Girilambone Change Chemistry

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@

Pergamon

Minemls

llngineerng,

Vol

10,No.

5,

pp.

467-481,1997

O 1997Elsevier

cience td

P :

50892-{875(97)00026-5

Printed

n

Great Britain.

All r iglrts reserved

0892-687

5/97

$17.00+0.00

EXPERMNCE IN

OPERATING THE

GIRILAMBONE

COPPER

SX-EW

PLANT IN

CHANGING

CHEMICAL

ENVIRONMENTS

G.M.

MILLER,

D.J. READETT

and P.

HUTCHINSON

CMPS&F Pty Limited,

central Plaza

Two, 66 Eagle

street, Brisbane,

Qld.

4000,

Australia

(Received

3 JuIy 1996;

accepted l0 February

1997)

ABSTRACT

The

copper SX-EW

plant

operated

by the

Girilambone

Copper

Company

(GCC)

has

suffered

a number

of severe

process

upsets mmediately

ollowing

commissioning.

The

organic

reagent was

degraded by the

action of manganese

entrained

from

the leach

solution. The reagent

chemistry was restored

by the

large scale

use of treatment

by

an

activated clay. A

further

problem

was identified

as the reduction

in

SX

performance

by

the

generation

of

silica

gels

in the organic reagent.

A novel

mechanism

has been

proposedfor

the

generation

ofthese

gels.

Application

ofthe mechanism

has

allowed

the

identification of alternate

operating con"ditions

o

prevent

their

formation.

These

altered

conditions

have resulted

in

further

equipment

developments to

treat the

symptoms

generated.

A new

design of loaded

organic coalescer

has removed

the

increased

entrainment of aqueous resulting

from

operation of the

upstream

extraction

stage in

organic continuity. A new

medium has been

developed

or

installation

in the settlers,

to

minimise the total entrainments reporting to the subsequentstages of the SX plant.

Application

of these techniques

has been shown to

be

generally

appropriate

by use

in

other operations suffering

poor

SX

performance.

@

1997 Elsevier

Science Ltd

Keywords

Non-ferrous

metallic ores; electrowinning;

solvent

extraction; mineral

processing

INTRODUCTION

GirilamboneCopper Company

(GCC)

operates

a medium sized

open

pit

mine near Nyngan

in

central New

South Wales, Australia.

The

processplant

at GCC, usesheap eaching

(HL)

followed

by

solvent

extraction

(SX)

and electrowinning

(EW)

to recover copper as LME

grade

'A'

metal

(Figure

1). Leaching

is accomplished

with

dilute

sulphuric acid solutions, which dissolve the copper

and other chemically

amenable

ore constituents.

The

SX

plant

selectively

extracts

the

copper

from

the

pregnant

iquor

solution

(PLS),

and transfers

it into

the

EW electrolyte for

plating

by a DC current

onto stainless steel cathode

plates.

Presented

t MineralsEngineering

96,

Brisbane,Australia,August

26-28, 1996

46 7



468

G. M. Milrer

rar

The commissioning

of the Heap

Leach-SX-EW plant

was

followed

by a

carastrophic

collapse

in

the

operation of the SX

section. The

phase

disengagement

imes increased

and

the

settlers

filled

with

stable

emulsion. The extraction

kinetics

decreased

and

the reagent

capacity

decreased;

resulting

in

a major

limitation

on the copper transfer

to the EW

plant.

On-site investigation

of the

cause

of the

situation

determined

that it was due to

the

presence

of manganese

n the

EW

electrolyte.

The

mechanisms

or

the

transfer to EW,

the method of it's

effects in the

SX and

the remediation

were

subject

to

intense

study

I

l].

The manganese

effects were eliminated

by the application

of a rehabilitarion

process

for

the

SX organic

[2]

and measures o prevent the oxidation of the manganese

o

permanganate

n

the EW.

Removal

of the manganese

effects and their

consequent

symptoms,

revealed

an underlying

problem

in

the

SX with continued

poor phase

disengagement.

This

was shown

[3]

to

be a silica

induced phenomena,

and

a

phenomenological

mechanismwas

postulated

o

explain he

observed

ield

behaviour

3].

Application

of

the mechanism allowed the

development

of a different

operating

technique n

the

process

plant,

to address

the silica effects, which was

contingentonthe

treatment

of the effects

of

the altered

process

egime

[4].

The results

of the

plant

changes were

unexpectedly

good,

with the

operation

attaining

alt

the

goals

of

production

rate

and

quality

[4,5].

,

CIRCI.IIT DESCRIPTION

The PLS from the heap each s pumped o a conventionallydesignedSX plant (Figure 1), consistingof

two stagesof extraction n series

E-1

and E-2), followed

by a

single stripping

stage

S-1).

The loaded

r)t5

]AMESON

t OLUIlN

srR0N6

ILTTTROIYTT

S

RONI

ELET IROLYI I

TANK

FARI4

TIRtUtI IN6

E E T

ROLYIE

SPENT

ELI(TROLTI

EW

PLANI

Fig.l

SX-EWPlant

Simplified

lowsheet

li l _4qu q _

I

l

I

I

| | r\*

I

r-\-i

5 l



The

Girilambone

opper

X-EW

planr

organic

from

El is stored n two

tanksconnected

n

series

o assist n

the

de-entrainment

f

aqueous.

From

here it is

pumped

to the strip

stage or removal

of the

copper nto

the EW

electrolyte.

Removal of the

entrainedorganic

in the strong

electrolyte

s achieved

with

a Jameson

lotation

column

followed by 30 minute retention

n

a surge ank;

and finally

in the

scavenger

EW

cells

where

the

final

traces

of organic are recovered

by the rising

oxygen

bubbles from

the

anode.

The

Jameson

lotation

cell

is the

second o be used n the recovery

of

organic from

electrolyte.

Copper

production

is

by electrowinning

on to

permanent

stainless

steel

blanks

at current

densities

up to

280

A/m2. The

growth

cycle is 7

days; with

final carhode

weight

of around

50 kg.

Typical PLS contains: 4

glL

of Cu,

3 to 6

glL

of Fe

(with

1

g/L

of ferric),

400

ppm

SiO2, 2

g/L

Al,

50

ppm

solids, 120

ppm

Mn and

a

pH

of 1.8.

MANGANESE

EFFECTS

ON SX

OPERATION

Development

of Manganese Problems

at

GCC

The developmentof the manganese roblem at GCC occurredquickiy. By the time the siruation was

recognised

a catastrophicoperationhad

developed

which entailed:

.

Loss of reagentkinetics

and capacity with

extreme raffinate

copper concentrations.

.

Stable emulsion filling

the extraction

stagesettlers.

.

Long

phase

break times in

both the field

and laboratory

ests.

r

10,000

to 15,000

ppm

entrainments

f both

phases

eaving

all settlers.

o

Minimal recovery

of organicby the flotation

column from

the

electrolyte,

with a layer

of

organic

forming on

the scavengerEW

cells.

.

High

organic loss to raffinate.

.

High loss

of electrolyteentrained

n the organic

lowing from

the strip

stage

o the E2

srage n

SX.

.

Extremely

poor product

quality

from the EW

scavenger

ells, and

deteriorating

quality

in the rest

of the EW

plant.

o MnO2 precipitatingon all EW surfaces.

.

Sticky cathodesand nodular growth

of the EW

product.

.

Purple colouration

of the electrolyte and formation

of CuCl2 on

the electrode

hanger

bars.

Thesesymptomswere interacting

and deteriorating

hourly.

Once he

situationhad

stabilised

he SX

plant

throughputwas constrained,

by the

high

entrainments,

o 60

percent

of design

capacity;

while

the

product

quality

from the EW

was acceptable rom

the commercial

cells but

of inferior

quality

from

the

scavenger

cells due to

'organic

burn'.

Mechanism of the Manganese

Problems

The

effects

of manganese

n

the

operation of the

copper SX

process

has only

been recently published.

Miller [ 1] hasdiscussedhe available iteratureand operational xperiences. o date ive copperSX plants

have reported adverse

effects rommanganese ntheirprocess

liquors. The

mechanism

of theproblem

is

reasonablystraight orward, but the consequent

ffects are

generally

multiple; with

complex

interactions

giving

further symptoms of

poor plant performance.

Manganous on

(Mn2+)

itself has no

effect on the operation

of the SX

plant.

It is

however ransferred

nto

the

EW electrolyteby the aqueous ntrainment

of the

pregnant

iquor

solution

PLS)

n the oaded

organic.

The highly

oxidising environment n the EW

cells can alter the

oxidation state

o Mn4+ or

Mn7+ Any

Mna+

produced

will

precipitate

as MnO2 in the

cells. If there is

sufficient iron

(Fe)

present

in

the

electrolyte his will

provide

a

pathway

or the higher

oxidation state

permanganate

Mn7+)

to be reduced

by

the

oxidationof Fe2+ to Fe3+.



470

Mnl+

- .

5Fe2+

:

5Fe3+

* Mn2+

G. M. Mi l ler

et a/

( l )

The

stoichiometric atio

s 5:1 Fe:Mn

or

5.1:l mass

atio orthis

reaction.

oprovide

a sufficient

hemical

equilibrium driving

force to

maintain

most of

the manganese

n

the Mn2+

state,a

10:

mass atio

has

been

found

to be required

1].

However

during

the early

commissioning

of copper

SX-EW

plants

here

s a low

concentration

of Fe in the

electrolyte.This

allows

any manganese

n electrolyte

o

be oxidised

and o

cause

consequent

roblems.

The normal chemical potential

n

the EW

cells'electrolyte

(Eh)

is about

400

mV.

Under

conditions

of

manganeseoxidation

this can rise

to 900 mV

[].

Under

such conditions

the range

of, and rate

of

deleterious eactionscan

increase

o an extent

that causes roblems

with

the reaction products

Il]

eg:

o

The

SX reagent s oxidised

and the

reaction

products

accumulate

n

the organic phase.

r

Chloride in the

electrolyte

will be reduced

o

Cl

2

and released

t a

greater

ate

than

previously.

r

Increased

corrosion of

the

plant

stainlesssteel

components

can

occur leading

to mechanical

failures.

Consequent Effects

of Manganese

Problems

Figure 2 shows,diagrammatically, hecascading ffectsof manganesence t reachesheelectrolyte.There

are a large number

of complex interactions

and

symbiotic

effects between

the

various

primary

and

secondary ymptoms.The

positive

eedback oops

hat also

exist ead o

catastrophic

ollapse

of the

process

integrity and

plant

operation. The

primary

effects, of

the high oxidation potential

of

the Mn7+

formed

in

the

electrolyte, are

related

to the oxidation

of the

SX organic reagent

].

This

gives

reaction products

which themselveshave the followins

effects:

r

Reduce

he chemical reaction

kinetics

of the extractant.

o

Reduce

he

reagent

capacity

o chelatewith

copper.

e

Create

polar

reactionproducts

which

reduce he

interfacial

ensioncharacteristics

f the

organic

phase

approximately 1000

ppm

ofdegradationproducts

s

all that s required

o alter

the surface

characteristics

ramatically, Miller[1]).

Production of MnO2

precipitates

which form

crud

Direct attack

on the EW lead anodes,

changing

voluminousPbO or Pb(OH)2

1].

Most

of these have further secondary

effects or interact

with

each other

to

give

accelerated process

collapse, as shown in Figure 2.

RESOLUTION

OF THE

MANGANESE

EFFECTS

The rehabilitation

programme

was aimed at reducing

and maintaining

the electrolyte

Eh at

around 400

mV,

maintaining

the

manganese

n the Mn2+ state, and removing

the

degradation

products

from the

SX organic

( to enable better phaseseparationand entrainmentcontrol). The initial reduction of Eh was attemptedwith

the addition of

ferrous

sulphate o the electrolyte. The

reduction was slow

and was supplemented

with

the

addition of SO2, by bubbling

into

one of the electrolyte anks

[1].

This was successful

n

obtaining an Eh

of 400 to

450

mV; and the

presence

of the iron at concentrations

above 1

g/l

was

sufficient

to maintain the

lowered Eh and the

mansanese n

the Mn2+ state.

The

rehabilitation

of

the

organic

was

achievedusing a treatmentwith

acid activatedclay.

This technique

was

developed

by Manison

[2],

in the mid 1980's. The

procedure

was implemented

on the

plant

organic

on a batch basis. Cycle times

for

the treatmentwere around 24 hours, for

a batch equivalent

o l07o

of

the circuit inventory. This

proved

to be inadequate

s he initial benefit rom

the treatedbatch

dissipated

within 12 hours. The extended reatment

imes were due to

the slow settlingof the clay from the

organic.

in the SX.

the

oxide

protection

layer

from PbO2

to a



47 1

he Girilambone opper

X-EW

plant

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47 2

G. M. Mi l ler et al

The cycle times were reduced to 1 to 2 hours

by installing

a

plate

and frame

filter

to remove

the clay,

before

returning the

treated organic to the

circuit. The

benefit

of this treatment

was

obvious,

as the

plant

organic

retumed toward

the original extraction

capacity

and kinetics.

The

phase

break times

improved

but

did not

return

to the

previous

levels, as

expected. The

recovery

of organic

in the

flotation

columns

also

did not improve as expected; and the

problems

associated

with

organic

burn in the

EW

plant

were

not

mitigated. In all, the organic nventory was

treatedabout

5 times o recover

he chemical

characteristics.

SILICA EFFECTS

ON SX OPERATION

Plant Responses and Field Observations.

Further investigationof the SX circuit

characteristics

howed hat there

was a high

level

of silica in

the

organic

phase.

This led to the identification

of silica as a

potential

major

contributor

to the

problems

of

poor phase

disengagement, igh levels of entrainment

and

poor

organic recovery

n the

flotation

columns.

Silica has been recognised or some ime as having

adverse ffects

onthe operation

of

SX

plants

[3-5].

It

has an inverse

pH

solubility characteristic, which indicates

hat any

carry over from

the extraction

section

to the strip stage,can form silica

precipitates

n the

strip operation. This

was the

case n the field,

where

the

strip

settlerwas full of crud, the organicentrained n

the electrolyte

o the flotation

columns

contained

up to 50 percent crud, and the stripped organic was carrying a high load of light, fluffy crud. The

performance

of

the Jameson lotation column is

shown in Figure

3.

The

theoretical

performance

curve for

the column has been developedby

Readett

5].

It is based

on a constant 10

ppm

entrainment

of organic

in the column

tails.

100 . 0

90.0

80.0

70.0

i

60.0

o

8

so.o

o

E

;e

4o.o

10.0

20.0

30.0 40.0

50.0

60.0

70.0

80.0

9o.o

.too.o

FreeOrganicn Feed

Fig.3 JamesonCell Organic recovery

-

prior

to Modifications

Several

plant

observations

gave

the first indication of the true cause of the

problem.

It

was noted that:

l.

2 .

a

J .

^

5 -

When E-l

was

run aqueouscontinuous

(as

it had

been since

plant

start

up) significant

quantities

of

non compacting crud were being

generated

hroughout the organic

phase.

Significant build up of crud was occurring

in

the strip stage.

Organic

recovered from

the

Jamesoncell contained significant

quantities

of

'gelatinous'

crud.

There was a

gelatinous

film adhering o sectionsof the Jameson ell and scavengerelectrowinning

cells.



The

Girilambone opper

X-EW

plant

A sample of the

gelatinous

material

was assayed

nd returned

a

SiO2 content

of

>

50% on

a dry

basis.

This was

believed to be indicative of the

presence

of

a colloidal

silica

(SiO2)

gel.

Further investigationhighlighted

that the silica level

in PLS had passed

he maximum

level

of 400

ppm

recommended n

the designcriteria, and

in

general,

silica levels n

all areas

of the

plant

were

excessive.

A summary of silica data is shown n

Table 1.

TABLE I

Silica Distribution Through

the

GCC SX Plant.

El aqueous

E2 aqueous

Stripped Organic

Jameson

colurnn orsanic

500

450-5 0

450

5,800

The solubility of silica, at the PLS

pH

of 2.0, is

around450

ppm;

while at the 180

g/l

in

the electrolyre,

is much ess.The extractionsystem

was

apparently

t silica saturation evels,

which implies

that

he oaded

organic

is

also

in

a similar state.

Site observationof the responses f various

plant

streams

o coalescing

f the entrainments,

howed

some

interesting

phenomena.

Coalescing

of aqueous rom organic, from

both aqueous

and organic

continuos

operation, was readily accomplished without

problems.

However

irrigation

of the organic from

an aqueous

continuousoperation,

prior

to coalescing locked he

coalescingmedia with

gels.

Irrigation

of the organic

from

an organic continuous operation caused no

problems

with

media blockage.

Development

of

an Empirical Mechanism

of Silica Effects

An

empirical

mechanism of the operation

at the GCC SX

plant

has

been developed

[3].

This

postulates

he

carry over of

silica from E-l to the strip

circuit by three routes:

o

Direct entrainment of PLS silica via

entrainment of aqueous n

the loaded organic.

.

Physio-chemicalattachment

of silica to the

polar

molecules

present

n the

organic

phase.

r

Indirect entrainment of silica via PLS

tied up as fluffu crud in

the loaded orsanic.

Once in the strip stage he silica

precipitates due

to

low

solubility at 180

g/l

acid) and forms

gels

and

solids.

These

gels

and solids subsequently absorb organic, form

crud and carry through

in the electrolyte

as

entrainment.

The solids tend to form compacting crud, while the

gels

form non-compacting,

non-settling

emulsions.

Both forms have been observed n the strip stage; with

significant

quantities

of compact crud

present

in the settler; and large

quantities

of

'fluffy'

solids evident in the electrolyte

entrainment.

The

postulated

mechanism allows an understanding of the

processes

nvolved in

the

poor

operating

characteristics

of the Jameson organic

removal

column.

These

were:

The high

proportion

f

non

settlable olids

n

the organic ntrainment

up

o +50%

of the otal

organic olume.)

Poor organic esponseo

flotation

due o the

presence

f

non-settlable

olids.

Reasonably

igh levels of organic

entrainment

n

electrolyte.

Poor hydrophobicityof

the

organicdue o the arge

proportion

of solids.

a

a

a



47 4

G. M. Miller

er al

The

ultimate aim of

the

process

nvestigation

and

development

was

to minimise

and

control

the

amount

of

organic appearing in the

scavenger

cells. The

first

step

to achieve

this

was

to improve

the

performance

of

the Jameson

column by improving

the

characteristics

f the

organic

being

fed

to it.

Throughout

the industry

E-l is

generally

run aqueous

continuous

to minimise

entrainment

of

aqueous

n

the loaded

organic. Some

operations,

however,

have

reported

the

benefits

of operating

E-l

organic

continuous, o control silica crud affectseg Olympic Dam and Chuquicamata 3]. Both of theseoperations

however

have been retrofitted

with a scrub

stage

o remove

the subsequent

igh

levels

ofaqueous

entrained

in

the organic.

The use

of

coalescers

n SX

circuits is

quite

common

in the

chemical

industry;

and

has

been recommended

for

use n mineral

processing

ircuits.

Olympic Dam

was

originally

supplied

with

a

combined

coalescer-

settler on copper SX raffinate,

before it

was fed

to the uranium

SX

circuit.

Certain patent

applications

by

Codelco, Chuquicamata

division exist

for coalescer

designs

and

media for

copper

SX

circuits.

On site

pilot

testwork

demonstrated

he viability

of

a coalescing

step

on the loaded

organic.

This

was

extended to a full

scale test

programme

to determine potential

performance

of

a coalescer

made

by

conversion of one of the loaded

organic

tanks.

The

physical

form of

the aqueous entrained

in

the organic

is changed

between

operation

in aqueous

continuity and

organic continuity. In

aqueous

continuity the

aqueous

s in the

form

of fine,

'bubble'

films

surrounding a core of

organic, within the

organic continuum.

This

is not readily

observable

n the

field due

to the opaque

organic. However,

a similar

phenomenon

can be observed

with

organic

films

surrounding

an aqueouscore in an aqueous

continuum,

arising from

an organic

continuous

operation.

These

fish

eyes'

are often seen n the raffinate

from E-2.

When

normal aqueous

haze'

coalesces rom the

organic,

two droplets

come together

o form

a larger

drop.

The larger drop volume has

a correspondingly

lower

surface

area. As

such some

concentration

of

interfacely

adhered species will

occur at the new

surface

until such

time as they

have

an opportunity

to

diffuse into the bulk mass

and return to

the

previous

average evels.

Typically the finest aqueoushaze is of the order of 10 micron radius. When two such drops coalescethe

actual surfacearea

of the two smaller

drops s l:l .26that

of

the larger

drop. Even

after

ten drops have

coalesced he surfacearea

eduction s

only l:2.15.

This coalescence rocess

s relatively

slow and multiple

contacts

can take many minutes

(with

7r to t hour required

for

significant

reduction

of entrainment

levels).

This

slow reduction in total

surface area allows

time for de-attachment

and diffusion

of

speciesaway

from

the interface into the

bulk of the drop.

Typical

aqueous

fish

eyes' are

of

the

order of I

to 2 mm diameter

with

a film

(skin)

thickness

of

approximately

0.01

microns.

When these ilms

collapse

eg

by contact

with air,

solids

or larger aqueous

drops) hey will form a single

solid'

droplet

of equivalentvolume

to the volume

of the

skin.

Calculations

contained

in Table

2 show that such a

typical fish eye would

collapse

to a droplet

of 31 micron

diameter;

with

a consequent urfacearea reduction

of 1:1030. This

collapse s

also extremely

rapid;

occurring in

fractions of a second. Thus the collapse of these skins produces extremely high surface concentration

gradients

or

adsorbed pecies;and allows ittle time

for these

gradients

o disperse

nto

the bulk solution.

As a result of these concentration

gradients,

silica

polymerisation

can

occur near

the drop surface

forming

nascent

gels

and

networks

within the aqueous

drop.

Any subsequentcoalescenceof these aqueous

drops can cause urther

gel

structure

growth

as the nascent

gels

are brought together and they become more

ordered.

This is the mechanism by which the

gel

formation

occurs from water

sprayed organic

(operating

aqueous

continuous and

producing

aqueous

fish

eyes'). The spray has

the effect of creating

small diameter

drops

of water

which

burst the

'skins'

on contact.

Only that

part

of the skin in

close

proximity

to the water

drop

combines with it. The rest of the skin

collapsesaway from

the

point

of

penetration,

into a single

drop

(like



The

Girilambone

opper

X-EWplant

a

pricked

balloon), due

to contraction

from

surface

tension.

The

reason hat coalescence

of these

skins directly

onto a media

substrate

does not

cause

such

gel

formation

is

probably

due o the following

mechanism.

The

skin

contacts

n, collapses

nd wets

he

medium.

As such

there is no immediate

small droplet

formation

and no

significant

reduction

in

surface

area.

Subsequent

collapsesof further

skins allows

a slow buildup

of larger

volumes

on the

surface

of the

media.

The

extra

time allows the interfacial

concentrationgradients

o be lowered

by

diffusion

into

the

bulk

aqueous.

The

combinationof low surfacearea eductionand onger ime for droplet ormationallows he silica

to

diffuse

from

the interface nto

the bulk, and

thus not form gels

during

the coalescing

stage.

An observation hat the

water

sprayed

organic had

higher

aqueous

evels

s easily

explained

by the

extra

water added.The fact that

this extra water

did not

separaten

the oaded

organic

ank(s)

s again

a

function

of the effects of the collapse

of the aqueous

kins.

Someof these

will

have formed

silica

gels

ar

the drop

interface.

These

gels

will have

fully encapsulated

he interior

aqueous

and will

carry

it

through

the

subsequent eparation

stages.

TABLE

2 Calculated

Droplet

Size and Area

Comparisons

l. Aqueous

Haze'

Radius,m

Volume,

m3

Area, m2

Area/Volume,

m2lm3

Equivalent No. of l0 micron

units

Area reduction cf l0

micron

l0 x l0-o

4 . 1 9

1 0 - 1 5

12.56

10-10

3.0x 105

I

I

12.6

10-6

8.38 10-15

1.994

10-e

2.38

l }a

2

r . 2 6

2155

x l0-il

4 . 1 9

l 0 - r a

58.33 10-e

1 3 . 9

1 0 4

l0

2 . 1 5

2. Aoueous

tlsh

Eves'

Radius, m

Film

thickness,m

Volume, m3

Area, m2

Area/Volume

Area reduction

Original

'fish

eye'

10-3

10-8

12.56

x 10-14

12.56 x 10-6

108

I

Equ v al

ent co l ap ed- sohd-'U-rop

31x 10-6

N/ A

12.56

l}-ta

1 . 2 1 5

1 0 - 8

9.67x l}a

r030

RESOLUTION

OF TIM

SILICA EFFECTS

Plant Modifications

The

process

electedor improvement

f the Jamesonell

performance

nvolved:

Modification f theNo 1 oaded rganic

ank o actasa coalescer

o remove

ntrained

queous.

A

plant

shutdownwas arranged

o modify and ill

the tank with the

medium

and hen o restart

with E-l organic ontinuous.

Operation f E-1 n organic ontinuity.

This

aterwas

possible

nly because

n organic ecycle

had

been

ncorporatedn

the original

design).



476

G. M. Miller

er

al

Operation

of El in Organic

Continuity

With the conversion of

E-l to

organic

continuous

operation,

extremely

significant

changes

occurred

to

the

operating regime

of the SX and

EW

plants.

These

nclude:

a

a

a

a

a

a

a

o

a

Virtual

elimination

of crud

production

n

E-1

(and

subsequently

-2).

Major reduction n crud production n the strip.

Elimination

of fluffy

crud in loaded

organic.

Virtual

elimination

of solids n

organic

entrained

n electrolyte.

Stabilisationof

the

level

of

organic entrained

n

electrolyte.

Jamesoncolumn

operation at

or above ts

theoreticalperformance

curve.

Consistently ow levels

of

organic entrainment

n

the Jameson

ell tails,

less

han

10

ppm.

Increase

n copper

quality

to LME

'A'

from

scavenger

ells

(due

o

the essening

f organic

burn7.

Total elimination

of silica

contained n

loaded

orsanic.

Aqueous entrainment

in E-l

organic outflow

after restart,

was

high

and with

erratic

levels.

Highest

measured evels were

20-25,000 ppm.

When

high

levels were

measured

a distinct

dispersion

band was

evident at the

discharge end of the

settler. Field

observations

ended

o correlate

higher

entrainments

with

deeperdispersionbands. There

was no

buildup of

crud at the interface

n E-l

or evidence

of fluffu

crud

in the organic.

E-l break times rose

to

4Vz

minutes soon

after

the change

and remained

there for

4

days. They

subsequently

ecreasedo the

current evel

of 2 to 3 minutes.

There

hasbeen

some

evidence

of rag

(stable

emulsion

films) in the aqueous

uring the

break; but this

coalesces

nto the

interfaceprior

to completion

of

primary

break. No residual rag

is evident.

Aqueous

solutionsare

clear

with some

'fish

eyes'

present

especially at high

suspended olids oadings.

A significant reduction

in crud

production

has

been observed n

the

strip settler.

Daily

crud removal

has

been reduced o less

han once

oer

month.

The entrainment

of organic in

electrolyte has

not been

significantly

reduced

but the

proportion

of

crud/solids associatedwith the organic has decreased.The percentage f solids was almost zero in the

samplesanalysed.

Jameson Column Performance

The Jameson ell tails

have

becomeconsistently

ower

than 10

ppm.

This compares

o

erratic

and higher

levels

prior

to the changes.These esults

are

consistentwith

the Jameson

ell

operating

model

[5];

which

concludes that the

cell

produces

a 10

ppm

tail

(from

suitable feed)

independent

of

the

feed

concentration.

This has

been successfullydemonstrated,

ince

the changes,

with feed

levels

up to

37

ppm.

The

feed

concentration vs recovery

curve is

plotted

in Figure

4. As

is evident

the field

performance

is at

or better

than the theoretical

performance

line

since the circuit

changes.

The organic recovered from

the Jamesoncell still

shows

poor

disengagement

haracteristics

rom

the crud

formed during the recovery process.

As such it is

directed to

the crud tank

for treatment

prior

to its

reintroduction

o the circuit.

Scavenger Cell Operation

With the consistently low levels

of organic in

strong electrolyte,

the skimming

of

organic from

the

scavenger cells

became

viable.

Each cell was fitted

with feed and

discharge

skimmers.

Product

quality

improved dramatically in

both

physical

appearance

and chemical

quality.



The Girilambone

opper

X-EW

plant

E

t00.0

90.0

80.0

70.0

60.0

50.o

40.0

30.0

20.0

10.0

tr

u o

EI

t o t

E E g

Eo

a

E

E

E

E

E

Eg

f

-

o

o

cr

t; A"t""t I

[=f "":"$11

o.o

].-

o-

0.0 10.0 30.0 40.0 50.0 60.0 70.0

80.0 90.0 100.0

FreeOrganic n Feed

Organic Recovery

-

post

Modifications

is.4 Jameson

Cell

Loaded Organic Silica

A seriesof

loaded

and stripped organic sampleswas

taken during to

the E-l flip to

organic continuity.

Figure

5

shows he silic, analysis

of theseorganic samples.As

can be seen he

silica level

dropped rom

487

ppm

in

loaded

organic

prior

to the flip; to zero

two weeks after the flip.

500.0

450.0

400.0

350.0

300.o

250.0

200.0

150.0

100.0

50.0

0. 0

511

1411

2111

SampleOate

--o-

Loaded

Org

--+-

Stripped Org

Fig.5

OrganicSilicaLevels

CL

CL

o

o

o

N

o

a



478

Other

G. M.

Miller

ral

points

to note

from

this

Figure

are:

A reduction

n

silica

level

between

oaded

and

stripped

organic.

This

shows

he precipitation

of

silica from

loaded

organic

by

the

high

acid

strip

stage.

The

concentration

of

silica in

loaded

organic

is intermediate

betweenpls

and

raffinate

values.

This

indicates he evel of silica s probablyat equilibriumwith the aqueous hase oncentrationswhen

operating

aqueous

ontinuous.

However,

the zero

silica evel,

when

operating

organic

continuous

in E-1

supports

he

postulated

mechanism.

Loaded

Organic

Coalescer

Figure

6 shows the

result for

the

coalescer

for

the first

two

months

of operation.

The

feed

entrainments

were

high with

very

wide fluctuations.

The

unit has

provided

a consistent

output

with

an average

200

ppm

aqueous n

the loaded

organic,

with

a maximum

of 400 ppm.

Backwashing

has

been

required

on

a four

weekly

cycle and has

been ntegrated

with

the maintenance

schedule.

The

high

feed

entrainment

evels

have

resulted

rom

the operation

of the E1

mixer

settler

n organic

continuitv.

at

1111 1311

January

1994

E

3 m E

E

U

20o

E

E

e

o

o

L

ul

i-:""1----:-::"41

Fig.6

Loaded

Organic

Coalescer

Aq

Entrainment

in Feed

and

Discharee

IMPROVED

SETTLER

OPERATION

System Development

The operation

of the

GCC SX

plant

was improved

with the

change

n E1

continuity

to organic

continuous.

However

the level of aqueous

entrainment

in

the loaded

organic

was

of concern

in

case t

'broke

through'

the

coalescer, into

the strip circuit.

Methods

of

reducing

this

entrainment

and

of

the large

fluctuations

in

the

entrainmentwere investigated.

Many

methods

of

entrainment

ontrol

have

been

ried

,

Millert4l.

Al l

have

been

partially

or

generally

successful

n clean

solutions.

However

ndustrial

solutions

equire

sysrems

that

can operate well

with large

quantities

of crud

present

n

the

settlers.

Those

systems

hat

are tolerant

of crud have

had the least

success

with

entrainment

control.



The Girilambone

opper

X-EW

plant

Coalescing

Requirements

The

primary

effect of

poor

settler

performance

s the

appearance

f a dispersion

band

of

significant

thicknessat the settlerdischarge.This leads o high

andhighly

erratic evels

of entrainments

n

the streams

advancing

from the settlers, which in turn leads

to effects such

as high organic

in raffinate

and

advance

electrolyte, high PLS entrainment n loaded

organic, and high electrolyte

entrainment

n

stripped

organic.

Thesesituations an becomeunstable nd require educed olumetric hroughputso satisfactorilystabilise

the operation.

The requirements

for in-settler

coalescing are different from

stream specific

uses

(such

as the loaded

organic

coalescer). n-settlercoalescingaims

primarily

to stabilise he

entrainment evels

at around

500-

1000

ppm;

which is the normal designcriteria for copper

circuits. The elimination

of

shock oads due to

entrainmentof

the dispersionband s important.

Streamspecificcoalescing

aims to reduce

entrainment

levels to 50-200

ppm

in order to reducecosts

organic

oss)

or

improve

downstream

process

effectiveness

(reduce

organic burn and minimise PLS to electrolyte).

There

s

about

an order of magnitudebetween he

success riteria for the two different

styles

of operation,

which leads o two different

setsof design criteria,

and solutions or the

problems.

The selectionof a

permanent

n-settler

coalescingmedium required

he

following

criteria

to be met:

Cheap,

easy to make, materials

readily

available, have intermediate

sudace tension

(so

that

both

continuities

could be treated successfully), chemically compatible, require

simple

installqtion,

density

greater

than electrolyte to

prevent

floating,

suficient open area to

allow crud to

pass

through unhindered.

One

of the

problems

n medium selection s that testing s not readily

done, except n

the industrial

plant

or a

large

pilot

unit. Even on a large

pilot

unit full hydraulic

similarity is not achievable.

For this reason

a scale

up factor was usedbasedon the streamcoalescer pecific low rate,

1m3lhrlm2

f media surface),

and the target

level

of

entrainment.A 1:4 ratio was

used as the basis.

A

packing

ype

having he following featureswas selected: andom

ype

packing,

available n various

sizes,

made from a commercialplastic andreadily available. The size of the packingwas selected asedon the

size of the openings

available for crud

passage.

This

allowed a

large

size to

be used, which in total

occupied

less

thal

40% o f the settler volume. The

packing

was contained

in coarse mesh

bags,

manufactured rom a solution

esistantmaterial,

o

prevent

heir escape nd

blockageof

pumps

and valves.

Operating

Results

The results

of the in-settler coalescingmedium addition have

been better than expected.

The addition

resulted

n immediate reductions n the entrainments rom all

stages reated.The operation

of the settlers

was more stable. With the levels of entrainment educed, he down stream mixer

was also more

stable,

with far fewer uncontrolled

changesof operatingcontinuity.

The settlers

were able to

perform

successfully nder

quite

adverse onditions.This included

maintenance

of full hydraulic

capacity with both:

r

Lower than design

emperatures

10oC

rather than 20oC).

o

3% higher than design

reagentconcentration.

.

Higher than

design solids n PLS

(up

to 200

ppm

cf

<20

ppm).

Under these

conditions he

settlerselection riteria would have esulted n a unit with

35

%

more area. The

capacity

was confirmed during summer operation

(closer

to nominal design

conditions) when the total

average

entrainment

loss of organic to raffinate was 10

ppm

over a 5 month

period.

This

again

demonstrates

he effectiveness f

the medium.

479



480

G. M.

Miller

era/

Recent

operation

of

the settlers

after

systempumping

upgrades)

has

shown,

that

under

close

to

design

conditions,

the

settlers

will treat

307o

morc

than

design

lows.

The

limitation

at

GCC

is

not in

the

settler

performance

but in

the

pumping

systems

ervicing

he

SX

plant.

It

is

estimated

hat

the

settler

capacity

s

at least

40% improved

over the

'conventional'

design

criteria.

This

allows

for

easy

upgrading

of

SX

plant

hydraulic

capacities,

without

the need

or more

or enlarged

settler

units.

Installationof the medium in anotheroperation,Miller[ 4], hasalso shown he benefitof this technique.

The

plant

was

operating

under severely

adverse

onditions.

Medium

was

added

o various

parts

of the

SX

settler

systems n

stages.The plant

throughput

was

doubled

from

50%

to 100%

of design

ate

in

a

period

of 4 months.

Figure

7 shows

he

accumulated

ffect

of the

medium

addition

on the

plant

feed

flowrate.

Medium

addition to the

settlers

reduced

he

aqueous

entrainment

n

the loaded

organic

from

+20,000 ppm

to less than

500

ppm.

The results

rom these

operations

how he

benefit

hat

can

be achieved

rom

the installation

ofcoalescing

medium

in the settler.

This

has

been ecognised

or some

considerable

ime;

however

the

development

of

a medium

that is

tolerant

of crud

and other

adverse

operating

conditions,

has now

been

Droven on a

continuous ndustrial

scale over

a

period

of nearlv

3

vears.

l;,.;;;-^,*;;;-l

f r om

30, 9 o 21r10when

;

S iO2

sa t u ra l i on

aused

I

t low.at€

o be reduced

nd

]

i

cont inuity

f l ipped

to organic

I

-=\-

i

M"d',-'.ddil-l

wash aunder

]

(8,12,s4)

I

---\-

9-

2OO

t

*

150

J

\

/ . ' -

i

Med ium

added o

I

52

laund€r

l

lry1r"I,*ll

__'1

__

I

Medium

dded

I

to Et sett ter

j

fl6:11lsa)uo l

I

" l_

190994

06.1G94

24-1G94

Fig.7 Plant

Throughput

11-11 . 94

3G11. 94

18. 12 . 94

05. 01 . 95

Oate

Increase

with Settler

Medium

Addition

CONCLUSIONS

The

development f

the understanding

f the

prime

and

consequent

ffects

of manganese

n

SX and EW

operations,has

assistedn

the

improvement

f

performance

f the

GCC

plant.

Now

that

there is

an

operationalmechanism,

hese

effectscan

be avoided

y simple

preventative

measures,

specially

uring

commissioning.

For

those operations

ikely to

have manganese

n

the PLS,

addition

of iron

into

the electrolyte

s

recommended

before

the SX

plant

is charged

with

extractant.

Monitoring

of the EW

Eh will

give

timely

warning

of any

potential

degradation

of the

organic.



The

Girilambone

opper X-EW

lant

481

The understanding

of

the effects

of silica on

the SX

plant,

has

been

advanced by the development of a

phenomenological

mechanism.

Application

of

this hasallowed he

plant

operation

o be altered o minimise

the silica

effects.

Development

of stream

speciflc coalescing

techniques and hardware, to address

the

consequent

ffects

ofthe

changed

operating

conditions,

has advanced he applicability ofthese

methods.

The

selection

of a

medium

for use

in the settlers

has enabled the

hydraulic capacity of the settlers to

be

improvedby between30 and 50 percent.The medium s tolerantof crud, cheapand easy o install. It also

provides a means

of

increasing

plant

capacities

without the

need for more or larger settlers.

The resolution

of the

problems in the

GCC operation

has been

the springboard

for the development of

a

number

of techniques

hat

have advanced

he

knowledge and

operation of the

SX circuit. Implementation

of these

techniques

has

been

found to

be

generally applicable

to other operations, and

are being

incorporated

in a

number of

new

projects.

ACKNOWLEDGMENTS

The

authors

would

like

to thank

the staff

and management

of

the Girilambone Copper

Company

for their

permission o

publish this

paper. The effort to

overcome he

problemswas huge; and

t is a credit

to them

that the

plant

operation

was restored

in such

a short

time. The

views

of the authors do not necessarily

reflect

those

of the

ComPanY.

REFERENCES

Miller,

G.,

The

Problem

of

Manganese

nd ts

Effectson Copper

SX-EW

Operations,

eds W.C.

Cooper

et al.

Copperg|-Cobre9S

649-663,

CIM

Santiago,

1995).

Mattison,

P.L., and

Champion,

W.H.,

Enhancement

f Solvent

Extractionby Clay

Treatment

of

Contaminated

Circuit

Organics,

Hydrometallurgy

Research

Development

and Plant

Practice, Eds.

K.

Ossco-Asarc

and

S. D.

Miller, 617-628,

Proc. AIME,

112 Annual

Meeting,

Atlanta,

(1983).

Readett,

D.J. &

Miller, G.M.,

The Impact

of Silica

on Solvent

Extraction:

Girilambone

Copper

Company,A CaseStudy, edsW.C. Cooperet al. Copper95-Cobre95, CIM, Santiago,679-691

(1ee5).

Miller,

G.M.,

Readet,

D.J.

& Hutchinson,

P., Entrainment

Coalescing

n Copper

SX Circuits

eds

D.C. Shallcross

et

al.. Proc.

ISEC 96,

Univ.

Melbourne,

Melbourne,

795-800

(1996).

Readett,

D.J., Experience

with

Column

Flotation

n

Electrolyte Clean-up

During

Process

Upset

Conditions

eds

D.C. Shallcross

et al.

Proc.

ISEC 96, Univ.

Melbourne,

Melbourne,

819-824

(1996).

l .

3 .

4 .

5 .

Girilambone Change Chemistry

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