The Need for a Comprehensive Methodology to Evaluate Tailings - - PowerPoint PPT Presentation

The Need for a Comprehensive Methodology to Evaluate Tailings Alternatives

Presenter: Aida Carneiro

Content

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What are Tailings? How can we dispose tailings? Reflections & Take-home lesson

What are Tailings?

• Material left over after the mineral processing operation
• Ground rock + process effluents
• Retaining structures or
• r in the form of piles (dry stacks )
• No financial gain
• Most cost effective (regulations and site specific factors)
• One of the largest elements of risk management and cost for a mine (Kerr and Ulrich, 2011)

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What are Tailings?

THE MINE PRODUCTION CYCLE

Run-of-mine (ROM) Mineral Processing Plant Tailings Concentrate Tailings Storage Facilities (TSFs) Slurry Tailings Thickened Tailings Filtered Tailings Paste Tailings

Increase realised benefits & increase costs???

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Common Alternative Options for Surface Tailings Disposal

Source: Taguchi, 2014

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Conventional Slurry Tailings

• < 45% solids
• Surface retaining structure
• Aim of reclaiming the water for use in the processing plant as required
• Two types of surface impoundments
• Water retention type dam
• Raised embankment

Upstream Downstream Centreline

Source: http://www.mining-technology.com/projects/highland/highland5.html

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Conventional Slurry Tailings

Source: Taguchi, 2014

7 Embankment

Thickened Tailings

• 45% < % solids < 65%
• Mechanical process of dewatering low solids concentrated slurry
• Homogeneous non-segregated mass upon deposition
• The idea is to stack the pulp to form a self supporting conical pile

reduced height and retention forces of the embankments

• Higher operating costs (dewatering)

Source: http://www.tailings.info/disposal/thickened.htm

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Paste Tailings

• 65% < % solids < 70%
• High rate and deep cone thickeners
• Flocculants and coagulants
• Tailings significantly dewatered
• do not segregate
• produce minimal bleed water when discharged
• Paste deposited to form a conical pile
• Layers of paste cease to flow desiccation cracks new layer

Source: http://www.tailings.info/disposal/paste.htm

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Source: http://www.srk.co.za/files/File/South- Africa/publicDocuments/Royal_Bafokeng_Styldrif/Nov2015/Appendi ces/Appendix_Q_Design_Docs.pdf

Filtered Tailings

• >70% solids (80% < % solids < 85% )
• Vacuum or pressure filtration
• Not transported by pipeline (MC < 20%)
• Conveyor or truck placed spread compacted
• Stable deposit (no em bankment for retention)
• High capital and operating costs

Mechanical dewatering process Costs

Source: http://www.tailings.info/disposal/drystack.htm Source: Cooling, 2015

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self-supporting tailings stack

Major Challenges

• Water Scarcity
• Regulations
• Risk of Failure
• Valuation Methods used for Long-term Projects (Net Present Value)

Drivers for a holistic approach to evaluate tailings alternatives

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Water Scarcity

• Water Issues
• High-level pressure regarding water usage
• Handling water: arid and cold regions
• Limitation of water supply (conflict mining x agriculture)
• Pumping water for long distances
• Water = Costs
• Pipe and Pump
• Purchase of water rights
• Establishment of bore fields
• Government usage or license fees

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Regulations

• Environmental regulations are increasing pressure placed on mining
• Tailings disposal practice is firmly on the regulatory and public agendas
• Environmental management = key variable in the business
• Environmental quality standards and technology to protect the

environment

• Public awareness about environmental issues (Social License to Operate)

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Risk of Failure

• Failures = breaching of the containing embankment structure

contamination of groundwater

• Small pond = reduced potential for water to transport large volumes of tailings

According to Taguchi, 2014:

• Dewatered tailings have lower likelihoods of failure
• The likelihood of tailings release from dewatered facilities is

about 65% less

Source: Taguchi, 2014

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Probability of Occurrence

Risk of Failure

Village of Bento Rodrigues

15 years Agreement US$1.7 Billion for the next 6 years depending on the remediation and compensation projects

Clean-up Costs

Source: http://www.abc.net.au/news/2016-02-29/bhp-samarco- dam-collapse-brazil-linked-to-ramping-up-production/7201022

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32,000,000 m3

Valuation Methods used for Long-term Projects (e.g. NPV)

Ct = $1,000,000

r = 7% ( d i s c o u n t r a t e s u s e d b y m i n i n g e n t i t i e s f o r c l o s u r e a n d r e h a b i l i t a t i o n c o s t s ) t = 30 years NPV = $140,000

Discounted Costs for Closure and Rehabilitation

$140,000

$1,000,000

NPV = Cash Inflows - Cash Outflows

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Valuation Methods used for long-term Projects (e.g. NPV)

Drawbacks of

• f NPV:
• Future remediation costs are substantial (under-emphasised)
• Pressure to maximise shareholder value (profits in the short term)

17 High density tailings disposal methods Additional initial capital expenditure Disfavored due to continued managerial emphasis on deferring expenditure

Realised Benefits of Dewatered Tailings Disposal

• Water recovery
• Less losses with seepage, interstitial water, and evaporation
• Cost savings (make-up water and reagents)
• Decreased land footprint
• Progressive rehabilitation (spreading the cost of closure over a longer time period)
• Lower reclamation and closure costs (reduced footprint and stable surface )
• Mitigated risks of catastrophic failure and tailings runout

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Reflection

• Non-monetary benefits should be taking into account
• Integrated tailings management
• Dewatered tailings have addressed many environmental problems
• Avoid some valuation methods
• Adoption of tailings options resulting in sustainable long-term benefits
• Sustainability = Economic impact + environmental burden + social indicators = sustainable objectives into

reality

Effective tailings management lies at the heart of creating a sustainable mining industry

Technical Environmental Risks Economic Social

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Questions?

THANK YOU!