Solvent Extraction (SX) reagent selection for high temperature, high

acid, high chloride and high Cu concentration leach solution at Port

Pirie and its impact on electrowinning

ByP. Crane, M. Urbani, K. Dudley, A. Horner and M. Virnig

Nyrstar Port Pirie Smelter

• The smelter is situated 230km north of Adelaide in South Australia on the Spencer Gulf.

Courtesy Google

Port PirieBroken Hill

Rich lead deposit

The smelter was built on a natural harbour allowing ease of product export

History: The smelter has been processing lead concentrates since 1889, after the ore field in Broken Hill was discovered.

Much expansion occurred during the 1950s and 1960s.

Zinc production commenced in 1967

Copper production commenced in 1984

Production Capacity: Lead – 235,000 Tonnes

Zinc – 45,000 Tonnes

Silver – 11.5 million troy ounces (357 Tonnes)

Gold - 16,000 million troy ounces (497 kilos)

Sulphuric Acid – 80,000 Tonnes

Copper – 4,500 Tonnes

Background

NPPS New Copper Inputs (tpa)

Lead Concentrates

71%

External Zinc

Residues

External Lead

Residues17%

4338 T

1041 T

12%711 T

Copper plant Feedstock mainly sourced from lead concentrates

NPPS Copper Process

• Copper is recovered from the lead furnace in the form of a matte, which is treated in the copper plant

• The Copper recovery process employs a unique mixed chloride-sulphate leach technology (formerly known as the BHAS process) developed by BHAS engineers.

• This aggressive chloride-assisted leach is followed by conventional Cu SX / EW processes operated under fairly harsh conditions.

Matte from CDF

Leach (primary and secondary)

Solvent Extraction

Residue/Neutralisation

Milling

Residue back to Sinter Plant

Electrowinning

Basic NPPS Copper Plant CircuitProcess description

•Ball Mill and Feed Hopper

Grinding• A conventional ball mill in closed circuit with a spiral classifier, treating 12,000 tpa

matte.

• Product goes to Primary Leach after thickening and storage.

To leach

Overall leach chemistry (effect of chloride not shown)

Cu2S + PbS + H2SO4 + 4H+ + 3/2 O2 PbSO4 + 2Cu2+ + 2S + 3H2O

Black Acid

PLS to Clarifier

Leach Thickener Underflow

PLS Underflow

Primary

Secondary To Neutralisation then Sinter Plant

•Leach Reactors

• Thickener U/F from 1st stage leach at 35-40% solids is pumped to a one-stage repulp reactor.

• Salt, white acid and Oxygen added.

• 4-5 hrs residence time.

• 2nd stage leach discharge washed with raffinate in a repulp mixer.

• Polysil added in repulp mixer for silica control, and Magnafloc added to Repulp Thickener as a settling aid.

• Repulp slurry is thickened; solids are sent to neutralisation and return to the sinter plant, whilst liquids go to 1st stage leach.

2nd Stage Leach and washing

•Salt addition to repulp reactor

NaCl prevents precipitation of CuS from Cu+ and S0.

•Preg Clarifier

•Leach Thickener

Was

hin

g

Str

ipp

ing

PregnantLeach Solution

Raffinate

Ext

ract

ion

SpentElectrolyte

AdvanceElectrolyte

Wash Water

Cu2+

Impurities

E1

E2

S2

S1

Cu2+

Cu2+

Cu2+

aqueous

organic

aque

ous

organic

organic

organic

organic

aqueous

aqueous

aqueous

Wash Water

• Conventional 2E x 1W x 2S circuit.

Copper SX

• Pregnant Leach Solution (PLS) containing approx. 40 g/L Cu, 20 g/L acid and 20 g/L Cl- at >40 deg C.

•SX Mixer-settlers, S1 and S2

Spent Electrolyte to S2 after cooling

Advance Electrolyte

• Two stage cascade systems in series with 15 cells per unit.

• Each cell has capacity for 40 stainless steel or titanium cathodes and 41 antimonial lead anodes

• Cathodes and anodes are connected to two 10,000A rectifiers.

Electrowinning

•Cell house

The use of the highly effective chloride – sulphate leach process results in several challenges for the operation of the Cu SX-EW plant, namely it:

• Produces a hot PLS, high in acid, chloride and copper content;

• Requires effective silica control and solids liquid separation;

• Requires a high SX extractant concentration and high O/A ratios;

• Requires careful monitoring of organic health and regular, effective, organic treatment.

Process Difficulties

Cognis visited Port Pirie in mid 2003 to view the plant operation and offer technical assistance. Main observations:

• Operating with high concentration of Acorga® M5640 (C9 aldoxime with TXIB modifier) and high O/A ratio.

• No phase separation under Organic Continuous conditions Forced Aqueous Continuous operation.

• Evidence of silica-based crud.

• Re-oximation stage due to high reagent degradation rate.

• Viscous organic with dark colouration after strong acid strip.

• High entrainment and resultant high Cl transfer to electrolyte (consistently >200 ppm Cl in electrolyte) titanium plates.

• Poor atmospheric environment in EW (low levels Cl2 gas).

Cognis Involvement

In August 2003, a sample of Port Pirie plant organic was analysed in Cognis’ Tucson laboratory. The main findings were:

• Extremely poor OC phase break >15 minutes at 25C

• Slow stripping kinetics – 62% after 30 sec (typically 95%)

• High nitro-C9 aldoxime level (16.2 % of total oxime)

• Excessive levels of hydrolysis product (aldehyde)

• High TXIB : C9 aldoxime ratio (0.38 compared to 0.28 in Acorga M5640)

• Presence of 2-cyano-4-nonylphenol and 5-nonylsalicylamide

• The organic did not respond to clay treatment

Cognis Involvement, cont.

33%(v/v) LIX® 674N-LV in SX 12 after a few load strip cycles then completely stripped.Note the clarity.

Stripping tests indicated the scale of the problem

33%(v/v) LIX® 674N-LV in SX 12 after a few load strip cycles then completely stripped.

Port Pirie plant sample completely stripped – 4 contacts with 250 g/L acid, O/A 2:1.

Red colour warning signs of nitration

NO2 +

OH

H

R

NOH

O2N

R

H

OH NOH

C9 Aldoxime Nitro C9 Aldoxime

HNO3 + H NO2 + H2O

Requires acid, nitrate and high ORP

Nitration of oximes

Catalysed by presence of modifiers (Virnig, et. al. Copper2003)

Stripped organic phases of all modified reagents: LIX 622N, M5640 and LIX 84-I + TDA; were red in colour

Effect of Modifiers

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 10 20 30 40 50Days

% (w

/v) A

ldeh

yde

or K

eton

eLIX 622N M5640 LIX 984N LIX 84-I LIX 84-I & TDA

Aldoxime + TDA

Aldoxime + TXIB

Ketoxime + TDA

Ketoxime + Aldoxime

Ketoxime

Effect of modifiers on oxime degradation in presence of nitrate

Cognis Manufactured Oximes

C9H19

OH

C

N

OH

CH3

C9 Ketoxime

C9H19

OH

C

N

OH

H

C9 Aldoxime

C12H25

OH

C

N

OH

H

C12 Aldoxime

© Copyright, Cognis Corporation, 2005

Acorga M5640 (incl. TXIB modifier) LIX 984

INCREASING REAGENT STABILITY

• Cease re-oximation of the organic, since:

– Re-oximated organics demonstrate poor physical performance

– Re-oximated organics are typically difficult to clean up

– Hydroxylamine may have been at least a partial source of the nitrogen oxide species

Cognis recommendations

Recommendations were all intended to improve the physical state and the performance of the organic phase.

• Convert reagent to a more stable non-modified reagent type to:

– Reduce rate of nitration

– Reduce rate of degradation

– Reduce viscosity of organic phase

Port Pirie accepted the Cognis offer.

LIX 984 was selected because:

• 50/50 blend of LIX 84-I (ketoxime) and LIX 860-I (C12 aldoxime), both of which are more stable than the C9 aldoxime present in Acorga M5640.

• LIX 984 contains no modifier Modifiers promote nitration.

• LIX 984 showed good chemical performance in initial screening tests.

Pre-LIX reagent addition plant profile (April 2004)

• Cu Mass balance OK

• High oxime concentration (43%(v/v))

• Low Cu net transfer (0.14 g/L Cu / % oxime)

• Low % Cu max load

• Laboratory PDT’s – aqueous continuous - 126 seconds, organic continuous - no separation after 15 minutes

• Again clay treatment had no effect, organic not filterable

• Extremely high viscosity (26.5 cSt compared to 3.9 cSt for fresh LIX reagent at 43%(v/v)

Acorga addition stopped in April 2004 and LIX addition commenced.

Regular plant monitoring involved:

• Chemical composition –C9 and C12 aldoxime, ketoxime, TXIB, hydrolysis and nitration products

• Chemical performance – Cu recovery, % Cu ML, Cu net transfer (g/L Cu / % oxime), extraction and stripping kinetics

• Physical performance – Plant PDTs, mixer continuity, temp, laboratory PDTs, Effect of clay treatment, viscosity

• Monitoring the Cl- concentration in the electrolyte

CONCENTRATION OF REAGENTS IN NPPS PLANT ORGANIC SINCE THE ADDITION OF LIX REAGENT

-

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

5/1/

04

8/1/

04

11/1

/04

2/1/

05

5/1/

05

8/1/

05

11/1

/05

2/1/

06

5/1/

06

8/1/

06

11/1

/06

2/1/

07

5/1/

07

8/1/

07

11/1

/07

2/1/

08

5/1/

08

Month

% o

f T

ota

l Co

mp

on

ents

by

Vo

lum

e

TXIBC9 AldoximeC12 AldoximeKetoximeC9 nitro aldoximes

Conversion rate tracked by decline in TXIB content

Parameter

Survey Date

May-04

Nov-04

Jan-05Jun-05

Nov - 06

Apr - 07

Oct - 07

Sept - 08

PLS Cu(g/L) 41.0 45.8 44.6 42.3 45.0 51.9 32.0 45.2

Raffinate Cu(g/L) 12.9 15.4 13.9 15.0 15.5 14.8 8.1 10.9

Cu recovery (%) 68.5 66.4 68.8 64.5 65.6 70.7 65.5 75.8

Reagent Conc. (vol%) 45.0 34.0 30.0 25.8 32.6 33.5 33.3 30.0

Net Transfer (g/L Cu/vol%) 0.150 0.220 0.234 0.255 0.229 0.273 0.174 0.211

% max load 59.0 66.4 65.5 83.9 81.5 88.2 65.5 74.6

Plant chemical performance

Parameter

Survey Date

May-04

Nov-04

Jan-05Jun-05

Nov - 06

Apr - 07

Oct - 07

Sept - 08

PLS Cu(g/L) 41.0 45.8 44.6 42.3 45.0 51.9 32.0 45.2

Raffinate Cu(g/L) 12.9 15.4 13.9 15.0 15.5 14.8 8.1 10.9

Cu recovery (%) 68.5 66.4 68.8 64.5 65.6 70.7 65.5 75.8

Reagent Conc. (vol%) 45.0 34.0 30.0 25.8 32.6 33.5 33.3 30.0

Net Transfer (g/L Cu/vol%) 0.150 0.220 0.234 0.255 0.229 0.273 0.174 0.211

% max load 59.0 66.4 65.5 83.9 81.5 88.2 65.5 74.6

Plant chemical performance

Parameter

Survey Date

May-04

Nov-04

Jan-05Jun-05

Nov - 06

Apr - 07

Oct - 07

Sept - 08

PLS Cu(g/L) 41.0 45.8 44.6 42.3 45.0 51.9 32.0 45.2

Raffinate Cu(g/L) 12.9 15.4 13.9 15.0 15.5 14.8 8.1 10.9

Cu recovery (%) 68.5 66.4 68.8 64.5 65.6 70.7 65.5 75.8

Reagent Conc. (vol%) 45.0 34.0 30.0 25.8 32.6 33.5 33.3 30.0

Net Transfer (g/L Cu/vol%) 0.150 0.220 0.234 0.255 0.229 0.273 0.174 0.211

% max load 59.0 66.4 65.5 83.9 81.5 88.2 65.5 74.6

Plant chemical performance

Kinetics Aug 03 Jul 05 Mar 06 Jun 06 Dec 06 Feb 07 Sept 08

Extraction @ 30 sec

- - 86 % 90 % 90 % 96 % 92%

Strip @ 30 sec

62 % 71 % 78 % 90 % 92 % 96 % 97%

Laboratory extraction and stripping kinetics

Date PDT (seconds)

OC AC

Apr 2004 No break 126

Jan 2005 No break 130

July 2005 No break 110

October 2005 >600 90

March 2006 >600 72

June 2006 600 100

December 2006 600 93

February 2007 474 109

April 2007 114 201

Oct 2007 49 26

Feb 2009 90 30

Laboratory PD tests using plant organic and plant PLS.

Plant physical performance

Extraction (OC) sec Strip (AC) (sec)

Pre CT Post CT Pre CT Post CT

April 04 No break No break - -

March 06 920 22 72 20

June 06 627 22 100 20

PD time before and after clay treatment.

Apr 04

Sep 04

Jan 05

Jul 05 Oct 05

Mar 06

Jun 06

Dec 06

Feb 07

May 08

Sept 08

Visc @ 25oC (cSt)

26.48 19.43 15.06 15.13 13.15 13.90 12.20 9.50 8.93 7.72 6.66

Viscosity of the plant organic

Chloride in electrolyte (and PLS)

0

20

40

60

80

100

120

140

160

180

200

3/04

/04

31/0

8/04

28/0

1/05

27/0

6/05

24/1

1/05

23/0

4/06

20/0

9/06

17/0

2/07

17/0

7/07

14/1

2/07

12/0

5/08

9/10

/08

Ch

lori

de

in e

lec

tro

lyte

(m

g/L

) a

nd

re

pu

lp O

/F (

g/L

)

0

10

20

30

40

50

60

70

80

90

100

Pe

rce

nt

LIX

re

ag

en

t in

cir

cu

it (

%)

Cl in electrolyte

Cl in repulp O/F

Percent LIX in circuit

EW Chloride vs TXIB in organic

0

20

40

60

80

100

120

140

160

180

200

3/04

/04

31/0

8/04

28/0

1/05

27/0

6/05

24/1

1/05

23/0

4/06

20/0

9/06

17/0

2/07

17/0

7/07

14/1

2/07

12/0

5/08

9/10

/08

Ch

lori

de

in e

lec

tro

lyte

(m

g/L

) a

nd

re

pu

lp O

/F (

g/L

)

0

3

6

9

12

15

18

21

24

27

30

TX

IB -

Pe

rce

nt

of

tota

l re

ag

en

t in

cir

cu

it

Cl in electrolyte

Cl in repulp O/F

TXIB (Percent of total reagent component)

• reduction in reagent concentration to <35vol% (now at 30%).

• improvement in extraction and strip kinetics.

• higher net transfer (>0.2gplCu/vol%).

• very significant improvement in phase separation behaviour.

• organic phase viscosity reduced by 75%.

• very significant decrease in chloride transfer to EW.

• reduction in electrolyte chloride level by ~90%.

• much easier plant operation.

Conclusions

The conversion of Acorga modified reagent to the more stable LIX non-modified reagent resulted in:

Acknowledgements

Nyrstar Port Pirie

Cognis

Co-authors and investigators: Kym Dudley, Mark Urbani, Dr Michael Virnig and Anissa Horner

Questions?