clarifying solutions for heap leaching with wso

> M i n e r a l P r o c e s s i n g > E n g i n e e r i n g D e s i g n > T r a i n i n g > S p e c i a l i s t S e r v i c e s > RESOURCE PROJECTS > TECHNOLOGY > INTEGRATED SERVICES > Mineral Processing > Engineering Design > Training > Specialist Services

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COPYRIGHT © 2012. MINERAL ENGINEERING TECHNICAL SERVICES. THESE NOTES ARE NOT TO BE COPIED OR REPRODUCED WITHOUT PERMISSION.

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IRR MANAGING WET & STICKY HIGH CLAY ORES

Clarifying Solutions for Heap Leaching with WSO

> RESOURCE PROJECTS > TECHNOLOGY > INTEGRATED SERVICES > Mineral Processing > Engineering Design > Training > Specialist Services


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> DISCLAIMER With respect to all the information contained herein, neither Mineral Engineering Technical Services Pty Ltd, nor any officer, servant, employee, agent or consultant thereof make any representations or give any warranties, expressed or implied, as to the accuracy, reliability or completeness of the information contained herein, including but not limited to opinions, information or advice which may be provided to users of the document. No responsibility is

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> COPYRIGHT © Passing of this document to a third party, duplication or re-use of this document, in whole or part, electronically or otherwise, is not permitted without the expressed written consent of Mineral Engineering Technical Services Pty Ltd.

> ACKNOWLEDGEMENTS This document is a dynamic record of the knowledge and experience of personnel at Mineral Engineering Technical Services. As such it has been built upon over the years and is a collaborative effort by all those involved. We are thankful for the material supplied by and

referenced from various equipment manufacturers, vendors, industry research and project partners.


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Who We Are

Mineral Engineering Technical Services

> Engineering Consultants with a focus on junior and mid-tier mining

companies

> Mineral Processing since 1988

> Global greenfields and brownfields project experience

> Guiding projects through the development path from testwork to

feasibility studies through to commissioning

> Commodity experience across a wide range minerals


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Introduction

> Wet sticky clay ores: gold, nickel, copper, uranium ores

> Process issues WSO

> Heap leaching WSO

> Testing

> Operations

> Conclusions


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Heap Leach Basics

> Percolation of leach solution through a heap of crushed or ROM

ore stacked on a prepared pad in closed circuit with product

recovery system

> Permanent and on-off pad systems are used

> Heaps can have a single lift or multiple lifts

> Crush size range is typically 4mm – 100mm depending on

economics and ore characteristics – percolation and size need

to expose mineralisation

> Number of crushing stages is typically 1 - 4

> Leaching operation can be single or multi stage


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Different Leaching Techniques

Leaching Methods

Percolation leaching Agitated leaching

In-situ Heap/dump Vat Thin layer Tank Vat


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Clays – An Introduction

> Clays cause inherent materials handling with mineral processing

and difficulties because of their wet sticky nature

> Clays are typically < 2 microns

> They have high surface areas and reactivity (swelling and

adsorbing power)

> There are many clay mineral groups-identification

> Mostly weathering products are above the water table or due

to argillic alteration

> The mineral processing issues are problematic


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Identification of Clay Minerals

> The kaolin serpentine group

o Kaolinite, dickite, nacrite and halloysite

> Serpentine group

o Chrysotile, lizardite,berthierine

> Talc pyrophyllite group

o Pyrophyllite

> Mica group

o Muscovite, paragonite, roscoelite, caladonite, illite,

phengite, serecite, biotite, phlogopite

> Smectite vermiculite group

o Montmorillonite, beidellite, nontronite, saponite, stevensite,

vermiculite

> Chlorite group

o Chlorite, clinichlore, chamosite, nimite, pennantite

> Mixed layer minerals

o Sepiolite-palygorskite/attapulgite

o Allophane and imogolite


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Crushing & Screening

> Bypass facilities so that simply passing

through the jaw crusher and into a

passive stockpile so it can be fed to a

ball mill using a front end loader is one

solution

> Secondary crushing and screening

may not be possible particularly if the

ore is wet and sticky. Cone crushers

bridge and screens become blinded

> Putting clay ores into bins or stockpile

with reclaim tunnels can be a disaster.

They simply don’t work. Feeding direct

into SAG mills is a much better option if

this suits the process

> Scrubbers ahead of crushing

Source: METS Media Library (2012)


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Heap Leaching

> High clay ores require agglomeration

with cement in an agglomeration drum

and time to cure before stacking

> If agglomeration is not used the

percolation will be very low and

effective recovery from the heap very

low. The cement addition rate required

is critical and can affect the economics

of the process


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Materials Handling

> For high clay ores Tunra type testing

to determine rill angles, angles of

repose and materials handling

characteristics is a must

> Only apron feeders are effective

feeders with high clay ores. The use

of stockpiles is not possible because

of rat holing and the difficulties

getting the ore to flow in a stockpile

or bin is extreme

> Conveying is also difficult requiring

the use of belt washing stations plus

increased tracking issues




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Heap Leaching Advantages

The history of copper, uranium and gold heap leaching goes back

hundreds of years. Nickel leaching is becoming more prominent. Heap

leaching lower grade ore is attractive :

> Capital cost is low, no tailings dam

> Amenable to treating low grade ores, unviable with traditional

processes

> Can be an ancillary operation based around existing infrastructure

> Medium to high metal recoveries are possible

> High quality products can be produced

> Labour costs are low


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Heap Leaching Disadvantages

> Reduced metal recovery

> Cash flow delays

> Leach kinetics are slow to change and difficult to analyse

> High risk with little margin for error

> High clay ores present unique challenges


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General Process Outline

Lower grade ores

Ore preparation

Comminution

Concentration and purification (e.g. SX/IX)

Recovery (e.g. electrowinning, precipitation)

Acid/alkaline leaching


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Heap Leaching

> Leach Pad Configuration:

o Considerations - Ore material properties (leaching characteristics, durability, etc.)

- Water balance

- Land availability and ground slope

- Project cost ( capital and operating)

o Pad configuration types: - Dedicated, single use pad (“standard” leach pad)

- On/Off or Reusable Pad

- Valley Fill

- Hybrid


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Standard Heap Leach


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Solution Collection Pipes


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Heap Leach Pads


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Single Use Pads

> Single Use Pad o Suitable for variable ore types and leach cycle times

o Typically large area for leach pad. Pad area based on ore

production, leaching cycle time, ore “aging”, etc.

o Flat topography to maintain geotechnical stability

o Large storm event pond

o Low initial capital costs

o Incremental pad expansion costs must be considered in

project cost


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Re Useable Pad


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Re Useable or ON/OFF


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Reusable Pad Considerations

> Reusable (on-off) pad

o Suitable for ore with short leach cycles and consistent

leaching characteristics

o Areas with limited flat terrain

o Requires a rinsed ore site/pad

o Durable “high-stress” liner system

o Practiced in wide range of climate conditions

o Smaller storm pond

o Costs: double handling of ore, rinsing system, rinsed ore

storage


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Valley Fill Pad


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Valley Fill Pad Considerations

> Valley fill pad

o Best suited for hard, durable ore with good drainage. Can

accommodate extended leach times

o Used in steep terrain (slopes up to 40%)

o Internal solution storage reduces external pond requirements

o Robust liner system (high hydraulic head and ore loads)

o Retaining structure for confinement of heap.

o High upfront capital cost


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Heap Leaching – Operational Issues

> Ore agglomeration

o Controlling agglomeration process to provide consistent

product (moisture important)

> Maintain highest heap height that preserves ore permeability

o Capital cost and land constraints

> Blending with more durable ore

o Logistics of blending and control

> Stacking method


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Heap Leaching – Operational Issues (cont.)

> Wet climates

o Positive water balance requiring

storage and treatment of excess

process solution.

o Dilution of solution grade.

o Ore heap instability due to high

saturation and erosion

> Low permeability ore

o Heap instability due to high

saturation

o Poor or delayed recovery

o High inventory (lock-up in pore

spaces)

o High cost


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Heap Leaching – Operational Issues (cont.)

Managing Water

> Solution management/heap stability problem:

o Increase solution and storm pond sizes

- Capital cost and land constraints

o Pump excess solutions onto the heap (‘sponge” effect)

- Does not reduce excess solution volume

o Rain skirts/Covers

- Capital cost

- Operationally intensive during rainy season

o Excess solution treatment/discharge


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Liner Guide

Foundation

Condition Underliner Overliner

Effective Stress at liner (Mpa)

<1.2 >1.2

Firm

Coarse Coarse

2 mm LLDPE or HDPE 2.5 mm LLDPE or HDPE Fine

Fine Coarse

2 mm LLDPE 2 mm LLDPE or HDPE Fine

Soft

Coarse Coarse 2 mm LLDPE 2.5 mm LLDPE

Fine 2 mm LLDPE 2.5 mm LLDPE

Fine Coarse 2 mm LLDPE 2.5 mm LLDPE

Fine 1.5 mm LLDPE 2.5 mm LLDPE

Notes:

1. Underliner refers the material directly beneath the geomembrane (primary geomembrane for double composite systems). Coarse or

fine refers to the general gradation. Testing and design calculations are required to assess impacts on geomembrane.

2. Overliner refers the material directly above the geomembrane (primary geomembrane for double composite systems). Coarse or fine

refers to the general gradation. Testing and design calculations are required to assess impacts on geomembrane. 3. Foundation conditions are presented in relative stiffness. Testing and design calculations are required to assess foundation impacts on

geomembrane.


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Typical Heap Leaching Flowsheet

HEAPS

CRUSHING

(OPTIONAL)

AGGLOMERATION

(OPTIONAL)

PRODUCT

RECOVERY

STACKING

LIXIVIANT

WATER

MAKEUP

ROM ORE

LIXIVIANT

(optional)

WATER

PLS POND

BARREN

SOLUTION

POND


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Two-Stage Counter-Current Flowsheet

PLS PONDBARREN

SOLUTION

POND

PRODUCT

RECOVERY

ILS

STAGE

PLS

STAGE

ILS POND

WATER MAKE- UP

LIXIVIANT

ORE FEED


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PLS Recirculation Flowsheet

PLS PONDBARREN

SOLUTION

POND

PRODUCT

RECOVERY

WATER MAKE- UPLIXIVIANT

ORE FEED HEAPS


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ON-OFF Pad Flowsheet

PLS POND BARREN

SOLUTION

POND

PRODUCT

RECOVERY

LoadingCuring

(option)

WATER MAKE- UP

LIXIVIANT

ORE FEEDLeaching Washing Draining Unloading

RESIDUE

ILS POND

HEAPS


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Heap Leach Plant & Ponds



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Agglomeration & Stacking

AGGLOMERATION & CONVEYING


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Agglomeration

To agglomerate means having particles sticking together into a small mass due to moisture, static charge or chemical reaction

> Why the need to agglomerate?

> Reduce fine particle sizes throughout ore pile

> Reduce fines/clay mobility – improve solution percolation, metal

recovery and rate

> Introduce leachant as soon as possible – improve leach cycles, less

aggressive leaching


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Eventual choking leading to by-passing

Fine migration with leachate

Fines build up

Fines bound by agglomeration

Agglomerated Not agglomerated

Favourable Unfavourable

Agglomeration (cont.)


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> Excessive fines treated by agglomeration – add a support rock

> Screening out of fines may be required for successful

agglomeration

> Improves heap permeability and improves oxygen availability –

important for bacterial leach and uranium

> Reduce surface ponding and minimise channelling – improve

recovery

> Improve heap solution drainage capacity – high rainfall

Agglomeration (cont.)


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> Agglomeration for crushed ore systems are common but not always

required for size distribution

> Agglomeration should always be considered to introduce early

leachant

> Ore with >15% of ore less than 75 microns will almost certainly require

agglomeration

> Leachant introduced into drum via spray/ dribble bar

> Drum should have varying pitch and speed to optimise process

> Leachant addition up to 70% of stoichiometric needs

> Agglomerates at the stack point should be as wet as can be handled

efficiently through the conveying system

Agglomeration - Operation


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Agglomeration - Binders

> Binders strengthen the adhesion of ore particles to form

agglomerates

> Dry binder added to ore at agglomerator entrance

> Liquid binder added with leaching solution. The leachant is

commonly the binder anyway

> Cement is a common solid binder in gold leaching. Also use lime

> Care when using additional organic binders. Can interfere with

downstream processing – particularly SX. Long term process


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Equipment

Rotating Drum

Belt Conveyor

> Set at the same angle

moving in the same direction.

Particles agglomerate when

they touch each other at the

transfer points between belts

> Reverse belt agglomeration

> When they bounce on the

belt upon landing



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Heap Building Methods

> Ore transport: trucks or conveyor system (generally including

portable “grasshoppers” – no trucks with agglomerates.

> Heap building methods: radial stacker, mobile stacking

conveyor system.

> Trucks, front-end loader, excavator – dump leaching

> Typical transport/ heap/ dump building combinations.

o Trucks all the way

o Trucks then stacker

o Trucks with excavator

o Conveyors then trucks

o Conveyors then front-end loader

o Conveyors then radial stacker

o Conveyors then mobile stacking conveyor

> Low ground pressure dozer can be used for surface levelling –

wide tracks


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Stacking Techniques (cont.)

> Figures on the left show plug-dumping plan view

shows overlapping mounds of ore, while cross section shows configuration with liner protection

Plug Dumping

> Ore is placed on leach pad in ‘lots’.

Difference between plug dumping

and ROM dumping is that there is no

heap compaction using this

technique.


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> Construction of heaps in the 1980s were typically 15 m in ore depth,

now they can be designed with depths of 230 m

> Heaps constructed in lifts, typically 4m to 10m high

> Depleted lifts are washed, dried, drilled, graded and rolled to seal

surface before overstacking. A plastic underliner not needed. Drainage

is needed

> Higher heap heights can be better based on economic grounds as

higher heaps can mean less ground disturbance – there are additional

costs associated with reclamation and heap closure

> Note: Heap heights may be regulated by government departments


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Heap Building Method Selection

> Conveyor/ radial stacker

o Preferred method in most cases

o More gentle placement of ore

o Suitable for agglomerates

o Suitable for less competent material

> Truck/ FEL stacking

o Only suitable for coarse ore – dump leaching

o Finer ore – seals surface and destroys agglomerates

> Excavator stacking

o Only for re-mining and stacking of sealed heaps. Try to

extract more metal


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> Materials handling issues require special attention when heap leaching

> Crushing can be highly problematic with screen blinding and low through

with cone crushers

> Agglomeration with cement is mandatory when processing WSO for

percolation and heap stability

> The amount of cement is that required to achieve minimum percolation not

to make hard marbles

> Gold recovery can be very high with WSO

> Column testing is mandatory to confirm leach kinetics, percolation, slumping

and reagent costs

Conclusions


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Acknowledgement

> Thanks to IRR for the opportunity to present

> Thanks to various companies, colleagues, engineers

> METS staff and consultants

> Thanks to laboratory staff & others

clarifying solutions for heap leaching with wso

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