S1_12_10_Xinyi_Wang_rev.pdf

8/9/2019 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!

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