design and operations of leach pads.pdf

8/14/2019 Design and Operations of Leach Pads.pdf

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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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General Overview


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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

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