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Presentation Copyright : TAKRAF 2016

AIChE Strategies for Sustainable Water Management for Mining Denver, Colorado October, 2016

Michael Blois Pr. Eng., QP, FIMMM


Dry Stack Tailings

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Safety Moment

Background to TAKRAF

Why consider Dry Stack Tailings – Risk Management

What is – “The Complete System”

Description of Tailings Types

Overview of Advantages & Disadvantages of Dry Stack Tailings

Design Criteria for Stacking

Stacking Systems

Filtration

Thickening


Is 99.9% accident free good enough?

What life would be like if 99.9% safe was good enough: • 20,000 incorrect drug prescriptions would be issued each year

• 50 babies dropped by doctors every day

• 500 incorrect surgical operations each week

• We would drink unsafe water for one hour each month

• 22,000 checks would be deducted from the wrong bank account every hour

• Your heart would miss 32,000 beats each year

99.9% isn’t very safe after all.

Safety is at the core of our culture and our way of living and doing things, at work and at home

We are committed to ensuring that all our offices and sites worldwide are safe, clean and healthy environments at all times for all stakeholders

SAFETY FIRST is the safety promise of the Tenova Group

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Some tailings dam failures since 2009 • Duke Energy, North Carolina 2014

– Cause: failure of pipe below surface – Results: US EPA issues new

regulations mandating placement of flyash as a landfill material, i.e. dry stacking in lined and covered facility

– Future: No tailings storage facilities allowed for power generation facilities

• Mt. Polley, British Columbia 2014 – Cause: failure due to unusual clays in

foundation and pond operating practices

– Conclusion: embankments not designed for water containment; too much water in tailings pond; not allowed to discharge excess water

Why Consider Dry Stack Tailings – Risk Management

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Some tailings dam failures since 2009 • Samarco, Brazil 2015 • Failure of dams #3, #4 and #5

– Failure of #3 and #4 caused failure of #5

• Cause: Changes in operating practice and approach from original design

• Significant loss of lives, environmental damage and financial loss to Vale & BHP


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Some tailings dam failures since 2009 (cont.)

• Luoyang Alumina, Henan

Province, China • August 16th , 2016 • 2 million cubic meters of

red mud • 300 villagers evacuated


Tailings dam failures • Number of tailings dam failures per decade • 193 total failures from 1960 to 2010 • 39 failures from 1990 to 2009


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Figures courtesy of: Tailings Dam Failures: A Review of the Last One Hundred Years (2010) by Shahid Azam & Qiren Li

• 20 failures across all regions from 2000 to 2009

• Failures since 2009 are not included.

We should be concerned – Average of >1 dam failure per year

Tailings impoundments are technically complex structures


The DST Concept Is Not New…!!!

The Disposal of Residues at Kalgoorlie - Harry Adams in 1909:

“Originally the conditions in this district varied mainly in the position of the mill…….in most cases the residue was in the form of filter-press cakes, suitable for conveying on belts, or in trucks, and stacking in a high dump.”

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(After Murphy & Caldwell TechnoMine 2012)

Presentation Copyright : TAKRAF 2016 9

TAKRAF – Complete Dry Stack Tailings System

Guelb II, Mauritania

An alternative to the storing of tailings in impoundments

Dewatering tailings through filtration removes approximately 85% of the water

Produces a ‘cake-like’ material which can be transported by conveyor or truck to a storage site

A low-risk and environmentally-socially responsible alternative to managing waste


Tailings Range From Wet to “Dry”

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Underflow from Conventional or High Rate Thickener • Pumpable with centrifugal pumps • Yield Stress 15-40 Pa

Underflow from High Density Thickener • Pumpable with centrifugal pumps (shear thinning may be

required) • Yield Stress <180 Pa Underflow from Paste Thickener • Not pumpable with centrifugal pumps • Positive displacement (PD) pumps required • Yield Stress 100 - 300 Pa

Product from Pressure Filter • Not pumpable • Use conveyor systems to transport • Solids content – 75 to 85% solids • Moisture content – 15 to 25% moisture


Water recovery and reuse required

Filtered tailings would have enough residual moisture to facilitate optimal compaction of filter cake

Reduced land area requirement for dry stack tailings facility as compared to conventional tailings storage facilities.

Seepage rates significantly lower than impoundments

Concurrent reclamation of the stack reduces shutdown time

Dry stack tailings facility can be viewed as easier to permit

Significantly cheaper to “bond” with the authorities.

Potential Advantages of Dry Stacked Tailings

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Water saving alone is seldom a justification for “dry stacking”.

If water loses can jeopardize plant performance, or makes the water resource unsustainable.

Technical Background - “We want to save water” – a common misconception

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Considerations for Tailings Storage Facility -- Seepage or Catastrophic Failure

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• Ground water seepage

• River water contamination

• Ocean contamination


Should not be regarded as a universal panacea.

Filtration performance, similar to thickening performance, is subject to

changes in ore mineralogy and processing characteristics, which can have a significant impact on the filtration rate and/or the moisture level achievable.

May be necessary to incorporate additional equipment for variance in

mineralogy thereby increasing capital and operating cost.

Potential Disadvantages of Dry Stacked Tailings

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Dry Stack Tailings: The Complete System


An alternative to the storing of tailings in impoundments.

Dewatering tailings through filtration removes

approximately 85% of the water

Produces a ‘cake-like’ material which can be transported

by conveyor or truck to a storage site.

A low-risk and environmentally-socially responsible

alternative to managing waste.


The Complete System: A Process Perspective !

An alternative to the storing of tailings in impoundments.

Dewatering tailings through filtration removes

approximately 85% of the water

Produces a ‘cake-like’ material which can be transported

by conveyor or truck to a storage site.

A low-risk and environmentally-socially responsible

alternative to managing waste.


15 000 to 18 000 metric ton/day Gold Leach where Au solution recovery is with Vacuum Belt Filters Reason for dry stack – gold and cyanide recovery and topography Product – filter cake at 19 – 22% moisture In situ moisture is 13%, generated by compaction & evaporation Operating cost – not specifically known; paid for by cyanide reagent recovered Plant water usage – 0.27 m3/ton ROM

Dry stack example - La Coipa

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Design Criteria for a Stack

Location

• Topography

• Geohydrology, geochemistry & ARD potential

• Climate

Rheology of Feed Material

• Mineralogy of the particles

• Solids density

• Solids concentration

• Particle size distribution

• Particle morphology

Degree of compaction

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Conveyability ??

Bearing Pressure


Design Criteria for a Stack - Which are Controllable?

Location

• Topography

• Geohydrology, geochemistry & ARD potential

• Climate

Rheology of Feed Material

• Mineralogy of the particles

• Solids density

• Solids concentration

• Particle size distribution

• Particle morphology

Degree of compaction

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Conveyability ??

Bearing Pressure


Trucking

Transportation and placement of dry stack tailings

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Conveying & Stacking


Economics in Stacking Methods

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Shiftable / Extendable Conveyors

Mobile Stacking Bridges

Grasshopper / Portable Conveyors

Trucking / Dozing

OPEX CAPEX

Spreaders


Stacking Technologies

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Material Handling - Equipment Selection

1. Allowable ground pressure needs to be taken into consideration • Rheological information is

necessary in selecting/dimensioning equipment

• Expect lower allowable ground pressure on a DST system when compared to a waste rock system

2. Crest to equipment’s track distance

• Also from rheological information

• Compared to waste rock stacking, expect to see bigger distances from equipment to dump area crest

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Mobile Conveyor Bridge

• Grasshopper type conveyors are most commonly tire mounted: higher bearing pressures.


• Receives material from Mobile Conveyor Bridge (MCB) or from Tripper car

• Dumps material from a safe distance into the low cast/high cast dumping location

• Adds flexibility to dump where fixed stackers can’t

Spreader


Stacking Scheme


• Less maintenance intensive

• Greater uptime • Less relocation time

• Less flexibility • Needs a relatively flat

original terrain

Mobile Stacking Bridge


Trucking


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Conveying - Conventional

• Example – El Abra, Chile • Capacity: 6,000 tonnes / hour • Length: 9,500 m (31,173 ft) • Elev. change: -510 m (-1,670 ft) • Speed: 6.1 m/s (1,200 ft / min) • Regenerative power: 5,500 kW

(7,400 hp)



Conveying – Pipe Conveyors

• Eliminates transfer towers • Requires less space • Simultaneous two-way

transport possible • Tight horizontal and vertical

curve radii • Up to 10,000 t/h material

transfer • Inclines up to 18 degrees

TAKRAF’s electronic training panel eliminates manual training of the belt. The 3-piece panel design reduces downtime during scheduled maintenance.


Filtercake Moisture Content ?

Filter Presses: typically 8 – 15% moisture

Vacuum Belt Filters: typically 12 – 20% moisture

Is it really necessary to achieve the lowest possible moisture content?

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Filter cycle has “dead times” when pressure chambers are filled and emptied, i.e. batch cyclic operation.

Relatively low unit capacity More complex cake handling system Capital and operating costs per ton can be high but moistures produced are low

Pressure filters – Delkor F.A.S.T. Filter

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Filters - Delkor

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Delkor Horizontal Vacuum Belt Filter • Simplified cake discharge & material handling • Simpler to operate


Filter Feed Conditions ?

Dependent on the viscosity of the feed slurry

Vacuum Belt Filters: • Need uniform belt coverage and cake thickness

Pressure Filters

• Higher feed pressures may cause greater pump wear • Batch process: storage capacity needed & agitator power requirements

Is it really necessary to achieve the lowest possible moisture content of the thickener underflow?

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Do not produce a conveyable product Capital and operating costs are low. Product rheological properties (medium to high Yield Stress) – lower than paste; still easy to

pump Large diameter units can be used; fewer machines, lower capital More consistent production of final product with a Yield Stress of 50 to 150Pa.

High Rate/Density Thickeners - Delkor

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TAKRAF / DELKOR Systems and Equipment

Process Systems Required for Dry Stack Tailings

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Sedimentation – Thickeners • Conventional

Thickeners • High Rate Thickener • High Compaction / High

Density Thickeners • Paste Thickeners

Filtration • Horizontal Vacuum Belt

Filter • F.A.S.T. Pressure Filter

Material Handling

• Overland Conveyor • Bridge Conveyors • Stacker Conveyors


TAKRAF – Complete Dry Stack Tailings System


An alternative to the storing of tailings in impoundments

Dewatering tailings through filtration removes approximately 85% of the water

Produces a ‘cake-like’ material which can be transported by conveyor or truck to a storage site

A low-risk and environmentally-socially responsible alternative to managing waste


Reduced footprint – land availability and cost, environmental and social impacts

Safety – reduced water storage and high dams, creation of stable landform less susceptible to liquefaction.

Expedite/progressive/concurrent rehabilitation Increased water recovery/recycle and decreased consumption

• Cost and environmental impacts of water consumption • Water availability and quality • Recovery of valuables from process water • Virtually eliminate evaporative water loss

Eliminate groundwater contamination Significantly cheaper to “bond” with the authorities.

Conclusion – Dry Stack Tailings

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Thank you

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