Sag Moly Cop

(1)

From FAG …

(fully)

to SAG …

(semi)

to BAG !

(barely)

The Theoretical Rationale behind

CURRENT TRENDS IN OPERATING PRACTICE

OF SEMIAUTOGENOUS GRINDING OPERATIONS

Dr. Jaime E. Sepúlveda

Moly

(2)

Feed the mill with large

rocks

(up to

10”-12”), so avoiding the traditional crushing,

classification and multiple storage stages of

intermediate size particles.

Use these rocks as a ‘zero-cost’ grinding

media:

Autogenous Grinding

.

Add large diameter steel balls (up to 6”):

The concept of

AUTOGENOUS

GRINDING

was born

from the idea of

avoiding the use and

Basic Concepts

SEMIAUTOGENOUS GRINDING

Basic Concepts

SEMIAUTOGENOUS GRINDING

Add large diameter steel balls (up to 6”):

Semiautogenous Grinding

.

Considering that

rocks

are lighter than

balls

,

it was assumed

(wrongly?)

that such rocks

should fall from the highest possible position

and therefore, SAG mills adopted their

typical

“pancake”

shape:

D>L

.

avoiding the use and

consumption of

steel

grinding balls

, by

replacing them with

the same

rocks

contained in the fresh

feed ore.

(3)

Alternative Circuit Configurations

SINGLESTAGE GRINDING (FAG or SAG)

Alternative Circuit Configurations

SINGLESTAGE GRINDING (FAG or SAG)

Product

Water

Feed

(4)

Alternative Circuit Configurations

DOUBLESTAGE GRINDING (DSAG)

Alternative Circuit Configurations

DOUBLESTAGE GRINDING (DSAG)

Water

Feed

Product

Water

Feed

(5)

Large

(> 4”)

Do they

Grind?

ROCKS

Do they

_grind

themselves?

Are they

ground by

media?

Yes,

less than

Balls

Yes

No

Semiautogenous Grinding

WHICH WOULD BE THE ACTUAL

ROLE OF THE ‘ROCKS’?

Semiautogenous Grinding

WHICH WOULD BE THE ACTUAL

ROLE OF THE ‘ROCKS’?

The mid size rocks,

denominated

Critical

Sizes

or

Pebbles

do

not act as grinding

media and they do not

allow themselves to be

ground.

They use up space in

the charge affecting

the

productivity

of

the mill.

As a corrective

measure, it has been

Medium

(2” to 4”)

Small

(< 2”)

Balls

Very

little !

No

Very

little !

Little !

require

large balls

No

Yes

measure, it has been

arranged for such

Pebbles

to leave the

charge through the

mill grate, classifying

and crushing them by

conventional methods.

(6)

Alternative Circuit Configurations

DOUBLESTAGE GRINDING

WITH PEBBLE CRUSHING (SABC

WITH PEBBLE CRUSHING (SABC-

-1)

1)

Alternative Circuit Configurations

DOUBLESTAGE GRINDING

WITH PEBBLE CRUSHING (SABC

WITH PEBBLE CRUSHING (SABC-

-1)

1)

Water

Product

Pebbles

Water

Feed

(7)

Water

Product

Pebbles

Alternative Circuit Configurations

DOUBLESTAGE GRINDING

WITH PEBBLE CRUSHING (SABC

WITH PEBBLE CRUSHING (SABC-

-2)

2)

Alternative Circuit Configurations

DOUBLESTAGE GRINDING

WITH PEBBLE CRUSHING (SABC

WITH PEBBLE CRUSHING (SABC-

-2)

2)

Water

Feed

(8)

Since

Fully Autogenous Grinding (FAG)

was first

proposed, early last century, there has been a

continuous evolution in operational practices with

regard to:

The addition of

increasing amounts

of steel balls

as ancillary grinding media,

The sustained

increment in diameter

of such

balls,

The removal and crushing of the critical sizes

(pebbles)

that otherwise would accumulate in the

load and …

The pre-crushing

(elimination)

of either the

With time, the fully

AUTOGENOUS

option

has been gradually

diverting from its

original conception to

load and …

_{The pre-crushing}

_{(elimination)}

_{of either the}

larger rocks or the intermediate particle size

fractions contained in the fresh feed ore.

Consequently,

little is left today

of the original

intention of using the larger rocks as

autogenous

grinding media for the smaller particles.

This presentation is aimed at illustrating the

theoretical rationale behind the observed

current trends in SAG operating practices, with

the aid of

Moly-Cop Tools 2.0

.

diverting from its

original conception to

become nowadays just

a simple case of a

poorly operated

CONVENTIONAL

BALL MILL

…

(9)

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

S

o

ft

w

a

re

f

o

r

th

e

A

n

a

ly

s

is

o

f

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

M

in

e

ra

l

G

ri

n

d

in

g

P

ro

c

e

s

e

s

P

ro

c

e

s

e

s

P

ro

c

e

s

e

s

P

ro

c

e

s

e

s

P

ro

c

e

s

e

s

P

ro

c

e

s

e

s

P

ro

c

e

s

e

s

P

ro

c

e

s

e

s

2.0

(10)

My Grandpa made it!

Moly

Moly-

-Cop Tools

Cop Tools

Moly

Moly-

-Cop Tools

Cop Tools

is available

is available free of charge

free of charge to

to

all interested parties

0.100

1.000 S

i

E

Balls on Particles

Rocks on Particles

Self-Breakage

Overall

Theoretical Background

SPECIFIC SELECTION FUNCTION,

ton/kWh

Theoretical Background

SPECIFIC SELECTION FUNCTION,

ton/kWh

The model included in

Moly-Cop Tools

was

first published at the

SAG 2001 Conference

by J. E. Sepúlveda,

“A Phenomenological

Model of

Semi-Autogenous Grinding

Processes in a

Moly-Cop Tools

Environment”

, Vol. 4,

pp. 301-315,

Vancouver, Canada.

After that, the model

has been providing

quite satisfactory

0.010

10

100 1000

10000

100000

1000000

Particle Size, microns

S

quite satisfactory

descriptions of actual

SAG processes, in all

cases where the

proper plant and/or

pilot scale data has

been made available.

(12)

Simulation N° 0

Remarks

Base Case Example

Ore Density, ton/m3 2.80

0.017 1000 ton/hr (all mills)

0.9 40.00 % Solids 4 76.72 % - 100# 167.0 P80 # of Cyclones 4.00 243 d50c Diameter 26.00 0.315 Bpf Height 78.00 0.331 Bpw Mesh # Inlet 10.00

Opening Vortex 10.00 76.10 % Solids

By-Pass Apex 5.00

D50/D Circ.

1000 ton/hr, Fresh Feed Mesh # 1 131488 F80 Opening 304800 2.90 % Moisture By-Pass 0.000 D50/Ds 1.00 1 m 100.00 Upper 0 ton/hr Split 0.00 Mesh # 1 1

Opening 304800 Lower 0 ton/hr

By-Pass 0.000 0.00 % of Feed 369 ton/hr D50/Ds 1.00 2.90 % Moisture 36.91 % of Feed m 100.00 2.90 % Moisture 61.50 % - 1/2" 61.50 % - 1/2" 2 F80 131488 % - 1.5" 58.97 Water, m3/hr 344

Diameter, ft 35.30 Grate Screen

Lenght, ft 15.00 5 10 Speed, % Critical 78.00 76200 13335 Charge Level, % 26.00 0.070 0.017 Balls Filling, % 10.00 0.70 0.90

⊕

∅

1

2 Complex Circuit Simulation ... SABC-1

Complex Circuit Simulation ... SABC-1

D50/D Circ.

m % - 200# in psi 10.19 Load, %

Mill Discharge (Guess) 2.367

29.66 (Actual) 2.367 (Delta) 0.000 89 Water, m3/hr 475 2.00 # of Mills Balls Filling, % 10.00 0.70 0.90 % Solids (slurry) 76.00 3.00 4.00 App. Density, ton/m3 3.331 % Solids 72.79

Gross kW 10093 % - 100# 21.26

kWh/ton 10.09 T80 6112

m3/hr 731 Mesh Opening Fresh Crushed Crushed

Feed Pebbles 1 Pebbles 2

1 12" 304800 100.00 100.00 100.00 m3/hr, Water 2 8" 203200 97.60 100.00 100.00 Size Distributions 3 6" 152400 83.93 100.00 100.00 4 4.15" 101600 73.57 100.00 100.00 5 2.95" 76200 67.87 100.00 100.00 6 2.1" 50800 62.82 100.00 100.00 7 1.48" 38100 58.97 100.00 100.00 8 1.05" 26670 53.78 98.07 98.07 9 0.742" 18850 49.78 90.24 90.24 10 0.525" 13335 42.74 61.50 61.50 11 0.371" 9423 38.32 48.04 48.04 12 3 6680 34.00 31.84 31.84 13 4 4699 29.28 23.55 23.55 14 6 3327 25.65 18.08 18.08 15 8 2362 22.57 14.32 14.32 16 10 1651 20.19 11.53 11.53 17 14 1168 18.16 9.20 9.20 18 20 833 16.79 7.80 7.80 19 28 589 15.65 6.65 6.65 20 35 417 14.66 5.74 5.74 21 48 295 13.79 5.06 5.06 22 65 208 12.84 4.43 4.43 23 100 147 12.01 3.96 3.96 24 150 104 11.12 3.50 3.50 25 200 74 10.28 3.10 3.10 19.00 Diameter, ft 24.00 Lenght, ft 76.00 Speed, % Critical 38.00 Charge Level, % 38.00 Balls Filling, % % Solids 60.01 72.00 % Solids (slurry)

m3

/hr 1723 5.395 App. Density, ton/m3 4631 Gross kW

9.26 kWh/ton

Current Min/Max Remarks SAG Power, kW 10093 11500 OK Pebbles, ton/hr 369 400 OK BM Power, kW 4631 3730 KO Product Size, P80 167.0 185.0 OK Pump Capacity, P*Q 17554 30000 OK Total Water, m3 /hr 1470 2000 OK PROCESS RESTRICTIONS

In conjunction with other unit operation

models, such as

Conventional Ball Milling

,

Hydroclassification

,

Screening

and

Crushing

,

the referred

SAG

model can be applied,

with

Moly-Cop Tools

, to represent fairly

(13)

1189 ton/hr, Fresh Feed Mesh # 1 131488 F80 Opening 304800 2.90 % Moisture By-Pass 0.000 D50/Ds 1.00 1 m 100.00 Upper 0 ton/hr Split 0.00 Mesh # 1 1

Opening 304800 Lower 0 ton/hr By-Pass 0.000 0.00 % of Feed D50/Ds 1.00 2.90 % Moisture m 100.00 2 61.50 % - 1/2" 2 F80 131488 % - 1.5" 58.97 Water, m3/hr 271

Diameter, ft 35.30 Grate Screen

Lenght, ft 15.00 5 10 Mesh # Speed, % Critical 78.00 76200 13335 Opening

Charge Level, % 26.00 0.070 0.017 By-Pass Balls Filling, % 10.00 0.70 0.90 D50/D

⊕

∅

1

2

Simulation N° 0 Remarks

371 ton/hr Base Case Example 31.19 % of Feed

2.90 % Moisture

Ore Density, ton/m3

2.80

61.50 % - 1/2"

Split 0 ton/hr 1189 ton/hr (all mills) 0.00 0.00 % of Feed 40.00 % Solids 62.52 % - 100# 270.0 P80 # of Cyclones 4.00 357 d50c Diameter 26.00 0.260 Bpf Height 78.00 0.273 Bpw Inlet 10.00

Opening Vortex 10.00 82.66 % Solids Apex 5.00

Circ.

Complex Circuit Simulation ... SABC-2

Balls Filling, % 10.00 0.70 0.90 D50/D % Solids (slurry) 76.00 3.00 4.00 m App. Density, ton/m3 3.331 % Solids 73.45

Gross kW 10093 % - 100# 25.85

kWh/ton 8.49 T80 5052

m3/hr 588 Mesh Opening Fresh Crushed Crushed

Feed Pebbles 1 Pebbles 2

1 12" 304800 100.00 100.00 100.00 m3/hr, Water 391 2 8" 203200 97.60 100.00 100.00

Size Distributions

Circ. % - 200# in psi 13.51 Load, %

Mill Discharge (Guess) 2.688

16.08 (Actual) 2.688 (Delta) 0.000 353 Water, m3 /hr 2.00 # of Mills 3 6" 152400 83.93 100.00 100.00 4 4.15" 101600 73.57 100.00 100.00 5 2.95" 76200 67.87 100.00 100.00 6 2.1" 50800 62.82 100.00 100.00 7 1.48" 38100 58.97 100.00 100.00 8 1.05" 26670 53.78 98.07 98.07 9 0.742" 18850 49.78 90.24 90.24 10 0.525" 13335 42.74 61.50 61.50 11 0.371" 9423 38.32 48.04 48.04 12 3 6680 34.00 31.84 31.84 13 4 4699 29.28 23.55 23.55 14 6 3327 25.65 18.08 18.08 15 8 2362 22.57 14.32 14.32 16 10 1651 20.19 11.53 11.53 17 14 1168 18.16 9.20 9.20 18 20 833 16.79 7.80 7.80 19 28 589 15.65 6.65 6.65 20 35 417 14.66 5.74 5.74 21 48 295 13.79 5.06 5.06 22 65 208 12.84 4.43 4.43 23 100 147 12.01 3.96 3.96 24 150 104 11.12 3.50 3.50 25 200 74 10.28 3.10 3.10 19.00 Diameter, ft 24.00 Lenght, ft 76.00 Speed, % Critical 38.00 Charge Level, % 38.00 Balls Filling, % % Solids 64.12 72.00 % Solids (slurry)

m3/hr 2009 5.395 App. Density, ton/m3 4631 Gross kW

7.79 kWh/ton

Current Min/Max Remarks SAG Power, kW 10093 11500 OK Pebbles, ton/hr 371 400 OK BM Power, kW 4631 3730 KO Product Size, P80 270.0 185 KO Pump Capacity, P*Q 27155 30000 OK Total Water, m3 /hr 1759 2000 OK PROCESS RESTRICTIONS

In conjunction with other unit operation

models, such as

Conventional Ball Milling

,

Hydroclassification

,

Screening

and

Crushing

,

the referred

SAG

model can be applied,

with

Moly-Cop Tools

, to represent fairly

(14)

Current Operational Trends in

SEMIAUTOGENOUS GRINDING

(15)

200

400

600

800 1000

1200

M

il

l

T

h

ro

u

g

h

p

u

t,

t

o

n

/h

r

5000

10000

15000

20000

25000

30000

M

il

l

P

o

w

e

r

D

ra

w

,

k

W

22% Total Filling

26% Total Filling

30% Total Filling

Effect of

% BALLS IN THE CHARGE

Effect of

% BALLS IN THE CHARGE

D = 36’

φφφφ

L = 15’

Vel. = 78% Crit.

Simulated

Conditions

Max. Power

0

200

0

5

10

15

20 % Balls

M

il

l

T

h

ro

u

g

h

p

u

t,

t

o

n

/h

r

0 5000

_M

il

l

P

o

w

e

r

D

ra

w

,

k

W

Vel. = 78% Crit.

% Solids = 76%

F80 = 131448 microns

Grate = 0.5”

Screen = 0.5”

Ball Size = 5”

Circuit Type = SABC-1

One of the first “diversions” from

Fully Autogenous Grinding

was the addition of large diameter balls with the purpose of

increasing mill power draw and so providing extra grinding

capacity, giving rise to the so-called

Semi Autogenous

option.

Under any circumstances, Operators must be alert not to

exceed the design

Maximum Power

of the mill motor and drive

mechanism.

(16)

200

400

600

800 1000

1200

M

il

l

T

h

ro

u

g

h

p

u

t,

t

o

n

/h

r

5000

10000

15000

20000

25000

30000

M

il

l

P

o

w

e

r

D

ra

w

,

k

W

22% Total Filling

26% Total Filling

30% Total Filling

Effect of

% BALLS IN THE CHARGE

Effect of

% BALLS IN THE CHARGE

D = 36’

φφφφ

L = 15’

Vel. = 78% Crit.

Simulated

Conditions

Max. Power

0

200

0

5

10

15

20 % Balls

M

il

l

T

h

ro

u

g

h

p

u

t,

t

o

n

/h

r

0 5000

_M

il

l

P

o

w

e

r

D

ra

w

,

k

W

Vel. = 78% Crit.

% Solids = 76%

F80 = 131448 microns

Grate = 0.5”

Screen = 0.5”

Ball Size = 5”

Circuit Type = SABC-1

Even at the same mill power draw,

balls

would be more

effective than

rocks

to convert the available power into

actual grinding, thanks to their higher density and spherical

shape.

(17)

11.5

12.0

12.5

13.0

13.5

14.0 k

W

h

/t

o

n

200

400

600

800 1000

1200

M

il

l

T

h

ro

u

g

h

p

u

t,

t

p

h

22% Total Filling

26% Total Filling

Effect of

% BALLS IN THE CHARGE

Effect of

% BALLS IN THE CHARGE

D = 36’

φφφφ

L = 15’

Vel. = 78% Crit.

Simulated

Conditions

11.0

11.5

2.0

3.0

4.0

5.0 Apparent Charge Density, ton/m

3

0

200 _M

il

l

T

h

ro

u

g

h

p

u

t,

t

p

h

26% Total Filling

30% Total Filling

In some cases, it is possible to identify an

Apparent Charge

Density

(determined by the balls/rocks ratio)

that minimizes

the overall

Specific Energy

requirement.

If the feed contains large rocks –

that essentially must

grind themselves

– we must assure that these large rocks

get to absorb the necessary proportion of the total

available energy, so the overall process can achieve optimal

performance.

Vel. = 78% Crit.

% Solids = 76%

F80 = 131448 microns

Grate = 0.5”

Screen = 0.5”

Ball Size = 5”

(18)

11.5

12.0

12.5

13.0

13.5

14.0 k

W

h

/t

o

n

200

400

600

800 1000

1200

M

il

l

T

h

ro

u

g

h

p

u

t,

t

p

h

22% Total Filling

26% Total Filling

Effect of

% BALLS IN THE CHARGE

Effect of

% BALLS IN THE CHARGE

D = 36’

φφφφ

L = 15’

Vel. = 78% Crit.

Simulated

Conditions

11.0

11.5

2.0

3.0

4.0

5.0 Apparent Charge Density, ton/m

3

0

200 _M

il

l

T

h

ro

u

g

h

p

u

t,

t

p

h

26% Total Filling

30% Total Filling

However, regardless of this ideal

Apparent Charge Density

that would optimize the energy

efficiency

(kWh/ton) of the

process, the overall

effectiveness

(mill throughput) of the

operation is always achieved at higher balls/rocks ratios, up

to the limit imposed by the available motor and drive

power.

Vel. = 78% Crit.

% Solids = 76%

F80 = 131448 microns

Grate = 0.5”

Screen = 0.5”

Ball Size = 5”

(19)

1000

1050

1100

1150

1200

1250

M

il

l

T

h

ro

u

g

h

p

u

t,

t

o

n

/h

r

Screen Opening = 1/2 inch

Screen Opening = 3/4 inch

Effect of

DISCHARGE GRATE OPENING

Effect of

DISCHARGE GRATE OPENING

D = 36’

φφφφ

L = 15’

Vel. = 78% Crit.

Simulated

Conditions

950 1000

0.0

1.0

2.0

3.0 Grate Opening, inches

M

il

l

T

h

ro

u

g

h

p

u

t,

t

o

n

/h

r

Vel. = 78% Crit.

% Solids = 76%

F80 = 131448 microns

% Filling = 28%

% Balls = 16%

Ball Size = 5”

Circuit Type = SABC-1

Another source of

“diversion”

of

SAG

milling technology has

been the empirical confirmation that removing and crushing

larger and larger pebbles (

by opening the discharge grate

slots

) invariably translates into substantially improved mill

grinding capacity.

In plain words … it is like “the

SAG

mill is asking help from

the

Crushers

”.

(20)

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

3200

to

n

/h

r

SABC-1

SABC-1 plus +6 inch Crushing

SABC-1 plus 6x2 inch Crushing

Effect of

FRESH FEED SIZE DISTRIBUTION

Effect of

FRESH FEED SIZE DISTRIBUTION

D = 36’

φφφφ

L = 17’

Vel. = 76% Crit.

% Solids = 78%

Simulated

Conditions

21%

600

800 1000

1200

20

30

40

50

60

70

80

90

100 % - 2" in SAG Mill Feed

Vel. = 76% Crit.

% Solids = 78%

% Filling = 28%

% Balls = 12%

Grate = 2”

Ball Size = 5”

Circuit Type = SABC-1

It has been repeatedly demonstrated in actual operational

practice that

“getting rid of the rocks”

ahead of the SAG

mill brings substantial throughput benefits, raising questions

about the effective contribution of such rocks to the

overall grinding process.

Taken from: J. E. Sepúlveda, “

A SIMULATION ANALYSIS OF THE NET EFFECT OF FEED PARTICLE SIZE

(21)

2400

2500

2600

2700

2800

2900

3000

to

n

/h

r

SAG 1

SAG 2

Effect of Feed Size

THE PELAMBRES CASE

Effect of Feed Size

THE PELAMBRES CASE

21%

D = 36’

φφφφ

L = 17’

Vel. = 76% Crit.

% Solids = 78%

Operating

Conditions

2200

2300

2400

40

45

50

55

60

65 % - 1.25" in SAG Mill Feed

Actual data in support of the previous statement was

provided by the

PELAMBRES

(Chile) operation, back in

2001, in the context of their “mine-to-mill” approach.

Taken from: R. Palomo, Moly-Cop 2001: IX Mineral Processing Symposium.

Vel. = 76% Crit.

% Solids = 78%

% Filling = 23%

% Balls = 15%

Grate = 2”

Ball Size = 5”

(22)

Effect of Feed Size

THE COPPERTON CASE

Effect of Feed Size

THE COPPERTON CASE

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

to

n

/h

r

Lines 1 - 3

Line 4

**(*) D. King (2005), SME-AIME Annual Meeting**

800

900 1000

30

35

40

45

50

55

60

(23)

Effect of

CIRCUIT CONFIGURATION

Effect of

CIRCUIT CONFIGURATION

1000

1200

1400

1600

1800

2000

2200

2400

2600

2800

3000

3200

to

n

/h

r

DSAG

SABC-1

SABC-1 plus +6 inch Crushing

SABC-1 plus 6x2 inch Crushing

SABC-2

D = 36’

φφφφ

L = 17’

Vel. = 76% Crit.

% Solids = 78%

Simulated

Conditions

600

800 1000

20

30

40

50

60

70

80

90

100 % - 2" in SAG Mill Feed

The grinding capacity of any given circuit improves as its

configuration evolves from

DSAG

to

SABC-1

to

SABC-2

;

that is, as the SAG mill contributes

less and less

to the

overall grinding task!

Also, as the larger feed rocks get to be

pre-crushed

, the

Ideal Apparent Charge Density

quickly approaches values

close to the limiting maximum value corresponding to just

‘balls plus slurry’

(~5 ton/m

3 ₎

_{; that is,}

_{Conventional Grinding}

_.

Vel. = 76% Crit.

% Solids = 78%

% Filling = 28%

% Balls = 12%

Grate = 2”

Ball Size = 5”

(24)

Effect of Balls/Rocks Ratio

IDEAL APPARENT CHARGE DENSITY

Effect of Balls/Rocks Ratio

IDEAL APPARENT CHARGE DENSITY

D = 36’

φφφφ

L = 17’

Simulated

Conditions

0 2000

4000

6000

8000

10000

12000

kW

(

N

et

)

Total

Balls

Rocks

Slurry

As

Total Mill Filling

is increased

(by the addition of large or

mid size rocks)

, at constant

Ball Filling

, the

Total Mill Power

Draw

increases, but the

Net Power absorbed by the Balls

actually decreases.

If one is to accept that rocks are

less effective

than balls as

grinding media (not to say, totally

ineffective

), then

Mill

Throughput

will be higher at lower

Total Filling

levels.

This empirical finding has led operators to run at fairly low

Total Filling

(below 24%)

and relatively high

(up to 20%)

Ball

Filling

levels.

L = 17’

Vel. = 70% Crit.

% Solids = 78%

% Balls = 12%

Grate = 0.5”

Ball Size = 5”

Circuit Type = DSAG

0

14

16

18

20

22

24

26

28

30

32

34

36

38

(25)

Meanwhile ... Has the

IDEAL MAKE-UP BALL SIZE

also been evolving?

Meanwhile ... Has the

IDEAL MAKE-UP BALL SIZE

also been evolving?

With the advent of

the new century, SAG

mill operators have

been consistently

1200

1400

1600

1800

2000

2200

2400

M

il

l

T

h

ro

u

g

h

p

u

t,

t

o

n

/h

r

F80, mm

27

56 been consistently

realizing the clear

advantages of using

larger and larger

balls, regardless of

the ore feed particle

size.

800 1000

1200

3.5

4

4.5

5

5.5

6

6.5

7

7.5 Make-up Ball Size, inches

M

il

l

T

h

ro

u

g

h

p

u

t,

t

o

n

/h

r

120

131 For every

‘grinding task’

, there is an

Ideal Make-up Ball Size

that maximizes mill throughput.

Quite often, this

Ideal Make-up Ball Size

turns out to be

larger than the largest commercially available ball size and

increases consistently for coarser and coarser feeds.

(26)

4.8

5.0

5.2

5.4

5.6 A

v

e

.

S

A

G

B

a

ll

S

iz

e

,

in

c

h

e

s

Meanwhile ... Has the

IDEAL MAKE-UP BALL SIZE

also been evolving?

Meanwhile ... Has the

IDEAL MAKE-UP BALL SIZE

also been evolving?

It should be noted

that this trend of

increasing make-up

4.0

4.2

4.4

4.6 '90

'92

'94

'96

'98

'00

'02

'04

'06

'08

A

v

e

.

S

A

G

B

a

ll

S

iz

e

,

in

c

h

e

s

increasing make-up

ball sizes has not yet

been offset by the

concurrent trend of

feeding the mills with

finer and finer

particles.

(27)

So ...

HOW ARE THEY RUNNING TODAY?

So ...

HOW ARE THEY RUNNING TODAY?

Mill

Ball

Total

Ball

F80

Charge

Facility

Diameter,

Length,

Filling,

Size,

Density,

Circuit Type

ft

%

in

mm

ton/m

3 Chuquicamata

32

15

15.0

28.0

5.0

120 3.75 SABC-1

Andina

36

15

14.0

30.0

5.0

76 3.54 SABC-2

Teniente SAG 1

36

15

14.0

33.0

5.0

170 3.46 SABC-2

Teniente SAG 2

38

22

15.0

31.0

5.0

100 3.64 SABC-2

Collahuasi

32

15

12.0

25.0

5.0

152 3.56 SABC-1

MEL Laguna Seca

38

20

19.0

26.0

5.5

80 4.37 SABC-1

MEL Los Colorados SAG 1

28

14

13.0

23.0

5.0

80 3.88 SABC-1

Data obtained from direct interviews to the listed operations.

MEL Los Colorados SAG 1

28

14

13.0

23.0

5.0

80 3.88 SABC-1

MEL Los Colorados SAG 2

28

14

13.0

23.0

5.0

80 3.88 SABC-1

MEL Los Colorados SAG 3

36

19

15.0

23.0

5.0

80 4.14 SABC-1

Candelaria

36

15

17.5

31.0

5.5

128 3.95 SABC-2

Mantos de Oro

28

14

14.0

30.0

6.0

64 3.52 Precrushing

Pelambres

36

17

19.5

30.0

5.5

90 4.10 Precrushing

El Soldado

34

17

14.0

25.0

5.0

117 3.83 SAC

Los Bronces SAG 1

28

14

17.0

30.0

5.0

60 3.88 Precrushing

Los Bronces SAG 2

34

17

17.0

30.0

5.0

60 3.88 Precrushing

(28)

120

140

160

180

200 F

8

0 S

iz

e

,

m

Chuquicamata

Andina

Teniente

Collahuasi

Escondida

Candelaria

So ...

HOW ARE THEY RUNNING TODAY?

So ...

HOW ARE THEY RUNNING TODAY?

Too many

balls!

FAG

40

60

80

100 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8

Charge Density, ton/m

3 F

8

0 S

iz

e

,

m

Candelaria

MDO

Pelambres

Anglo

Data obtained from direct interviews to the listed operations.

Not enough

balls!

BAG

(29)

It is very likely that many of

the members of this audience

would

would not

not

not share with me the

share with me the

‘rightfulness’

of all of my

todays statements.

For now, in my defense, I just

CONCLUDING

REMARK

CONCLUDING

REMARK

For now, in my defense, I just

wish to express that, in real

life ...

nobody is free of

making mistakes !!!