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The Future of Tailings Disposal in South

Africa

Mine Tailings Africa Conference 6-7 March 2012

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Kimberley – the beginning

Tailings disposal really kicked off in Kimberley diamond fields

Weathered rock washed to release diamonds –Yellow ground Hard rock left to weather before washing – Blue ground

Tailings & grits stored in dumps –source of diamonds today!

Slimes not controlled – discharged into streams

In diamond mining generally Tailings -10 mm to 1 mm

Grits 1 mm to 150 µm

Slimes - 150 µm

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Mining legacy

TSFs are some of the largest man-made structures

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Bafokeng No 4

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7 km

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Mining legacy

TSFs are some of the largest man-made structures

They are a lasting legacy of mining operations – there for EVER

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What the mining companies wish

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Mining legacy

TSFs are some of the largest man-made structures

They are a lasting legacy of mining operations – there for EVER No quite true on the Witwatersrand, but

Cannot destroy matter, so retreated tailings retain their volume

Tailings storages fail, killing people and causing environmental harm

There is a demand by society for TSF designs to

Limit risk to the environment

Limit risk to people

Be stable “for ever”! 

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Outline today

Tell you something about my journey

Relate some history about tailings disposal in South Africa Look at the development of TSF design in SA

Consider the SA and African TSF market today

Look at trends in tailings disposal

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My history

“Pre-ordained” to work in the mining industry 

Great grandfather a Cornish tin miner Came to Johannesburg in mid 1890’s 

Brought family out soon after 2nd Boer War

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Early mining scenes – mid 1890’s 

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My history

“Pre-ordained” to work in the mining industry 

Great grandfather a Cornish tin miner Came to Johannesburg in mid 1890’s 

Brought family out after 2nd Boer War

My earliest mining recollections are yellow mine dust in my gran’s house

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Josie’s old dumps and slimes dams 

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My history with tailings

Earliest recollections are of yellow mine dust in my gran’s house

Then playing on the slimes dams at Wemmer Pan on weekends (1959) Being petrified of climbing the steep sides

The fun of exploring the many erosion caves on top

Learning corners much flatter and easier to climb

Never courageous enough to use corrugated iron to surf the sand dumps

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A steep slimes dam - Norseman

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Surface erosion gullies

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My history with tailings

Earliest recollections are of yellow mine dust in my gran’s house

Then playing on the slimes dams at Wemmer Pan on weekends (1959) Being petrified of climbing the steep sides

The fun of exploring the many erosion caves on top

Learning that the corners had mush flatter and easier slopes

Never courageous enough to use corrugated iron to ride the sand dumps

Taken to Sachs dam at Premier Diamond Mine (1960) Slimes dam built using loosely dumped tailings

Dam was sliding down the slope

Profs Jennings and Casagrande called in to find solution!

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Cullinan slimes dam

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Sach’s 

Dam

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Getting into tailings

Never planned to work in mining, despite Chamber of Mines bursary

First job with Union Corporation on Verwoerd Dam construction Then when lecturing at Wits

Designed a 13 m ɸ 35 m deep caisson for Harmony headgear

Piled foundations for Unisel headgear and winder house

Rock replacement foundations for new St Helena process plant

 Approached by Gary Rae - Fraser F Alexander

Joined FFA as its 1st design engineer

Now been with Golder in Aus for 20 years

So having established my credentials, into tailings disposal

Really just building big mud castles!

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Mining exposed weathered reef

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Stamp mills

Stamp mills introduced 1885

Fresher rock more difficult to break-up by hand Coarse crushing in stamp mills

60 to 65% coarser than150 µm

In 1912 there were 9449 mills processing 25.5 Mt/yr

Last stamp mills in SA1918

Stamp mills still operating in Zimbabwe – Zamas Zamas mine

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Stamp mills – note gum log supports

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Cyanidation & milling

Cyanidation introduced in 1890 – from Scotland

Started with treatment of sand only Cones (cyclones) used to separate sand and slime

Slimes 16 to 33% of product

Sand washed in vats

Later both sand and slime treated, but separately

Last sand plant in 1918

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Sand vats

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Cyanidation & milling

Cyanidation introduced in 1890 – from Scotland

Started with treatment of sand only Sand washed in vats

Last sand plant in 1918

Cones (cyclones) used to separate sand and slime

Slimes 16 to 33% of product

Then sand and slime treated separately 

Sand dropped out into cocopans

Manhandled to dump

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Cocopans moved by hand!

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Cyanidation & milling

Cyanidation introduced in 1890 – from Scotland

Sand treatment introduced in 1890 Last sand plant in 1918

Sand and slime treated separately

Cones (cyclones) used to separate sand and slime

Sand washed in vats

Manhandled to dump

Sand batch dropped into cocopans

Manhandled to dump

Hauled by endless rope onto sand dump

Finally by conveyors

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An endless rope sand dump

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Dumping & hauling

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Early gold mining

Cyanidation introduced in 1890 – from Scotland

Sand treatment introduced in 1890 Sand and slime treated separately

Cones (cyclones) used to separate sand and slime

Sand washed in vats

Last sand plant in 1918

Manhandled to dump

Sand batch dropped into cocopans

Hauled by endless rope onto sand dump

 Advancing face often failed

Cocopans would end up at the toe Mule teams used to recover them!!

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Today reprocessing sand dumps

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Early slimes dams

Dumping slimes into veld could not continue

Mines surrounded by good farming land So slimes dams had to be built

Used gravity to get tailings slurry to slimes dam

Needed to be downhill of and close to plant

Slimes wheels used to lift slurries to gain head

Pumps in early development

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Tailings wheel – slurry lift “pump” 

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Early slimes dams

Dumping slimes into veld could not continue

Mines surrounded by good farming land So slimes dams had to be built

Used gravity to get tailings slurry to slimes dam

Needed to be close to and downhill of plant

Slimes wheels used to lift slurries to gain head

Pumps in early development

Few pipes, so used wooden launders or furrows

Dams at toe of sand dumps – cause of dump failure?

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Tailings slurry launders

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Early slimes dams

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Rotating mills – total slimes

 Air agitation and filtration allowed efficient cyanidation of slimes

Introduction of rotating mills in 1904 lead to ALL tailings treatment Total slimes - 75% (

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Rod Mills

March 8, 2012 41 MINE TAILNGS, JOHANNESBURG 2012

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Vacuum filters to remove cyanide solution

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Rotating mills – total slimes

 Air agitation and filtration allowed efficient cyanidation of slimes

Introduction of rotating mills in 1904 lead to all tailings treatment Total slimes - 75% (

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Scientific method criteria

1917 Chemical, Metallurgical and Mining Society

Still mainly daylight operations Emphasised choosing flat land for slimes dam

Ideal slimes dam

22 ha for 50 000 tpm (1 ha / 1 000 tpm = 1 m/yr)

Equivalent to 337 claims – Crown Deep and Langlaagte Deep mines

Gang 1 intelligent foreman (white)

 8 to 10 able bodied labourers

Problems

Wooden penstocks – easily crushed

Cracks & leaks in walls – frequent wash-outs

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Awareness – from 1917

Toe trench 900 wide by 500 deep - slimes trench and key

Excavated earth used to form toe wall Looked to use dry ground away from water

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Toe trench and toe wall

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Awareness – from 1917

Toe trench 900 wide by 500 deep - slimes trench and key

Excavated earth used to form toe wall Looked to use dry ground away from water

When soggy ground

French drains installed in toe drain

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Toe drain and toe wall

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Day wall system

Irrigation (day wall) system developed by Fraser Alexander

Started at Ferreira Deep in 1904  Allowed

Development of freeboard

Control of supernatant

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2 cell system

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Day wall system

Irrigation (day wall) system developed by Fraser Alexander

Started at Ferreira Deep in 1904  Allowed

Development of freeboard

Control of supernatant

Build walls with shovels – special shovels

500 mm wide by 100 mm high Sloped inwards

Maximum height 20 m

Single point delivery - puts limit on cycle time

Rate of rise reduced to 150 mm/mnth

Developed “rule of thumb” method to size a new slimes dam 

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Night wall system

Night wall developed when 24 hours sliming introduced

Night wall ~ 3 times Day wall width  Allowed controlled supervision free night (16 hpd) deposition

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Early night trench system

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Wooden penstock

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Idealised Day wall/Night wall system

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Day wall Night wall

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Pool wall system

Single slimes delivery point difficult to manage at night

Pool at far side of slimes dam Difficult to control location of pool

Introduction of pool wall by FA changed operations

 Allowed:

Pool location to be held around penstock

Development of adequate freeboard

No need for night wall – reduction in work load!

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D l f h P l W ll

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Development of the Pool Wall system

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SA ld li d l ll

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SA gold slimes dam pool wall

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P l ll i K l li i t d d 1993

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Pool wall in Kalgoorlie – introduced 1993

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D l t

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Developments

Developments to manage slimes dams

Slurry pumps and steel piping Day wall, night wall and pool wall to manage pool

Concrete penstock boxes – raised periodically

Newer developments include:

Penstock rings - eliminates raising of concrete towers

Safe handling system for rings – reduces risk of death! Penstock towers - ERGO

Mechanisation – reduces day wall blowouts/ratholes

In-wall delivery stations – minimises pipe lifting

Multiple discharge locations

Reduces cycle time More uniform product in wall

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“R i f d” t k

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“Reinforced” penstock 

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Wooden slat controlled

Steel pipe riser

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Th lti t ERGO t k t

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The ultimate - ERGO penstock tower

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Design criteria 1949 1

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Design criteria 1949 - 1

Gold slimes now 85 to 95%

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Design criteria 1949 - 2

1 m by 600 mm toe trench – stops bulging failures!

Excavated material forms toe wall Introduced concept of step-ins to prevent wall failures

Return water 15 to 20% of slurry water

Secrets of operating

Maintain walls in good condition

Ensure supernatant runs off daywalls to pool

Have sufficient penstock capacity to remove rainfall runoff

Operating cost 0.5 c/t

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Typical wet toe failure Millsite

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Typical wet toe failure - Millsite

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Saaiplaas foundation failure & liquefaction

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Saaiplaas foundation failure & liquefaction

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George Donaldson NBRI

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George Donaldson - NBRI

In 1953 George investigated seepage problems on East Rand

First technical study of slimes dams in SA (maybe globally?) Looked at seepage, underdrainage design and stability

Winkelhaak had extensive French drains

1959 published book on geotechnical aspects of slimes dam design

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The problem!

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The problem!

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The seepage analysis

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The seepage analysis

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George Donaldson - NBRI

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George Donaldson - NBRI

In 1953 George looked at seepage problems on East Rand

Winkelhaak had extensive French drains

First technical study of slimes dams in SA (maybe globally?)

Looked at seepage, underdrainage design and stability

1959 published book on geotechnical aspects of slimes dam design

Main innovation was

Introduction of planned underdrainage Suggested drains around toe the logical location

St Helena first slimes dam to incorporate new drain concepts

Concluded

Can build to 40 m at 3 m/yr

Outer slope of 18º

Eliminates foundation failure risk

Helps rehabilitation

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New slimes dams - Seepage control

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New slimes dams - Seepage control

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Remember

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Remember

 All done without a computer

Mostly long multiplication and division

No slope stability program

No seepage program

Slide rule at best

No CAD or plotters

Flow nets developed and drawn by hand

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And so

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And so

SA remans uniquely suited for upstream raising

Semi-arid climate – higher evaporation than rainfall

Relatively flat ground –  mainly ring-dyke construction

Low seismic risk (but remember Welkom’s earthquakes?) 

To prevent failure design must control

Rate of rise

Pool water location and size Freeboard to meet Design Storm requirement

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So is Australia - Kalgoorlie

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So is Australia Kalgoorlie

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Upstream raising above rock dam - China

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Upstream raising above rock dam China

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Rock dam

Upstream tailings raise

And so

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And so

But not all SA is suitable for ring-dyke construction

 A few usable valleys - Barberton and Steelport areas

High rainfall areas – Lowveld, KwaZuluNatal

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Not everywhere is flat! Barberton area

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Not everywhere is flat! Barberton area

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1st CIP plant

And so

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d so

But not all SA (or Africa) is suitable for ring-dyke construction

 A few usable valleys - Barberton and Steelport areas

High rainfall areas – lowveld, KwaZuluNatal

Much of African is

Hillier

Wetter

Has significant seismicity Lesotho is a good example

SA engineers must look to the world for design methodologies

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High rainfall & seismicity – Solomon Islands

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g y

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Other deposition systems

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p y

Spigots

Cyclones

Earth or rock valley dams

In pit

Underground

In river or ocean

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Spigots

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p g

Used to split coarse material from slimes for outer perimeter beach

 Already in use at RPM in 1947

Tailings 55% -75 µm 

Slurry at 30% solids

150 mm delivery pipe

Supported on wooden trestles

75 mm spigots at 2 m intervals Outer walls built by hand

Used in SA mainly for

Diamonds

Iron ore

Coal

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Full pipe spigot – coal combined rejects

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p p p g j

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Cyclones

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y

Used extensively in South America

Steep valleys

High seismicity

Very few cycloned dams in SA

Finer tailings

Low seismicity

Plenty of real estate (still true??) Used very successfully at Ergo and Daggafontein

Modified centreline construction

Used for Sheba gold mine TSF in early 1980’s 

Valley dam

High rates of rise Upstream raised

Limited other uses for gold, platinum and diamonds

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Multiple cyclones – Ergo early days

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y g y y

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Daggafontein cyclone operation

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Diamonds - Botswana

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Cyclone station - Chile

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Compacted cyclone underflow dam - Chile

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Other Containments

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Concrete faced waste rock dam - Peru

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Coarse coal rejects to contain fines

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In river (Indonesia) – not acceptable

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Deep sea tailings disposal – limited locations

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TAILINGS HEAD TANK

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Foundation failures

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Los Frailes

Merriespruit

Wall failure

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Most wall failures are really foundation failures

Poor foundations

Seismic action

So need to carry out comprehensive site investigations under wall

Drilling depth at least as high as dam

TSFs in China and USA planned to >300 m high

Remove poor soils and, were appropriate, weak rock Ensure good contact between foundation and wall

Provide an adequate cut-off to limit seepage forces under wall

Monitor the wall

Piezometers

Inclinometers and survey beacons

Settlement gauges/rings

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Preparing clay core – rock abutment contact

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March 8, 2012 105

Fully instrumented earth/rock dam lined TSF

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Overtopping

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Need to provide and operate with adequate freeboard

EU regulations require PMF freeboard storage

SA 1:50 yr requirement inadequate in most of Africa

Need to meet IFC or World Bank criteria

Provide emergency spillways at all stages of operation

EU regulations require PMF spillways

Queensland - capacity dependent on Hazard category of TSF

1:100 to 1:10 000

Size decant/penstock/pumps appropriately

Operate pool correctly!!!!

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Start of 70 m wide stepped chute spillway

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Uncontrolled release of water

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Carry out daily time step stochastic water balance

Vital in tropical regions

Estimate supernatant volume correctly

Use settling tests – not in situ density measurements

Size return water dam appropriately

Queensland –  2 to 4 month wet period 1:20 year AEP for RWD and TSF

Size return water pumps appropriately

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Coal rejects codisposal return water pumps

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March 8, 2012 110

Seepage into groundwater

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This is essentially an uncontrolled release

Very difficult and expensive to control once started

Has become more of a focus by EPAs

EU regulations demand at least a single liner

 Australia moving to liners for all TSFs

SA lining requirement for TSFs now hazard related

Goes to mining companies maintaining a social permit to operate

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1st HDPE liner for residue (??) - gypsum

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March 8, 2012 112

120 ha Nickel residue storage (LDPE)

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Spillway & abutment

Earth/rock dam

Oman – HDPE cover to prevent seepage

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Dust

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Remember my early recollections of mining in Johannesburg?

Dust off dry surfaces can be a real issue

Difficult and can be costly to manage

Keep surfaces wet by rotating deposition

Spray dry surfaces with dust palliatives

Cover surfaces with larger material

Use fences and vegetation

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Bauxite tailings adjacent to a town

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Erosion

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 All tailings surfaces erode

Loose, granular, weakly cemented, unstable particles

Surface water management probably greatest challenge

During operations and especially post closure

Rigid engineered structures rarely work

Tailings continues to settle and move

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Wind and water erosion - Kalgoorlie

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March 8, 2012 119

Design team to minimise risk

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Need a competent & experienced team, including:

Tailings engineer

Geotechnical engineer

Hydrologist

Hydrogeologist

Metallurgist

Geochemist

Seismologist

Geomorphologist

Landscape architect

Botanist

Design drafter

Project manager

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“New” technologies 

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Paste and thickened tailings

In-line flocculation

Filtration

Codisposal

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Paste and thickened tailings

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Slurry needs secondary thickening after process

Possible with advent of deep tank thickeners

May need positive displacement pumps – lots of power!

Maximises

Water recovery

Initial settled density

May eliminate need to line base  Allows early rehabilitation access

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Paste TSF - Bulyanhulu

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In-line flocculation

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 Addition of flocculants just before discharge

Rapid dewatering

TSFs

Steeper beaches

Higher settled density

Higher water recoveries

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Beach and density improvement -China

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March 8, 2012 127

Prior to flocculation

After flocculation

In-line flocculation

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 Addition of flocculants just before discharge

Rapid dewatering

TSFs

Steeper beaches

Higher settled density

Higher water recoveries

Coal tailings Use recyclable pits

Excavation for disposal within days

Dumped with mine waste - codisposal

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Coal tailings

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March 8, 2012 129

Coal tailings removal after 3 days

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Filtration

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Range of filters to match tailings and tonnage

Recovers maximum volume of water

Transport by conveyors & trucks

Co-dispose with mine waste rock

Build an engineered dump

No new coal TSFs in Queensland

Coal - mix coarse and fine rejects Dry stacking may reduce seepage issues

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Compacted filtered tailings dump

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Filtered – risk of static liquefaction

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Flow of filtered tailings

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March 8, 2012 135

Trends in South Africa

f

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Increased concern about failure to contain

Surface water releases

Groundwater contamination

Dust

Visual pollution

Pressure on land availability

Settlements around TSFs in Rustenburg

Crown slimes dams and SOWETO

Water supplies are nearing their limit

Need to maximise water recovery

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TSF closure

N l ti

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No easy solutions

SA Chamber of Mines tried grassing slimes dams for over 20 years

“Old man” Cook 

Rand mines took over the mantle (Brian Cook)

Where Digby Wells got started!

Reasons

Very erodible material – very little clay to “bind” particles 

Salts, pH and metals are a problem

Steep sides – well above agricultural slopes

Mines required to flatten to 1:7 in Queensland

Return to grazing

Cost in excess of $40 000 /ha (R300 000)

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Closure - PasteRock ®  

C t ll d l f thi k d filt d t ili dd d t t k

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Controlled volume of thickened or filtered tailings added to waste rock

Mixed and then placed in a “thin” cover layer  

Has use in providing low permeability covers – control of AMD

Scale of use limited by waste size and mixing equipment

Could be used to dispose of tailings with mine waste (codisposal)

Used for coal rejects - Bulga, Mt Thorley

Planned for Namibian copper mine Daggafontein example

 A dry PasteRock cover

 An erosion resistant matrix of rock & soil

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In closure

N l ti

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No easy solutions

Tailings disposal will become more costly

Engineering input will increase

SA has an urgent need to train more tailings design and operationalengineers

This means more geotechnical engineers!!

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The end – thanks