demonstrating successful operational and closure

Integrated Mine Waste Management and Closure Services

Specialists in Geochemistry and Unsaturated Zone Hydrology

Demonstrating Successful Operational and Closure Strategies for Waste Rock Storage Facilities – Building Better Dumps

May 2018

O’Kane Consultants and Earth Systems





The Issue

• The cost of Closure is rising rapidly, worldwide.

• The ability to successfully close a site is decreasing rapidly.

• Stranded liabilities are increasing due to poor Closure outcomes .

• Bonding for Closure has become part of Permitting.

• Investors are increasingly considering the impacts of closure liabilities.

• The costs of closure bonds are increasing as community and regulator expectations are continuing to rise.

• Almost all recalcitrant Closure issues are water quality related, and virtually all of these are ARD / AMD related.

• Another key indicator of the lack of Closure success is the trend toward “treatment in perpetuity”.

• Treatment in perpetuity is not acceptable to some stakeholders, particularly as the legacy of unmanageable sludge issues become more evident.

• If we are to address the Closure Issue – what do we focus on?

• What are the key AMD issues and how to we address them?



Key Discussion Points

1. “Building Better Dumps” is a concept that speaksto issues around Mine Closure…

– The “Solution” to the Issues…

• Involves multiple technologiesand methodologies; and

• Is entirely site-specific.

– The scale of a site’s liability is defined andvalued on a site-specific basis

– Sites manage liability in different ways

– Progressive Rehabilitation / Closure is a“best practice” concept that jurisdictionsdefine differently.

Site A – Liability?

Site B – Liability?



Key Discussion Points

2. Waste Rock Dumps (WRDs) are the large percentage ofthe source of pollution at mine sites.

– We will provide information on this point

3. Seepage from WRDs, particularly its water quality,commonly results in unfunded and unrecognized liabilityfor operators, owners, stakeholders.

– Liability indicates a project’s economicsnot being as optimized as first thought

4. There are a number of technologies / methodologies available, which can be implemented during waste placement, to build a “Better Dump”.

– We will summarize and define these technologies / methodologies (tools)

– The proposed metric for evaluating these tools, in terms of building a “Better Dump” is the mass of stored acidity generated within the WRD during operations and closure.

5. Can building a “Better Dump” represent an opportunity to manageliability and better define / implement the concept ofProgressive Rehabilitation / Closure?



ML-ARD / AMD Quiz

• Each mine site has multiple ML-ARD / AMD Generating Domains(i.e. potentially long term pollution sources).

– With limited resources, what should INAP Member Companies focus on?

– What is the pollution % from each domain?

– What is the relative importance of:

• Climate

• Sulfide content

• Grainsize / surface area

• Air entry

• Moisture content

• Oxygen concentration

• Tonnages

• Void surface area

• Bacterial activity0

2

4

6

8

10

12

14

0 2 4 6 8 10 12

PO

R (

wt.

%/y

r Fe

S 2)

Average Particle Size (mm)

Pyrite Oxidation Rate (POR) vs particle size (Waste Rock)



Polluting Domains at a Mine Site

• Primary ML-ARD / AMD generating domains include:

– Waste rock dumps;

– Tailings storage facilities;

– Wallrock (pit and underground mine voids);

– Heap leach pads;

– Ore stockpiles;

– Most ML-ARD / AMD from underground mines is derived from wasterock left in the mine to facilitate mining.

• Acidity load studies conducted over many years at multiple siteshave demonstrated that 60-80 % of all pollution (acidity) is derived fromwaste rock materials.

• Relative to waste rock, tailings materials are almost invariably moresulfidic, much finer grained and are therefore far more reactive thanwaste rock materials – how can they generate less acidity?

• Rapid pore gas oxygen depletion and diffusion controlled oxygenresupply means that tailings materials are so reactive that they areroutinely self limiting in their acidity generation capacity.



TSFs vs WRDs

• TSFs (generally):

– Finer-textured;

– Lower air flow capacity(gas diffusion dominated system)

– Near surface dominated gas flow characteristics



TSFs vs WRDs

• WRDs (generally):

– Coarser-textured;

– Higher air flow capacity(gas advection dominated system)

– Interior and near surface gas flow characteristics

• TSFs (generally):

– Finer-textured;

– Lower air flow capacity(gas diffusion dominated system)

– Near surface dominated gas flow characteristics



Behaviour of Waste Rock Materials

• Sulfide oxidation within waste rock materials initially produces highly soluble acidic salts.

• Saturation pH values are commonly <3.0 for such salts.

• These acidic salts are rapidly dissolved, and can be potentially flushed from end-dumped waste rock materials, even at low pore-water seepage rates.

• Subordinate secondary salts can be generated by reaction between acid water and some (potassic) waste rock materials – jarosite type salts. Silicate neutralisation and acidity storage.

• Jarosite type salts display a relatively very low solubility and have a saturation pH of 3.8-4.2.

• Melanterite type salts are the primary pollutants until most sulfides have been depleted.

• Stopping sulfide oxidation will stop the formation of both types of salts.

• Controlling sulfide oxidation is principally an oxygen control process (i.e gas transport; advection and diffusion).

• Gas transport during waste placement (i.e. oxygen control during waste placement) is strongly influenced by site-specific considerations (including cost!), and can be achieved via informed geotechnical construction practices; this can be further enhanced with simple but strategic geochemical placement of waste materials.

• Waste Rock generates the majority of pollution from mine sites – generally 60-80 wt.% of acidity loads.



Potential INAP Project

• We believe that a new INAP project, focusing on building waste rock dumps (WRDs) “better” is a critical step forward for the industry and needs to be the “new norm”.

• If this is of interest to INAP members, then a detailed proposal can be developed.

• “Solving tomorrow’s problems today” is a key consideration of this proposal, which will substantially lower closure costs and avoid long-term liabilities associated with treatment in perpetuity.

• This project represents an opportunity to muchmore effectively define, and implement,“progressive mine rehabilitation / closure”

Almost 50% of the mining companies surveyed are treating

in perpetuity.



Purpose & Context of Proposed Project

• Introduce and demonstrate “Best Practicable” commercial scale methods for reducing contaminant loads from proposed (greenfield) and existing (brownfield) WRDs as a progressive closure plan to all INAP Member companies.

• “Best Practicable” must consider site-specific costs versus site-specific benefits.

• Methods include established, new and emerging techniques for controlling ARD / AMD.

• Methods incorporate both geotechnical and geochemical approaches to control ARD / AMD. This combination is vital.

• Key ARD / AMD management aspects include:

– Air entry control (physical) – managing lift height and internal WRD air-flow capacity;

– Air entry control (chemical) – NAF materials for pre-emptive oxygen consumption;

– Optimise moisture retention to lower air entry and maximise carbonate and silicate neutralisation;

– Passivate sulfide grains to prevent oxidation;

– Net percolation control;

– Alkaline blending (neutralisation and sulfide oxidation rate control).



Established and Emerging Strategies

1. Managing waste placement lift heights and internal WRD air-flow capacity to limit advective gas transport:

• For example, thin lift, base-up dump construction (or Base-Up, Layered and Compacted dumps (BULC)), created by paddock dumping and compacted to limit air entry and optimise moisture retention and silicate neutralisation.

2. Strategic installation of multiple, thin oxygen consuming layers within evolving waste rock dumps. Incorporated into BULC dumps or end dumped waste rock piles. Oxygen consuming materials can include any sulfide bearing NAF materials.

3. Encapsulation of PAF materials with low permeability (e.g. high moisture content) NAF material to retard air entry. Multiple layers can be (progressively) installed.

4. Interim covers on top of lifts that encourage water retention such that vertical air-flow capacity is reduced. These interim covers can be combined with other control methods throughout the construction life.

5. Alkalinity generating materials at the top of waste rock piles can lead to the passivation of pyrite. This design will rapidly release sufficient alkalinity to facilitate a progressively deepening pyrite passivation front below the cover system.

There are approximately 5 fundamentally important, established and emerging waste rock construction methods aimed at lowering or preventing ARD / AMD, with geotechnical & geochemical components.



Established and Emerging

ARD/AMD Strategies

Paddock dump, compaction into thin lift and encapsulation.



Passivation with alkalinity producing layers

Established and Emerging

ARD/AMD Strategies



Established and Emerging ARD/AMD Strategies

– Reduce Segregation and Manage Vertical Gas Transport



Proposed Work Program

• Phase 1:

– Review and Summary of Technologies /Methodologies.

• Phase 2:

– Choose Sites and Design Demonstrations and/orEvaluate a Site’s Existing WRD data.

• Phase 3:

– Field Scale Technology / MethodologyDemonstrations.

• Phase 4:

– Develop a WRD Construction Guidance Document and Decision Tree Tool.



Proposed Work Program – Phase 1

PHASE 1 – REVIEW & SUMMARY OF TECHNOLOGIES

The purpose is review and summarise the (5) key technologies that are available for improving the construction of WRD, including an assessment of the physicochemical conditions that optimise their commercial viability.

• Description of the predicted (conceptual) benefits of each technology.

• Literature review on sites that have implemented such methods (eg. air entry control, oxygen consumption, sulfide passivation or net percolation control) to lower ARD / AMD generation from waste rock materials.

• Assessment of current benefits of each technology based on the literature review.

• Failure modes assessment for each technology to communicate wider opportunities for commercial applications.

• Key output will be a Technology Review Document providing a summary (1-3 pages) for each technology, listing the potential risks and opportunities for successful implementation.




PHASE 2 (OPTION 1) – CHOOSE SITES AND DESIGN DEMONSTRATIONS

• Ideally, each INAP Member Company could nominate a demonstration site for Phase 3 works.

• Demonstrations would involve the installation of one baseline WRD and ?five technology demonstration WRDs at each site.

• Ideally, the chosen sites (from various companies) should include a variety of commodities, mineralisation styles, physical and geochemical material characteristics, topographies and climates.

• Develop detailed (generic) demonstration WRD designs to demonstrate each individual technology (not combined) at agreed INAP Member sites. In this way, the benefit of ‘identical’ thin-lift, base up designs, for example, will be assessed at multiple sites.

• Develop detailed monitoring, sampling and analytical protocols for the demonstration testwork.




PHASE 2 – (OPTION 2) CHOOSE SITES AND DESIGN DEMONSTRATIONS and/or Evaluating a Site’s Existing WRD Data

This output will be specific to a site’s WRDs.

• Is there a solution, using the different technologies / methodologies that a site can manage liability for current WRDs… and also Future WRDs at the site.

• A site’s existing WRDs and future WRDs (built “better”) could be monitored to evaluate and compare site-specific commercial scale performance

• Ideally, the chosen sites (from various companies) should include a variety of commodities, mineralisation styles, physical and geochemical material characteristics, topographies and climates.

• Develop detailed monitoring, sampling and analytical protocols for the demonstration testwork.




PHASE 3 – FIELD SCALE TECHNOLOGY DEMONSTRATIONS

The key output will be a report documenting and assessing the merits of each of the WRD construction technologies.

• INAP Member companies to establish six prototype-scale demonstration piles at their nominated sites.

• Conduct pore gas and seepage water quality monitoring for the duration of the demonstration program.

• INAP to collate and review data, and provide a summary report assessing the benefits of each of the five technology approaches at each site.

• Reports will include data summaries from each site.

• The report will also identify the optimum waste rock closure strategy for each individual demonstration site, which will likely include one or more technologies.




PHASE 4 – WRD CONSTRUCTION GUIDANCE DOCUMENT

• Based on the results of the WRD demonstrations at multiple sites, develop an INAP Waste Rock Construction Guidance document, possibly incorporating a Decision Tree Tool to facilitate evaluation of the optimum technology(ies) for commercial scale application at all INAP Member sites.



Moving Forward

• INAP Management is seeking feedback from its Member Companies as to their interest in supporting this proposal.



A few Additional Thoughts

• Where is this work going….???

• Is it moving towards calculating a “value”, or in essence higher, or lower, “negative value” in relation to mine effluent collection and treatment, and

• in the context of whatever economic evaluation tool is chosen

– NPV (a cash flow approach)

– IRR (investment profitability approach)

– Project liability

• Can we utilize this basic concept to communicate, in general, “value” when applying the different proposed methodologies / technologies?

• Because, we are taking, for example Code #3 material, and reducing its risk by building the WRD “better”.




www.ktunaxa.org



A few Additional Thoughts… This is More than Changing its Name

www.ktunaxa.org

Almost 50% of the mining companies

surveyed are treating in perpetuity.



Contact Details

Dr Jeff Taylor - Director

[email protected]

Phone: +61-402 158 682

www.acidmetalliferousdrainage.com

www.earthsystems.com.au

www.earthsystemswater.com

www.esanalytical.com

Mike O’Kane, P.Eng.

[email protected]

Phone: +1 403 660 4489

www.okc-sk.com



demonstrating successful operational and closure

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