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White paper: Holistic tailings management solutions

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HOLISTIC TAILINGS MANAGEMENT SOLUTIONS

AbstractTailings are fine-grained typically silt-sized (1–600 μm) waste produced in the quantities between 5 and 7 billion tons per year globally. As the composition of ores is getting more complicated, the amount of tailings per produced ton of metal rises. Currently, the portion of tailings within the ores can be as high as 90–98% for some copper ores and for 99.9% with gold ores, and increasing, leading to a real concern over the growing amount of tailings waste from mining.

This paper introduces an approach to holistic tailings management solutions, including considerations for the design of an integrated solution and the technology options available. The paper includes information on how site water management, materials handling, and tailings storage facility considerations tie in with the technology solution in order to create an integrated or ‘holistic’ solution offering.

At best the design of the tailings management solution works back to front and starts with considerations for a suitable Tailings Storage Facility (TSF), including its footprint, impact on the environment, size and location of dams, water management (dry or wet climate), geochemical and geotechnical aspects (seismicity, overburden, acid drainage, or metals leaching), reagents (e.g. cyanide) present in tailings and the cost and quality of dams and earthworks. As an emerging topic in tailings processing, ‘holistic tailings management’ practices are attracting high interest among mining and metallurgical processing operations and project developers. With a rapid growth in the size of the TSF and the increasing scarcity of water, new technologies and design strategies are required to meet technical and profitability related challenges.

White paper

Dr. Piia Suvio, Jason Palmer, Arturo G. del Olmo and Janne Kauppi Materials Management, Dewatering, Outotec Ltd


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Outotec’s tailings technology solutions include equipment and services that are suitable for almost every tailings facility and can include thickened tailings and paste, including suitable piping and pumping. Furthermore, Outotec is also at the forefront of dry stacking technology development and can supply filtration equipments and holistic plants to meet the growing demand for tailings filtration and filtration solutions. Further to surface tailings management, Outotec is a world leader in tailings backfill disposal and can provide both hydraulic and paste backfill plant solutions globally. As with surface-based tailings management solutions, the design of underground solutions starts with considerations for the available storage space underground. Backfill solutions can be operated with or without a binder, which is required depending on the tailings type and consistency. Outotec can offer a turnkey backfill solution, extending to operation and maintenance set-ups.

Paste and dry stacking technologies combined with closed water loops are the best available technologies for conserving water within the concentrator environment. However, this may lead to process water challenges with reagents and fines being recycled within the production processes. In conventional tailings systems the process waters originate from natural sources and/or mine dewatering ground waters. In such systems it is estimated that a Cu process located in a temperate zone uses around 0.9–0.6 m³ of water per ton of ore, whereas a dry stacking system located in a temperate zone uses 0.2–0.15 m³ of water per ton of ore, resulting in water savings up to 25% or even 80% respectively.

Tailings material handling can be divided into two categories of slurry pumping and dry cake material conveying and stacking. Centrifugal pumps are often used for pumping fine ground tailings material to the TSF. When transporting over longer distances, multi-stage slurry pumping is commonly used. Pumping of paste requires special pump modules and high-pressure pipelines. The rheology of the material is governed by the solid particle size distribution, solid form and solid content in the slurry, and must be taken into account in planning. In dry stacking solutions, landfilling and conveying is mainly dictated by the selection of the TSF type, location, and size. The material handling system must support the requirements of the mine and concentrators for tailings variability, production rates, overburden/gangue/ore logistics and production targets over the lifetime.

Currently, conventional tailings dam breaches account for most environmental incidents related to extractive industries. Due to the risks, social license to operate mining ventures is increasingly dependent on the ability to demonstrate that the TSF will perform adequately long term and should be designed and operated in a way that ensures very little, if any, potential for uncontrolled releases or impact on the environment. The design of a tailings management solution should always start from the TSF-end of the solution. The process starts with a comprehensive evaluation and full understanding of the site-environmental settings (geological, geotechnical, hydrological, hydrogeological and hydro-chemical) and an integrated assessment framework to screen the scope and evaluate alternatives for the design, build, operation and closure of the TSF. TSF closure plays an important part in risk prevention and should include decommissioning, rehabilitation and performance monitoring for a required period of time.


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Table of contentsIIntegrated tailings management solutions ....................... 1

Abstract ................................................................................ 1

Key words ............................................................................. 3

Table of contents ................................................................. 3

Tailings in mineral processing ........................................... 6

Holistic tailings management solutions ............................. 6

Outotec surface and underground tailings management solutions ....................................................... 8

Site water management – lower operational risks ............ 9

Materials handling for tailings .......................................... 11

Tailings storage facility (TSF) ............................................ 12

Conclusions ....................................................................... 14

References/additional resources ...................................... 15

For more information ........................................................ 15

Key wordsHolistic tailings management, surface tailings, dry stacking, tailings backfill, concentrator, mine waste, tailings storage facility, process tailings, materials handling, site water management (SWM), life of mine


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Mineral ore

Primarycrushing

Rougherflotation

Cleanerflotation

PSI /Courier

HIG millregrind

Tailingsthickening

Alternative tailings disposal methods

Paste backfill

Tailings dam

Concentratethickening Concentrate

filtration

Metalconcentrate

SAG mill

Ball mill

Reactor Reactor

COMMINUTION CONCENTRATION DEWATERING

Separation

Use / reuse

Use / reuse

Use / reuse

Use / reuse

Use / reuse

Use / reuse

Reactor Separation Waterquality

monitoring

Polishingfilters

Polishingfilters

Polishingfilters

Separation

Use / reuse

MINERALS CONCENTRATION MANAGEMENT

SITE WATER MANAGEMENT

Water quality monitoring

Waterquality

monitoring

Fresh / mine water treatment Process water treatment Effluent treatment

Use / reuse

Tailingsfiltration

Dry stacking

Use / reuse

Use / reuse

OUTOTEC'S TECHNOLOGY SCOPEOUTOTEC'S TECHNOLOGIES FOR THE ENTIRE VALUE CHAIN


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Mineral ore

Primarycrushing

Rougherflotation

Cleanerflotation

PSI /Courier

HIG millregrind

Tailingsthickening

Alternative tailings disposal methods

Paste backfill

Tailings dam

Concentratethickening Concentrate

filtration

Metalconcentrate

SAG mill

Ball mill

Reactor Reactor

COMMINUTION CONCENTRATION DEWATERING

Separation

Use / reuse

Use / reuse

Use / reuse

Use / reuse

Use / reuse

Use / reuse

Reactor Separation Waterquality

monitoring

Polishingfilters

Polishingfilters

Polishingfilters

Separation

Use / reuse

MINERALS CONCENTRATION MANAGEMENT

SITE WATER MANAGEMENT

Water quality monitoring

Waterquality

monitoring

Fresh / mine water treatment Process water treatment Effluent treatment

Use / reuse

Tailingsfiltration

Dry stacking

Use / reuse

Use / reuse

OUTOTEC'S TECHNOLOGY SCOPE

Figure 1 Typical copper concentrator from Outotec Minerals Processing Technologies

OUTOTEC'S TECHNOLOGIES FOR THE ENTIRE VALUE CHAIN


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Tailings in mineral processing Mines and mineral processing plants generally produce significantly more waste than the marketable commodity itself. Overall, the grade of metal ores is decreasing and, at the same time, the amount of waste rock removed to access the ores is increasing. It is estimated that the annual mine waste and tailings production ranges from 5 to 7 billion tons per year (Mudd and Boger 2014). The proportion of tailings within the ores can be as high as 90–98% for some copper ores and is still increasing (Nagaraj, 2005). Gold plants process ores with up to 99.9% of tailings and only few grams of gold.

This trend will continue as the mineral processing industry is required to increase ore processing capacity (Figure 1) in order to achieve the same level of production. As a consequence, extractive industries have advanced technology for grinding and improved the efficiency of processing technology to allow higher beneficiation capacities of more complex ores. The complexity of the tailings management solutions has increased along with the scale of operations and the waste tailings generated are also getting finer in nature and therefore more difficult to handle.

Waste tailings or leach residues are as complex and variable as the processes and ores from which they are generated. Typically they are fine-grained typically silt-sized (1–600 μm) solids that remain after the recoverable minerals have been extracted. During processing, these solids are mixed with process water, chemicals used in extraction and other unwanted compounds leached from the ore during processing. Other than the waste tailings, whether it’s an open pit or an underground mine, there are also other waste streams, including overburden, waste rock and varying amounts of excess process or impacted water.

Holistic tailings management solutionsCareful planning of the Tailings Storage Facility (TSF) and the treatment of the waste streams is required long before operations begin, throughout the mine life and for long term sustainable remediation after closure (cradle to grave). As an emerging topic in tailings processing, ‘holistic tailings management’ practices are attracting high interest among mining and metallurgical processing operations and project developers. With a rapid growth in the size of TSFs and the increasing scarcity of water, new technologies and design strategies are required to meet technical challenges. In addition to the technical challenges, the risks related to conventional TSFs have increased and mining and metallurgical companies are looking for strategies to offset the rising risks, costs and resource inefficiencies (water losses) relating to tailings management.

Unfortunately, over the long history of mining there have been tailings dam failures and poorly managed operations. With increased social awareness and stricter government regulations it is of greater importance in the earlier planning stages to develop a solution that has minimum impact, long-term reliability and a sustainable solution in order to obtain a license to operate. Holistic tailings management solutions balance the investment with risk reduction and resource efficiency to achieve a technically and economically feasible solution.

Thickening

Thickening

Filtering

Design process – Outotec’s dewatering capability

Tailings Storage FacilityDry stacking, paste deposition,thickened tailings, in-pit disposal, water management

ConcentratorFlotation

Pumping Conveying

Pumping

Figure 2 Outotec’s Holistic Surface Tailings Management Solution


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Leading mining and metallurgical organizations are looking for innovative holistic solutions, which include tailings dewatering, materials handling, TSF-related services, as well as related process water treatment that solve their tailings issues, as outlined in Figure 2 for a surface tailings management solution. As technologies develop, traditional methods can become outdated and organizations are under pressure to adopt the best available technologies and best practice solutions. Newer technologies, such as paste and filter cake dry stacking (high density tailings solutions) result in solutions that provide geotechnical and geochemical stability. The increased stability substantially decreases risks and reduces the environmental footprint, meaning that these solutions also enable smoother permitting and commencement of operations. The most technically feasible solution with the lowest life of mine cost is typically influenced by the source material availability, the geographic conditions, the production rate and local legislation. Analyzing the available technologies to arrive at the best holistic solution requires a deep understanding of the available technologies, combining process, geotechnical and strategic planning, including mine cash flows.

Tailings management solution design should start with considerations for a suitable TSF type, including the required footprint and impact on the environment, size and location of dams, water management (dry or wet climate), geochemical and geotechnical aspects (seismicity, overburden, acid drainage or metals leaching), reagents (e.g. cyanide) present in tailings and cost and quality of dams and earthworks. Site conditions vary greatly depending on the location (mountains, high arctic, rainforest, arid regions, temperate regions, etc.), each having a significant influence on design. Design requirements are also governed by the regulatory issues, earthwork costs and water availability. Even though some tailings may have acid generation potential or contain heavy metal, much of the waste is inert and can be safely stored in stacks or dams that are stabilized and rehabilitated at the end of the mine life. Leach residues that can contain acids, strong-base cyanide or other toxic compounds are often considered to be the most harmful types of tailings and require secure storage. In these cases, the advantages of increased stability and reduced footprint play an important role.

To achieve a low environmental impact, minimized water losses, resistance to high seismic activities and savings at the rehabilitation stage following the closing of the mine, companies often opt for a dry stacking solution or other best available technologies. These alternatives are often perceived as having higher set-up costs, but in many cases dry stacking can result in considerably lower OPEX (earthworks, closure, etc.) costs. A detailed analysis has shown that using BAT can enable an improved internal rate of return (IRR) and corporate shareholder value to be realized. This is particularly the case when considering risks and potential liabilities.


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Outotec surface and underground tailings management solutionsOutotec’s tailings technology solutions include equipments and services that are suitable for almost every tailings facility and can include thickening from low density to high rate and all the way to paste thickeners. Pumping of tailings streams can be a complex issue and Outotec can also provide relevant pumping and piping systems to suit the thickening technologies, creating a seamless solution.

Outotec is a world leader in tailings backfi ll disposal and can provide both hydraulic and paste backfi ll plant solutions globally. As with surface based tailings management solutions, the design of the underground solution starts with the considerations of the available excavation voids underground. The idea of backfi ll solutions is to fi ll the voids for rehabilitation and construction purposes, after the extraction of the mineral. Backfi ll solutions can be operated with or without a binder. Cement is often used as a binder and is required depending on the tailings type and consistency. Outotec can offer a full scope of services for backfi ll solution, extending to construction and operation and maintenance of backfi ll operations. The full offering of Outotec tailings management solutions can be seen in Figure 3.

Figure 3 Outotec Tailings Management Solution Offering

High ratethickener

TAILINGSPOND

TAILINGSPOND

TAILINGSPOND / BEACH

DISPOSAL

UNDERGROUNDBACKFILL

DRY STACKDISPOSAL

DRY STACKDISPOSAL

High compressionthickener

High ratethickener




Filtering

Classification

Binder

Filtration

Filtration

Backfill plant

Paste thickener

Overland converyorand stacking

Standing converyorand stacking

Centrifugalpumping

Shear thinningpumping

Positivedisplacement

pumping


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Site water management – lower operational risksWater is the commodity that has driven the mining industry for decades. Often used frivolously, modern economic and social pressures are forcing a change to reduce water usage while improving the quality of water and effluents. Water is used in many processes within mineral processing and large quantities of it is lost within the tailings processing and disposal area. New technologies that can increase the recovery of water are actively being developed, but the key to improving the efficiency of water use and reducing risks lies in closing water loops and increasing the slurry density in wet tailings processes.

Paste and dry stacking technologies combined with closed water loops are the best available technologies for conserving water within the concentrator environment. With a shift from conventional tailings technologies towards paste and dry stacking, water efficiency is vastly improved, but this may lead to process water challenges with impurities, reagents and fines being recycled within the production processes. Traditionally, the water processes are designed to input enough water into the processes for operational purposes and the water flows within the mineral processing environment vary depending on the tailings management technology used. The water flow set-up for a conventional tailings management process is shown in Figure 4. In conventional tailings systems, the process waters originate from natural sources and/or mine dewatering waters. The amount needed is directly related to the environmental conditions and filterability of the tailings dam, which indicates how much water is lost in this process stage. With these kinds of process conditions it is estimated that a Cu process located in a temperate zone uses between 0.6–0.9 m³ of water per ton of ore (Jansson et al., 2014; Kotiranta T. et al., 2015).

Minedewatering

Concentrate

Tailings

Naturalwaters

Processwater

Effluent

Run ofmine

Mineralprocess

Minedewatering

Concentrate

Tailingsmethod

Naturalwaters

Processwater

Effluent

Run ofmine

Mineralprocess

Waterprocesses

Figure 4 Water Flow Set-up for Conventional Tailings Management Solution

Figure 5 Water Flow Set-up for Dry Stacking Tailings Management Solution

A shift towards more advanced tailings processing options, such as dry stacking, not only changes the set-up of the water flows, but also the water quality. This change is largely due to the shorter retention times of water in the processes, when moving from a conventional tailings dam, with a 30–60-day water retention time, to a dry stack/high density process, where the water is in contact with the solids for only a few hours, while the tailings and water are separated in the thickener. When using a conventional tailings dam, there is a perception that it clarifies suspended materials via settling, but in actual fact this is not always the case. In many cases, a tailings dam with a long water retention time actually changes the water quality due to the bio/chemical reactions taking place in the dam. These changes may be harmful, especially for polymetallic mineral processes. In some cases, metal recovery or selectivity may be negatively impacted without suitable process water treatment.

The water set-up for a dry stacking tailings management process is shown in Figure 5. In the dry stacking model the amount of process make-up water is strongly reduced due to the removal of the open wet tailings dam, which loses much of the water. Now, the water can be much more effectively captured and reused back in the process. The estimated water usage drops to 0.15–0.2 m³ of water per ton of ore in a Cu refinery plant located in a temperate zone. Water recovery is essential in mining areas that have an arid climate or in environmentally sensitive areas such as water conservation and excess cold areas (Jansson et al., 2014; Kotiranta T. et al., 2015).


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Another issue to consider, when closing water loops is the effect that the change will have on effluent streams and on contaminants within them that may concentrate and accumulate in the processes and therefore causes disturbances, as outlined in Figure 6. This leads to a need to bleed some of the water from the water recycling loop and treat it safely to ensure safe discharge into the environment as required.

By switching from conventional tailings with low water recycling to paste and dry stacking technology solutions, it is possible to reduce the operational risks of the processes as outlined in Figure 7. The major effect of going for more advanced tailings management solutions is the reduction in socio-political and economic risks related to the processes. At the same time, water reuse can be improved when switching from conventional solutions towards paste and dry stacking solutions with water savings of up to 25% or even 80% respectively. However, the rate of water savings is dependent on the final layout of the tailings management solution and on the climate zone, in which the mine and the process are located.

kEUR

low

med

ium

Ris

k le

vel

high

MEUR

Risk value>BEUR

Conventional tailings management

Paste management

Filtered management

Dam wall breakage (upstream)

Pollution of both surface and groundwater through seepage

Sociopolitical acceptance

Image risk for whole group

Water shortage during dry months

Risk of total operation

kEUR

low

med

ium

Ris

k le

vel

high

MEUR

Risk value>BEUR

Conventional tailings management

Paste management

Filtered management

Dam wall breakage (upstream)

Pollution of both surface and groundwater through seepage

Sociopolitical acceptance

Image risk for whole group

Water shortage during dry months

Risk of total operation

Closed

Fines

Residual reagent

Metals

Etc

SO4, SXOY

OpenFresh water usage

New waterreuse concepts

Incr

easi

ng p

roce

ss d

istu

rban

ce

Figure 6 Effects of Closing the Process Water Loops

Figure 7 Risk Levels Related to the Different Tailings Management Solutions


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Materials handling for tailingsToday’s material handling can be divided into two categories: slurry pumping; and dry cake material conveying and stacking. Both transport types have their own challenges and specific technology-related considerations are required at the early phases of design and engineering.

Hydro transport with centrifugal pumps is a typical way of transporting fine-ground tailings material into TSF. Two-phase slurry pumping with some entrained gas is a common solution for tailings transport. Over short distances, this can be relatively simple, but as the distance increases and the terrain changes, designing a cost-effective and reliable tailings pipeline can become a complex task requiring experience and good testing. Following the increasing water recovery from modern, high-density thickeners, pumping of the underflow becomes more complex as the viscosity of the slurries increases and laminar flow pipelines with high-pressure pumps are required.

In order to achieve a high beach angle tailings storage system using paste deposition, the rheology of the tailings stream must be carefully assessed and will have a significant impact on the slurry pipeline. Paste requires special pump modules for hydro transport, high-pressure pipelines and engineered spreading towers for large area deposition to reach the optimum stack height and necessary storage volume. Paste optimizes the storage capacity available reducing the need for TSF wall raises and enabling the disposal of more tailings within the same footprint.

Paste rheology depends on the particle size distribution of the solid, the form of the solid, and the solid content of the slurry and needs to be taken into account at the early stages of the planning. Costs related to the pumping system can often be high and a holistic design using techno-economic studies to select the most sustainable alternative over the life of mine should be used. Paste stack is fed from the top and has a thin layered disposal structure in order to minimize ARD/AMD seepage.

Filtered tailings storages are subject to different rules than wet tailings dams due to the dry nature of the compacted solids. Filtered tailings cake can be stacked and compacted as sand and soil, and entrained water does not create any need for dams, or follow-up of mandatory dam safety rules. However, other national rules may apply, such as landfill rules.

Landfilling and conveying can be executed in multiple ways, which are mainly dictated by the selection of the TSF type, location, and the size. The first challenge is to select a material handling system that supports the requirements of the mine and the concentrators’ requirements for tailings variability, production rates, overburden/gangue/ore logistics and production targets over lifetime. In small to medium-sized mines it is typical to use dump trucks or the mine fleet, FELs, compactors and earthmovers for tailings transport and placement, especially if they can be integrated into ore and site rock logistics by back-loading.

If the TSF’s location and size are conducive to the mine’s logistics, leasing the construction equipments or even outsourcing stacking provides an attractive alternative. The operational costs (OPEX) related to trucking alternatives are sensitive to fuel costs and global oil prices. Alternatively, tailings cake transport can be carried out using belt conveyors, feeders, splitters, belt trippers and spreaders. These equipments are well proven and commonly used within the construction and aggregate raw material industries. Similar systems are used for heap leaching facilities for creating homogenously crushed ore leach stacks. Usually, the conveyor systems require a higher up-front investment by the mine owner, but provide significant benefits over the trucking option for large TSFs and for long-distance TSF alternatives. They may also offer a considerably lower TCO over the mine’s lifetime. Since the dry stack system design is dependent on the TSF’s topology, location, stack height and shape, flat surfaces are the preferred option for location, but valley/mountain areas are also possible.


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Tailings storage facility (TSF)Directive 2006/21/EC of the European Parliament defines a mining waste facility as any area designated for the accumulation or deposit of extractive waste, whether in a solid or liquid state or in solution or suspension. Facilities are deemed to include any dam or other structure serving to contain, retain, confine or otherwise support such a facility, and also to include, but not be limited to, heaps and ponds. Excavation voids, where waste is replaced for rehabilitation and construction purposes are not included here.

Obtaining a social licence to operate mining ventures is increasingly dependent on the ability to demonstrate that that the TSF will perform adequately in the long term. For example, in some areas of the world, regulators currently require TSFs to be designed to be capable of remaining safe and stable for 1000 years (ANCOLD 2012). Furthermore, TSFs should be designed and operated in a way that ensures very little, if any, potential for uncontrolled release of tailings or impact on the environment (Australian Centre for Geomechanics, 2015). However, conventional tailings dam breaches account for most of the environmental incidents related to extractive industries (Edraki, 2014) and the production of larger volumes of tailings and associated water is prompting increased scrutiny of TSFs from both society and regulators. As a consequence, there has been increasing interest towards more advanced tailings management, including thickened tailings, paste and dry stacking solutions, in order to overcome risks related to conventional tailings management, environmental impact, social responsibility and economics. Further to advanced tailings management options, new management methods that improve the physical and/or chemical stability have been developed, including environmental desulphurization, covers built with tailings and co-disposal of tailings and waste rock (Bussière, 2004). In order to address the risks, best practices are being discussed and continuously evaluated globally. There has also been significant industry collaboration in the last few decades including activities around ICOLD, the Global Acid Rock Drainage Guide (GARDGuide) and others (Patel, 2015).

Current legislation states that operators must take all of the measures necessary to prevent or minimize any adverse effects on the environment and human health brought about as a result of the management of extractive waste. Due to the special nature of tailings waste and its management, regulators have considered it necessary to introduce specific application and permit procedures in respect of waste facilities. In addition, most regulators have been required to take necessary measures to ensure that the competent authorities periodically reconsider and, where necessary, update permit conditions (Directive 2006/21/EC). Furthermore, the directive introduces requirements as regards location, management, control, closure, and preventive and protective measures to be taken against any threat to the environment in the short- and long-term perspectives, particularly against the pollution of groundwater by leachate infiltration into the soil.

The best available practices and technologies with respect to tailings storage require risk-based analysis for the design and selection of operational alternatives. This approach is inclusive of the management of safety, health, the environment, and the community to levels acceptable to stakeholders. To ensure all measures are taken from the operational point of view, operators are required to prepare a detailed ‘Waste Management Plan’ for the minimization, treatment, recovery and disposal of extractive waste based on the principle of sustainable development. The aim of the plan is to prevent or reduce waste production and its harmfulness and encourage the recovery of extractive waste by means of recycling, reusing, or reclaiming such waste. This Plan must also be environmentally sound and in accordance with existing environmental standards at the community level, while ensuring safe short- and long-term disposal of the extractive waste, in particular by considering different tailings disposal technologies (conventional vs. BAT).

As mentioned earlier, the design of a tailings management solution should always start from the TSF-end of the solution. The TSF design process starts with a comprehensive evaluation and full understanding of the site-environmental settings (geological, geotechnical, hydrological, hydrogeological and hydro-chemical) in order to define the background and extreme conditions to support the design, as well as the impact assessment. Hydrology study plays a key role in early design together with geotechnical studies of soil types and the bearing capacities of each type under triaxial pressure. The bearing capacity of tailings can also be studied with variable moisture levels and it is possible to use soil/tailings stabilization methods for critical structures. Natural compaction over time and energy-enhanced compaction studies are necessary for edge construction design for landslide prevention of the dry stack TSF. Construction can be organized so that it enables continuous rehabilitation to prevent rainfall-enhanced ARD/AMD seepage or wetting of TSF to avoid mudslides.


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The physical and chemical characteristics of tailings are governed by the nature and body of the ore and can vary even within the same deposit. Ore processing adds water and a range of chemical agents to the solid tailings stream, which then affects the physical and chemical behavior of the slurry and therefore potentially poses an additional environmental problem (Ritcey, 2005). Therefore, the site-setting appraisal must be complemented by an assessment (characterization) of the waste materials to be stored, as well as the available construction materials or other waste streams from the mineral processing operations. This information needs to be complemented by a continual inspection review and assessment to confirm all assumptions that have been made. The whole process is normally assessed by means of a risk-based analysis, which must be periodically updated to help identify, prioritize, and improve engineering design and/or management controls, including emergency and contingency plans.

One of the most effective ways to reduce the risks related to tailings disposal is to use an integrated assessment framework to screen scope and evaluate alternatives for the design, build, operation, and closure of the TSF. Such an integrated approach enhances preventive environmental management practices (Carvalho, 2014). Decommissioning and closure of TSFs is a complex process that requires specialized ongoing consideration and management, where the objective is to create a safe, stable, non-polluting landform. TSF closure should be viewed as a whole-of-life process that includes decommissioning, rehabilitation and performance monitoring for a required period of time. The closure plan should include details on (Government of Western Australia, 2015): • Final landforms and drainage structures (e.g. surface drainage works, covers, encapsulation cells, armoring) • Progressive rehabilitation including materials handling, placement (e.g. topsoil and vegetative material) • Monitoring and validation against agreed closure criteria • Monitoring and maintenance program until relinquishment and• Unplanned or contingency closure plan


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ConclusionsThe solutions, strategies and approach described in this paper are gaining broad industry awareness and appeal globally and are forming the future trends of tailings management. With a rapid growth in the size of the TSF and the increasing scarcity of water, solutions, technologies and design strategies are crucial to meet the technical and process-related challenges.

At best the design of tailings management solution works back to front, starting with considerations for a suitable TSF, including its footprint, impact on the environment, size and location of dams, water management (dry or wet climate), geochemical and geotechnical aspects (seismicity, overburden, acid drainage, or metals leaching), reagents (e.g. cyanide) present in tailings and cost and quality of dams and/or earthworks. As an emerging topic in tailings processing, ‘holistic tailing management’ practices are attracting high interest among mining and metallurgical processing operations and project developers.

Outotec’s tailings technology solutions include equipment and services that are suitable for almost every tailings facility and can include thickened tailings, paste, including suitable piping and pumping. Furthermore, Outotec is at the forefront of dry stacking technology development and can also offer full turnkey backfill solutions extending to operation and maintenance set-ups.

Paste and dry stacking technologies combined with closed water loops are the best available technologies for conserving water and it is estimated that a Cu process located in a temperate zone uses around 0.9–0.6 m³/t ore, whereas a dry stacking system located in a temperate zone uses 0.2–0.15 m³/t ore. However, closing the loops may lead to process water challenges with impurities, reagents and fines being recycled within the production processes, which require suitable treatment that should be considered during the tailings solution design.

Material handling is an important part of tailings solutions. Centrifugal and positive displacement pumps are commonly used for tailings and thickened tailings, whereas paste requires special pump modules and high-pressure pipelines. The pipe and pumping considerations are related to the rheology of the material, whereas in dry stacking solutions, the landfilling and conveying is mainly dictated by the selection of TSF type, location and size.

Currently, conventional tailings dam breaches account for most of the environmental incidents related to extractive industries. The process of considering a suitable TSF starts with a comprehensive evaluation and full understanding of the site-environmental settings (geological, geotechnical, hydrological, hydrogeological, and hydro-chemical) and an integrated or holistic assessment framework should be used to screen scope and evaluate alternatives for the design, build, operation and closure of the TSF. TSF closure plays an important part in risk prevention and should include decommissioning, rehabilitation and performance monitoring for a required period of time.


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References/additional resourcesAustralian Government (2007), Department of Industry, Tourism and Resources Tailings Management – Leading Practice Sustainable Development Program for the Mining Industry Avalable at: http://www.industry.gov.au/resource/Documents/LPSDP/LPSDP-TailingsHandbook.pdf

Australian Centre for Geomechanics (2015) Paste and Thickened Tailings – A Guide 3rd Edition, Edit Jewell, R.J. and Fourie, A.B.

Australian National Committee on Large Dams Inc. (ANCOLD), www.ancold.org.au − Guidelines on tailings dams: Planning, design, construction, operations and closure (2012)

Bussiere (2004) Colloquium 2004: Hydrogeotechnical properties of hard rock tailings from metal mines and emerging geoenvironmental disposal approaches

Carvalho (2014) From a literature review to a framework for environmental process impact assessment index. J. Clean. Prod.

Driussi and Jansz (2006) Technological options for waste minimization in the mining industry. J. Clean. Prod.

Edraki (2013) Third International Seminar on Environmental Issues in Mining, Santiago, Chile.

Edraki (2014) Designing mine tailings for better environmental, social and economic outcomes: a review of alternative approaches. Journal of Cleaner Production.

Directive 2006/21/EC. Directive 2006/21/EC of the European parliament and of the council of 15 March 2006 on the management of waste from extractive industries and amending Directive 2004/35/EC. Official Journal of the European Union.

Fourie (2012) Perceived and realised benefits of paste and thickened tailings for surface deposition. Paste 2012. Australian Centre for Geomechanics, Perth, Australia.

Government of Western Australia (2015) Guide to the preparation of a design report for tailings storage facilities (TSFs) Available at: www.dmp.wa.gov.au/Documents/Safety/MSH_G_TSFs_PreparationDesignReport.pdf

IEPI&RP, 2015. Independent Expert Engineering Investigation and Review Panel. Report on Mount Polley Tailings Storage Facility Breach

Jansson, K.; Kauppi, J; Kotiranta, T.; Towards minimum impact Cu concentrator – A conceptual study, Materia: 4, 2014, 64–67.

Jansson K.; Kauppi, J.; Kotiranta, T.; Towards minimum impact Cu concentrator – A conceptual study; IMPC SUSTAINABILITY SYMPOSIUM, 2014, Santiago de Chile.

Kotiranta T.; Horn S.; Jansson K.; Reuter M.A.; Towards a “Minimum Impact” Copper Concentrator: A Sustainability Assessment, Procemin SYPHOSIUM, 2015, Santiago de Chile

Lindsay, 2015. The risk, public liability, & economics of tailings storage facility failures. Lindsay Newland Bowker & David M. Chambers

Mudd and Boger (2014) The ever growing case for paste and thickened tailings towards more sustainable mine waste management. Aust. Inst. Min. Metall. Bull.

Nagaraj, D.R. (2005) “Minerals Recovery and Processing” in Kirk-Othmer Encyclopedia of Chemical Technology, Wiley-VCH doi:10.1002/0471238961.1309140514010701.a01.pub2

Palmer, J.; Operational results and future trends of filtration technology in minerals processing, Paste Conference, 2015, Cairns, Australia.

Patel, K. (2015) ‘The importance of tailings management’ published in Industrial Minerals on Sept. 26, 2015, by Kasia Patel, North American Editor.

Ritcey (2005) Tailings management in gold plants. Hydrometallurgy.

For more informationFor more information, please contact [email protected] or the authors, [email protected], or [email protected]

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