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Design and Operation of
Heap Leach Pads
By:
John F. Lupo, Ph.D.
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Purpose of Presentation
Summarize advancements made inthe design and operation of heap
leach pads:
Design and construction of leach
pads and working with operations
over the last 20 years
Working with difficult ore material
types (saprolite, laterite,
agglomerated ore, etc)
Construction and operational
problems in harsh environments
(high rainfall, freezing temperatures,
heat, etc).
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Subset of Topics Covered
Leach Pad Configuration
Liner System Design
Ore Properties TestingOperational Considerations
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Leach Pad Configuration
General Overview
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Leach Pad Configuration
Pad Configuration Types:
Dedicated, single use pad (standardleach pad)
On/Off or Reusable Pad
Valley FillHybrid
Considerations:
Ore material properties (leachingcharacteristics, durability, etc.)
Water balance
Land availability and ground slope
Project cost (capital and operating)
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Single Use Pad
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On/Off Pad
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On/Off Pad
Suitable for ore with short leach cyclesand consistent leaching characteristics.
Areas with limited flat terrain.
Requires a rinsed ore site/pad.
Durable high-stress liner system.
Practiced in wide range of climateconditions.
Smaller storm pond.
Costs: double handling of ore, rinsingsystem, rinsed ore storage.
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Valley Fill Pad
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Hybrid Pads
Combination dedicated, single use padwith partial internal solution storage
Single use pad combined with on/off padValley fill pad with a portion used as an
on/off pad
Side-hill leach padsDump leach (no liner)
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Liner System Design
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Liner Design Advancements
Experience with geosynthetics underhigh loads and harsh conditions
Operation of heap leach pads withsignificant ore loads (+130 m)
Construction and operation of very
large leach pads (+ 1.5 billion tonnesand covering 10 km2 across varyingfoundation materials)
Solution collection pipe performanceunder high ore load
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Liner Design Components
Foundation materials
Underliner soils
Geomembrane liner Overliner materials (drainage and/or
protection layers)
Solution collection/air injection piping
Not
normally
considered
liner
design
Strong interaction between each
component and the overall system.
Construction Quality Assurance
program needed to achieve goodliner performance
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Typical Single Composite Liner
Overliner Layer:
-Drainage/protectionlayers
-Solution collection
pipes
-Air injection pipes
Geomembrane
Underliner
Foundation
Ore
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Typical Double Composite Liner
Secondary
Geomembrane
UnderlinerFoundation
Primary
GeomembraneLeak Detection Layer
Ore
Overliner Layer:
-Drainage/protectionlayers
-Solution collection
pipes
-Air injection pipes
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Underliner Design Considerations
Seepage control
Environmental impact
Economic impact
Interaction with geomembrane liner
Prefer compacted native soil with a
minimum saturated hydraulicconductivity of 1 x 10-8 m/s (World
Bank Standard)
Admixtures maybe considered
Geosynthetic Clay Liner (GCL)
limited
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Underliner
40% slope
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Geomembrane Considerations
Geosynthetics preferred over otherliner materials (asphalt, concrete,etc).
Typical: HDPE, LLDPE, and PVC(smooth and textured)
Overall seepage control(environmental & economic issues)
Foundation settlement
Puncture by ore load and traffickingHeap stability (slippage along
interface)
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Geomembrane Liner Testing
Load Testing: Compatibility ofgeomembrane liner with rest of linersystem under anticipated ore loads
Interface Shear: Shear strength ofinterface for heap stability analysis
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Geomembrane Interface Shear
Overliner
Geomembrane
Underliner
Normal Stress
Shear Stress
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Overliner Design Considerations
Protect geomembrane (ore loads,mine equipment trafficking, etc)
Medium for solution collection, airinjection, etc
Protect solution collection/ air injection
piping (ore loads, mine equipmenttrafficking, etc)
Prefer native free-draining sand and
gravels durable materials.Hydraulic properties of overliner
govern solution collection pipe design.
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Overliner Placement
Note: Overliner placed directly overgeomembrane and pipes
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Ore Properties Testing
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Material Test Types
Geomechanical propertiesHeap stability
Ore compression
Settlement
Ore durability
Hydraulic propertiesPercolationFlow versus ore load
Draindown moisture content (waterbalance and inventory)
Metallurgical testing (not covered)
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Typical Geomechanical Tests
Unconfined
Compression
TriaxialCompression
DirectShear
Circular Failure
Block Failure
Tests simulate varying stressconditions within heap
Ore
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Typical Hydraulic Tests
Column Tests: Recovery
Percolation rates
Leaching parameters (time, concentration, etc)
Moisture contents (drain down, leaching)
Load-Percolation: Sustainable percolation (unsaturated flow) under
load
Compression of ore (settlement and density)
Load-Permeability: Saturated hydraulic conductivity under load
Ore degradation
Overliner characteristics
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Hydraulic Testing
Colum
nTe
sts
Load-Percola
tion
Load
-Perm
eabilit
y
Tests simulate varying hydraulic
conditions within heap
Ore
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Operational Considerations
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S O
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Select Operational Issues
Wet ClimatesPositive water balance requiring
storage and treatment of excess
process solution.Dilution of solution grade.
Ore heap instability due to high
saturation and erosionLow Permeability Ore
Heap instability due to high saturation
Poor or delayed recoveryHigh inventory (lock-up in pore
spaces)
W t Cli t
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Wet Climates
O ti l I
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Operational Issues
Solution management/heap stabilityproblem:
Increase solution and storm pond sizesCapital cost and land constraints
Pump excess solutions onto the heap
(sponge effect)Does not reduce excess solution volume
Rain Skirts / Covers
Capital costOperationally intensive during rainy season
Excess solution treatment/discharge
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R i Ski t
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Rain Skirts
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I t lift Li
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Interlift Liner
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THANK YOU FOR
YOUR TIME