Search Documents

By S Thacker, M Noakes

The Newmont Tanami Operations (NTO), formerly the Granites Gold Mine, commenced operation in the mid-1980s with tailings deposition evolving over the past three decades as production has increased and the operation has expanded. Paddock-style tailings storage facilities (TSFs) and in-pit tailings deposition have fulfilled the tailings requirements for NTO over its lifetime with the technical specifications of these facilities improving over time in line with the positive development of standards, guidelines and best practice.This paper reviews the options for tailings storage facilities at NTO and the many considerations that have been analysed and deliberated upon before settling on specific TSF types and designs. It also explains the operating philosophies of the tailings deposition and how the facilities have always strongly maintained the optimum capture and retrieval of water. The current TSF design and criteria is presented, along with the introduction of dry tails harvesting for use in paste production as a backfill product for the underground mine. Tailings deposition and recovery remains a critical function of the Granites process to ensure long-term operation and gold production.CITATION:Thacker, S and Noakes, M, 2015. Newmont Tanami Operations – tailings storage facilities, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 305–314 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By D Luppnow, C Hore

In-pit tailings storage can provide many advantages when compared to typical above-ground tailings storage facilities (TSFs). As regulations become more restrictive and existing mines expand into new pits, the motivation and opportunities for in-pit tailings disposal is increasing.The Langer Heinrich uranium orebody follows a palaeo-river channel and is mined as an open pit operation. The mine pits intersect two main aquifer systems, one at the surface and one at the base of the orebody/pits. The tailings storage methodology is full in-pit disposal in multiple TSFs for the life-of-mine. Continuity of the initial hydrogeological conditions is incorporated in the design by the use of the pervious surround concept and the reinstatement of the lower aquifer (palaeochannel aquifer) at the base of the pit. Containment embankments are required to facilitate the staging of the TSFs development and are constructed using waste rock liberated during the mining of the pits. All of the TSFs are equipped with decant structures and an underdrainage system is included to improve water recovery, enhance consolidation and increase tailings density.This paper presents the design of a unique in-pit tailings storage solution for the Langer Heinrich mine in Namibia owned by Paladin Energy Ltd.CITATION:Hore, C and Luppnow, D, 2015. In-pit tailings disposal at Langer Heinrich – tailings storage facilities in a unique hydrogeological setting, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 373–380 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By P J. Vardon, L A. van Paassen, Y Yao, A F. van Tol

Thin-lift atmospheric fine drying (AFD) is a technique used to dewater mine and oil sand tailings, which utilises both self-weight consolidation and atmospheric evaporation. The disposed layers undergo a cyclic drying and rewetting process due to precipitation and deposition of additional lifts on top of the dried layer. The current research aims to optimise the deposition process via use of a numerical model and realistic atmospheric conditions, including both periods of drying and wetting. The model is based upon water balance and includes large strain considerations. A number of material behaviours are characterised using empirical fitting curves based upon laboratory measurement of material characteristics, including both the shrinkage and water retention curves for drying and rewetting. The model is able to model multiple lifts, simulating field scale and realistic climatic conditions within timescales suitable for engineering practice (eg seconds or minutes). The model has been previously validated against controlled laboratory experiments and utilised to simulate field tests. A series of simulations are presented to illustrate the ability of the model to be used as a practical tool for the optimisation of a tailings deposition strategy.CITATION:Vardon, P J, Yao, Y, van Paassen, L A and van Tol, A F, 2015. The use of a large-strain drying and consolidation model to optimise multilift tailing deposits, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 263–270 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By Y Li, Z Fu, D J. Williams, E Topal

Mine waste rock is unavoidable in the recovery of ore by open pit mining methods. Effective management of waste rock movement covers the removal and placement of the waste rock, generally in a surface dump in the most cost-effective way while satisfying the long-term environmental expectations. Since the 1960s, there has been significant research carried out into planning of ore movement from open pit mines such that the overall net present value (NPV) of the project can be maximised. Currently, several software packages are available to achieve this task as a common practice within the mining industry. However, planning of mine waste rock movement is still achieved manually, as the available software does not consider optimal waste rock movement and dump design. This paper describes a tool to optimise waste rock placement, which minimises the haulage cost while creating environmentally friendly waste rock dumps through selective placement and encapsulation of the reactive waste rock in the dump. The embedded methodology in this tool has been developed based on the mixed integer programming (MIP) modelling technique to optimise the waste rock movement. The methodology provides an easily-manipulated and fully-automatic tool for professionals to complete waste rock dump scheduling in four main steps: data input, model construction, model computation and solution retrieval. The application of the new tool into a real case project in this paper shows that it can determine economically and environmentally optimised waste rock dump schedules in an acceptable time frame.CITATION:Fu, Z, Li, Y, Topal, E and Williams, D J, 2015. A new tool for optimisation of mine waste management in potential acid forming conditions, in Proceedings Tailings and Mine Waste Management for the 21st Century, pp 333–342 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By H Barrie, L Ameglio

"Current methods for acid rock drainage (ARD) mitigation revolve around insulation of the waste from oxygen in the atmosphere with water and dry (soils and liners) covers. Both are of limited effectiveness and present significant drawbacks. Furthermore, while they reduce oxygen influx, they reduce but do not prevent ARD.The inert gas mixture (IGM) technology has been designed to overcome the deficiencies of gas transfer into tailings and waste rock materials across the surface and instead block oxidation by controlling the transfer of oxygen from the atmosphere. Inert gas is injected into the mine waste at low flow rates and the positive but low flow purges the oxygen that tends to diffuse into the sulfide waste across the surface. The positive flow of IGM compensates for inward oxygen diffusion and creates a pressure drop across the cover layer preventing inward diffusion of oxygen and, hence, acid generation.The IGM processes are evaluated in this paper: theoretically, with a review of the theory of ARD and the current state of knowledge about the performance of notably dry covers as atmospheric oxygen barriers via models to predict the performance of the IGM technique practically, with a bench-scaled experiment.The results demonstrate the effectiveness of IGM to prevent oxidation of sulfide minerals and ARD in waste rock. The laboratory experiments further identified key variables to be used to monitor performance and control efficiency of IGM, which is now awaiting field-scale application.The IGM technology is a patented process by Terraquest Technologies Ltd (Canada) in USA, Canada and Australia. The IGM technology can be cost-effectively manufactured on-site with commercially available compressors and gas filtration membranes. It is predicted that low-cost covers can then be utilised with IGM, which in turn lowers the overall capital costs of ARD mitigation.CITATION:Ameglio, L and Barrie, H, 2015. Acid rock drainage prevention using inert gas mixture technology, in Proceedings Tailings and Mine Waste Management for the 21st Century, pp 85–96 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jul 27, 2015

By J Pearce, M Barteaux, S Pearce

The prediction of how waste materials will evolve geochemically within waste storage facilities has been the subject of hundreds of thousands of hours researched by geoscientists globally. Despite the quantity of research there are a number of significant areas of uncertainty that remain as partially resolved issues. One of the most significant issues is the applicability of scaling laboratory test results to field conditions, and the use of laboratory data for predictive calculations to determine geochemical evolution of waste materials in the field. This issue has arisen predominantly as a result of the relative paucity of field monitoring data from waste rock storage facilities (WRSFs) and the fact that laboratory test methods are not typically linked to specific field conditions; rather they are based on generic standardised methods and designed primarily to simulate accelerated weathering conditions that do not relate to field conditions in a linear manner.To address these specific issues the authors have in the last two years made significant progress in the development and deployment of advanced field monitoring equipment within numerous WRSFs. O’Kane Consultants (OKC) has previously reported the findings from data collected from these monitoring installations in a number of papers presented throughout 2013–2014. This valuable site data has subsequently been used by OKC as the basis to design and engineer advanced customisable site-specific kinetic leach columns at OKC’s geochemistry research laboratory. These columns represent an important advancement in kinetic column assessment methodology as they have been designed to replicate the field internal conditions within waste facilities.Key features of the columns include their capacity, size and technical specifications; including fully programmable solenoid-controlled air supply with variable flow and pressure control and in-line heating option, automated temperature control and monitoring, automated oxygen consumption and carbon dioxide production monitoring, and soil moisture/matric suction monitoring.This flexibility of the design not only allows for more accurate field-based assessment of pyrite oxidation rates (POR) but also assessment of the potential effectiveness of waste management options such as deposition within a reduced oxygen environment, for example, as simulations of reduced net percolation rates or oxygen ingress rates can be accommodated.CITATION:Pearce, S, Pearce, J and Barteaux, M, 2015. Advanced customisable leach columns – a new kinetic testing method to simulate site-specific conditions, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 137–144 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By K Banerjee, C Dube

Veolia Water Technologies was contracted by a global coal mining company to design a retrofit acid mine drainage treatment facility using DenseSludge™ technology on a former coal refuse disposal site. The project constraint was to reuse current facilities in order to reduce additional capital work cost and avoid additional footprint requirements while improving treatment performance and reducing sludge production and chemical consumption. The initial installation of 454 m3/h served as a pilot plant to demonstrate the benefits of the process and ultimately provided design criteria for the new facility. The pilot demonstrated the benefit of the technology by reducing sludge volume by 90 per cent compared to conventional processes currently in use. The sludge that is reinjected into the mine contains less water, which reduces the volume of water that returns to the mine pool for treatment and mine water balance. Furthermore, the pilot plant reduced lime usage compared to conventional processes by operating at a lower pH set point, demonstrating steady pH control and stoichiometric lime utilisation.CITATION:Dube, C and Banerjee, K, 2015. Sludge conditioning technology to reduce sludge and the cost of acid mine drainage treatment, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 105–110 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By D Reid, A Fourie

The in-pipe treatment of slurries with polymer addition shortly prior to deposition is a noteworthy emerging technology of increasing popularity. Although polymer treatment has been shown to substantially modify and improve depositional and dewatering behaviour in a significant number of cases, the impacts of polymer treatment on geotechnical performance of tailings are less well understood. For example, certain combinations of polymer and slurry type have been shown to result in lower final densities at a given vertical effective stress. Despite these lower densities, polymer-treated tailings often exhibit peak undrained shear strengths consistent with untreated material. However, the sensitivity and/or brittleness of the material may be negatively influenced by the looser state created. Although these changes have been studied, most testing available in the literature was undertaken on relatively ‘fresh’ samples of polymer-treated material. However, significant shear may occur following treatment and prior to the commencement of settling and self-weight consolidation as the material moves down the beach.To study the effects of shearing on the subsequent performance of polymer-treated tailings, a test program consisting of consolidation, triaxial and direct simple shear tests was undertaken on presheared polymer-treated material. Materials used were identical to those used in previously published studies on the impacts of polymer treatment in a ‘fresh’ condition. Shearing of the polymer-treated material generally appeared to lessen the impacts of the polymer treatment process. However, the behaviour of the material when sheared indicated that the polymer was still impacting the behaviour of the material in some respects. The results indicate the importance of the consideration of shearing on material behaviour when planning and designing a tailings deposit where polymer treatment is to be implemented.CITATION:Reid, D and Fourie, A, 2015. Effects of shear on the behaviour of polymer-treated slurries, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 215–224 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By P Kappen, R N. Collins, K M. Spiers

X-ray absorption spectroscopy (XAS) is a synchrotron-only technique used to determine chemical speciation, providing a powerful alternative to most traditional ‘wet chemistry’ and lab-based speciation methods. XAS is an element specific method that can be used to address a variety of systems, ranging from heterogeneous to homogeneous, polycrystalline to amorphous, and solid to liquid. The strength of XAS in identifying and managing chemical species in tailings and mine waste is demonstrated, with the presentation of highly relevant studies into lead, uranium, chromium and arsenic speciation. In each example, waste samples are compared with known standards, allowing an assessment to be made of the quantity of particular chemical species in each.CITATION:Spiers, K M, Collins, R N and Kappen, P, 2015. ‘Forget the wet chemistry’ – how the Australian Synchrotron can help with tailings and mine waste management, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 145–148 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By D J. Williams

The approach to the disposal and storage of mine tailings is slowly evolving. Tailings disposal has been based on minimising short-term capital and operating costs, with rehabilitation costs discounted by the application of a high discount factor in a net present value approach to accounting. This has led to the widespread adoption of surface tailings storage facilities (TSFs) to store slurried tailings delivered by robust and cheap centrifugal pumps and pipelines. Depending on the site climate, rate of rise of the tailings, nature of the tailings and the extent to which supernatant water is removed from the surface TSF, the tailings may or may not dewater, densify and gain strength. High rates of rise of dilute tailings to a facility used to store both tailings and supernatant water results in a wet, low-density, soft tailings deposit that not only occupies a large storage volume but also presents rehabilitation difficulties. A low tailings density results in high containment wall costs, very high rehabilitation costs and a low potential for future land use or ecological function. Overall, the cost of slurried tailings disposal, thought to be low, is actually high. However, low rates of rise, even of dilute tailings, in a dry climate with efficient supernatant water removal can produce a dewatered, high-density, stiff tailings deposit that may occupy a large footprint but to shallow depth that is relatively easy to rehabilitate. There are advantages in dewatering tailings in the processing plant to recover process water and chemicals, facilitate tailings disposal in a more solid form and facilitate rehabilitation. However, the cost of dewatering in-plant can be high, and the process water may not lend itself to reuse. There are also advantages in removing supernatant water to facilitate solar and wind drying of exposed tailings, although water is lost to evaporation and the dried tailings may best be harvested prior to inundation by fresh tailings or rainfall run-off. This paper discusses the background and trends towards the elimination of conventional surface slurried TSFs, with examples presented of the management of black coal and other tailings, including those that are clay mineral-rich.CITATION:Williams, D J, 2015. Towards the elimination of conventional surface slurried tailings storage facilities, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 11–24 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By T Huynh, K Tungpalan, E Wightman, M Edraki, S Palaniandy

Most preventive environmental management practices promote proactive integrated approaches to waste management. For example, life cycle assessment is often used to find the ‘hot spots’ of environmental burdens. This kind of approach is often based on generic data and has rarely been used for tailings. Besides, life cycle assessments are less useful for designing operations or simulating changes in the process and consequent environmental outcomes. It is evident that an integrated approach for tailings research linked to better processing options is needed.The aim of this Nextmine™ project is to develop new tailings management models by streamlining orebody characterisation, process optimisation and rehabilitation. We present an integrated tailings management approach and preliminary results from a case study. Combined grinding and flotation models were developed using geometallurgical data from the orebody, to predict the properties of tailings produced under various processing conditions. The modelling scenarios based on the case study data provide the capacity to predict the composition of tailings and the resulting environmental management implications. For example, the type and content of clay minerals in tailings will affect the geotechnical stability and water recovery. Clay content will also influence decisions made for paste or thickened tailings and underground backfilling.CITATION:Edraki, M, Huynh, T, Wightman, E, Tungpalan, K and Palaniandy, S, 2015. An integrated approach to proactive tailings management, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 323–332 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By D Veneziano, J Van Dyck, R Snow, W Pytel, O Zanoli

Best practice standards generally recommend assessment of the environmental and societal risks posed by tailings storage facilities, but they rarely specify how the analysis should be made. As a case study, this paper describes a safety assessment of the Zelazny Most tailings pond operated by the Hydrotechnical Unit of KGHM Polska Miedz SA in Poland. The complete assessment includes a failure mode effect criticality analysis (FMECA) that considers all conceivable failure modes, but this paper focuses on one key mode, the loss of stability during the planned raising of the crest above its current level. Reliability against static dam failure considers uncertainty on the safety factor in a limit equilibrium approach. The threat of dynamic (earthquake induced) instability is assessed by developing a model of future seismicity as a function of the mining plan and considering uncertainty on the induced permanent displacements along critical sliding surfaces. We quantify the additional level of protection against outflow provided by the beach using an event tree with expert-assigned probabilities. Continuous monitoring of the dam for premonitory signs of instability and a set of loss-prevention plans in the case of a spill provide additional layers of protection; their effectiveness is quantified by estimating the fraction of the population that could be evacuated as a function of warning time. The probabilistic analysis indicates that the safety targets are met and produces practical recommendations on how to maintain and improve the safety level while the dam crest is raised above its current level.CITATION:Van Dyck, J, Pytel, W, Veneziano, D, Snow, R and Zanoli, O, 2015. Safety of a tailings storage facility against dam instability, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 253–262 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By D Luppnow, H Rourke

Recent disasters such as the failure of the Mount Polley tailings embankment remind us of the risks that tailings facilities pose. It is widely recognised that dam-break assessments are a vital tool in identifying the consequences of the failure of a facility, which in turn can be used to develop emergency action plans. A typical assessment includes an estimation of breach parameters and outflow volume, followed by the preparation of an inundation map to illustrate potential flow extents and downstream impacts. This paper focuses on the estimation of outflow volumes, which is an area that the authors feel can be improved. Presently, many types of analyses assume that the volume of tailings released is only a function of the storage volume and dam height. After a review of several documented tailings failures, it has been found that the extent and depth of the supernatant pond needs to be considered as it is just as important, if not more so, as the storage volume and dam height. Tailings facilities with excess water storage have a higher risk of failure as they are more susceptible to overtopping, piping and liquefaction failures. In addition, they pose greater failure consequences as the saturated conditions will lead to more material being mobilised.This paper has reviewed available information on a number of tailings dam failures and proposes an alternative estimation of potential tailings release volumes as a function of supernatant water stored on the facility for use in dam-break analyses. In a broader sense, the paper seeks to shift the current risk paradigm from tailings dam heights to volumes of water stored and provides a basis for continuing research and discussion.CITATION:Rourke, H and Luppnow, D, 2015. The risks of excess water on tailings facilities and its application to dam-break studies, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 225–230 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By R McIlwraith, B Breul

Two case studies are presented in this paper. The first one discusses a roller compacted concrete water supply dam that was constructed in El Mauro in Chile to provide water for agriculture activities downstream of a copper mine during the dry season. The 23 m high dam used a bituminous geomembrane (BGM) as the low permeability upstream facing element on the dam to control seepage through the dam. This is the first time that a BGM has been used in this application. A deep cut-off trench was used to control seepage beneath the dam and through the abutments. This paper briefly presents the design of the dam, including selection of the concrete mix and maximum aggregate size that the use of the Coletanche BGM allowed, and provides details of the construction, quality control and assurance of the installation of the BGM. An ultrasonic apparatus was used as part of the quality control on the BGM seams.The second case study discusses a tailings dam in Cerro Lindo, Peru (near Chincha), where a watertight BGM was installed on the upstream face. Results are presented of the survey done by a consultant on the behaviour of the dam and in particular of the BGM following an earthquake of magnitude 8.1 in Chincha close to the site. These findings on-site were checked by trials in a laboratory in California. Test results are given and explained.CITATION:Breul, B and McIlwraith, R, 2015. Case histories – roller compacted concrete dam waterproofing with a bituminous geomembrane in Chile and a tailings dam in Peru subject to an earthquake of 8.1 magnitude, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 367–372 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By D A. Williams, P J. Chapman

Constructing upstream raises with tailings is an accepted and cost-effective practice in Western Australia, where the climatic conditions are favourable, desiccation (and hence overconsolidation) occurs rapidly due to air drying and there is a perceived low seismic risk. This is in contrast to many other settings, where there is either a positive water balance, high seismicity or a combination of both. In recent times, there has been an increased focus on seismicity in areas of Australia that have historically been considered to be of low seismic risk. The increased focus is driven by two recently published documents used by tailings practitioners and increased awareness from corporate entities, particularly those with mines in high-seismicity regions such as South-East Asia and South America (particularly Chile).The increased awareness has resulted in increased rigour being applied to seismic design of tailings storage facilities (TSFs) in general, and particularly upstream-raised TSFs. This paper compares the results of a seismic stability assessment for an upstream-raised TSF located in the Goldfields region of Western Australia, which has historically been considered a low seismic area, with a seismic stability assessment carried out for a crossvalley TSF containing similar tailings but located in a high-rainfall, high-seismic setting in South-East Asia. The influence of the adopted design earthquake values on the results of the assessments and the potential impact of the maximum design earthquake (MDE) on the design approach is presented for both cases. The results indicate that although the Western Australian site is located in an area thought to have low seismic risk, the screening level analyses suggest that the MDE could result in liquefaction of the tailings materials. Not surprisingly, liquefaction was also indicated for the South-East Asian site. The outcomes of the assessment are also presented.CITATION:Chapman, P J and Williams, D A, 2015. Seismic design of upstream-raised tailings storage facilities in a semi-arid, low-seismicity setting, in Proceedings Tailings and Mine Waste Management for the 21st Century, pp 157–162 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By Y Durkheim, P Saunier, L Ameglio

"In the last decade Afitex developed the Draintube™ geocomposite, which provides simultaneous drainage and waterproofing functions. This new type of drain tubes planar geocomposites (DTPG) differs from other geocomposites as the drainage core is composed of multiple corrugated and perforated pipes instead of biaxial or triaxial nets. It is furthermore associated with needle-punch stitched layers of non-woven geotextiles, which act either as capillary mediums or as filters.In this paper, the structure of the Draintube™ drainage composite is presented along with its key properties and the drainage mechanism associated with its particular structure.The relevance of this kind of structure is then reviewed based on past and current laboratory bench evaluations and field installations for mining applications such as the covering of acid rock drainage (ARD) tailings for the Central Manitoba Mine (Canada) site-rehabilitation; and as a pregnant solution collection layer in heap leach pads.Some of the demonstrated critical advantages of Draintube™ in the mining industry are as follows: reduction of the thickness, hence lower volume of granular drain layers improvement of fluid and gas collection and reduction of the hydraulic load reduction of secondary collector network mechanical protection of the sealing membrane fast and economical installation of interlifts stability under extreme conditions (compression, temperature, pH) increased stability of entire covering system and reinforcement of protection of dykes filtration of the covered material customised drainage positive connection of the geocomposite to collector pipes enable leaks detection (using a conductive textile layer) with an electrical test.CITATION:Saunier, P, Ameglio, L and Durkheim, Y, 2015. Tubular drainage and lining geocomposite for mine tailings and heap leach pads, in Proceedings Tailings and Mine Waste Management for the 21st Century, pp 297–304 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jul 27, 2015

By S Joyce, Z Agioutantis, D van Zyl, D Shields

Over the past 15 years, the mining industry has begun to incorporate the concepts of sustainable development and sustainable mining practice across the life cycle of mineral operations. This requires addressing economic issues, community impacts and concerns and environmental protection, and is captured in part by the phrase ‘design for sustainability’ (McClellan et al, 2009). Over the same period, the industry has seen a gradual decline in ore grades for many mineral commodities. As a result, large volumes of tailings and mine waste rock are being produced around the world, and it is expected that the annual production volumes of these materials will increase, even if there is not a significant change in the demand for materials.Another related thread of change has been the realisation that societies need to move away from linear economies (raw materials, production, consumption, disposal) towards more circular ones. This will help societies become more resource efficient, which is defined by the United Nations Environment Programme as reducing the total environmental impact of the production and consumption of goods and services, from raw material extraction to final use and disposal. The goal is to create more with less and deliver greater value with less input. Circular economies require thinking in terms of the waste hierarchy (reduce, reuse, repurpose, recycle, recover, landfill).The challenge is that the waste hierarchy was originally designed to address embodied mineral content in products rather than mine waste and tailings generation. It will need to be reconsidered in a mine life cycle context, focusing on a value-based conception of waste (Van Ewijk and Stegemann, in press).In parallel to these changes, it has remained an imperative in the mining industry to dispose of these waste materials as economically as possible while protecting the environment. Single handling of these materials has been the main target, which reduces the life cycle costs of their management but may make reuse of waste and tailings technically more difficult or economically infeasible.This presentation explores a rethinking of the large volume earthen material waste issue at mines. The underlying theme is that some or all of these materials can be valuable resources for the future that can positively contribute to sustainable development. These resources can offer economic gains to firms, communities and societies; contribute to environmental well-being; enhance social interactions with the previously mined landscape if handled properly; and, with proper policies in place, reduce governance commitments. Each of these topics will be briefly explored. This will be followed by a discussion of approaches to manage design and operations to allow future resource recovery.CITATION:Van Zyl, D, Shields, D, Agioutantis, Z and Joyce, S, 2015. Waste not, want not – rethinking the tailings and mine waste issue, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 7–10 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By D A. Williams, J C. J Boshoff

The properties of tailings that emanate from laterite nickel processing plants are significantly different to most other mine tailings. They typically comprise a mixture of fine materials that are made up of altered clays, chemical residues and salts. Neutralisation processes that are undertaken prior to tailings discharge result in a high proportion of gypsum in the tailings. The salinity of the pore fluid is commonly higher than 140 g/L of salts, dominated by magnesium sulfate. Hydraulically-placed tailings that undergo solar evaporation typically reach dry densities of less than 1 t/m3 of insoluble solids. In situ water contents after many months of drying may be as high as 80 per cent, and peak undrained shear strengths are unlikely to be greater than 20 kPa.This type of material is not conducive to upstream raising, from both a practicality and overall slope stability perspective. Even at rates of rise of less than 1 m/a, it is difficult to effect upstream raising on unaltered laterite nickel tailings. However, the authors have successfully designed and implemented upstream-raised laterite nickel tailings storage facilities. The upstream raises have been formed from both imported natural materials and air-dried and compacted tailings borrowed from the tailings beaches.Drying and associated strength gain has been achieved through various means of mechanical intervention, repeatedly exposing a zone of tailings to the atmosphere for evaporation. Field trials have been undertaken to optimise the approach, and the findings from the trials have been implemented in practice to allow stable upstream raises to be constructed. The cost savings and reduced environmental impact compared to high-volume downstream raises have been significant.CITATION:Williams, D A and Boshoff, J C J, 2015. Upstream raising of laterite nickel tailings storage facilities, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 271–280 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By S Bouzalakos, W Timms, H Malli

Combining ultramafic mine tailings and acidic mine drainage via mineral carbonation to sequester carbon dioxide, presents an opportunity to minimise waste on mine sites. Low pH mine water with trace element concentrations can be effectively treated by high magnesium mine tailings, a useful source of finely ground reactive matrix. By using milled tailings for mineral carbonation, there are negligible energy requirements for communition of ore rocks to reduce particle size. This study aimed to assess the technical applicability of reacting ultramafic tailings and acidic mine water through mineral carbonation technology in the mining industry. Dissolution has been identified as the rate limiting stage in mineral carbonation; hence the study focused on identifying optimal dissolution conditions. Ultramafic tailings (particle size <100 µm) derived from serpentinite ore, were reacted with a typical mine water that was synthesised in the laboratory. Through variances in the solid to liquid ratios and temperature of dissolution, a maximum five per cent magnesium dissolution efficiency was reached at 50 g/L and 100°C. The acidic mine water was neutralised (from pH <2 to pH ~6) and iron, copper and zinc ion concentrations reduced significantly during the formation of solid precipitates. Carbonation was undertaken by injecting carbon dioxide into the magnesium-rich solution to form stable carbonates. The experimental work demonstrated proof of concept; however, dissolution efficiency and carbon dioxide sequestration was low, indicating that further research would be required before larger scale implementation.CITATION:Malli, H, Bouzalakos, S and Timms, W, 2015. Ultramafic mine tailings to treat acidic mine water and lock away carbon through mineral carbonation, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 133–136 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By J Boshoff

The management and operation of tailings storage facilities (TSFs) are often neglected until the process plant has to shut down as a result of this negligence or as a result of a catastrophic failure as was the case during the recent TSF failure in North America.TSFs are often regarded as non-assets and do not receive the attention they deserve in terms of technical expertise and financial provision. A TSF is not a simple structure but a complex and dynamic structure that changes throughout its operational life. The operational life of a TSF is the period in which there is the greatest opportunity for risks to occur. The failure of a TSF is normally not as a result of a single event but as a result of a consequence of events. These events are often not recognised in time due to a number of factors.Process plants and slurry pumping systems are operated at suboptimal conditions in order to maintain throughput. At the same time, the tailings properties are compromised in terms of slurry density and particle size distribution amongst other things. Tailings deposition cycles and drying cycles are not well understood and the tailings management strategy is not well tuned in terms of maximising consolidation and improving in situ densities. Pond control is also neglected. These are aspects that form the keystone to the effective utilisation of available deposition area as well as the frequency and cost of future embankment raises.Apart from operational issues, forward planning in terms of budget requirements, increases in tailings throughput, embankment raises, pipe replacements, etc are normally put on the back burner. Available deposition space at the time seems to render this planning obsolete.The bottom line is that responsible tailings management and proper forward planning can limit liability and reduce the bottom line in terms of cents per ton if correctly implemented by suitably qualified tailings managers and engineers.The aspects that need to be considered as part of responsible tailings management are highlighted in this paper.CITATION:Boshoff, J, 2015. Responsible tailings management, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 317–322 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015