailings and waste rock can potentially decrease ARD potential.However, there are limited studies that quantify the effect of mixture ratio of waste rock and tailings on the water quality.This study presents a developed methodology to design and test different waste rock and tailings mixture ratios through leveraging particle packing theory for binary mixtures.The mineralogy and chemical properties of the mixtures is first presented.Three columns of mixture materials were mounted for a series of leaching tests over a period of about two years to experimentally simulate the impact of different mixture ratios on the water quality.The preliminary results of the leach column tests demonstrate that the ratio of waste rock and tailings of the commingling mixtures influences the unsaturated hydrogeological behaviour and the water quality.The study also provides fundamental data to investigate the hydrogeological and geochemical behaviour of the tailings and waste rock mixtures.The approach used in this study can be implemented to determine an optimised mixture ratio to minimise ARD and alleviate the damaging environmental impacts of segregated disposal.
A key component of underground distribution system (UDS) design for paste backfill is a pressure indicating transmitter (PIT), which allows the pressure at the instrument's location to be measured and used to provide several useful diagnostic functions.These functions include the determination of friction losses and overpressures as well as the detection of pipe breakage or blockage and confirmation of flushing progress.Unfortunately, the usefulness of these PITs can be compromised due to the demanding nature of the application in which the cemented paste will fill up any dead leg in the instrument mounting branch of the pipe spool and prevent pipeline pressures from being accurately measured by the sensor.This requires mounting the PIT close to the pipe's inside diameter, which can lead to sensor damage.PIT accuracy has been found to be unreliable due to these issues, and PITs frequently require cleaning or replacement.This paper discusses a planned PIT mounting spool design that uses a protective liner on the inside diameter of the pipe.The liner allows pressures to be transmitted to the PIT while avoiding the sensor head damage or dead leg build-up problems that currently make PIT usage unreliable.
Lundin Gold's Fruta del Norte project, which is currently the largest gold deposit in Ecuador, achieved commercial production in February 2020.The project includes a mine plan that incorporates both bulk and selective mining methods.Most areas mined will use conventional transverse stoping and will be supported by the drift-and-fill mining method in zones of smaller dimension or with poor geotechnical quality.Backfill is used as a ground support medium with the majority of voids to be filled using cemented paste fill.A paste plant, used to supply the required backfill tonnage, has been constructed directly over the orebody.The design of the paste plant is unique, accounting for challenges in topography, a sensitive local environment and challenging feed tailings.The paste plant was successfully commissioned in quarter three 2020.In this case study, the design is described in how it caters for the unique requirements of the project.Further to this, construction and commissioning challenges faced and lessons learned are documented.
Dundee Precious Metals' Ada Tepe mine is located approximately 3 km south of the town of Krumovgrad in south-eastern Bulgaria.It is an open pit mining operation comprised of a process plant, which employs a conventional crushing, grinding, and flotation process for gold and silver extraction.Currently, the tailings are being deposited as a thickened tailings in their integrated mine waste facility (IMWF).Cells are created out of waste rock to retain the thickened tailings.These cells are built within two valleys adjacent to the open pit, starting with initial starter platforms at the base of each valley, continuing up the two valleys until the two parts join at a higher elevation to form a single facility.As the cells are filled and lifts completed, the front berms are progressively rehabilitated.There are two collection sumps at the bottom of each valley from which water is pumped up to the top of the hill into the raw process water reservoir for use within the process.There is limited space on site and filtered tailings was contemplated to reduce construction complexity and placement effort in the IMWF, increase flexibility for future tailings placement, and reduce costs associated with further consolidating the thickened tailings and pumping water to the current reservoirs.In 2021, a feasibility study for producing filtered tailings within a limited footprint to improve the operability of the IMWF commenced.This consisted of assessing the area required for the filtration plant, overall design efficacy, taking into account the filterability of the tailings, transportation of the filtered tailings, examining the filtered tailings storage requirements and modifying the IMWF deposition strategy to suit filtered tailings instead of thickened tailings.This paper describes the general benefits of filtered tailings as well as some of the challenges in implementing such a system.In addition to the key design considerations for the filtration plant, outlining the specific operational benefits and identifying recoverable costs for this site are discussed.
Mine wastes, specifically tailings, are commonplace in mining operations and most mines dispose of their tailings wastes in wet impoundment structures.Consequently, the failure of wet impoundment structures is one of the most significant environmental liabilities for mining operations and recent failures have highlighted the perils of this type of tailings disposal strategy.Likewise, water scarcity continues to be a growing concern at many mines globally, specifically within arid regions.Risk mitigation priorities along with water resource conservations are steering the mining industry's waste management of tailings away from wet impoundment and towards dewatered tailings and dry stack disposal.The handling of dewatered tailings is most efficiently performed with the operation of automatic conveyance systems and the deposition of the tailings achieved by mobile conveyor stacking systems.Lab testing and analysis have identified that mine waste tailings characteristics vary widely between mine samples due mostly to the ore's mineral composition, particle size distribution, and moisture content.Evaluating the mine site's tailings material samples for their conveyability and measuring their change in surcharge angle is the key to understanding how the tailings react at different moisture levels while being transported along the length of an overland conveyor.The results of the conveyability tests are used for the design and strategy for the material handling and waste disposal stacking systems.This paper will present case studies of multiple tailings samples, from various mine sites, at specifically determined moisture levels.During the conveyor simulation tests, the samples were measured and recorded for the initial angle of repose, surcharge angle, and material density.This paper aims to demonstrate that there are often significant differences between tailings samples' physical and dynamic properties and how that relates to the parameters needed for accurate conveyor engineering design.
Dry stacking of filtered tailings is becoming an increasingly widespread approach to tailings management.Dry stacking can potentially offer some significant advantages over traditional tailings deposition, such as lower geotechnical risk, greater water return, much lower overall waste volume, and ease of reclamation and closure, thereby enabling a higher level of post-closure land use.However, filtration and compaction costs, and the operational complexity of dry stacking, can make it challenging.It has been shown that commingling of filtered tailings and waste rock can improve the geotechnical performance of the stack, and it has the potential to allow stacks to be constructed more rapidly in higher lifts, making dry stacking more economical for large operations.This paper presents an overview of recent research into the geotechnical properties of filtered tailings and waste rock blends.Results from a series of shear strength and consolidation tests are also presented.It is shown that the addition of waste rock to filtered tailings stacks significantly increases the shear strength and reduces the pore pressure response during placement.This could potentially allow higher and faster lifts to be stacked safely.
The rheology of tailings that have been discharged onto a tailings storage facility (TSF) and allowed to sediment out, consolidate and then undergo liquefaction is significantly higher than the rheology of the slurry in the initial discharge stream.This can be ascribed to a combination of factors that include higher solids concentration, stress state and history, re-establishment of flocculant bonds, and natural coagulation and agglomeration measurement of the rheology of the liquefied tailings therefore requires that samples undergo similar sedimentation and consolidation processes without disturbing the samples.In addition, many TSFs are constructed of two different materials, where coarser tailings are separated from the tailings stream using hydrocyclones and used to contain and confine finer tailings or applied as drainage layers.On liquefaction of the fines, the liquefied rheology will be influenced by the coarser, better-drained tailings as this is entrained with the fine tailings.Moreover, some of the supernatant water that accompanies the liquefied tailings during flow liquefaction will be entrained with the tailings, effectively diluting the liquefied slurry and impacting the rheology.All of these factors need to be considered in the course of a dam break analysis due to the influence of rheology on the fluid dynamics during flow and therefore of the resulting inundation characteristics.This paper describes laboratory and semi-pilot scale testing methods developed and applied by the authors in dam break analyses.The tests are able to address the factors of sedimentation, consolidation, stress history, material combinations and mixing, as well as supernatant water.The influence of these factors as measured in the tests is described.
Tailings dam failures, claiming human lives and causing catastrophic environmental impact, are unfortunately still frequently reported around the world.The tailings dam break simulation using site-specific parameters has now become an essential and critical part of the design, operation and closure cycle of every tailings storage facility (TSF), and is a requirement in many guidelines such as ANCOLD (2012), CDA (2021) and ICMM (2020). Urging from the mining industry and regulatory authorities for the development of better and more comprehensive simulating techniques that can accurately predict the flow behaviour of liquefied tailings in the hypothetical scenario of a tailings dam breach has significantly increased in recent years.The tailings deposited in a TSF often form a density profile with depth as the tailings consolidate and gain strength.This process increases the solids concentration and shear strength of the tailings within the TSF to a range that often makes direct measurement of the rheological properties of samples from the site using conventional bob and cup rotary viscometry impractical.Consequently, this imposes a challenge for obtaining reliable results from the tailings dam break simulation and needs to be overcome.A methodology is proposed in this paper for estimating the rheological properties of liquefied tailings at high solids concentrations when the direct measurement technique is impractical.The method is based on combining site-specific parameters such as the in situ dry density with laboratory-measured parameters such as the residual shear strength of the tailings after failure, and the bob and cup rotary viscometry data at lower solids concentrations.The method can be applied to establish a comprehensive understanding of the rheological behaviour of liquefied tailings at the wide range of solids concentrations required for dynamic tailings dam break modelling.
Proper application of unsaturated soils to thickened or filtered tailings has substantial potential to optimise such tailings deposition.Unsaturated behaviour bears on both the geotechnical and geo-environmental performance of these deposits.Geotechnically, there is an increase in strength through both additional densification, and the presence of suction, as well as a stress history effect.The latter is especially important to understand in situ measurements in previously desiccated deposits; geo-environmentally, unsaturated behaviour strongly bears on seepage generation, as well as management or mitigation of acid generation.This paper summarises a body of work on experimentation, numerical simulation, and field data relating to different aspects of unsaturated behaviour and their relevance to practical outcomes for design of thickened or filtered tailing deposits.An important new outcome from this summary is the suggestion to characterise the extent of the stiffness imparted by drying, especially due to the possible risk of strength loss in thick deposits when the tailings eventually yield under self-weight.
One of the most significant operational problems that paste backfill systems face is detection and mitigation against slack flow.Slack flow occurs when there is an excess of gravity head energy within the reticulation system, resulting in high-velocity conditions that increase wear.It is a primary cause of borehole failure.Hydraulic modelling can predict where slack flow might occur and is a principal component in designing a reticulation system to mitigate against slack flow.However, hydraulic modelling relies on accurate rheological measurements to estimate friction losses and requires a distinct predetermined pipeline route.Both these factors become increasingly hard to evaluate during operation; variation in tailings mineralogy or PSD can cause significant shifts in the rheological characteristics of the paste, and as-built reticulation networks frequently differ from the designed routing and/or pipe class.Furthermore, providing real-time feedback to plant operators via hydraulic grade lines is difficult.In a study conducted by Paterson & Cooke for Boliden's Garpenberg mine located in central Sweden operating a paste backfill system, three distinct methods were developed to detect slack flow in real-time from underground Pressure Instruments (PI).These methods provided immediate feedback to plant operators on whether the system was in slack flow, regardless of filling location and tailings variability.This paper provides details of each of the three methods, including derivation, implementation, and comparison to operational data.
The management and production of dry tailings present some considerable advantages to mining companies.The advantages are based on the technology selected, the composition of material and a number of other process variables.Rapidly developing dewatering technologies and reliable equipment for the production of dry tailings are making it viable in an increasingly large number of high tonnage operations.Various techniques for the production and handling of dry tailings have become the most desired trend, with different options available.This paper reviews existing and potential applications of dry tailings technology for the treatment and management of wastes from coal and copper tailings operations.The advantages of coarse particle flotation (CPF) with regards to tailings are shared.The influence of particle size distribution, plant configurations, the composition of tailings and the management thereof are discussed, based on recent tailings applications.Recent changes to thickener and filtration technologies are provided.
The number of paste operations has grown since the early application of thickened tailings for backfill in the 1970s.Backfilling underground void stopes with paste is often a competitive backfill option compared to alternatives.Therefore, having suitable tailings is critical for paste backfill.Ideally, a paste system delivers a homogeneous, non-settling fluid with good flowability.Once placed, the paste should generate little bleed water and develop the required strength using the least amount of binder possible.The paste's quality depends on the tailings' properties, like mineralogical composition, related to the ore deposits' geological evolution and formation.For example, epithermal gold systems are formed in a proximal volcanic setting and are triggered by an intense, hot, fluid migration process.This type of deposit has a different mineralogical footprint and alteration surrounding than an orogenic gold deposit, which experienced a different alteration and ore formation history, being formed along major fault zones.These differences, in addition to the required ore comminution processes, are reflected in the tailings produced from a given ore body and, therefore, impact the characteristics of the available tailings material to make a paste backfill product.Modern, stateof-the-art paste backfill admixtures are increasingly used to optimise paste backfill mix designs and to manage problematic tailings properties.This paper outlines the impact of using water-reducing admixtures on the solid content increase and strength gain of paste.Data from 13 different mine sites for three common deposit types -orogenic gold Iodes, VMS-SEDEX deposits, and epithermal deposits -have been collected for this study.Special attention is given to the impact of their particle size and their phyllosilicate content on the water-reducing potential and strength.
The global inventory of tailings is currently >55 billion m 3 and is forecast to increase to almost 70 billion m 3 by 2025.The cost of these tailings includes the construction and maintenance of tailings storage facilities (TSFs), the liability of catastrophic releases, environmental damages, and erosion of social licence to continue mining.Billions of dollars and decades of research have been spent searching for improved technologies to better dewater tailings and reclaim TSFs.The ElectroKinetic Solutions Inc. (EKS) tailings dewatering technology (EKS-DT) process has been developed to dewater legacy and fresh tailings in situ, using electrokinetics.Over more than a decade of lab and field-scale testing has significantly improved the technology's dewatering effectiveness and reliability and confirmed its commercial viability.The process is less costly compared to current tailings management technologies and excels in its ESG performance.EKS has shown through a field demonstration that very fine-grained tailings (i.e.average particle size <6 microns) with an initial solids content of 20% (kg/kg) can be dewatered to >60%. EKS has also produced a forecasting model. The model accurately forecasts dewatering time and energy consumption for different designs and operating schedules, critical information for designing commercial installations.A 1,700 m 3 field demonstration from 2019 to 2021 proved that the technology is commercially viable.During this time, over 1,100 m3 of water was removed from the tailings and the energy consumption was <15 kWh per m 3 of water released.The process was operated year-round through two harsh winters.The process operated as well during the ice-covered period as during warmer months.The installation was operated continuously by the automated control system without an onsite operator.The design of the first commercial installations of the technology is now underway.The engineering design process for the field demonstration and for commercial systems will be discussed, including the role of the EKS model.
It has become common practice for mining tailings to be thickened before being deposited in a tailings storage facility (TSF) to increase water reclamation, reduce overall footprint and comply with current environmental regulations.TSFs that impound thickened tailings (TT) typically consist of distribution systems along the TSF embankments or in the basin's perimeter, defined by a deposition plan.These main deposition systems include linear distribution discharges or manifolds, a pressurised radial distributor or a distribution box with a series of spigots discharging over the TSF.Other deposition options may be considered for conditions where the site's topographic surface is relatively flat or the basin is somehow constrained to allow for perimeter filling.For example, TT can be deposited within a TSF basin with a flat topography using spigots located on elevated discharge platforms that are relocated throughout the TSF's life span.TT can either be discharged onto the TSF surface from the top or the bottom of these discharge platforms.The discharge platform is susceptible to abrasion when TT is discharged from the top of the platform.Alternatively, a hydraulic design challenge is introduced when TT is discharged from the bottom of the platform with the aid of gravity as the rising tailings could block the exit as deposition progresses.This paper provides a methodology that has been applied in large tailings projects with gravity distribution and discharge systems, and a design guide for its application in the industry.
It is good practice in the early phases of a new mine design, or when a new tailings storage facility (TSF) is required at an existing mine, to consider alternatives and carry out trade-off studies for tailings storage.These studies should include multiple sites and at least two disposal methods or technologies with the aim of identifying the best tailings management system for the project, generally the most cost-effective, socially and environmentally acceptable system.Dry stacking is gaining credibility and is seen as a preferred technology to manage project specific risks for various reasons: lower risk of failure, increased water conservation and water cost saving, project stakeholders and environmental considerations, better geochemical mitigation, and possible improvement in metal recovery during filtration through additional mineral dissolution.In some cases, the drivers for considering dry stacking are obvious, such as a mine located in a dry climate or new regulations, but in other places this is less obvious. This paper evaluates the outcomes of a number of such trade-off studies mostly in Southern Africa or arid regions of Africa, which include:• Whether dry stacking was recommended for consideration in the next phase of the project or not, and why.• If dry stacking was recommended, whether it was taken forward to implementation or not.The paper also looks at two mines where filtered tailings has been implemented, their overall TSF operating and stability performance, as well as opportunities and challenges of the technology.No names of the mines are included, as the focus is on whether there is an increased move towards dry stacking, and what obstacles are being experienced.
Building on the experience of successful smaller-scale dewatered tailings stack operations with production rates of up to 35,000 tpd, filter-pressed tailings stacking is being considered as a technically and economically viable alternative of dewatered tailings management for even higher production rates, pushing 50,000 to 100,000 tpd, involving intensive earthworks operations and intricate construction sequencing plans.The need to establish dewatered tailings solutions as a sound business option for large-scale projects in water-stressed nations like Chile and Mexico is motivated by water (the lack of availability, rising cost of water and sustainable water use) but also by dam safety, lowering the risk profile of the large conventional tailings storage facility portfolios.This paper will present the fundamental aspects of the design and operation of dewatered stacks based on practical planning and operational experience.This will ultimately provide some guidance on "how high is too high?" in the context of critical state soil mechanics and other relevant geotechnical aspects and a case study providing some reference on the planning of a dewatered stack.
The main challenge in mining with backfill is to design a flowable backfill capable of ensuring good stability of the backfilled stopes after placement and hardening.This would require, among other things, a good understanding of the physics (particle size distribution curve) and the mineralogy (presence of sulphides and/or clay minerals) of the mine waste, the correct determination of the required strength (based on the factor of safety), the correct definition of the rheological parameters (slump S, critical solids mass concentration %Cw-cr, adequate shear yield stress τY and viscosity µ), the proper selection of the backfill mix recipe (formulation taking into account the physico-chemical properties of the mixture ingredients), the correct design of the backfill retaining barricades (horizontal pressure), the good understanding of the hydromechanical properties (self-weight consolidation), the better control of the filling sequences (dissipation of the pore water pressure), the long-term compressive and shear strengths of the backfill, the reduction of the backfilling operation costs (possibility of reducing the amount of binder used), the prediction of the cemented rockfill and paste backfill strength.
LKAB operates three mines in northern Sweden, where the climate is subarctic with an average temperature of about 0 o C. LKAB's long-term overall objective includes feasibility considerations of thickened or filtered tailings combined with waste rock co-disposal covering cyclic economy considerations and landscape forming.At the Kiruna underground mine, about 3.5 Mtonnes of tailings and 12 Mtonnes of waste rock are generated annually.Crushing to less than 30 mm is part of the sorting plant processing, and the rock is deposited in stockpiles while the tailings are pumped conventionally to water-holding impoundments.The aim is to indicatively test the pipeline pumping of paste-rock mixtures at solids concentrations by weight of over 85% to limit segregation and leakage during deposition in nearby old pit holes.A test was carried out at a paste thickener with direct access to fresh paste, which was mixed in a concrete mixer with crushed rock from the processing.A 38 m long loop with a pipeline inner diameter of 0.075 m was equipped with a concrete type of pump.Unfortunately, a second test in a larger pipe could not be carried out at the planned time.LKAB then had the opportunity to test a laboratory-scale concrete industry device, the sliding pipe rheometer, Sliper, developed to simulate concrete pipeline pumping frictional resistance in a 0.126 m diameter pipeline.Initial loop results with crushed rock particles of up to 10 mm with a rock-to-paste mass ratio R:P of 1.2:1 showed a pressure requirement of about 25 kPa/m at 0.7 m/s for a total solids content of 84% by weight corresponding to 65% by volume and a water content of 19% (Solids density 3000 kg/m 3 ).The 10 mm product loop pressure results agreed relatively well with simulated Sliper data scaled to 0.075m from 0.126 m for Cw 85-86% and R:P of up to 2.6:1 at 0.7 m/s.The 30mm Sliper result at 89% indicated a pressure requirement of 14 to 24 kPa/m at 0.7 m/s for R:P of 2.6:1 and 3.5:1, respectively.With a 0.15 m diameter pipeline, a pumping requirement of 20 kPa/m at 84% and 0.7 m/s was also discussed regarding feeding requirements.The results form the basis for a planned larger-diameter test.Long-term flexibility factors related to tailings availability and clarification of suitable routings and allowed water contents may necessitate that the wider diameter loop test includes a limited once-through pipeline pumping demonstration feeding arrangements.Variations in the rock-to-tailings ratio related to tailings availability and disturbances can be investigated.The system feasibility for filling depressions may cover a concentration span starting from about 75% by weight which means a more stratified flow where the coarsest particles form a sliding bed.
