Remining Old Tailings Dams
John A. Meech and Jessica Xing Ye Wang
The University of British Columbia
The Norman B. Keevil Institute
of Mining Engineering
Vancouver, British Columbia
2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITION
SHECHTMAN INTERNATIONAL SYMPOSIUM
Outline
Background
Tailings Retreatment
Tailings Retreatment Model
– Design and Economic Module
– Disposal and Reclamation Module
– Risk Assessment Module
– Decision-Making Module
Validation and Verification
Conclusions and Recommendations
2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITION
SHECHTMAN INTERNATIONAL SYMPOSIUM
Issues with Old Tailings Dams
Stability (slopes, erosion, chemicals)
Aquatic Emissions (acid, metals)
Atmospheric Emissions (toxic gases, mercury)
Dust releases
Dam failures
High-grades of values
Revegetation and reclamation
2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITION
SHECHTMAN INTERNATIONAL SYMPOSIUM
Environmental & Social Concerns
• Physical Stability
•
 Failure
 Dust Issues
Chemical Stability
 Acid Rock Drainage
 Metal Pollution
Dam Failure - 1994
Merriespruit Mine, South Africa
Sources: http://www.tailings.info/merriespruit.htm
• Social Concerns:
 Poor reputation of mining
 Close monitoring by
public/aboriginals/ NGOs
 Political pressure (local/global)
 Regulation requirements
Dust - Colomac Mine
Yellowknife, NWT
ARD
Britannia Mine, BC
http://www.aadnc-aandc.gc.ca/eng/1100100026732/1100100026841
Tailings Retreatment Processes
Mining
Processing
Disposal
Reclamation
• Hydraulic Mining
• Mechanical Excavation
• Grinding
• Heap leaching
• Tank leaching
• Flotation
• Flotation concentrate/tailings
leaching
• New surface impoundment
• Underground/open pit backfill
• Sub-marine/lake
• Water treatment plant
• Passive treatment
• Covers (water/dry covers)
• Revegetation
Simplified Flowchart
of
Retreatment Method
Tailings Retreatment
 Investment opportunity
 Revenue from metal extraction
 Offset of rehabilitation costs
 Dam Failure prevention
 Elimination of pollution remediation costs
 Long-term liability reduction
2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITION
SHECHTMAN INTERNATIONAL SYMPOSIUM
Tailings Retreatment Model
A Model to Assist Decision-making on Retreatment of Copper Tailings Dams
Model addresses two issues:
• Economic benefits
• Improvements in long-term liability
“Should you reprocess the tailings?”
How does it work?
• Input via a set of questionnaires
• Data processed by model
• Generates a report
Framework of the
Tailings
Retreatment Model
Tailings Retreatment Model
An Excel spreadsheet model including:
 Mathematical calculations
 Fuzzy Logic Rule-based System
2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITION
SHECHTMAN INTERNATIONAL SYMPOSIUM
Tailings Retreatment Model
Fuzzy Sets
Rule Base
Fuzzy Associative Memories
Site Characteristics
Submarine Disposal
Poor
Mod
Good
Low
Low
Low
Low
Mod
Low
Mod
Mod
High
Low
Mod
High
Environmental
Sustainability
Weighted-Inference Method Defuzzification Method
a
DoB
  W * DoB
conc
i
i
i 1

z
m
i 1
[ DoB( zi ) * Sup( zi )]

m
i 1
DoB( zi )
DoB = Degree of Belief (0-100) and Sup = Supremum
Design and Economic Module
Mass Balance
Economic Criteria
Capital and Operating Cost
NPV & DCFROR
Tonnage Rate Optimization
A Project NPV @ 5%
Copper Recovery Project
Saving on Current Remediation Cost
B Base Case PV @5% and Avoidance of Future Failure Costs
C Total NPV @5%
Sum of A & B
Flowsheet Selection
D Project NPV @10% Not Used
Sensitivity Analysis
Procedure for Flowsheet
Selection and Economic Analysis
E DCFROR
Not Used
Flowsheet Alternatives
- Excavation or Monitor Mining
- Grinding coarse or bulk
1. Flotation (bulk)
2. Regrinding (coarse) + Flotation
(bulk)
3. Flotation (bulk) + heap leaching
flotation tailings
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 of
leach residue
11. Regrinding (coarse) + Tank
leaching (bulk)
Complete Retreatment Flowsheet –
over 1,000 combos
Flowsheet Alternatives
- Excavation or Monitor Mining
- Grinding coarse or bulk
1. Flotation (bulk)
2. Regrinding (coarse) + Flotation
(bulk)
3. Flotation (bulk) + heap leaching
flotation tailings
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 of
leach residue
11. Regrinding (coarse) + Tank
leaching (bulk)
Complete Retreatment Flowsheet –
over 1,000 combos
Flowsheet Alternatives
- Excavation or Monitor Mining
- Grinding coarse or bulk
1. Flotation (bulk)
2. Regrinding (coarse) + Flotation
(bulk)
3. Flotation (bulk) + heap leaching
flotation tailings
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 of
leach residue
11. Regrinding (coarse) + Tank
leaching (bulk)
Complete Retreatment Flowsheet –
over 1,000 combos
Flowsheet Alternatives
- Excavation or Monitor Mining
- Grinding coarse or bulk
1. Flotation (bulk)
2. Regrinding (coarse) + Flotation
(bulk)
3. Flotation (bulk) + heap leaching
flotation tailings
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 of
leach residue
11. Regrinding (coarse) + Tank
leaching (bulk)
Complete Retreatment Flowsheet –
over 1,000 combos
Flowsheet Alternatives
- Excavation or Monitor Mining
- Grinding coarse or bulk
1. Flotation (bulk)
2. Regrinding (coarse) + Flotation
(bulk)
3. Flotation (bulk) + heap leaching
flotation tailings
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 of
leach residue
11. Regrinding (coarse) + Tank
leaching (bulk)
Complete Retreatment Flowsheet –
over 1,000 combos
Design and Economic Module
Base Case Economic Analysis - Future Failure Cost
5 year failure probability = 5%
Year of certain failure = 50
Weibull Cumulative Failure Probability vs. Time
Disposal & Reclamation Module
INPUTS
Alternatives Definition
(Scoping)
Site Characteristics
Tailings Characteristics
Option 2
Option1
…....
Option n
Local Climate
Topography
Land
Disturbance
Cost
Environment
& Stability
Alternatives Evaluation (Scoring and Ranking)
Preferred Disposal and
Reclamation Methods
Social and Political
Acceptance
Weight Factors
Tailings Disposal and Reclamation
Selection Module
Disposal & Reclamation Module
Risk Assessment Module
Identify Potential
Failure Modes
and Mechanisms
FAM Map
for
Risk Characteristics
What can
happen?
Hazard
Assessment
Exposure
Assessment
How likely is
it to happen?
What are the
consequences
if it happens?
Consequence
Assessment
Risk
Characterization
What is the risk
of each failure
mode?
Risk Assessment Module
Hierarchy of
the Risk
Assessment
Module
Decision-Making Module
• Decision-Making Criteria:
• Economic
Performance
Economic
Issues
=
NPV
@5%
• Environmental
Performance
=
DoB
• Current Risk
=
DoB
Technical
Issues
SocialEnviron
mental
Issues
Three Pillars of Decision-Making
about Tailings Retreatment
Validation and Verification
Four hypothetical cases
Element
Scale
Grade, %Cu
Dust Problem
Dam Stability
Effluent pH
Acid Generation
Potential
Remediation
Project
Impact on
Community
MINE A
Large
0.12
No
Poor
>7
MINE B
Large
0.18
No
Medium
3-4.5
MINE C
Medium
0.12
Yes
Poor
5-6
MINE D
Small
0.18
Yes
OK
5-6
High
Medium
Low
Low
WTP
None
None
None
High
High
Medium
Low
Validation and Verification
Model Results
Environmental
Risk Factor
Performance
(DoB)
(DoB)
Cases
Economic
Benefit
(NPV@5%)
Retreatment
Recommendation
(DoB)
Mine A
$135.5 M
80
56
95
Mine B
Mine C
Mine D
$177.3 M
$ -13.1 M
$ 10.8 M
67
66
18
Expected Results
88
85
84
95
24
43
Cases
Economic
Benefit
Current
Environmental and
Social Risk
Environmental
Performance
Retreatment
Recommendation
Mine A
Mine B
Mine C
Mine D
Medium
Very-Good
Very-Low
Low
High
Medium to High
Medium to High
Low
Medium
High
High
High
High
High
Medium
Medium
Validation and Verification
Project Economic Sensitivity Analysis
Percent Change in Input Variable to Yield an NPV @5% = 0.0
Cu Head Grade or Price
Capital or Operating Costs
MINE A
-25%
+40%
MINE B
-28%
>+50%*
MINE C
+10%
-15%
MINE D
-8%
+20%
* Actually gives an NPV of $100M
2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITION
SHECHTMAN INTERNATIONAL SYMPOSIUM
Recommendations
Conclusions
Conclusions
• 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 to enter or modify internal parameters
Practical "real" cases of copper tailings to be tested
2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITION
SHECHTMAN INTERNATIONAL SYMPOSIUM
THANK YOU FOR LISTENING!
Questions?
2014 SUSTAINABLE INDUSTRIAL PROCESSING SUMMIT AND EXHIBITION
SHECHTMAN INTERNATIONAL SYMPOSIUM