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Leaching of low grade limonite and nontronite ores by fungi metabolic acids
Minerals Engineering 19 (2006) 1274–1279 This article is also available online at: www.elsevier.com/locate/mineng
Leaching of low grade limonite and nontronite ores by fungi metabolic acids J.A. Tang, M. Valix
*
Department of Chemical Engineering, University of Sydney, NSW 2006, Australia Received 2 December 2005; accepted 4 April 2006 Available online 12 June 2006
Abstract This study was designed to investigate the nature of nickel and cobalt dissolution from limonite and nontronite ores. Leaching was achieved using 0.2–3 M of citric, lactic and malic acids. The effect of acid type, acid activity, oxygen reduction potential and pulp density on metal dissolution was studied systematically. The effect of leaching on the mineralogy of the ore was investigated by optical microscopy and by synchrotron based X-ray diffraction. From the experiments, it was shown that nickel and cobalt dissolution were dependent on acid activity, oxygen reduction potential, pulp density and mineralogy. The extent of metal dissolution was less affected by the type of acids. The trend of selectivity in limonite and nontronite are Co > Mn > Mg. Metal selectivity was intimately associated with the host minerals containing nickel and cobalt. Ó 2006 Published by Elsevier Ltd. Keywords: Bioleaching; Oxide ores; Leaching
1. Introduction With the continuous depletion of high grade nickel sulphide ores, there is the need to win metals from the abundant low grade nickel laterite ores. Nickel laterite ores remain important to the future supply of Ni and Co as they contain the bulk of known nickel and cobalt reserves (80% and 90–95%, respectively). Commercial nickel laterite processing routes such as high pressure acid leaching, Caron process, ferronickel and nickel matte smelting techniques are energy intensive and operational costs are high (Valix et al., 2001a,b). There is a need for viable processes that can address the economic and environmental restrictions currently associated with the processing of nickel laterite. Microbial leaching of oxide ores has the potential to offer a much needed step-change in the technology for processing laterite ores.
*
Corresponding author. Tel.: +61 2 9351 4995; fax: +61 2 9351 2854. E-mail address: [email protected] (M. Valix).
0892-6875/$ - see front matter Ó 2006 Published by Elsevier Ltd. doi:10.1016/j.mineng.2006.04.009
Bioleaching involves the utilization of heterotrophic fungi and their metabolic products to dissolve nickel and cobalt from low grade nickel laterite ores. Current studies have shown that laterite ores are amenable to leaching with the organic acid excreted by heterotrophic organisms (Bosecker, 1997; Valix et al., 2004). However, commercial application of the process has been less successful. This is due to process inefficiencies such as poor metal recovery. This problem is particularly prevalent in limonite ore, characterized by high iron content in the form of goethite (FeOOH) and nontronite, characterized by clay minerals consisting of illite, kaolinite and chlorite. Attempts to elucidate the dissolution behaviour of the laterite minerals in the bioleaching process have included parametric investigations of chemical leaching independent of the organism. Parameters including particle size, pulp density, temperature and period of leaching have been investigated (Alibhai et al., 1993; Tzeferis, 1994; Tzeferis and Agatzini-Leonardou, 1994; Bosecker, 1987; and Sukla and Panchanadikar, 1993). The main outcomes from these investigations include the suggestion of relative effectiveness of the
J.A. Tang, M. Valix / Minerals Engineering 19 (2006) 1274–1279
organic acids. The majority of researchers suggest citric acid performs more effectively compared to the other metabolic acids. This is with the exception of Sukla and Panchanadikar (1993), who suggest oxalic acid as the most effective acid in leaching the laterite minerals. The poor dissolution of metals from limonite and nontronite ore in comparison to the saprolitic minerals was also commonly observed among these investigations. In this study the nature of the dissolution behaviour of limonite and nontronite in citric, malic and lactic acids was investigated. Oxalic acid was found to generally form very stable precipitates (Valix et al., 2004). As such oxalic acid was not included in this leaching study. The role of the type of metabolic acid in metal dissolution and selectivity were investigated. In particular the effect of acid activity, oxygen reduction potential and pulp density on metal dissolution was studied. Mineralogical analyses of the raw ore and leached residues were used to support the observed metal dissolution. 2. Experimental 2.1. Materials The laterite ores used in this study were limonite and nontronite from New Caledonia. About 4 kg of each ore type was first milled (mean particle size of 64 lm). Sample division was achieved by feeding the ground ore into a Jones riffle until a representative sample was obtained. The chemical analyses of these ores are shown in Table 1. These composition values are typical of commercial grade nickel laterite. 2.2. Chemical leaching Chemical leaching tests were conducted using analyticalreagent grade citric, malic and lactic acid. Acid concentrations of 0.2–3 M were prepared with deionised water. The ore pulp density used included 2, 3.5, 5, 7.5 and 10 wt%. Each slurry was prepared by transferring 10 ml of the prepared acid and the respective ore load into a 30 ml batch reactor, which was then placed in a shaker of 120 rpm at a fixed temperature of 25 °C. A reactor was sampled every day for a period of 24 days for kinetics observations. Valix et al. (2001a,b) have shown that electrosorption of dissolved metals onto the mineral residues can be avoided by conducting leaching below the isoelectric point of limonite (6.6) and nontronite (2) ores. The limonite and nontronite mineral residues have tended to approach isoelectric points of 2.3 and 1.5 (Tang, 2004). Use of concentrations
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above 0.2 M acids enabled the solution pH to be maintained below the isoelectric point of the raw ores and their corresponding residues. The extent of metal dissolution was monitored by taking sub-samples of the slurry and the dissolved metals were determined by Varian Vista AX CCD Inductively couple plasma atomic emission spectrometry (ICP-AES) using standard procedures. The pH and the oxygen reduction potential (ORP) were also measured with the period of leaching, by pH-mV-temp meter TPS WP80D. The pH and ORP readings have errors of ±0.01 pH and ±1 mV, respectively as specified in the TPS manual. A platinum electrode with Ag/AgCl as the reference system was used in measuring the solution oxygen reduction potential. 2.3. Mineralogical analyses Mineralogical analysis of the raw and leached ore residues were carried out using optical microscopy and synchrotron radiation based X-ray power diffraction in Australian National Beamline Facility at Photon Factory, Japan. The facility was accessed through the Australian Synchrotron Research Program. The procedure included loading the ore in a 0.3 mm glass capillary tube. The capillary tube was placed and aligned in front of the X-ray beam using a goniometer. Studies were conducted in a vacuum with a gauge pressure of 1 torr. The X-ray has a wave˚ . A current of 400 mA was used. length of 1.1 A 3. Results and discussion 3.1. Leaching pH Previous investigations of the chemical bio-leaching of limonite and nontronite ores demonstrated poorer recovery in comparison to the saprolitic nickel lateritic minerals. To elucidate the nature these metal dissolution, the leaching behaviours were correlated to the acid activities of the metabolic acids, oxygen reduction potential and pulp density. The effects of leaching on the ore mineralogy were also monitored as a function of time. The conditions during leaching were established from the measured pH and the oxygen reduction potential of the slurry during leaching. The corresponding acid activity was deduced from the measured pH using Eq. (1). Hþ (mole/litre) = 10ðpHÞ
ð1Þ
A mass balance around the hydrogen ion was conducted by measuring the residual H+ from the difference between the original and the final hydrogen ion after 24 days of
Table 1 Chemical analysis of limonite and nontronite ores
Limonite Nontronite
Al (wt%)
Co (wt%)
Cr (wt%)
Cu (wt%)
Fe (wt%)
Mg (wt%)
Mn (wt%)
Ni (wt%)
Zn (wt%)
2.14 1.28
0.25 0.23
0.78 2.64
0.044 0.033
39.50 10.54
2.85 2.05
1.07 0.37
1.66 2.49
0.14 0.044
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J.A. Tang, M. Valix / Minerals Engineering 19 (2006) 1274–1279 80
0.06 Limonite - Citric Acid 0.05
Limonite - Malic Acid
0.04
Limonite - Lactic Acid
0.03
Nontronite - Citric Acid
0.02
Nontronite - Malic Acid
0.01
Nontronite - Lactic Acid
Metal Dissolution (wt%)
Residual [H+] (mole/litre)
0.07
70
Ni - Citric Acid Ni - Malic Acid
60
Ni - Lactic Acid Co - Citric Acid
50 40
Co - Malic Acid Co - Lactic Acid
30 20 10 0
0
0 0
0.02
0.04
0.06
0.08
0.1
0.02
0.12
0.04
0.06
0.08
0.1
0.12
Initial [H+] (mole/litre)
Initial [H+] (mole/litre)
Fig. 1. Residual acid activity in the mineral slurry with pulp density 5 wt% minerals ores after 24 days of leaching as a function of the original acid activity.
leaching. The residual H+ was related to the original hydrogen ion content of the acids in Fig. 1. It is observed that excess acids were used for all leaching tests, which would indicate sufficient lixiviant was available for metal dissolution for both ores. 3.2. Effect of acid activity and types of acids Previous studies have postulated that various acids exhibit differences in effectiveness in dissolving metals from laterite minerals (Alibhai et al., 1993; Tzeferis and Agatzini-Leonardou, 1994; Tzeferis, 1994; Bosecker, 1987; Sukla and Panchanadikar, 1993). This postulation was tested by relating the metal (Ni and Co) dissolved after 24 days of leaching in citric, malic and lactic acids from limonite and nontronite ores to the corresponding acid activities in Figs. 2 and 3, respectively. There appears to be no relative difference in the effective leaching achieved by the various acids. These results suggest the extent of metal dissolution is dependent on the acid activity rather than the type of metabolic acids used. The results in Fig. 2 also suggest optimal metal dissolution required controlled used of H+. Increasing the H+concentration up to 0.028 mole/l appears to increase metal
Fig. 3. Nickel and cobalt recovery from nontronite after 24 days of leaching in pulp density 5 wt% as a function of acid activity leached by various organic acids.
dissolution from limonite. Further increase in the hydronium concentration resulted in less effective metal dissolution. Cobalt dissolution in Fig. 3 also supports this observation. Cobalt dissolutions from nontronite continue to increase up to 0.035 mole/l. Ni, however, seems to be less dependent on hydronium concentrations and continues to increase in dissolution as pH lowers. It is also apparent that cobalt shows greater amenability to organic acid leaching in comparison to nickel. There are no free nickel and cobalt in the laterite minerals. These metals are intimately associated with various gangue minerals. It would suggest the difference in the minerals hosting nickel and cobalt would result in the variation in selectivity observed when these metals are leached. 3.3. Effect of pulp density The effect of pulp density on nickel and cobalt dissolution from limonite and nontronite are shown in Figs. 4 and 5, respectively. Leaching was conducted with 3 M acid for a period of 24 days. The corresponding slurry pH and ORP are summarized in Table 2. All slurries had ORP in the range of 275–500 mV, suggesting the metal dissolutions
100 90
Metal Dissolution (wt%)
Ni - Citric Acid 100 Ni - Malic Acid 80
Ni - Lactic Acid
60
Co - Citric Acid
40
Co - Malic Acid Co - Lactic Acid
20
Metal Dissolution (wt%)
120
80
Ni - Citric Acid
70 Ni - Malic Acid
60 50
Ni - Lactic Acid
40
Co - Citric Acid
30
Co - Malic Acid
20 Co - Lactic Acid
10
0 0
0.05 [H+] (mole/litre)
0.1
Fig. 2. Nickel and cobalt recovery from limonite after 24 days of leaching in pulp density 5 wt% as a function of acid activity leached by various organic acids.
0 0
1
2
3 4 5 6 7 8 Pulp Density (wt%)
9 10 11
Fig. 4. Nickel and cobalt recovery from limonite as a function of pulp density by various 3 M organic acids.
J.A. Tang, M. Valix / Minerals Engineering 19 (2006) 1274–1279
80
Metal Dissolution (wt%)
70 60
Ni - Citric Acid
50
Ni - Malic Acid
40
Ni - Lactic Acid
30
Co - Citric Acid
20
Co - Malic Acid
10
Co - Lactic Acid
0 0
1
2
3 4 5 6 7 8 Pulp Density (wt%)
9 10 11
Fig. 5. Nickel and cobalt recovery from nontronite as a function of pulp density by various 3 M organic acids. Table 2 Solution pH and ORP of limonite and nontronite slurries as a function of pulp densities and acid type of 3 M Acid type
Limonite
Nontronite
Pulp density (wt%)
pH
ORP (mV)
Pulp density (wt%)
pH
ORP (mV)
Citric
2 3.5 5 7.5 10
1.32 1.64 1.68 1.58 1.47
384.1 282.0 339.0 312.4 372.2
2 3.5 5 7.5 10
1.37 1.57 1.62 1.54 1.49
411.1 307.3 327.1 305.8 384.2
Malic
2 3.5 5 7.5 10
1.52 1.64 1.81 1.75 1.66
438.5 343.2 361.0 321.7 449.1
2 3.5 5 7.5 10
1.28 1.67 1.72 1.74 1.54
500 339.3 364 342.8 455.2
Lactic
2 3.5 5 7.5 10
1.71 1.91 2.00 2.03 2.09
398.7 299.0 336.0 292.6 425.6
2 3.5 5 7.5 10
1.67 1.85 1.84 1.91 1.75
410.0 275.6 309.8 306.8 423.2
occurred in slightly oxidized conditions. Reducing condition (e.g., in citric acid leaching of limonite the ORP is 282 mV and pH of 1.64) which occurred at pulp densities of 3.5 wt% resulted in Co recoveries of 90% and Ni of
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33%. Whereas at the lower 2% pulp density, where the ORP is 384 mV and despite the lower pH of 1.32, metal recoveries were lower (Co is 63% and Ni is 26%). Similar behaviour were also observed in leaching with malic and lactic acids and of nontronite ore. These test results suggest that oxidising conditions suppressed metal dissolution. The most reducing condition that promotes metal dissolutions among the solid to liquid ratios is generally found between 5 wt% and 7.5 wt%. As shown in Fig. 4, nickel and cobalt dissolution from limonite in citric, malic and lactic acid increased with the pulp density up to 5.7 wt%. Nickel and cobalt dissolution from nontronite in all three metabolic acids, as demonstrated in Fig. 5, increased up to a pulp density of 5.8 wt%. In general, metal dissolutions increased with increasing solid to liquid ratio up to an optimal pulp density of 5.75 wt%, where further increases of pulp density led to lower metal recovery. The bioleaching reactions of Ni laterite ores consist of a number of parallel reactions that contribute to the overall observed pH and ORP. The reactions include metal complexation, reduction, and oxidation reactions. In addition components of the minerals also act as buffers. The large components of the ores investigated, limonite and nontronite, consist of Fe and Mn oxides and clays which have high H+ ion buffering capacities. The ion H+ is used by the ores in destabilising the minerals to promote metal complexation with the organic acid anion. At the low pulp density, the complexation reaction predominates and there is a general uptake of H+ and thus reduction in solution pH. As the pulp density is increased, and as the clay and Fe and Mn oxides hydrolyse, they release H+ to reduce the solution pH. In addition as the solution pH increases, a more oxidising environment is generated which appear to suppress the complexation reaction. Although a greater H+ is generated at the higher pulp density, the combined lower complexing agent to ore ratio and higher oxidising conditions, both contribute to lower metal dissolution. 3.4. Selectivity of leaching The relative selectivity for metal dissolution from limonite and nontronite are shown in Tables 3 and 4. As shown,
Table 3 Metal dissolution from limonite as a function of acid activity at pulp density 5 wt% Acid conc. (M) +
2
[H ] (10 ) Co Mn Mg Ni Cr Al Cu Zn Fe
Citric acid
Malic acid
Lactic acid
0.2
0.5
2
3
0.2
0.5
2
3
0.2
0.5
2
3
1.0 88.8 76.1 63.4 31.5 18.8 13.6 9.6 4.5 3.9
1.9 91.5 75.0 65.8 33.2 20.0 14.1 11.3 4.8 4.4
4.6 89.1 75.5 66.0 32.9 19.7 14.2 15.6 4.9 4.9
10 83.6 70.1 63.4 30.9 18.8 12.5 9.5 4.7 4.4
1.5 79.6 67.4 64.9 31.6 19.0 13.2 10.6 4.5 4.0
1.6 77.8 67.8 65.0 31.0 18.8 12.8 9.4 4.4 3.8
5.1 81.3 68.4 63.3 31.6 18.9 13.5 10.7 4.8 4.5
5.5 90.1 75.7 66.5 33.7 19.8 15.0 10.2 5.0 5.1
0.6 78.5 68.3 56.0 26.3 17.3 11.3 15.2 3.9 2.1
0.9 85.9 71.9 64.0 31.3 18.3 13.9 12.6 5.1 3.5
2.8 99.4 79.9 68.3 37.3 21.7 17.4 10.8 5.7 6.0
3.5 91.9 79.4 66.7 34.8 20.5 17.2 10.5 5.7 6.5
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Table 4 Metal dissolution from nontronite as a function of acid activity at pulp density 5 wt% Acid conc. (M)
Citric acid
[H+] (102) Co Mn Mg Cu Al Ni Fe Cr Zn
Malic acid
Lactic acid
0.2
0.5
2
3
0.2
0.5
2
3
0.2
0.5
2
3
1.0 46.9 47.3 22.0 18.5 17.4 11.0 7.1 8.5 4.1
1.9 33.2 32.2 14.5 9.7 10.9 5.6 1.2 1.4 2.6
4.6 65.7 65.8 32.3 18.2 22.2 16.3 10.5 8.0 3.7
10 62.7 61.2 33.6 19.0 23.0 17.6 12.3 9.0 2.3
1.5 39.2 37.5 21.6 18.7 10.4 8.2 3.4 3.7 2.0
1.6 39.9 37.4 19.9 18.7 9.6 7.7 3.0 3.3 1.7
5.1 56.9 53.2 29.7 15.7 17.8 14.0 7.9 6.2 1.4
5.5 61.9 57.9 32.6 15.8 21.2 16.9 10.9 7.8 1.9
0.6 36.4 33.6 14.6 18.0 9.6 5.7 1.6 2.3 2.3
0.9 42.9 40.8 17.0 14.3 11.7 7.3 2.7 2.8 1.5
2.8 62.3 54.9 24.5 17.5 22.0 13.1 6.9 5.5 1.6
3.5 67.9 59.6 27.9 17.5 26.2 14.9 8.1 6.4 1.5
the relative selectivity in limonite is Co > Mn > Mg > Ni > Cr > Al. The trend observed in nontronite is Co > Mn > Mg > Cu > Al > Ni. The mineral composition of the Table 5 Minerals composition of laterite ore identified by polarizing and ore microscopy (Tang, 2004) Minerals content/chemical formula
Ore type
Serpentine (Mg,Fe,Ni)3Si2O5(OH)4 Pyroxene (Mg,Fe)2Si2O6 Olivine (Mg,Fe)2SiO4 Chlorite (Mg,Fe,Al)5-6 (Si,Al)4O10(OH)8 Kaolinite/illite Al4Si4O10(OH)8 Goethite, Hematite, and iron matrix (Fe,Ni)O(OH), Fe2O3 Titaniferous pyrite (Fe,Ti)S2 Nickeliferous pyrite (Fe,Ni)S2 Magnetite (Fe3O4) Ilmenite FeTiO3
Limonite (%)
Nontronite (%)
15 1 <1 5 Nil 75
1-2 Nil Nil 48 46 1–2
1–2 <1 <1
1–2 Nil <1 <1
laterite ores are shown in Table 5. As shown in Table 5, Mg is closely associated with serpentine species. The greater dissolution of Mg in both ore bodies suggests the amenability of the serpentine phase in limonite nontronite to organic acid attack. The X-ray diffraction results in Figs. 6 and 7 suggest that very little transformation occurs during leaching. This is with the exception of serpentine peak after 7 days of leaching which confirms its amenability to acid attack (see Tables 3 and 4). As suggested in Table 5, iron and aluminium are strongly associated with goethite and illite. The poor dissolution of iron and aluminium, as suggested by Tables 3 and 4, indicate the poor reactivity of goethite and illite in the organic acids used in this study. These are confirmed by the lack of transformations of these minerals in Figs. 6 and 7. The greater selectivity demonstrated by cobalt suggest that this metal is hosted largely
G Q GI Q
G G G
G
Intensity (I/Io)
G
Q
G
G
GG
G
G Q
G
G G
20
25
Q
QG
Q G
GG
G G
G G
2θ (degree)
30
G G
M Ma
Ma
C Ma G Q
GI
Q
C
G I C M
Ma
Ma
3 days Ma
G I C M
Q G
M
G
Raw Nontronite Ma
Ma
G
M CMaC
Q G
5 35
7 days
C
GI Q
Ma
G I C M
G Q
Raw Limonite
15 days Ma
Q
GI
7 days
G
S
15
G G
C Ma
G
15 days GG
G G G
G
G
G
Q
G
10
G
G
G
G
20 days
G
Q
Intensity (I/Io)
G
G I C M
40
45
Fig. 6. Synchrotron X-ray diffraction pattern of raw and solid limonite residues leached with citric acid as a function of time. (G: goethite, S: serpentine, Q: quartz) (Valix et al., 2004).
10
15
20
25 30 2θ (degree)
35
40
45
Fig. 7. Synchrotron X-ray diffraction pattern of raw and solid nontronite residues leached with citric acid as a function of time. (G: goethite, I: illite, Q: quartz, C: cochromite, Ma: magnetite, M: magnesiochromite) (Valix et al., 2004).
J.A. Tang, M. Valix / Minerals Engineering 19 (2006) 1274–1279
by the serpentine group in limonite and nontronite. Whereas nickel, which shows poorer dissolution may be hosted largely by goethite ad the illite phases. These are consistent with suggestions that in limonite, goethite is the host mineral for nickel, while cobalt is found to be associated with a manganese phase that is also rich in nickel (Georgiou and Papangelakis, 2004). Effective dissolution of both cobalt and nickel in limonite will thus require the dissolution of goethite, serpentine and manganese phases, while nontronite requires the dissolution of illite and serpentine phases. 4. Conclusions Metal dissolution is affected by the hydronium ion concentration rather than the type of acid. However, the effect of the hydronium ion requires careful control of the oxygen reduction potential during leaching. A highly oxidizing condition, (>430 mV) appear to suppress nickel and cobalt dissolution. This emphasizes the importance of pH and ORP control during the bio-leaching of nickel laterite ores. In general optimal leaching of nickel and cobalt are achieved with 5.75 wt% pulp densities. Nickel and cobalt dissolution is intimately associated with the amenability of host minerals to organic acid attack. The poorer nickel dissolution is associated with the resistance by goethite and illite to acid attack in limonite and nontronite, respectively. Greater cobalt dissolution in limonite and nontronite is consistent with the amenability of serpentine to acid attack. These results suggest the importance of oxygen-reduction potential, acid activities of the metabolic acids, pulp density and mineralogy in effecting metal dissolution in the bioleaching of limonite and nontronite minerals.
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Acknowledgements The authors would like to acknowledge the Australian Research Council for their funding support towards this project. References Alibhai, K.A.K., Dudeney, A.W.L., Leak, D.J., Agatzini, S., Tzeferis, P., 1993. Bioleaching and bioprecipitation of nickel and iron from laterites. FEMS Microbiology Reviews 11, 87–96. Bosecker, K., 1987. Leaching of lateritic nickel ores with heterotrophic microorganisms. Acta Biotechnologica 7 (5), 389–399. Bosecker, K., 1997. Bioleaching: metal solubilization by microorganisms. FEMS Microbiology Reviews 20, 591–604. Georgiou, D., Papangelakis, V.G., 2004. Characterization of limonitic laterite and solids during sulphuric acid pressure leaching using transmission electron microscope. Minerals Engineering 17, 461–463. Sukla, L.B., Panchanadikar, V., 1993. Bioleaching of lateritic nickel ore using a heterotrophic micro-organism. Hydrometallurgy 32, 373–379. Tang, L.J., 2004. Bioleaching of low grade nickel laterite ore with heterotrophic micro-organisms, Thesis (Ph.D.), Department of Chemical Engineering, Graduate School of Engineering, University of Sydney, Australia. Tzeferis, P.G., 1994. Leaching of a low grade hematitic laterite ore using fungi and biologically produced acid metabolites. International Journal of Mineral Processing 42, 267–283. Tzeferis, P.G., Agatzini-Leonardou, S., 1994. Leaching of nickel and iron from Greek non-sulphide nickeliferous ores by organic acids. Hydrometallurgy 36, 345–360. Valix, M., Cheung, A., O’Connor, F., Kennedy, S., 2001a. In-situ kinetic study of laterite reduction. AINSE Progress Report for 01/138P. Valix, M., Usai, F., Malik, R., 2001b. The electro-sorption properties of nickel on laterite gangue leached with an organic chelating acid. Minerals Processing 14 (2), 205–215. Valix, M. Tang, J.Y., Cheung W.H., 2004. Biological leaching of nickel laterites: use of synchrotron based X-ray diffraction in elucidating the amenability of laterite minerals to fungi metabolic acids, Paper presented to CHEMECA 2004, Sydney.
Leaching of low grade limonite and nontronite ores by fungi metabolic acids J.A. Tang, M. Valix
*
Department of Chemical Engineering, University of Sydney, NSW 2006, Australia Received 2 December 2005; accepted 4 April 2006 Available online 12 June 2006
Abstract This study was designed to investigate the nature of nickel and cobalt dissolution from limonite and nontronite ores. Leaching was achieved using 0.2–3 M of citric, lactic and malic acids. The effect of acid type, acid activity, oxygen reduction potential and pulp density on metal dissolution was studied systematically. The effect of leaching on the mineralogy of the ore was investigated by optical microscopy and by synchrotron based X-ray diffraction. From the experiments, it was shown that nickel and cobalt dissolution were dependent on acid activity, oxygen reduction potential, pulp density and mineralogy. The extent of metal dissolution was less affected by the type of acids. The trend of selectivity in limonite and nontronite are Co > Mn > Mg. Metal selectivity was intimately associated with the host minerals containing nickel and cobalt. Ó 2006 Published by Elsevier Ltd. Keywords: Bioleaching; Oxide ores; Leaching
1. Introduction With the continuous depletion of high grade nickel sulphide ores, there is the need to win metals from the abundant low grade nickel laterite ores. Nickel laterite ores remain important to the future supply of Ni and Co as they contain the bulk of known nickel and cobalt reserves (80% and 90–95%, respectively). Commercial nickel laterite processing routes such as high pressure acid leaching, Caron process, ferronickel and nickel matte smelting techniques are energy intensive and operational costs are high (Valix et al., 2001a,b). There is a need for viable processes that can address the economic and environmental restrictions currently associated with the processing of nickel laterite. Microbial leaching of oxide ores has the potential to offer a much needed step-change in the technology for processing laterite ores.
*
Corresponding author. Tel.: +61 2 9351 4995; fax: +61 2 9351 2854. E-mail address: [email protected] (M. Valix).
0892-6875/$ - see front matter Ó 2006 Published by Elsevier Ltd. doi:10.1016/j.mineng.2006.04.009
Bioleaching involves the utilization of heterotrophic fungi and their metabolic products to dissolve nickel and cobalt from low grade nickel laterite ores. Current studies have shown that laterite ores are amenable to leaching with the organic acid excreted by heterotrophic organisms (Bosecker, 1997; Valix et al., 2004). However, commercial application of the process has been less successful. This is due to process inefficiencies such as poor metal recovery. This problem is particularly prevalent in limonite ore, characterized by high iron content in the form of goethite (FeOOH) and nontronite, characterized by clay minerals consisting of illite, kaolinite and chlorite. Attempts to elucidate the dissolution behaviour of the laterite minerals in the bioleaching process have included parametric investigations of chemical leaching independent of the organism. Parameters including particle size, pulp density, temperature and period of leaching have been investigated (Alibhai et al., 1993; Tzeferis, 1994; Tzeferis and Agatzini-Leonardou, 1994; Bosecker, 1987; and Sukla and Panchanadikar, 1993). The main outcomes from these investigations include the suggestion of relative effectiveness of the
J.A. Tang, M. Valix / Minerals Engineering 19 (2006) 1274–1279
organic acids. The majority of researchers suggest citric acid performs more effectively compared to the other metabolic acids. This is with the exception of Sukla and Panchanadikar (1993), who suggest oxalic acid as the most effective acid in leaching the laterite minerals. The poor dissolution of metals from limonite and nontronite ore in comparison to the saprolitic minerals was also commonly observed among these investigations. In this study the nature of the dissolution behaviour of limonite and nontronite in citric, malic and lactic acids was investigated. Oxalic acid was found to generally form very stable precipitates (Valix et al., 2004). As such oxalic acid was not included in this leaching study. The role of the type of metabolic acid in metal dissolution and selectivity were investigated. In particular the effect of acid activity, oxygen reduction potential and pulp density on metal dissolution was studied. Mineralogical analyses of the raw ore and leached residues were used to support the observed metal dissolution. 2. Experimental 2.1. Materials The laterite ores used in this study were limonite and nontronite from New Caledonia. About 4 kg of each ore type was first milled (mean particle size of 64 lm). Sample division was achieved by feeding the ground ore into a Jones riffle until a representative sample was obtained. The chemical analyses of these ores are shown in Table 1. These composition values are typical of commercial grade nickel laterite. 2.2. Chemical leaching Chemical leaching tests were conducted using analyticalreagent grade citric, malic and lactic acid. Acid concentrations of 0.2–3 M were prepared with deionised water. The ore pulp density used included 2, 3.5, 5, 7.5 and 10 wt%. Each slurry was prepared by transferring 10 ml of the prepared acid and the respective ore load into a 30 ml batch reactor, which was then placed in a shaker of 120 rpm at a fixed temperature of 25 °C. A reactor was sampled every day for a period of 24 days for kinetics observations. Valix et al. (2001a,b) have shown that electrosorption of dissolved metals onto the mineral residues can be avoided by conducting leaching below the isoelectric point of limonite (6.6) and nontronite (2) ores. The limonite and nontronite mineral residues have tended to approach isoelectric points of 2.3 and 1.5 (Tang, 2004). Use of concentrations
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above 0.2 M acids enabled the solution pH to be maintained below the isoelectric point of the raw ores and their corresponding residues. The extent of metal dissolution was monitored by taking sub-samples of the slurry and the dissolved metals were determined by Varian Vista AX CCD Inductively couple plasma atomic emission spectrometry (ICP-AES) using standard procedures. The pH and the oxygen reduction potential (ORP) were also measured with the period of leaching, by pH-mV-temp meter TPS WP80D. The pH and ORP readings have errors of ±0.01 pH and ±1 mV, respectively as specified in the TPS manual. A platinum electrode with Ag/AgCl as the reference system was used in measuring the solution oxygen reduction potential. 2.3. Mineralogical analyses Mineralogical analysis of the raw and leached ore residues were carried out using optical microscopy and synchrotron radiation based X-ray power diffraction in Australian National Beamline Facility at Photon Factory, Japan. The facility was accessed through the Australian Synchrotron Research Program. The procedure included loading the ore in a 0.3 mm glass capillary tube. The capillary tube was placed and aligned in front of the X-ray beam using a goniometer. Studies were conducted in a vacuum with a gauge pressure of 1 torr. The X-ray has a wave˚ . A current of 400 mA was used. length of 1.1 A 3. Results and discussion 3.1. Leaching pH Previous investigations of the chemical bio-leaching of limonite and nontronite ores demonstrated poorer recovery in comparison to the saprolitic nickel lateritic minerals. To elucidate the nature these metal dissolution, the leaching behaviours were correlated to the acid activities of the metabolic acids, oxygen reduction potential and pulp density. The effects of leaching on the ore mineralogy were also monitored as a function of time. The conditions during leaching were established from the measured pH and the oxygen reduction potential of the slurry during leaching. The corresponding acid activity was deduced from the measured pH using Eq. (1). Hþ (mole/litre) = 10ðpHÞ
ð1Þ
A mass balance around the hydrogen ion was conducted by measuring the residual H+ from the difference between the original and the final hydrogen ion after 24 days of
Table 1 Chemical analysis of limonite and nontronite ores
Limonite Nontronite
Al (wt%)
Co (wt%)
Cr (wt%)
Cu (wt%)
Fe (wt%)
Mg (wt%)
Mn (wt%)
Ni (wt%)
Zn (wt%)
2.14 1.28
0.25 0.23
0.78 2.64
0.044 0.033
39.50 10.54
2.85 2.05
1.07 0.37
1.66 2.49
0.14 0.044
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0.06 Limonite - Citric Acid 0.05
Limonite - Malic Acid
0.04
Limonite - Lactic Acid
0.03
Nontronite - Citric Acid
0.02
Nontronite - Malic Acid
0.01
Nontronite - Lactic Acid
Metal Dissolution (wt%)
Residual [H+] (mole/litre)
0.07
70
Ni - Citric Acid Ni - Malic Acid
60
Ni - Lactic Acid Co - Citric Acid
50 40
Co - Malic Acid Co - Lactic Acid
30 20 10 0
0
0 0
0.02
0.04
0.06
0.08
0.1
0.02
0.12
0.04
0.06
0.08
0.1
0.12
Initial [H+] (mole/litre)
Initial [H+] (mole/litre)
Fig. 1. Residual acid activity in the mineral slurry with pulp density 5 wt% minerals ores after 24 days of leaching as a function of the original acid activity.
leaching. The residual H+ was related to the original hydrogen ion content of the acids in Fig. 1. It is observed that excess acids were used for all leaching tests, which would indicate sufficient lixiviant was available for metal dissolution for both ores. 3.2. Effect of acid activity and types of acids Previous studies have postulated that various acids exhibit differences in effectiveness in dissolving metals from laterite minerals (Alibhai et al., 1993; Tzeferis and Agatzini-Leonardou, 1994; Tzeferis, 1994; Bosecker, 1987; Sukla and Panchanadikar, 1993). This postulation was tested by relating the metal (Ni and Co) dissolved after 24 days of leaching in citric, malic and lactic acids from limonite and nontronite ores to the corresponding acid activities in Figs. 2 and 3, respectively. There appears to be no relative difference in the effective leaching achieved by the various acids. These results suggest the extent of metal dissolution is dependent on the acid activity rather than the type of metabolic acids used. The results in Fig. 2 also suggest optimal metal dissolution required controlled used of H+. Increasing the H+concentration up to 0.028 mole/l appears to increase metal
Fig. 3. Nickel and cobalt recovery from nontronite after 24 days of leaching in pulp density 5 wt% as a function of acid activity leached by various organic acids.
dissolution from limonite. Further increase in the hydronium concentration resulted in less effective metal dissolution. Cobalt dissolution in Fig. 3 also supports this observation. Cobalt dissolutions from nontronite continue to increase up to 0.035 mole/l. Ni, however, seems to be less dependent on hydronium concentrations and continues to increase in dissolution as pH lowers. It is also apparent that cobalt shows greater amenability to organic acid leaching in comparison to nickel. There are no free nickel and cobalt in the laterite minerals. These metals are intimately associated with various gangue minerals. It would suggest the difference in the minerals hosting nickel and cobalt would result in the variation in selectivity observed when these metals are leached. 3.3. Effect of pulp density The effect of pulp density on nickel and cobalt dissolution from limonite and nontronite are shown in Figs. 4 and 5, respectively. Leaching was conducted with 3 M acid for a period of 24 days. The corresponding slurry pH and ORP are summarized in Table 2. All slurries had ORP in the range of 275–500 mV, suggesting the metal dissolutions
100 90
Metal Dissolution (wt%)
Ni - Citric Acid 100 Ni - Malic Acid 80
Ni - Lactic Acid
60
Co - Citric Acid
40
Co - Malic Acid Co - Lactic Acid
20
Metal Dissolution (wt%)
120
80
Ni - Citric Acid
70 Ni - Malic Acid
60 50
Ni - Lactic Acid
40
Co - Citric Acid
30
Co - Malic Acid
20 Co - Lactic Acid
10
0 0
0.05 [H+] (mole/litre)
0.1
Fig. 2. Nickel and cobalt recovery from limonite after 24 days of leaching in pulp density 5 wt% as a function of acid activity leached by various organic acids.
0 0
1
2
3 4 5 6 7 8 Pulp Density (wt%)
9 10 11
Fig. 4. Nickel and cobalt recovery from limonite as a function of pulp density by various 3 M organic acids.
J.A. Tang, M. Valix / Minerals Engineering 19 (2006) 1274–1279
80
Metal Dissolution (wt%)
70 60
Ni - Citric Acid
50
Ni - Malic Acid
40
Ni - Lactic Acid
30
Co - Citric Acid
20
Co - Malic Acid
10
Co - Lactic Acid
0 0
1
2
3 4 5 6 7 8 Pulp Density (wt%)
9 10 11
Fig. 5. Nickel and cobalt recovery from nontronite as a function of pulp density by various 3 M organic acids. Table 2 Solution pH and ORP of limonite and nontronite slurries as a function of pulp densities and acid type of 3 M Acid type
Limonite
Nontronite
Pulp density (wt%)
pH
ORP (mV)
Pulp density (wt%)
pH
ORP (mV)
Citric
2 3.5 5 7.5 10
1.32 1.64 1.68 1.58 1.47
384.1 282.0 339.0 312.4 372.2
2 3.5 5 7.5 10
1.37 1.57 1.62 1.54 1.49
411.1 307.3 327.1 305.8 384.2
Malic
2 3.5 5 7.5 10
1.52 1.64 1.81 1.75 1.66
438.5 343.2 361.0 321.7 449.1
2 3.5 5 7.5 10
1.28 1.67 1.72 1.74 1.54
500 339.3 364 342.8 455.2
Lactic
2 3.5 5 7.5 10
1.71 1.91 2.00 2.03 2.09
398.7 299.0 336.0 292.6 425.6
2 3.5 5 7.5 10
1.67 1.85 1.84 1.91 1.75
410.0 275.6 309.8 306.8 423.2
occurred in slightly oxidized conditions. Reducing condition (e.g., in citric acid leaching of limonite the ORP is 282 mV and pH of 1.64) which occurred at pulp densities of 3.5 wt% resulted in Co recoveries of 90% and Ni of
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33%. Whereas at the lower 2% pulp density, where the ORP is 384 mV and despite the lower pH of 1.32, metal recoveries were lower (Co is 63% and Ni is 26%). Similar behaviour were also observed in leaching with malic and lactic acids and of nontronite ore. These test results suggest that oxidising conditions suppressed metal dissolution. The most reducing condition that promotes metal dissolutions among the solid to liquid ratios is generally found between 5 wt% and 7.5 wt%. As shown in Fig. 4, nickel and cobalt dissolution from limonite in citric, malic and lactic acid increased with the pulp density up to 5.7 wt%. Nickel and cobalt dissolution from nontronite in all three metabolic acids, as demonstrated in Fig. 5, increased up to a pulp density of 5.8 wt%. In general, metal dissolutions increased with increasing solid to liquid ratio up to an optimal pulp density of 5.75 wt%, where further increases of pulp density led to lower metal recovery. The bioleaching reactions of Ni laterite ores consist of a number of parallel reactions that contribute to the overall observed pH and ORP. The reactions include metal complexation, reduction, and oxidation reactions. In addition components of the minerals also act as buffers. The large components of the ores investigated, limonite and nontronite, consist of Fe and Mn oxides and clays which have high H+ ion buffering capacities. The ion H+ is used by the ores in destabilising the minerals to promote metal complexation with the organic acid anion. At the low pulp density, the complexation reaction predominates and there is a general uptake of H+ and thus reduction in solution pH. As the pulp density is increased, and as the clay and Fe and Mn oxides hydrolyse, they release H+ to reduce the solution pH. In addition as the solution pH increases, a more oxidising environment is generated which appear to suppress the complexation reaction. Although a greater H+ is generated at the higher pulp density, the combined lower complexing agent to ore ratio and higher oxidising conditions, both contribute to lower metal dissolution. 3.4. Selectivity of leaching The relative selectivity for metal dissolution from limonite and nontronite are shown in Tables 3 and 4. As shown,
Table 3 Metal dissolution from limonite as a function of acid activity at pulp density 5 wt% Acid conc. (M) +
2
[H ] (10 ) Co Mn Mg Ni Cr Al Cu Zn Fe
Citric acid
Malic acid
Lactic acid
0.2
0.5
2
3
0.2
0.5
2
3
0.2
0.5
2
3
1.0 88.8 76.1 63.4 31.5 18.8 13.6 9.6 4.5 3.9
1.9 91.5 75.0 65.8 33.2 20.0 14.1 11.3 4.8 4.4
4.6 89.1 75.5 66.0 32.9 19.7 14.2 15.6 4.9 4.9
10 83.6 70.1 63.4 30.9 18.8 12.5 9.5 4.7 4.4
1.5 79.6 67.4 64.9 31.6 19.0 13.2 10.6 4.5 4.0
1.6 77.8 67.8 65.0 31.0 18.8 12.8 9.4 4.4 3.8
5.1 81.3 68.4 63.3 31.6 18.9 13.5 10.7 4.8 4.5
5.5 90.1 75.7 66.5 33.7 19.8 15.0 10.2 5.0 5.1
0.6 78.5 68.3 56.0 26.3 17.3 11.3 15.2 3.9 2.1
0.9 85.9 71.9 64.0 31.3 18.3 13.9 12.6 5.1 3.5
2.8 99.4 79.9 68.3 37.3 21.7 17.4 10.8 5.7 6.0
3.5 91.9 79.4 66.7 34.8 20.5 17.2 10.5 5.7 6.5
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Table 4 Metal dissolution from nontronite as a function of acid activity at pulp density 5 wt% Acid conc. (M)
Citric acid
[H+] (102) Co Mn Mg Cu Al Ni Fe Cr Zn
Malic acid
Lactic acid
0.2
0.5
2
3
0.2
0.5
2
3
0.2
0.5
2
3
1.0 46.9 47.3 22.0 18.5 17.4 11.0 7.1 8.5 4.1
1.9 33.2 32.2 14.5 9.7 10.9 5.6 1.2 1.4 2.6
4.6 65.7 65.8 32.3 18.2 22.2 16.3 10.5 8.0 3.7
10 62.7 61.2 33.6 19.0 23.0 17.6 12.3 9.0 2.3
1.5 39.2 37.5 21.6 18.7 10.4 8.2 3.4 3.7 2.0
1.6 39.9 37.4 19.9 18.7 9.6 7.7 3.0 3.3 1.7
5.1 56.9 53.2 29.7 15.7 17.8 14.0 7.9 6.2 1.4
5.5 61.9 57.9 32.6 15.8 21.2 16.9 10.9 7.8 1.9
0.6 36.4 33.6 14.6 18.0 9.6 5.7 1.6 2.3 2.3
0.9 42.9 40.8 17.0 14.3 11.7 7.3 2.7 2.8 1.5
2.8 62.3 54.9 24.5 17.5 22.0 13.1 6.9 5.5 1.6
3.5 67.9 59.6 27.9 17.5 26.2 14.9 8.1 6.4 1.5
the relative selectivity in limonite is Co > Mn > Mg > Ni > Cr > Al. The trend observed in nontronite is Co > Mn > Mg > Cu > Al > Ni. The mineral composition of the Table 5 Minerals composition of laterite ore identified by polarizing and ore microscopy (Tang, 2004) Minerals content/chemical formula
Ore type
Serpentine (Mg,Fe,Ni)3Si2O5(OH)4 Pyroxene (Mg,Fe)2Si2O6 Olivine (Mg,Fe)2SiO4 Chlorite (Mg,Fe,Al)5-6 (Si,Al)4O10(OH)8 Kaolinite/illite Al4Si4O10(OH)8 Goethite, Hematite, and iron matrix (Fe,Ni)O(OH), Fe2O3 Titaniferous pyrite (Fe,Ti)S2 Nickeliferous pyrite (Fe,Ni)S2 Magnetite (Fe3O4) Ilmenite FeTiO3
Limonite (%)
Nontronite (%)
15 1 <1 5 Nil 75
1-2 Nil Nil 48 46 1–2
1–2 <1 <1
1–2 Nil <1 <1
laterite ores are shown in Table 5. As shown in Table 5, Mg is closely associated with serpentine species. The greater dissolution of Mg in both ore bodies suggests the amenability of the serpentine phase in limonite nontronite to organic acid attack. The X-ray diffraction results in Figs. 6 and 7 suggest that very little transformation occurs during leaching. This is with the exception of serpentine peak after 7 days of leaching which confirms its amenability to acid attack (see Tables 3 and 4). As suggested in Table 5, iron and aluminium are strongly associated with goethite and illite. The poor dissolution of iron and aluminium, as suggested by Tables 3 and 4, indicate the poor reactivity of goethite and illite in the organic acids used in this study. These are confirmed by the lack of transformations of these minerals in Figs. 6 and 7. The greater selectivity demonstrated by cobalt suggest that this metal is hosted largely
G Q GI Q
G G G
G
Intensity (I/Io)
G
Q
G
G
GG
G
G Q
G
G G
20
25
Q
QG
Q G
GG
G G
G G
2θ (degree)
30
G G
M Ma
Ma
C Ma G Q
GI
Q
C
G I C M
Ma
Ma
3 days Ma
G I C M
Q G
M
G
Raw Nontronite Ma
Ma
G
M CMaC
Q G
5 35
7 days
C
GI Q
Ma
G I C M
G Q
Raw Limonite
15 days Ma
Q
GI
7 days
G
S
15
G G
C Ma
G
15 days GG
G G G
G
G
G
Q
G
10
G
G
G
G
20 days
G
Q
Intensity (I/Io)
G
G I C M
40
45
Fig. 6. Synchrotron X-ray diffraction pattern of raw and solid limonite residues leached with citric acid as a function of time. (G: goethite, S: serpentine, Q: quartz) (Valix et al., 2004).
10
15
20
25 30 2θ (degree)
35
40
45
Fig. 7. Synchrotron X-ray diffraction pattern of raw and solid nontronite residues leached with citric acid as a function of time. (G: goethite, I: illite, Q: quartz, C: cochromite, Ma: magnetite, M: magnesiochromite) (Valix et al., 2004).
J.A. Tang, M. Valix / Minerals Engineering 19 (2006) 1274–1279
by the serpentine group in limonite and nontronite. Whereas nickel, which shows poorer dissolution may be hosted largely by goethite ad the illite phases. These are consistent with suggestions that in limonite, goethite is the host mineral for nickel, while cobalt is found to be associated with a manganese phase that is also rich in nickel (Georgiou and Papangelakis, 2004). Effective dissolution of both cobalt and nickel in limonite will thus require the dissolution of goethite, serpentine and manganese phases, while nontronite requires the dissolution of illite and serpentine phases. 4. Conclusions Metal dissolution is affected by the hydronium ion concentration rather than the type of acid. However, the effect of the hydronium ion requires careful control of the oxygen reduction potential during leaching. A highly oxidizing condition, (>430 mV) appear to suppress nickel and cobalt dissolution. This emphasizes the importance of pH and ORP control during the bio-leaching of nickel laterite ores. In general optimal leaching of nickel and cobalt are achieved with 5.75 wt% pulp densities. Nickel and cobalt dissolution is intimately associated with the amenability of host minerals to organic acid attack. The poorer nickel dissolution is associated with the resistance by goethite and illite to acid attack in limonite and nontronite, respectively. Greater cobalt dissolution in limonite and nontronite is consistent with the amenability of serpentine to acid attack. These results suggest the importance of oxygen-reduction potential, acid activities of the metabolic acids, pulp density and mineralogy in effecting metal dissolution in the bioleaching of limonite and nontronite minerals.
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Acknowledgements The authors would like to acknowledge the Australian Research Council for their funding support towards this project. References Alibhai, K.A.K., Dudeney, A.W.L., Leak, D.J., Agatzini, S., Tzeferis, P., 1993. Bioleaching and bioprecipitation of nickel and iron from laterites. FEMS Microbiology Reviews 11, 87–96. Bosecker, K., 1987. Leaching of lateritic nickel ores with heterotrophic microorganisms. Acta Biotechnologica 7 (5), 389–399. Bosecker, K., 1997. Bioleaching: metal solubilization by microorganisms. FEMS Microbiology Reviews 20, 591–604. Georgiou, D., Papangelakis, V.G., 2004. Characterization of limonitic laterite and solids during sulphuric acid pressure leaching using transmission electron microscope. Minerals Engineering 17, 461–463. Sukla, L.B., Panchanadikar, V., 1993. Bioleaching of lateritic nickel ore using a heterotrophic micro-organism. Hydrometallurgy 32, 373–379. Tang, L.J., 2004. Bioleaching of low grade nickel laterite ore with heterotrophic micro-organisms, Thesis (Ph.D.), Department of Chemical Engineering, Graduate School of Engineering, University of Sydney, Australia. Tzeferis, P.G., 1994. Leaching of a low grade hematitic laterite ore using fungi and biologically produced acid metabolites. International Journal of Mineral Processing 42, 267–283. Tzeferis, P.G., Agatzini-Leonardou, S., 1994. Leaching of nickel and iron from Greek non-sulphide nickeliferous ores by organic acids. Hydrometallurgy 36, 345–360. Valix, M., Cheung, A., O’Connor, F., Kennedy, S., 2001a. In-situ kinetic study of laterite reduction. AINSE Progress Report for 01/138P. Valix, M., Usai, F., Malik, R., 2001b. The electro-sorption properties of nickel on laterite gangue leached with an organic chelating acid. Minerals Processing 14 (2), 205–215. Valix, M. Tang, J.Y., Cheung W.H., 2004. Biological leaching of nickel laterites: use of synchrotron based X-ray diffraction in elucidating the amenability of laterite minerals to fungi metabolic acids, Paper presented to CHEMECA 2004, Sydney.