S1_12_10_Xinyi_Wang_rev.pdf
Transcript of S1_12_10_Xinyi_Wang_rev.pdf
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GENERIC DECISION-MAKING ONRETREATING COPPER TAILINGS DAMS
Xinyi (Jessica) Wang (Presenter)Worleyparsons, Canada
John A. MeechNBK Institute of Mining Engineering, University of British Columbia, Canada
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• Physical Stability
Failure
Dust Issues
• Chemical Stability
Acid Rock Drainage
Heavy Metal Pollution
Background - Environmental and Social Concerns
Social Concerns:
Poor reputation of miningindustry
Close monitoring bypublic/aboriginals/ NGOs
Political pressure (local/global)
Regulation requirements
Source: http://www.tailings.info/merriespruit.htm
http://www.aadnc-aandc.gc.ca/eng/1100100026732/1100100026841
Dam Failure
Merriespruit Mine, Virginia, South AfricaDust - Colomac Mine
Yellowknife, NWT
ARD
Britannia Mine, BC
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Tailings Retreatment - Processes
Mining
• Hydraulic Mining
• Mechanical Excavation
Processing
• Grinding
• Heap leaching
• Tank leaching
• Flotation
• Flotation concentrate/tailings leaching
Disposal
• New surface impoundment
• Underground/open pit backfill
• Sub-marine/lake
Reclamation
• Water treatment plant
• Passive treatment
• Covers (water/dry covers)
• RevegetationSimplified Flowchart
of
Retreatment Method
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Tailings Retreatment—Why?
Investment opportunity
Revenue from metal extraction
Offset of rehabilitation costs
Failure prevention
Elimination of pollution remediation costs
Long-term liability reduction
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Tailings Retreatment ModelA Model to Assist Decision-making on Retreatment of Copper Tailings Dams.
How does the model work?•User input through questionnaire
•Data processed by model
•Generates a report
Model answers two questions:•Economic benefits
•Improvement in long-term liability
“Should you reprocess the tailings?”
Framework of the
Tailings Retreatment
Model
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Tailings Retreatment Model
Research Strategies:An Excel spreadsheet model including:
Mathematical calculation
Fuzzy logic system
Structure of Fuzzy Expert System
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Tailings Retreatment Model• Fuzzy Set
Definitions
Submarine Disposal
Site Characteristics
Poor Mod Good
Environmental
Sustainability
Low Low
Low
Low
Mod Low Mod Mod
High Low
Mod
High
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Design and Economic ModuleMass Balance
Capital and Operating Cost
NPV & DCFROR
Tonnage Rate Optimization
Flowsheet Selection
Sensitivity Analysis
Procedure for Flowsheet Selection
and Economic Analysis
A Project NPV @ 5% Copper Recovery Project
B Base Case PV @5%
Saving on Current Remediation Cost Plus
Avoidance of Future Failure Costs
C Total NPV @5% Sum of A & B
D Project NPV @10% Not Used
E DCFROR Not Used
Economic Terminology
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Flowsheet Alternatives1.Flotation (bulk)
2.Regrinding (coarse) + flotation
(bulk)
3.Flotation (bulk) + heap leachingof flotation tailings (new TSF)
4.Flotation (bulk) + tank leaching
of concentrate
5.Flotation (bulk) + heap leaching
of concentrate pile
6.Heap leaching (bulk)7.Heap leaching (coarse)
8.Agglomeration/heap leaching
(bulk)
9.Tank leaching (bulk)
10.Tank leaching + flotation
(leach residue)11.Regrinding (coarse) + tank
leaching (bulk)
Complete Copper Processing
Flowsheet – over 1,000 combos
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Design and Economic Module
Weibull Cumulative Failure Probability vs. Time
Base Case Economic Analysis - Future Failure Cost
5 year failure probability = 5%
Year of certain failure = 50
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Disposal and Reclamation ModuleAlternatives Definition
(Scoping) Site Characteristics
Option1 Option 2 Option n…....
Land
Disturbance
Cost Environment
& Stability
Alternatives Evaluation (Scoring and Ranking)
Tailings Characteristics
Local Climate
Topography
Social and Political
Acceptance
Weight Factors
INPUTS
Preferred Disposal and
Reclamation MethodsProcedure of Tailings Disposal and
Reclamation Selection Module
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Risk Assessment Module
•What canhappen?
HazardAssessment
•How likely is itto happen?
ExposureAssessment
•What are theconsequencesif it happens?
ConsequenceAssessment
•What is therisk of eachfailure mode?
RiskCharacterization
Identify Potential
Failure Modes
and Mechanisms
Risk Assessment Procedures
FAM Map
forRisk Characteristics
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Decision-Making Module
• Decision-Making Criteria: EconomicIssues
Social-Environment
al Issues
TechnicalIssues
Three Pillars of Decision-Making
on Tailings Retreatment
• Economic
Performance -
NPV
@5%
• Environmental
Performance- DoB
• Current Risk - DoB
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Validation and Verification• Four hypothetical cases
Element MINE A MINE B MINE C MINE DScale Large Large Medium Small
Grade, %Cu 0.12 0.18 0.12 0.18
Dust Problem No No Yes Yes
Dam Stability Poor Medium Poor OKEffluent pH >7 3-4.5 5-6 5-6
Acid Generation
PotentialHigh Medium Low Low
Remediation
Project WTP* None None None
Impact on
CommunityHigh High Medium Low
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Validation and VerificationModel Results
Cases
Economic
Benefit(NPV@5%)
Risk Factor
(DoB)
Environmental
Performance(DoB)
Retreatment
Recommendation(DoB)
Mine A $135,534,000 80 56 95
Mine B $177,315,000 67 88 95
Mine C $-13,135,000 66 85 24
Mine D
$10,808,000
18
84
43
Expected Results
Cases
Economic
Benefit
Current
Environmental and
Social Risk
Environmental
Performance
Retreatment
Recommendation
Mine A
Medium
High
Medium
High
Mine B Very-Good Medium to High High High
Mine C Very-Low Medium to High High Medium
Mine D Low Low High Medium
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Validation and Verification
• Project Economic Sensitivity Analysis
Cu Head Grade/Price Cap / Op Costs
MINE A -25% +40%
MINE B -28% >+50%*
MINE C +10% -15%
MINE D -8% +20%
Percentage of Change in Input Variable to Give a 0 NPV @5%
* Actually gives an NPV of $100M
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Conclusions & Recommendations
• The model is able to:• Conceptually design a tailings retreatment process
• Evaluate economic and environmental benefits
• Assist in multi-criteria decision-making
Further modules or rules for:
• Detailed mining method selection
• Unit processing operations selection
• Additional reclamation technologies User interface for modifying internal parameters
Practical “real” cases of copper tailings to be tested
C o n c l u s i o n
s
R e c o m m
e n d a t i o n s
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Questions?THANK YOU FOR YOUR ATTENTION!