February 2015

Assessing options for tailings management

  • By Cary Ehrman, Principal Environmental Scientist, Golder Associates

Effective evaluation of tailings management options is essential to delivering the best practice environmental outcomes at lowest cost.

Mining projects worldwide are facing unprecedented scrutiny and demands from investors, regulators, communities and stakeholders. The ability to understand and assess environmental, social, economic and technical risks and opportunities during planning and design has become essential for the success of a project.

When assessing options for tailings management, companies have historically drawn upon a wealth of experience and had an economic and technical emphasis. Frequently, preferred options are selected based on an informal assessment of pros and cons, with no clear record for future reference of the processes involved in coming to a decision. Often these assessments do not take into account the trade-offs or balance between competing objectives and stakeholder drivers, or document that the most sustainable approach was selected.

Use of a decision support tool, such as GoldSET, provides a comprehensive solution by embedding sustainability into options analysis. Inspired by ISO 26000 on Corporate Social Responsibility and international best practices on environmental stewardship and social responsibility, GoldSET is a customisable and web-based, multi-criteria analysis tool that:

  • Structures the decision process
  • Supports proactive client and stakeholder engagement
  • Compares performance, allowing companies to optimise solutions
  • Visually communicates performance and benefits.

Project options are assessed by scoring performance indicators, which GoldSET then aggregates by dimension, based on their relative ranks and weight. Results are presented in a visual diagram that illustrates the strength and weaknesses of each option.

GoldSET uses a five-step process:

1. Project description

The user ‘sets the scene’ and identifies the context in which the project and decision-making are taking place. Objectives of the project are established and the assessment is tailored to site conditions.

2. Options development

Suitable options that may meet project objectives are identified. These options will then be assessed from an economic, social and environmental perspective. Additional information is included to describe the option’s suitability in meeting the physical site constraints. The user can also undertake a fatal flaw analysis of the options using a screening module that assesses whether an option meets overall minimal requirements.

3. Indicator selection

Environmental, social, economic and technical indicators are project-specific and developed in consultation with the client and nominated stakeholders. Both qualitative and quantitative indicators can be used. GoldSET allows for a tailored weighting scheme to be used. Weighting of indicators is typically based on the likely impact of the project outcome on that issue; the higher the impact, the more weight that can be assigned to a given indicator.

4. Scoring of indicators

GoldSET calculates the aggregate score for each option and compares its performance across the three dimensions of sustainable development (environmental, social and economic).

5. Interpretation and decision-making

The graphical and numerical results are presented as a visual diagram illustrating the strengths and weaknesses of each option with regard to environmental, social and economic indicators (Figure 1).

Screen Shot 2015-02-02 at 4.13.09 pm

The best approach from a sustainability standpoint is depicted as:

  • The biggest triangle
  • Highest performance in each dimension
  • Balanced performance between all dimensions.

The evaluation process is iterative by nature and further refining can be accomplished as additional information becomes available. This visual diagram further allows one to easily see where alternatives are underperforming so options can be ‘tweaked’ to perform better in key areas.

GoldSET can also be run using a fourth dimension that incorporates assessment of the technical performance of the alternatives. This aspect accounts for the various phases in the lifecycle of a project, including planning/permitting, design, construction, operation/maintenance/monitoring and decommissioning.

Indicators representing the technical aspect of a project can relate to:

  • Option design complexity
  • Reliability
  • Flexibility and efficiency of the option
  • Impact to other processes
  • Risk management.

When incorporating technical performance, the visual diagram is depicted as a diamond rather than a triangle (Figure 2).

Screen Shot 2015-02-02 at 4.13.01 pm

The GoldSET approach can be illustrated by evaluating options for management of tailings:

1. Conventional slurry

The unconsolidated, low density of the conventional slurry may limit the ability to control seepage and impact on groundwater. This option may not perform as well in the environmental aspect, but would receive higher scores for technical ease and low cost.

2. Slurry discharge with polymer addition to accelerate water removal

The addition of the polymer to the slurry could improve the ability to separate the water from the tailings and offer recycling of water back to the process plant. This could improve environmental performance, but also steepen the beach slope, making it more difficult to fill the facility.

3. Thickened paste tailings discharge

With thickened tailings, some of the control measures that increase cost could be avoided. However, the removal of water and mechanically depositing tailings increases cost. A solution for water disposal would also be required.

4. Thickened paste with chemical addition to immobilise contaminants

With the addition of chemicals to thickened tailings, it may be possible to further reduce free water and contaminant mobility.

The above four options offer varying levels of water consumption and present different operational challenges, technical risks, capital and operating costs. The GoldSET module for Tailings Technology Selection provides a comprehensive framework to support the evaluation of options for managing large-scale mining wastes – including tailings – from design to closure.

Case study

GoldSET was used to assess tailings management options at Mine ‘X’ during the pre-feasibility stage. The objective of the study was to provide a detailed assessment of both process technologies and deposition layout options to identify a sustainable solution for tailings management over the long term.

At Mine ‘X’, a first-run assessed five process technologies comprising:

  • Filter cake
  • Paste
  • Slurry
  • Slurry with cyclone and thickened tailings.

Evaluation indicators included each of the four sustainability dimensions:

  • Environmental indicators were selected to assess the footprint and amount of clearing, habitat impacts, watershed and stream diversion
  • Social indicators assessed distance from a drinking water source, distance to residences, tourist activities and infrastructure; impacts to traditional land use and presence of a cultural heritage asset; land tenure; and visual impacts
  • Economic indicators assessed claims and surface rights, dam volume, expansion possibilities, financial consequences of a dam failure, pipeline length or hauling distance; and site surface area (liner, cover)
  • Technical indicators were selected to assess reliability verses complexity, including such areas as conflict with other industrial activities, design complexity, flexibility of system, project-level confidence and perception of overall risk, reliability of system, along with site accessibility and adaptability.
  • The technical dimension was further broken down into sub-systems of the design, comprising cover system, dewatering and transport, reactivity of tailings deposit, tailings deposit and dam stability; and tailings storage and flood water storage capacity.

The indicators were weighted with the client, other consultants working on the project and stakeholders through workshops, questionnaires sent to affected communities and in consultation with traditional landowners and regulators.

A second run was undertaken to assess six deposition scenarios based on the most appropriate process technology that was identified in the first run. Running the assessment for both the process technologies and the deposition options allowed for comparison of 30 different scenarios.

The most sustainable option fortailings management was identified, combining both a process technology and deposition layout. The graphic outputs of GoldSET were instrumental in communicating the overall impacts and benefits associated with each scenario to stakeholders and supported rigorous and transparent decision-making by the client.

This process was also in line with International Council on Mining and Metals’s Sustainable Development Principles, which seek to integrate sustainable development considerations within the corporate decision-making process.

Conclusion

The ability to understand and assess the environmental, social, economic and technical risks and opportunities during project planning and design – in a transparent fashion – is fast becoming essential to the success of a project.

Site-specific factors such as the nature and volume of tailings, depositional methods, environmental performance, financial considerations and social acceptance make the process of selecting the most favourable option a challenge.

A decision support tool such as GoldSET can be used to assist in this challenge and illustrate and balance whether the option is technically feasible, the degree to which your environmental compliance and social license criteria can be met and the cost of building and operating the system.

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