basics of mining and mineral processing

8/12/2019 basics of mining and mineral processing

1/179

20 12 Am er i ca s Sch oo l o fM i n e s

W Scott DunbarUniversity of British Columbia

www.pwc.com

Basics of Mining and Mineral Processing


2/179

Agenda

GeologicalConcepts

MiningMethods

MineralProcessingMethods

MineWasteManagement

MiningandMoney

AFutureofMining


3/179

PwCPwC

Th e m a i n t o p i cs

Crushingand

grinding

Smeltingand

refining

Solutionextraction

Electrowinning

Flotationof

sulfides

3

Goldoreprocessing

Pressureoxidation

ofconcentrate



4/179

PwCPwC

Ot h er t o p i cs

Physicalseparation

Coal

4

Bioleaching

Diamonds Oilsands

Uranium

Industrial

minerals



5/179

A l l t h e ch em i st r y y o u n eed t o k n ow


6/179

PwCPwC

M eet a t om A

electron

nucleuswith

protons

Nucleuscontainspositivecharges

Eachelectronhasanegativecharge

Numberofpositivecharges=numberofnegativecharges

+

+

+

+

+ +

+ +

+

+

+

+

Inthiscase12electrons

12protons

MineralProcessingMethods 6


7/179

PwCPwC

Th e po si t i v e i o n A +

Takeawayoneelectron

AtomAbecomesapositiveionA+

AA+ +e

+

+

+

++ ++ ++

+

+

+Inthiscase

11electrons

12protons



8/179

PwCPwC

Th e n ega t i v e i o n A

Addoneelectron

AtomAbecomesanegativeionA

A+eA

+

+

+

++ ++ +

++

++ Inthiscase

13electrons

12protons



9/179

PwCPwC

S im i l a r l y

Takeawaytwoelectrons

AA++ +2e(orA2+ +2e)

Addtwoelectrons

A+2eA2

Canbegeneralizedtonelectronsif

atomswillallowit



10/179

PwCPwC

I o n s ex i st i n so l u t i o n ( y o u ca n t t o u ch t h em )

Saltorsodiumchloride

NaCl (s)Na+

(aq)+Cl

(aq)

s solid

aq inaqueoussolution

Na+

Cl

NaNa+ +e

Cl +eCl



11/179

PwCPwC

The g o a l o f p r o cessi n g a n d r ef i n i n g m et a l s

istogetthemetalsintosolutionaspositiveions

Some examples:

Copper Cu+2

Gold Au+

Lead Pb+2

Zinc Zn+2

Somemetalsionizemoreeasilythanothers

ThisishardtodoTheseareeasier

toionize



12/179

PwCPwC

An d o n ce t h ey a r e i n so l u t i o n

electricitycanbeusedtoaddelectronstothemetalionsandplate

themassolidsontoasolidsurface

www.csiro.au/helix/sciencemail/activities/CopperCoat.htmlMineralProcessingMethods 12


13/179

PwCPwC

K i t ch en ch em i st r y ( y o u ca n d o t h i s)

9Vbatterysnapwithalligatorclips

Glasscontainer

Coppersulphate

fromgardenstores

http://www.csiro.au/helix/sciencemail/activities/CopperCoat.html/



14/179

Cr u sh i n g a n d Gr i n d i n g


15/179

PwCPwC

Gy r a t o r y cr u sh er f i r st t h e b l a st , t h en t h i s

Therockiscrushed

betweenthespindle

andtheinnershell

Hydraulichammer

Thespindleofthecrusher

moveseccentricallyabout

theverticalaxis

www.sandvik.com

Result:1050mm

sizeparticles

Topof

spindle

15MineralProcessingMethods


16/179

PwCPwC

No t es: Gy r a t o r y Cr u sh er

16

Crushing is the second stage of rock breakage or comminution, the first stage being blasting. Primary

crushing is often done in the pit or underground. For hard rock a gyratory crusher is often used. The

goal is to reduce rock particles to 1050 mm size. The rotation speed of a gyratory crusher is 85100

rpm.The picture on the right shows the top of the spindle of a gyratory crusher. A pneumatic rock breaker is

also shown. This is operated by a human whose job is to use the breaker to break up the large

fragments. Blasting should have broken all the rock into a smaller size.

Secondary or even tertiary crushing might be necessary in the

mill to ensure that rock breakage occurs to the required size.Secondary and tertiary crushing would be done by a cone

crusher (see picture at right) the operation of which is similar

to a gyratory crusher except that the conical crushing head is

supported from below rather than by an overhead spider. The

feed to the crushing head is from a large bowl. Cone crushers

operate at higher rotation speeds than gyratory crushers.

www.metsominerals.com



17/179

PwCPwC

Bagd a d : I n -p i t cr u sh er , co n v ey o r , a n d

s t o c k p i l e



18/179

PwCPwC

Tw i n i n -p i t c r u sh er s a n d co n v ey o r s a t H VC



19/179

PwCPwC

AG an d SAG M i l l s t h e co a r se g r i n d

19

SAGmill

HuckleberryMine

Autogenous (AG):

ore tumbled in water to selfgrind the ore particles

Semiautogenous (SAG):ore particles and steel balls tumbled with water

Result:


20/179

PwCPwC

No t es: AG an d SAG m i l l s t h e co a r se g r i n d

20

Autogenous (AG) mills use large particles of ore as grinding media. For an ore to successfully grind

autogenously, the ore must be hard and it must break along boundaries between mineral grains to

produce particles large enough to grind the remaining particles to sufficiently fine size. If an ore cannot

be ground autogenously to sufficiently fine sizes, semiautogenous grinding is used in which steel balls

and the ore itself are tumbled to break the ore.Autogenous grinding has two advantages, (1) it reduces metal wear and (2) the use of large ore

particles as grinding media means that the need for secondary and tertiary crushing stages is reduced

or eliminated.

AG and SAG mills are available for both wet and dry grinding. The diameter of AG and SAG mills is

normally two to three times the length. Larger diameter mills are common in North America whilelonger mills are more common in Europe. A large diameter mill relies on the rocks and balls falling

through a large distance to break up the ore while a long mill relies on longer residence time.

The size of the feed to a AG/SAG mill can be large and is limited to that which can be fed to the mill by

conveying systems. Because of this the need for secondary and tertiary crushing is often eliminated.

AG/SAG mills can also grind ore with high moisture and clay content, which is otherwise difficult to do.



21/179

PwCPwC

I n si d e a l a r g e SAG m i l l

21

LinerreplacementinHighland

ValleySAGmill



22/179

PwCPwC

Ba l l M i l l t h e f i n e g r i n d

www.porcupinegoldmines.ca

Result:partcles ofsize~0.075mm



23/179

PwCPwC

No t es: B a l l m i l l t h e f i n e g r i n d

23

Grinding mills break up the ore particles into finer particles with a range of sizes.

Aball millgrinds material by rotating a cylinder with steel grinding balls, causing the balls to fall back

into the cylinder and onto the material to be ground. Grinding action is byimpact. Ball mills are used to

grind material 0.25 inch and finer down to a particle size between 20 to 75 microns (0.0008 to 0.003

in). The rotation is usually between 4 to 20 revolutions per minute, depending on the diameter of themill; the larger the diameter, the slower the rotation. If the peripheral speed of the mill is too great,

the mill begins to act like a centrifuge and the balls do not fall back into the center of the mill, but stay

on the perimeter.. The point where the mill becomes a centrifuge is called the critical speed", and ball

mills usually operate at 65% to 75% of the critical speed.

The power requirements of ball mills depend on the energy required to grind the feed particles to aparticular size and on the dimensions and operating conditions of the mill.



24/179

PwCPwC

Cy cl o n e sepa r a t e coa r se f r om f i n es

Fines

Coarse

Inlet

Separates coarsegrained particles from finegrained

particles in a slurry. Also calledclassification.

Slurry pumped in at high pressure. Creates low pressure in

center of the cyclone (as in a tornado)

Finegrained particles to the topoverflow

Coarsegrained particles to the bottom underflow



25/179

PwCPwC

Gr i n d i n g Ci r cu i t a t B a g d a d

Concentratorcapacity

75,000tpd



26/179

PwCPwC

No t es: Gr i n d i n g Ci r cu i t a t B a g d a d

26

Crushers, AG mills and SAG mills, ball mills, and cyclone separators are configured intogrinding circuits

depending on the way the ore breaks up into finer sizes which depends mostly on the hardness of the

ore. The distribution of the size of particles resulting from one component of a grinding operation

governs the configuration of the grinding circuit and the equipment used in the grinding circuit.Grinding circuits typically involve secondary crushing or regrinding, cycling particles from the output of

one unit back to the input of the unit.

At Bagdad five grinding circuits in the mill process about 3000 tons of ore per hour. The output of an

AG mill is fed into a screen. The coarse material from the screen is passed to a cone crusher and fed

back into the AG mill. The cone crusher is used to break up larger particles which would otherwisesimply cycle through the AG mill. The fine material from the screen is fed into a closed ball mill circuit.

The output of the ball mill is separated into coarse and fine fractions in a cyclone, the coarse fraction

(underflow) is recycled and the fine fraction (overflow) is pumped to the flotation tanks.

In the absence of AG or SAG mills, there would be a rod mill followed by a closed circuit ball mill.

However, a rod mill is less efficient at grinding rock than an AG or SAG mill.



27/179


28/179

PwCPwC

Gr i n d i n g Ci r cu i t a t H i g h l a n d V a l l ey

Concentratorcapacity

135,000tpd



29/179

PwCPwC

No t es: Gr i n d i n g Ci r cu i t a t H i g h l a n d V a l l ey

29

At Highland Valley there are five parallel grinding lines which process a total of 5400 tonnes of

crushed ore per hour. Two of the grinding lines employ autogenous mills (AG) and three employ semi

autogenous (SAG) mills. Each mill feeds two closedcircuit ball mills which reduce the ore to sandsized

particles which feed the flotation circuits.

Each grinding circuit grinds and regrinds to ensure that the entire feed is reduced to sand size. The

ore exiting the AG or SAG mill is fed into vibratory grizzly feeders which separate the ore into

undersize and oversize. The undersize goes to the ball mill circuit while the oversize returns to the AG

or SAG mill. The ball mill circuits employ cyclones to separate sand from coarser particles. Coarse

particles are returned to the ball mill while finer sand particles (the overflow) go to the flotation cells.It is usually not possible to distinguish an AG from a SAG mill based on its appearance.

Why are there two ball mills at HVC and one at Bagdad. Partly this is related to the larger tonnage

throughput at HVC, approx 1150 tons per hour versus 600 tons per hour at Bagdad. However, it is also

related to the power required to grind the rock into particles fine enough for flotation, Since there is a

limit to the size of a ball mill, the harder the rock, the more mills that are needed to deliver the power.

This does not necessarily mean that the rock at HVC is harder than that at Bagdad. The mill at HVC is a

combination of machinery from other mills and it may be that it was good enough at the time.



30/179

PwCPwC

A g r i n d i n g ci r cu i t a t H i g h l a n d V a l l ey

ballmillSAGmill

cyclones



31/179

PwCPwC

En er g y co n sum p t i o n o f cr u sh i n g a n d

g r i n d i n g

31

Largestconsumerofenergyataminesiteiscrushingandgrinding

Crushing:from

>50mm

to10

50

mmGrinding:from


32/179

F l o t a t i o n o f Su l f i d es


33/179

PwCPwC

Air

Concentrate

Tonext

flotationcell

Add

collector

Slurryfrom

grinding

Add

frother

F l o t a t i o n t h e ba si c i d ea

Frothermakesfrothstiffandstable

Frothers arealcohols

bubble

sulfideparticle

Collectormakessulfide

particleshydrophobic

Collectorsarelikesoaps



34/179

PwCPwC

N o t es: F l o t a t i o n t h e bas i c i d ea

34

Froth flotation is the most common method for separating sulfide minerals from each other and from

waste minerals organgue.

The particles from the grinders are mixed with water to form a pulp in a flotation cell. An organic

chemical called a collector is added. It selectively coats the surface of the mineral of interest and

renders it hydrophobic, meaning literally afraid of water. You all have used a collector called soap;

soap coats dirt particles rendering them hydrophobic.

A stream of air bubbles is passed through the pulp. Being hydrophobic, the particles attach to the

bubbles which, of course, are filled with air. The bubbles float to the surface and collect in a froth layer

that either flows over the top of the cell into a channel at the base of the cell. (Some froths are thickand may have to be skimmed.) A frother, such as a long chain alkyl alcohol, is added to stabilize the

froth layer. The froth on a beer will float things (yuk!), but the froth is not stable so beer cannot be

used in sulfide flotation.

The first use of flotation to separate sulfides was at the Broken Hill mine in Australia where they used

eucalyptus oil as a collector. Collector chemistry has advanced considerably since then so that different

metal sulfides in an ore can be sequentially floated by the use of different types of collectors and

adjustment of the chemistry (typically the acidity) of the cell.



35/179


36/179

PwCPwC

The f r o t h co p p er co n cen t r a t e

Wetconcentrate

~27%copper



37/179

PwCPwC

No t es: T he f r o t h copper co n c en t r a t e

37

A simple materials balancing can be used to determine the amount of ore, K, needed to produce one

ton of concentrate. This is known as the concentration factor. At Highland Valley the ore grade is 0.43%

Cu and the recovery of copper in the concentrator is 85%. The concentrate is 28% copper. Thus

K(tons) 0.0043 0.85=1(ton) 0.28

From which K ~ 77 tons. This ignores ore dilution, d%, which adds a factor 1d to the left hand side ofthe above equation. If drilling and blasting are properly controlled, dilution at an open pit mine is

small.

There is an upper limit to the concentration of a metal in a concentrate depending on the mineral in

the ore. This is the direct proportion by atomic weight of the metal to the molecular weight of the

mineral. Some approximate atomic weights are given in the table below:Copper Iron Lead Zinc Sulfur

64 56 207 65 32

For a copper concentrate made from chalcopyrite (CuFeS2), the copper concentration limit is 34.8%,

i.e., 64/(64+56+232) = 0.348. Similarly the concentration limit of lead in a lead concentrate made

from galena (PbS) is about 87% and for a zinc concentrate made from sphalerite (ZnS), theconcentration limit is about 67%. A mine that has bornite (Cu5FeS4) in its ore can achieve quite high

copper concentrations; unfortunately bornite is relatively rare.



38/179


39/179

PwCPwC

No t es: Fl o t a t i o n c i r cu i t s

39

On the left is a simple flotation circuit for mineral concentration. The numbered triangles show the

direction of flow. In a conditioning tank the collector is added to the slurry (often called pulp) from the

grinding circuit. The conditioned pulp [1] is fed to a bank ofroughercells which remove most of the

desired minerals to produce a concentrate froth. The tails from the rougher flow [2] to a bank of

scavenger cells where the pulp is refloated and the froth is returned [3] to the rougher cells foradditional treatment. The scavenger tailings is usually barren enough to be discarded as tails but in

some cases may be sent tocleanercells to be refloated.

More complex flotation circuits have several sets of rougher, scavenger, cleaner and recleaner cells, as

well as intermediate regrinding of pulp or concentrate. On the right is a picture of the bank of

flotation cells (blue motor housings) at the Neves Corvo copper/zinc mine in Portugal.Recovery of metals by flotation varies depending on the complexity of the ore. For a simple ore

containing only copper with some gold byproduct recovery can be 9095%. Recovery is lower for

polymetallic ores which may contain roughly equal proportions of desirable metals.



40/179

PwCPwC

Sepa r a t i o n o f Cu a n d M o co n cen t r a t es

In column vats at Bagdad (2005 quantities)

Sodium

hydrosulfide

Incolumnvats

Cu/Mo

concentrate

Sodium

hydrosulfide

molybdenite concentrate58%Mo

copperconcentrate

27%Cu

Pressure

leach

SmelterStripscollectoroffchalcopyriteparticles



41/179

PwCPwC

No t es: Sepa r a t i o n o f Cu an d M o con cen t r a t es

41

Both copper and molybdenum minerals are floated in the first stage, leaving iron sulfides and other

waste minerals behind as tailings. The concentrate is then sent to a column flotation vat and sodium

hydrosulfide added to remove the collector from the surfaces of the chalcopyrite so that it sinks to the

bottom of the vat. The molybdenite floats to the surface since it is naturally hydrophobic.

The molybdenite (MoS2) in the concentrate may be purified for use in lubricants. Almost all

molybdenum ore is converted by roasting to molybdic oxide (MoO3). The oxide may be added directly

to steel to form a hard alloy that can withstand high temperatures; such alloys are used in making high

speed cutting tools, aircraft and missile parts, and forged automobile parts.

Other useful compounds of molybdenum include ammonium molybdate, used in chemical analysis for

phosphates; and lead molybdate, used as a pigment in ceramic glazes.



42/179

PwCPwC

Con cen t r a t e l o g i st i cs i n BC

BaggedmolyconcentrateatHVCshippedeast

byrail

VancouverWharves

leadzincconcentratesin

copperconcentratesoutwww.pnwship.com/canada/concentrates

Newloaderfor

copperconcentrates



43/179

PwCPwC

The g r a d e-r eco v er y b a t t l e

43

Chalcopyrite

particle

Chalcopyriteparticle

withnonsulfideinclusion

Chalcopyriteparticlewith

attachednonsulfidecrystal

Allowcollectormoretimetoadheretochalcopyriteparticles

Result:increased recovery of all particles with chalcopyrite, but

concentrate grade decreases



44/179

PwCPwC

N o t es: Th e g r ad e-r eco v er y ba t t l e

44

This is a common problem in all sulfide concentration processes.

The flow rate and tank size are designed to give the minerals enough time to be coated with collector

(commonly called activation). Recovery depends on the flow rate. As the input flow rate decreases, the

sulfide particles have more chance to be exposed to the collector and adhere to the bubbles so thatrecovery increases. However, the grade of the concentrate decreases because more silicates are

recovered along with the target sulfide.

One solution is to use finer grinding. However, this can be costly and would only be done if there was

the possibility of recovering valuable metals.



45/179

PwCPwC

Bagd a d co p p er co n cen t r a t e



46/179

Sm el t i n g a n d Ref i n i n g


47/179


48/179

PwCPwC

Sm el t i n g o f co p p er co n cen t r a t e

Oxygentakes

electronsoffsulphur

becauseoxygenwantsthemmore

ofcopperconcentrate

UndowhatNaturedidwhenformingthesulfide

oxygen

sulfur

dioxide

Ironoxides(slag)

copperanode

(9598%pure)

Addelectrons

tocopper

Addelectrons

toiron


copper

concentrate

CuFeS2

N S l i f


49/179

PwCPwC

N o t es: Sm el t i n g o f copp er con cen t r a t e

49

1 chalcopyrite + oxygen ironoxide + covellite + sulphur dioxide

2CuFeS2 + 3O2 2FeO + CuS + SO2

2 covellite + oxygen chalcocite + sulphur dioxide

CuS + O2 Cu2S + SO2

3 chalcocite + oxygen copper + sulphur dioxide

Cu2S + O2 2Cu + SO2

Three chemical reactions involving copper sulfides occur in a smelter (1,200C).

The copper and iron oxide collect at the bottom of the furnace to form mattecopper whichis tapped off and burned in a converter furnace to remove iron oxides and sulphur resulting

in blister copper. Oxygen in the blister is then burned off using natural gas to form anode

copper which is 95 to 98% pure and must be refined to produce cathode copper which is

99.99% pure.

Limestone (CaCO3) is added to the furnace. When heated it decomposes to calcium oxide

(CaO) and carbon dioxide (CO2). Calcium oxide reacts with silica (SIO2) and iron oxide (FeO)

which remain solid at 1,100C to form calcium and iron silicates which melt to form a slag.

The slag is lighter than matte so it floats on top of it from where it is removed and taken to

a disposal site.



50/179

PwCPwC

D ou b l e en t r y ch em i st r y ( i n a sm el t er )

Electrons

Account Reaction Debit Credit

Sulfur 4S2 4S+4 (in4SO2) 24

Copper 2Cu+1 2Cu(whatiswanted) 2Iron 2Fe+3 2Fe+2(in2FeO) 2

Oxygen 5O2 10O2 (in2FeOand4SO2) 20

Balance 24 24

Remember:Yousawdoubleentrychemistryherefirst!

chalcopyrite + oxygen copper + iron oxide + sulfurdioxide

2CuFeS2 + 5O2 2Cu + 2FeO + 4SO2



51/179

PwCPwC

T h e Sm el t er a t M i am i A r i zo n a

51

Coppersulfidesinconcentrate

Copperanode



52/179

PwCPwC

An d w h a t a b o u t t h e su l p h u r d i o x i d e?

52

ThatstheSO2thatresultsfromsmeltingasulphide

Itsapoisonousgasbutcanbeconvertedtosulphuricacid

Sulphuricacidisusedincarbatteries,thepaperandfertilizer

industries.Itcanalsobeusedtoleachcoppersulphides(seelater)

Vitriol thehistoricnameofsulphuricacid



53/179

PwC

H ow t o m a k e su l p h u r i c a ci d f r om su l p h u r d i ox i d e

53

The diagram on the previous slide shows the contact process which starts with the

following reaction:

2SO2(g)+O2(g)2SO3(g)inthepresenceofvanadiumoxidecatalystat400450C

The sulphur trioxide gas could be bubbled through water but that results in an

uncontrollable reaction. Instead the gas is absorbed into a highly concentrated

solution of sulphuric acid to form a liquid called oleum (or fuming sulphuric acid)

and then the oleum is mixed with water to produce sulphuric acid

H2SO4(l)+SO3(g)H2S2O7(l)

H2S2O7(l)+H2O(l)2H2SO4(l)

Note that twice as much sulphuric acid is made as was originally used to make the

oleum.



54/179

PwCPwC

E l ect r o -Ref i n i n g o f Copp er An ode

++++

++++

++Anodefromsmelter

9598%copper

Cathode

99.99%copper

Insolubleimpuritiesformslimesonanode

(couldincludegold,silver,platinum,palladium)

CopperionCu+2

Powersupply electronflow

Useelectricalenergytoforcecopperionsoffanode

54MineralProcessingandRefining


55/179

PwC

N o t es: E l ect r o -Ref i n i n g o f Copp er An ode

55

The anode copper plates from the smelter are placed on one side of a tank filled with

sulphuric acid and cooper sulphate as an electrolyte. The power supply forces the copper

atoms in the anode to give up two electrons each (to oxidize) forming Cu+2 ions. The

electrons flow through the circuit and end up at the negatively charged cathode while the

copper ions flow through the electrolyte toward the cathode. The electrons and ions

combine at the cathode to produce 99.99% pure copper, hence the name cathode copper.

After about two weeks in the cells the cathodes are harvested.

MineralProcessingandRefining

Attheanode Atthecathode

CuCu+2+2e

oxidationofcopper

Cu+2 +2eCu

reductionofcopper

Impurities, which may include gold, silver, platinum and palladium depending on the origin

of the concentrate, form slimes on the decomposed anode. They are extracted later by avariety of processes.

Cop p er r ef i n er y a t H a r j a v a l t a sm el t er ,


56/179

PwCPwC

Cop p e e e y a a j a a a s e e ,

F i n l a n d

56

www.boliden.com



57/179

L ea ch i n g Rea ct i o n s & H eap L ea ch i n g

L h i f i d d l f i d


58/179

PwCPwC

L ea ch i n g o f copp er o x i d es an d su l f i d es

Withdiluteacid

Eachreactionproducescoppersulfate.Recoverymaybepoor.

+

Azurite

Tenorite

Chalcopyrite

Chalcocite

Lowgrade

oxidesand

sulfides

Copper

Sulfate

WaterCarbon

Dioxide

Sulfur

Dioxide

Sulfur

lixiviant

Diluteacid

Sulfuric

Acid



59/179

D um p l ea ch p a d s a t M o r en ci A r i zo n a


60/179

PwCPwC

D um p l ea ch p a d s a t M o r en ci , A r i zo n a

Lowgradeore~0.2%

Pregnantleachsolution(PLS)withcoppersulfate CuSO4

60

www.geomineinfo.com/mining_photos.htm


H eap l ea ch i n g


61/179

PwCPwC 61

Leach pads can be divided into four categories: conventional or flat pads, dump leach

pads, valley fills and on/off pads. Conventional leach pads are relatively flat, either graded

smooth or terrain contouring on alluvial fans such as in the Chilean Atacama desert,

Nevada and Arizona, and the ore is stacked in relatively thin lifts (5 to 15 m typically). The

lifts in dump leach pads are much thicker (up to 50m). Valley fill systems are leach pads

designed in natural valleys using either a buttress dam at the bottom of the valley, or a

leveling fill within the valley.

On/off pads (also known as dynamic heaps) are hybrid systems. A flat pad is built with a

robust liner system. Then a single lift of ore, from 4 to 10 meters thick, is loaded andleached. At the end of the leach cycle the spent ore is removed for disposal and the pad

recharged with fresh ore. Usually loading is automated, using conveyors and stackers.


L ea ch i n g o f g o l d o r e w i t h cy a n i d e


62/179

PwCPwC

L ea ch i n g o f g o l d o r e w i t h cy a n i d e

gold + sodium

cyanide + water + oxygen

sodium

aurocyanide +

sodium

hydroxide

4Au + 8NaCN + 2H2O + O2 4NaAu(CN)2 + 4NaOH

The Elsener reaction

62

Leachingdoneinheapleachpadsortanks

This is the basis of two processes for extracting gold:MerrillCrowe: uses zinc to precipitate gold

Carbon adsorption: adsorb aurocyanide onto activated carbon

Lixiviant

Cyanide+water


Go l d h eap l ea ch pa d


63/179

PwCPwC

Go l d h eap l ea ch pa d

Driptrickle

irrigation

system

on

top

of

pad

RubyHillGoldMine,Nevada,USA

www.miningtechnology.com/projects/rubyhill/rubyhill6.html


Seep a ge i n a l ea ch p a d


64/179

PwCPwC

Seep a ge i n a l ea ch p a d

Recoveryisuncertainandvariesoverthelifeofthepad

Typicalgoldrecoveries:4070%

lessconsolidated

moreflow

moreconsolidated

andmorefines

lessflow

Notedifferencein

colorattopofpad

mineralparticle

Leach pad, Anchor Hill pit, South Dakota

Photo courtesy Robertson Geoconsultants

64

continuous

irrigation



65/179

Ag g l om er a t i o n o f g o l d o r e


66/179

PwCPwC

Ag g l om er a t i o n o f g o l d o r e

66

Fines plug voids between particles

and cause a loss of permeability

which prevents the flow of

lixiviant. Agglomeration of the

fines into larger particles creates

larger voids through which the

lixiviant can flow.

ore+cement+

lixiviant

Rotatingagglomerationdrum



67/179

So l u t i o n Ex t r a ct i o n E l ect r o -w i n n i n g



68/179

N o t es: So l u t i o n ex t r a c t i o n (SX )


69/179

PwC

N o t es: So l u t i o n ex t r a c t i o n (SX )

69

The water and copper sulfate form a solution known as a pregnant leach solution or PLS. The PLS ispumped into a solvent extraction plant (the SX or extraction stage) where it is mixed with an organicsolvent, an acid which we will label HR, to denote a hydrogen atom and a long chain hydrocarbonmolecule R. (This is the oily stuff seen in the tanks.) The copper sulfate and HR react in the mixer asfollows:

The sulfuric acid goes back to the heap leach pad and the copper organic phase CuR 2 goes to thestripping stagewhere it is mixed with a stronger acid solution to strip the copper from the CuR2

Now the copper sulfate solution is much richer in copper. The organic acid is recovered and reused.

Copper

sulphate + Organic

acid Loaded

organic + Regenerated

Sulphuric acid

CuSO4 + 2HR CuR2 + H2SO4

Loaded

organic +

Sulphuric

acid

Copper

sulphate +

Regenerated

organicacid

CuR2 + H2SO4 CuSO4 + 2HR


E l ect r o -W i n n i n g ( EW )


70/179

PwCPwC

g ( )

++++

++++

++Anode

(leadtinalloy)

Cathode

(starterplate)

Powersupply electronflow

Winthecopperfromthesolution

CoppersulfateCuSO4

solutionfromSXplant

CopperionCu+2

Sulphuric acid H2SO4toSXplant

70MineralProcessingandRefining

No t es: El ect r o -W i n n i n g ( EW )


71/179

PwC

g ( )

71

The copper sulfate solution is called an electrolyte. At the anode, electrical energy splits water into

hydrogen and oxygen to give a hydrogen ion, two electrons and oxygen. The power supply causes the

electrons to flow through the circuit to the cathode. Being positively charged, the copper ions are

attracted to the negatively charged cathode where they combine with the electrons to form copper

metal.

At the anode: H2O2H+1 + 0.5O2+ 2e (oxidation of hydrogen)

At the cathode: Cu+2 + 2e Cu (reduction of copper)

Copper that is 99.999% pure (five nines) has been produced using the SX/EW process.

In electrowinning the copper is in a solution (the electrolyte) whereas in electrorefining the copper

from the smelter forms the anode of the cell. Electrowinning requires much more energy than

electrorefining because more energy is required to break down water to provide electrons than to

oxidize copper to the Cu+2 state and provide two electrons.

Note: Oxygen is formed at the anode and produces bubbles. In addition, the hydrogen ions, H +1,

combine with the sulfate ion, (SO4)2, produce sulfuric acid in the tank, H2SO4. When the bubbles reach

the surface they burst, liberating an aerosol of sulfuric acid called acid mist. This is not good for thehealth of operators in the tank house. Chemical additives are used to reduce the size of the bubbles

and to put a thin layer of foam over the electrolyte to keep the bubbles from reaching the surface.


Ba g d a d : SX / EW f a ci l i t y


72/179

PwCPwC

Electrowinning

plant

Severalsolventextractionand

solventstrippingstagesinparallel


E l ect r o -W i n n i n g P l a n t s


73/179

PwCPwC

Quebrada Blanca

Harvestingandwashingcathodes

atBagdad


An odes an d Ca t h odes


74/179

PwCPwC

Anode

(leadtinalloy)

Cathode

Copper

Starters


Pr essu r e l ea ch i n g o f con cen t r a t e


75/179

PwCPwC

anotherwaytooxidizesulfides

ExperimentalfacilityatBagdad,

Arizona


Th e p r essu r e l ea ch p r ocess


76/179

PwCPwC 76

Coppersulfatetoelectrowinning

Molybdenumoxide tosteelcompanies


N o t es: Th e p r essu r e l each p r ocess


77/179

PwCPwC 77

In a stainless steel reactor vessel the concentrate slurry is agitated or stirred for about 30 minutes. The

temperatures used range between 212450F (100232C) and the pressures used range between 200

600 psi (13794137 kPa)

For chalcopyrite concentrate there are actually two chemical reactions:

chalcopyrite+oxygen

copper

sulfate

+ferrous

sulfateCuFeS2+4O2 CuSO4+FeSO4

ferroussulfate+oxygen+water ferricoxide(rust)+sulfuricacid

4FeSO4+O2+4H2O 2Fe2O3+4H2SO4Iron:Fe+2 insulfateoxidizedtoFe+3 inironoxide.

Some copper concentrates are dirty and contain impurities such as antimony, bismuth, arsenic and

mercury. These are found within the iron oxide (rust) that precipitates during the leach. Any preciousmetals in the concentrate would also be found in the iron oxide. These can be extracted using cyanide

leach processes (see later).

For molybdenite concentrate the chemical reaction is

Molybdenite +oxygen+water Molybdenumoxide+sulfuricacid

MoS2+4.5O2+2H2OMoO3+2H2SO4Bagdad is currently using their autoclave to oxidize their molybdenite concentrate.



78/179

Pr o cessi n g o f Go l d O r e


Ba si ca l l y w e w i l l see h ow


79/179

PwCPwC

0.116ozperton

~3.97gm pertonne

this

istransformedtothis


M er r i l l -Cr ow e p r o cess


80/179

PwCPwC

zinc

dust +

sodium

aurocyanide gold +

sodiumzinc

cyanidecomplex

Zn + 2NaAu(CN)2 2Au + Na2Zn(CN)4

Goldprecipitateisfilteredandthensmeltedtoproducegoldbar

80

gold + sodium

cyanide + water + oxygen sodium

aurocyanide + sodium

hydroxide

4Au + 8NaCN + 2H2O + O2 4NaAu(CN)2 + 4NaOH


The Elsener reaction

W h y zi n c?


81/179

PwCPwC

Becausezincgivesupelectrons(oxidizes)morereadilythangold

Agoldionwillpickupanyelectronszincprovidesandprecipitate

Zincsolid Zincinsolution Twoelectrons

Zn(s) Zn+2(aq) + 2e

Goldinsolution + Twoelectrons Goldsolid

2Au+(aq) + 2e Au(s)

Zincisusedtoprecipitatemetalsfromsolutioninthefollowingorder

Iron Cadmium Cobalt Nickel Tin Lead Antimony Copper Silver Gold

Fe+2 Cd+2 Co+2 Ni+2 Sn+2 Pb+2 Sb+3 Cu+2 Ag+2 Au+1



82/179

N o t es: M er r i l l -Cr ow e as a sy st em

Ore is first crushed and ground, then placed in leach pads. (It may also be crushed and ground and


83/179

PwCPwC 83

Ore is first crushed and ground, then placed in leach pads. (It may also be crushed and ground and

placed in stirred tanks for leaching.) A sodium cyanide solution is added to the ore which produces a

solution of sodium aurocyanide and sodium hydroxide.

gold+sodiumcyanide+oxygen+water sodiumaurocyanide +sodiumhydroxide

4Au+8NaCN+O2+2H2O4NaAu(CN)2+4NaOH

The aurocyanide complex involves Au+, gold with one electron missing.. When zinc dust is added to thesolution, the gold is reduced and precipitated as a solid. This is known as zinc cementationand actually

consists of two reactions:

zinc+sodiumcyanide+oxygen+water sodiumzinccyanide+sodiumhydroxide

Zn+4NaCN+O2+H2ONa2Zn(CN)4+2NaOH

zinc+sodiumaurocyanide gold+sodiumzinccyanideZn+2NaAu(CN)2 2Au+Na2Zn(CN)4

The aurocyanide is deaerated (oxygen removed) to stop the first reaction from producing sodium zinc

cyanide which would force the second reaction to the left and redissolve the gold. The resulting solids

are filtered producing a barren solution and then smelted to produce a gold bar.

The MerrillCrowe process is used when the ore has a high silver to gold ratio as silver cannot berecovered using activated carbon methods (see next slides). However, if the ore contains a large

amount of clay, the filtering process in MerrillCrowe can become difficult.


Ad so r p t i o n o f a u r o cy a n i d e


84/179

PwCPwC 84

Resultisloadedcarbon

30020,000g/t

Produced by burning of carbon rich materials such as

coal, wood or coconut shell. Steam or chemicals are used

to develop microporosity. Enormous internal surface

areas where adsorption can occur. (1 gm of activatedcarbon has 500 m2 of surface area.)

ontoactivatedcarbon

Activatedcarbon

particle


Th r ee w a y s a d so r b g o l d o n t o ca r b o n


85/179

PwCPwC 85

CarboninPulp(CIP)

Leachandadsorbinseparatesetsoftanks

CarboninLeach(CIL)

Leachandadsorbinthesametanks

Carbonin

Column

(CIC)

Leachinheapandadsorbintanks


Ca r b o n i n L ea ch (CI L )


86/179

PwCPwC

Crush,grind,

thicken

cyanide

Ore

Leachandadsorbinthesametanks

RegeneratedcarbonLoaded

carbon

Barren

leachate

Stripcarbon

andelectrowin

slurry

carbon

Tailings


N o t es: Ca r bon i n L ea ch


87/179

PwCPwC 87

Leaching and adsorbing in the same tanks has the advantage of lower capital costs. It is also

used when the ore is naturally carbonaceous (pregrobbing) to force adsorption onto the

activated carbon. However, leaching and adsorption in the same tank leads to

concentration gradients which must be broken down. This is done using greater agitation

than that required in CIP tanks. The result is loss of precious metals from the carbon andlower recovery than in CIP.


Ca r b o n i n Pu l p ( CI P)


88/179

PwCPwC

Carbon

adsorption

Cyanideleach

Regenerated

carbon

Crush,grind,

thickenOre

Loaded

carbon

Barrenleachate

Leachandadsorbinseparatesetsoftanks

Stripcarbon

andelectrowin

Tailings


No t es: Ca r b o n i n Pu l p

I CIP th ld i d i t fi ti l d d l i t l hi t k


89/179

PwCPwC 89

In CIP the gold ore is ground into fine particles and passed as a slurry into leaching tanks.

The pregnant solution from the leach tanks is then pumped into tanks containing activated

carbon particles. The activated carbon flows in the opposite direction to the leachate.

The number of tanks may vary between 4 and 8 depending on the rate of production.

The leaching and adsorption are done in separate sets of tanks. The advantage of this is

simplicity and the recovery can be over 95%. However, naturally occurring carbon in the

ore will compete with the activated carbon (pregrobbing) and any silver or copper

present will compete with the gold during adsorption.


Ca r b o n i n Co l um n (CI C)


90/179

PwCPwC 90MineralProcessingMethods

H eap L ea ch Pad s a n d Pr eg Pon d s


91/179

PwCPwC

LeachPad Initialstage

Pierina Mine,Peru

(MerrillCroweProcess)www.cosapi.com.pe

Heapleachpadand(empty)preg pond

CortezMine,Nevada


No t es: H eap L ea ch Pad s an d P r eg Pond s


92/179

PwCPwC 92

Left: The initial stage of one of several leach pads at the Pierina mine in Peru. The

pad is underlain by a polyethylene liner (HDPE). The pregnant solution collects in a

sump and is piped to a pregnant solution pond, also underlain by a liner.

The leach pad and the preg pond at Cortez are shown on the right. There were

several preg ponds, each lined with HDPE. The pond shown was empty at the

time. (Beautiful scenery, but it was very cold that day)


CI C Ad so r p t i o n Tan k s a t Co r t ez


93/179

PwCPwC 93

Hard to get a picture of the whole

adsorption tank facility at Cortez. You

have to go there to really appreciate it.


Th b i l (CIC) i ft d i j ti ith h l h f ld

No t es: Ca r b o n i n Co l u m n (CI C)


94/179

PwCPwC

The carbonincolumn (CIC) process is often used in conjunction with heap leach of gold

ores. Thepregnant solutionof sodium auric cyanide from the leach pad is collected in a

pond and passed through tanks where the gold is adsorbed onto activated carbon

particles. Activated carbon acts like a sponge to gold cyanide complexes in solution such as

sodium auric cyanide.The leachate flows in the opposite direction to the carbon particles so that the gold

concentration of leachate decreases downstream and the amount of gold on the carbon

increases upstream. Gold is stripped (eluted) from the loaded carbon by a solution of

cyanide and caustic soda. The stripped carbon particles are recycled.


St r i p ca r b o n a n d el ect r o -w i n


95/179

PwCPwC

Loaded

carbon Acid

wash Stripping

Sodium

hydroxide90C

Regenerated

carbon

Electrowinning

Furnace

1200C

Dor

~4090%gold

Cleancathode

dryslimes

2

AurocyanideAu CN

95

2

Au CN e Au 2CN


No t es: St r i p c a r b o n an d el ect r o -w i n

The carbon is first washed with acid to remove calcium that has precipitated on the carbon


96/179

PwCPwC 96

The carbon is first washed with acid to remove calcium that has precipitated on the carbon,

as well as to clean fines out of the carbon pores. Aurocyanide is then stripped (eluted) from

the loaded carbon by a hot solution of caustic soda (NaOH) and sodium cyanide. This

essentially reverses the Elsener equation to break up the sodium aurocyanide

The stripped carbon particles are recycled. The solution is pumped into electrowinning

tanks where the gold is plated onto a cathode. The electrowinning chemical reaction is

where e is an electron. The reaction could go either direction, but the application of

electric current forces it to the right causing a reduction of the gold ion in the aurocyanide

complex. Other metal cyanide complexes may be present resulting in impurities on the

cathode. After electrowinning the cathodes are cleaned and the resulting slurry is dried

and then refined to produce a dor bar containing mostly gold.

The electrolyte may contain other metal ions (e.g., copper) as well as the cyanide ion CN.

The electrolyte can be treated to recover the cyanide for reuse. Recovery of the other

metals is also possible.

2Au CN e Au 2CN

2 2NaAu(CN) Na Au CN


E l ect r o -w i n n i n g cel l s


97/179

PwCPwC 97

MtRawdon goldmine,Queensland

Source:Mintrex PtyLtdhttp://mintrex.com.au

stainlesssteel,rubberlined


W ash o f f ca t h o d es


98/179

PwCPwC

Hemlo/DavidBellmine(Barrick Gold)

PhotocourtesyBernKlein,Dept ofMiningEngineering,UBC


An d f i n a l l y t h e do r pou r


99/179

PwCPwC 99

MtRawdon goldmine,Queensland

Source:Mintrex PtyLtdhttp://mintrex.com.au


W h en t o u se t h ese m et h od s


100/179

PwCPwC

MerrillCrowe Used if silverdominantinore

Filteringdifficultifclayspresent

Heapleach

CarboninLeach(CIL) Lowcapitalcosts onesetoftanks

Carbonaceous ores

LowerrecoverythanCIP

CarboninPulp(CIP) Highcapitalcosts twosetsoftanks

Noncarbonaceousore

High recovery(~95%)

CarboninColumn(CIC) Lower operatingcosts

Usedforlowergradeores

Heapleach


New m on t M i n i n g : R oa st er a t Ca r l i nNe v a d a


101/179

PwCPwC 101

Somegoldorescontain

naturalcarbon

Goldisadsorbedonto

thecarbonasinCIL

process

Thisreducesrecovery

Roasterusedtoburncarbonandreleasegold


Ref r a ct o r y g o l d


102/179

PwCPwC 102

Goldmixedinwithasulfide,typicallypyriteorarsenopyrite

Cannotbeleached

~450microns

free

goldgoldin

arsenopyrite


An a u t o cl a v e


103/179

PwCPwC

Source:www.metsoc.org

inwhichsulfidesarebrokendownresultinginoxidesand

sulfuricacid

Usedtoreleasegoldfrom

refractorygoldore

(Itwillnotfly)

Sulfidesarefirstseparated

byflotation


N o t es: An au t o c l a v e

Autoclaving is used to process a variety of ores or metal products and is done in one of two ways:


104/179

PwCPwC 104

Pressure oxidation of minerals high pressure and temperature (e.g., at Bagdad)

Pressure leach high pressure in acid or alkaline conditions

For refractory gold ores where precious metals are locked within sulfide minerals such as pyrite, the

sulfur in these minerals has to be oxidized so that the sulfide minerals are broken down and the gold

can be released. Following oxidizationBase metals are released into solution to be processed by electrowinning

Precious metals are leached using cyanide

In a pressure leach of sulfide minerals an autoclave operates at temperatures >175C and pH < 2, the

following chemical reactions oxidize the iron and sulfur in pyrite. First the sulfur is oxidized:

2FeS2+ 7O2+ 2H2O

2FeSO4+ 2H2SO4 (oxidize sulfur from S1

to S+6

)Next, the iron loses an electron and forms an iron oxide which precipitates (downpointing arrow).

Sulfuric acid is also formed.

2FeSO4+ O2+ H2O Fe2O3+ 2H2SO4 (oxidize iron from Fe+2 to Fe+3)

Electrons are taken from the sulfur and iron atoms. The oxygen atoms get all the electrons in these

reactions.



105/179

Ot h er M et h o d s

Gr a v i t y co n cen t r a t i o n sh a k i n g t a b l e


106/179

PwCPwC

www.odm.ca/pages/heavy.html

slimestailings

Reciprocating

motor

heavier

particles

middlings

orewater


Gr a v i t y con cen t r a t i o n - cen t r i f u g a lc o n c e n t r a t o r


107/179

PwCPwC

Usedtoseparatefreegoldparticles

Water

cavityConcentratingcone

www.knelson.com


Gr a v i t y co n cen t r a t i o n

Shaking table


108/179

PwCPwC 108

A shaking table consists of a sloping deck with a riffled surface. A motor drives a small arm

that shakes the table along its length, parallel to the riffle and rifle pattern. The shaking

motion consists of a slow forward stroke followed by rapid return stroke. Water is added to

the top of the table perpendicular to the table motion. The heaviest and coarsest particlesmove to one end of the table while the lightest and finest particles tend to wash over the

riffles and to the bottom edge. Intermediate points between these extremes provides

recovery of the middling (intermediate size and density) particles.

Centrifugal concentrator

A centrifugal concentrator consists of a riffled cone or bowl that spins at high speed tocreate forces in excess of 60 times that of gravity. Slurry is introduced into the cone; the

centrifugal force produced by rotation drives the solids toward the walls of the cone. The

slurry migrates up along the wall where heavier particles are captured within the

riffles. Injecting water through the holes located in the back of the riffles fluidizes the

riffled area. The fluidization process prevents compaction of the concentrated bed andallows for efficient separation of heavy minerals.


Sl u i ce bo x


109/179

PwCPwC

gravel&sandhere

rifflescatchheavier

particles

waterflow

http://nevadaoutbackgems.com/design_plans/DIY_equipment.htm


T r om m el scr een


110/179

PwCPwC

Largersize

screen

Smallersize

screen

www.metso.com


M agn et i c sep a r a t i o n


111/179

PwCPwC

Nonmagnetic

material

Magneticmaterialfalls

awayatundersideofdrum

Nonmagnetic

shell

Stationary

permanentmagnet

Feed

leveler


M ag n et i c sep a r a t i o n i n i r o n o r e p l a n t


112/179

PwCPwC

www.metso.com



113/179

N o t es: Pr o cessi n g w i t h ba ct er i a

Biooxidation of sulfides in refractory gold ore

Gold is often embedded in the crystal structures of pyrite and arsenopyrite. In the presence ofbacteria, the following reactions oxidize the sulfur in these minerals and break them up to release the

gold


114/179

PwCPwC 114

gold.

Pyrite: FeS2+ 14Fe+3 + 8H2O 15Fe

+2 + 2(SO4)2 + 16H+ (1)

Arsenopyrite: FeAsS + Fe+3 + 3O2 + 2H2O 2Fe+2 + (AsO4)

3 + 2(SO4)2 + 4H+ (2)

Fe+2 to Fe+3: 4Fe+2 + O2

+ 4H+ 4Fe+3 + 2H2

0 (3)

The Fe+3 generated in Reaction 3 is consumed in Reaction 1.

Bioleaching for copper

The speed of the oxidation of copper/iron sulfides (and other metal sulfides) is vastly increased by the

introduction of Thiobacillus ferrooxidans bacteria to the system. In the presence of Thiobacillus

ferrooxidansthe chemical reaction is:

4CuFeS2+11O2+6H2O 4CuSO4+4Fe(OH)3+4S(oxidizeironfromFe+2 toFe+3)

Bioleaching vs Biooxidation?

Bioleaching refers to the use of bacteria, principally Thiobacillus ferrooxidans, Leptospirillum

ferrooxidansand thermophilic species ofSulfobacillus,AcidianusandSulfolobus, to leach metal such as

copper, zinc, uranium, nickel and cobalt from a sulfide mineral into solution (water). Metal is recovered

from these solutions and the solid residue is discarded.Biooxidation refers to a pretreatment process that uses the same bacteria as bioleaching to catalyze

the degradation of mineral sulfides, usually pyrite or arsenopyrite, which host or occlude gold, silver or

both. Biooxidation leaves the metal values in the solid phase and the solution is discarded.

http://technology.infomine.com/biometmine/biopapers/biomet_bioleaching.asp


B i o l ea ch i n H ea p o r T a n k s


115/179

PwCPwC

TankleachAshanti Gold,Ghana

960tpd pyrite/arsenopyriteCourtesyofLawrenceConsultingLtd

Bioleachingofnickel/coppersulfidesTitanResources,Australia

www1.titanresources.com.au



116/179

Coa l

Fo r m a t i o n o f Coa l St ep 1

Deposition of organic debris in a swamp peat bog


117/179

PwCPwC

Depositionoforganicdebrisinaswamppeatbog

Burnsbog,FraserDeltahttp://gsc.nrcan.gc.ca/urbgeo/vanland/delta_e.php


No t es: Fo r m a t i o n o f Coa l St ep 1

Step 1: The first step in coal formation is accumulation of organic debris in a peat swamp. Inmost environments, such as the forest floor, plant material decays as fast as it is produced,

it d t l t H i t t t t th t d t t i


118/179

PwCPwC 118

so it does not accumulate. However, in a peat swamp, stagnant water that does not contain

oxygen inhibits the decay of organic material allowing it to accumulate and form peat.

Burying the peat with sediment further inhibits the decay of peat.


For m a t i o n o f co a l St ep s 2+

Successivesedimentarydepositscoverpeatandformcoal


119/179


Peat20

1

Coal

20:1volumereduction

lossofwaterandgasescoal

N o t es: Fo r m a t i o n o f Coa l St ep s 2+

Steps 2+: Over time (millions of years) the sea level may rise and fall allowing organics toaccumulate as peat A transgression is where the shoreline moves landward, often due to a

relative rise in sea level resulting in the land surface being covered by the sea


120/179

PwCPwC 120

relative rise in sea level, resulting in the land surface being covered by the sea.

Plant life on land began to evolve about 450 million years ago and so there are no coal

deposits older than that. Most coal deposits were formed during the warm Carboniferousperiod 360 to 290 million years ago.

Burial of peat by overlying sediments results in an increase in the temperature and

pressure. One change that happens is compaction; it is estimated that coal results from a

20 to 1 compaction of peat, i.e., the coal is 1/20 the thickness of the original peat layer. Inaddition to compaction there is a loss of moisture and volatiles. Much of the water that is

lost was trapped in pore spaces and is expelled during compaction. Some of the water, plus

the volatiles (gases) are released due to chemical changes in the peat.


Coa l r a n k u ses a n d g r a d e

Increasingrank(carboncontent)


121/179

PwCPwC

Handfired

or

automaticstovesMetallurgical

(coking)Thermal

coal

if

sulfurcontentlow

AnthraciteSubbituminous BituminousLignitePeat

Forthe

garden

Increasingpressureofcompaction

Anthracite delivers high energy per unit weight and burns cleanly with little soot, making it ideal for heating.

However, its high value makes it prohibitively expensive for power plant use. Other uses include the fine particles

used as filter media.

Coalgradereferstotheamountofashandsulfur content.Lowgradecoalhashigh

ashand/orhighsulfur content.Ashisnoncombustibleandsulfur isjustnotgood.


No t es: I s co a l a m i n er a l ?

This question can lead to some heated debates. We could start with the idea (Skinner,

2005) that all solids are potential minerals and then see if coal fits the expanded definition


122/179

PwCPwC 122

of a mineral:

An element or compound, amorphous or crystalline, formed through biogeochemical

processesThere are biogeochemical processes involved in the formation of coal. However, they lead

to a solid which includes carbonized plant remains. There is a wide variety of compounds in

these plant remains and for this reason it is difficult to define a characteristic chemical

composition or set of compounds that make up coal. For this reason coal is usually referred

to as a rock a combination of minerals.

Coal is the official state mineral of Kentucky (even though coal is not a mineral) and

the official state rock of Utah. (Source: wikipedia)

References:http://en.wikipedia.org/wiki/Coal

Skinner, HCW, 2005. Biominerals,Mineralogical Magazine69 (5): 621641

MineralProcessing

Methods

Can ad i a n Coa l Resou r ces


123/179

PwCPwC 123MineralProcessing

Methods

U S Coa l R esou r ces

lignite


124/179

PwCPwC

lignite

sub

bituminou

s

http://en.wikipedia.org/wiki/Coal

bituminous

124MineralProcessing

Methods

N o t es: Coa l Resou r ces an d P r od u ct i o n

Proven reserves of coal worldwide are about 845 billion tonnes. This is enough coal to last

almost 120 years at current rates of consumption.


125/179

PwCPwC 125

The US has the largest reserves of coal in the world, about 237 billion tonnes, and produces

about 1 billion tonnes of coal per year. (China produces 3.2 billion tonnes per year.)

Canada has about 7 billion tonnes of reserves and produces about 75 million tonnes of coal

per year. Canada is the second largest metallurgical coal exporter, Australia being the first

largest.

Current (2011) coal prices are about $200/tonne.

References:

http://en.wikipedia.org/wiki/Coal

http://www.nrcan.gc.ca/eneene/sources/coachaeng.php

MineralProcessing

Methods

Coa l P r ocessi n g

Purpose

Removeincombustiblematerialsuchasdirtandrocktoincreasethe


126/179

PwCPwC

heatingvalueorcarboncontentofthecoal

Incombustiblemineralmaterialreferredtoasash

Sometimesknownascoalwashing

Methodsused

Screens

Densemediaseparation

FlotationDrying

126Mineral

Processing

Methods

W h a t d oes co a l l o o k l i k e?

Yellowandorange


127/179

PwCPwC

0 2 mm

Sporesfrom

vegetation

Wellpreserved

wood

Blackmaterialis

charcoalorminerals

(e.g.,silicates)

g

dotsaresporesor

algae


Coa l p r ocessi n g


128/179


Coal processing is sometimes referred to as coal cleaning because it removes silicate minerals such assands, silts, clays and ash from the coal.

There are several types of breakers. A rotary breaker consists of an outer fixed shell and an inner

N o t es: Coa l p r ocessi n g


129/179

PwCPwC

rotating drum with perforations. Typical rotational speed of the drum is 1218 rpm. Lifter plates pick

up the runofmine coal which then falls onto the drum. The softer coal breaks and passes through the

perforations while the harder rock is transported to the waste stream. In addition to the cleaning(removal of rock), a size reduction is also achieved.

The total surface area of a volume of fine particles is larger than the surface area of a coarse particle

of the same volume. Since heat release from a coal particle is proportional to surface area, fine

particles are desired for both thermal and metallurgical applications. However, during processing and

transport, only the surface of the coarse particles oxidizes whereas an entire fine particle may oxidize

lowering its thermal value. Thus, both thermal and metallurgical coal are ground to fine sizes at the

location where it is used.

Usually the fine particles of thermal coal are so dirty that they cannot be cleaned. Often they are

discarded but it might be possible to blend the fines with coarse coal to achieve an overall acceptable

ash content.

The fines of metallurgical coal (also known as coking coal) can usually be floated to obtain clean coal.

The flotation is an added expense, but the value of the metallurgical fines is high. Sometimes the

clean fines are agglomerated to form coarse particles.


D en se m ed i a sepa r a t i o n t h e ba si c i d ea

Feed


130/179

PwCPwC

Fluidmedium

SG=w

MaterialwithSG>w

(sinks)

MaterialwithSG


131/179

PwCPwC

Densemedia

drums

Cyclones

Source:www.flsmidthminerals.com/Company/Press+Room/Product+Brochures/HMS+Drum+Plant.htm


E l k v i ew M i n e, B r i t i sh Co l um b i a

Capacity:5.6mtpa


132/179

PwCPwC 132

Reserves:376.1mt


Co a l t r a n sp o r t a t i o n sy st em i n BC


133/179


T r a i n l o a d s a n d b o a t l o a d s


134/179

PwCPwC 134

TrainnearElkviewloadout

CoalloadedatWestshore


Rock sl i d e o n r a i l r o u t e i n BC ea r l y 2 0 11


135/179

PwCPwC

Source:Teck 1st quarter2011presentationreport

Thisrockslidetook710daystoclearup



136/179

Coa l t r a n sp o r t a t i o n sy st em i n Co l om b i a


137/179


Th e st r i p r a t i o fo r co a l m i n es

The strip ratio of a coal mine may be very high (1112 at Elkview)

and it can vary considerably during the mine life


138/179

PwCPwC

and it can vary considerably during the mine life.

The compensating factor is that the yield of one tonne of coal ore ismuch larger (~ 60%) than the yield of one tonne of a metal ore. Also

processing coal ore costs much less than processing metal ores.

www.miningtechnology.com/projects/fording/fording7.html

CrosssectionofgeologyatEagleMountain,BC



139/179

D i a m o n d s

W her e d i am o n d s a r e f ou n d

Mostlyinveryoldrocksinthecenterofcontinents


140/179

PwCPwC 140

>2.5by

1.62.5by


141/179

PwCPwC

, , p p , ,

years old.

Other than that described above, the location of diamond deposits cannot be related to

any plate tectonic activity within the last 100200 million years. This is because the

formation of diamonds and diamond deposits more related to processes deep in the earth

rather than the shallow crustal processes that lead to base and precious metal deposits.

http://www.amnh.org/exhibitions/diamonds/


H ow d o d i a m on d s f o r m ?


142/179

PwCPwC 142

150 200km

Continental

plate

Upper

mantle

Diamond

formation

Nondiamond

bearing

Diamond

bearing

Kimberlite

pipes


No t es: H ow d o d i am o n d s f or m ?

Diamonds are formed by recrystallization of graphite (carbon) at high pressure and temperature (9001200C) at depths greater than 150 km in a region below the earths crust known as the mantle. They

are transported to the surface by magma under considerable pressure. Dissolved gases in the magma

expand and the magma combines with boiling groundwater to result in an explosive supersonic

eruption at the surface The high speed prevents the diamonds in the magma from re crystalizing as


143/179

PwCPwC 143

eruption at the surface. The high speed prevents the diamonds in the magma from recrystalizing as

graphite. The result is a carrotshaped pipe or vent at the surface and a small volcanic cone.

The pipes contain minerals such as garnets and pyroxenes which are formed in the mantle. Fragments

of crustal rock are also present. The rock in the pipes is called kimberlite, after the city of Kimberley,

South Africa, where pipes were first discovered in the 1870s. Pipes occur in clusters and the pipes in a

cluster are typically at most tens of kilometres apart.

http://www.amnh.org/exhibitions/diamonds/

Diamonds from kimberlite pipes have been agedated and found to be between 3,300 million to 990

million years old. However, the kimberlite rock was intruded only about 100 million years ago. Given

the age of the diamonds, the carbon source is most likely carbon trapped in Earth's interior at the time

Earth formed 4,600 million years ago. (Kirkley, MB et al, 1991, Gems and Gemology,27:225)

Two things which make diamonds rare: Only about 1 in 50 kimberlite pipes contain diamonds. Secondly

explosive eruptions that produce kimberlite pipes seem to have stopped occurring. The youngest

kimberlite pipe in the world is in the Lac de Gras area of Canada and is about 50 million years old.

(Davis WJ and Kjarsgaard BA, 1997,Journal of Geology,105:503510)


H ow t o f i n d a k i m b er l i t e p i p e i n t h e A r ct i c

Countindicatormineralsin

theglacialtillKimberlite

pipe


144/179

PwCPwC 144

#pyrope per20

kgsample

0

110

1150

51150

>150

Pyrope Mg3Al2(SiO4)3Atypeofgarnet

Takesamplesoftill

Count#ofindicatormineralgrainsinsamples

Iceflow

pipe



145/179

They r ea l l y a r e i n t h er e ( som ew her e)

Glacial till in Lac de Gras area, NWT


146/179

PwCPwC 146

Kimberlite boulderintilldeposit

http://gsc.nrcan.gc.ca/mindep/method/kimberlite/index_e.php#indMineralProcessingMethods

D i a v i k D i am on d M i n e

Onasunnysummersday


147/179

PwCPwC

Inwinter(35C)

Seasonaliceroad

OpenFebruarytoApril

The

AntiBling

147

June9,2011


Photos courtesy of Diavik Diamond Mines Inc.

Left: Pit formed inside a dam constructed in a lake called Lac de Gras. Construction during 20002003

shown. Mining occurs year round.

Top right: The ice road extends 600 km from Tibbitt Lake (outside Yellowknife) to the Jericho Diamond

Mine. Seventyfive per cent of the road is ice, built over frozen lakes. Diavik is about 370 km from

No t es: D i a v i k D i am o n d M i n e


148/179

PwCPwC

Tibbitt Lake. Travel time to Diavik is 1519 hours depending on load weight.

Bottom right: Rough diamonds. The larger diamond on the lower left of the picture weighs about 8carats and is worth C$30,000. The manner in which these diamonds are separated from the waste is

interesting. See part C.

Diavik Mines data:

27.2 Mtonne reserves at 3.9 carats/tonne, four orebodies (pipes)

Annual ore production: 1.5 to 2 million tonnes

Annual diamond production: maximum 8 million carats

Mine life: 16 to 22 years. Production began January 2003, capital cost: C$1.3 billion

Underground operation under development in 2007, expected to begin in 2009. Capital cost of

underground development as of November 2007 is US$787 million.

Open pit operation will cease in 2012.


H ow d o y ou cr u sh d i a m on d o r e?

Verycarefully withaHighPressureGrindingRoll(HPGR)


149/179

PwCPwC

Adjustgapbetween

rollerstomaximum

expecteddiamondsize


No t es: H i g h p r essu r e g r i n d i n g r o l l s

A High Pressure Grinding Roll (HPGR) machine consists of a pair of counterrotating rolls, one fixed andthe other floating. Ore feed is introduced into the gap between the rolls. The position of the floating

roll can be adjusted. A hydraulic spring system maintains grinding pressure on the floating roll. The

pressure and roll speed can be adjusted during the grinding to adapt to changing feed properties.

C i ti i HPGR i d i t ll l t l b i Thi lt i d t th t h


150/179

PwCPwC 150

Comminution in a HPGR is done virtually completely by compression. This results in a product that has

a higher percentage of fines than can be achieved with a SAG or AG mill where comminution is done bya combination of compression and shear. Coarse particles in the HPGR product exhibit extensive

cracking which reduces the amount of grinding work to be performed in a downstream ball mill.

HPGR technology was originally developed for the cement industry. Diamond mines adopted the

technology in the early 1980s for crushing kimberlite ore. HPGRs are now being used or considered for

use in crushing gold and base metal ores where they would replace SAG and AG mills in a grinding

circuit. Base and gold metal ores are typically harder than kimberlite.

HPGR units have a 610% higher capital cost than SAG mills and an issue is wear of the roll surface

(which is typically studded), particularly in gold and base metal ore processing. However, this is offset

by the low cost of replacing wear surfaces, short equipment delivery times, and a high throughput rate.

Energy costs of a HPGR are also significantly lower most of the energy in a SAG or AG mill circuit is

consumed moving the mill cylinder itself.


H PGR t est f a c i l i t y a t N BK (UB C)


151/179


D en se m ed i a h y d r o cy cl o n e p l a n t

Toseparatekimberlite (light)fromdiamonds(heavy)


152/179

PwCPwC

www.stornowaydiamonds.com


D i am on d o r e p r o cessi n g X -r a y sep a r a t i o n

Densemediaseparationincyclones

resultsindiamondconcentrate

(diamonds heavy kimberlite light)


153/179

PwCPwC

(diamondsheavy,kimberlite light)



154/179


155/179

Oi l San d s

Or i g i n o f o i l sa n d s

Resources~1.7trillionbarrels

Conventional marine organic origin in the


156/179

PwCPwC

southwest of Alberta

Oil flows to the northeast

The lowering of the temperature to less

than 80C allowed biodegradation of the

lighter oilsTheresult:thickbitumenwithsand

Map by Norman Einstein, May 10, 2006


No t es: Or i g i n o f o i l sa n d s

For the geologically inclined:

The following author favors a coalification origin for oil sands:

http://www.searchanddiscovery.net/documents/2004/stanton/index.htm

But this author (and others) favor a marine source similar to conventional oil:


157/179

PwCPwC 157

( )

Hein, F. J., 2006. Heavy Oil and Oil (Tar) Sands in North America: An Overview & Summary ofContributions. Natural Resources Research, 15(2): 6784

It is clear that the oil sands could not flow to where they are in their current condition. The fluid oil,

whatever its origin, has been degraded by bacteria, a process which removes the lighter hydrocarbon

molecules, leaving behind the bitumen in between grains in these oil sands. Some current research is

directed toward enhancing this biodegradation process in deep oil sand deposits and collect theresulting gases as an energy source ie to exploit the oil sands in situ.


Sep a r a t e b i t u m en f r om sa n d a n d w a t er

Addhotwater

Transport slurry to extraction plant


158/179

PwCPwC

Transportslurrytoextractionplant


F l o t a t i o n o f b i t u m en

Airbubblesattachtobitumen

Floatstosurfaceasfroth

Bitumen


159/179

PwCPwC 159

Bitumen

Water

Sand/Clay



160/179

A Pr o b l em

Thispitisabout90mdeep


161/179

PwCPwC 161

80%ofthebitumenresourceliesbelow100m

Butoilsandsareunstable

www.guardian.co.uk/environment/2011/oct/05/1


One a l t er n a t i v e: St eam Assi st ed Gr a v i t yD r a i n a g e

BUT

Considerableenergyis

required to form steam


162/179

PwCPwC 162

requiredtoformsteam

Steamcanescapeintothelowerpressuregaspoolmakingit

unavailableforheatingbitumenSource:EnergyResourcesConservationBoard


SAGD i n st a l l a t i o n i n A l b er t a

Operatingat250C


163/179



164/179

U r a n i u m

U r a n i u m i n Ca n a d a t h e A t h a b a sca B a si n


165/179

PwCPwC

~300m

depth


No t es; U r a n i u m i n Ca n a d a t h e A t h a b a sca B a s i n

The Athabasca Basin is composed of a sedimentary deposit of sandstones overlyingdeformed metamorphic basement rocks. In geological terms the combination of these two

rock types is an unconformity, a buried erosion surface separating rock units of different

ages. It results when there is a hiatus between the deposition of older underlying rocks and

younger overlying rocks, allowing erosion to occur.


166/179

PwCPwC 166

Uranium is a large atom and does not fit into the crystal structure of typical rock types. Onetheory is that magmatic activity deformed the underlying metamorphic rocks and

hydrothermal fluids from the magma transported uranium and deposited it in large

quantities at the base of the sandstones. (See next slide)

Unconformitytype uranium deposits host high grades relative to other uranium deposits

and include some of the largest and richest deposits known. Other significant depositsoccur in the MacArthur Basin in the Northern Territory, Australia.


Cr o ss-sect i o n a t Ci g a r L a k e u r a n i u m m i n e


167/179

PwCPwC

http://commons.wikimedia.org/wiki/File:Uranium_deposit%28Cigar_Lake%29.png

(Sandstone)

(Quartzcap)

(Weatheredsandstone)

(Uraniumore)

(Metamorphicbedrock)

(Claycover)


U r a n i u m M i n i n g i n Sa sk a t ch ew a n

Remotemining

methodstoavoid

exposuretoradiation


168/179

PwCPwC

Groundfreezingtocontrolgroundwater

Jetboring

essentiallywashore

outofground

Excellentanimationat:http://www.cameco.com/mining/cigar_lake/jet_boring_animation/



169/179

I n si t u ex t r a ct i o n o f u r a n i u m

Oxygenatedwaterwith

peroxideorcarbonate


170/179


No t es: I n -si t u ex t r a ct i o n o f u r a n i u m

Applicable to deposits of uranium in sandstone and confined betweenimpermeable layers. Deposits in Australia, western US and Kazakhstan.

Injection wells pump a chemical solution typically sodium bicarbonate and

oxygen into the sandstone layer containing uranium ore. The solution dissolves

Documents

basics of mining and mineral processing