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The flotation of slime–fine fractions of Mt. Keith pentlandite ore in de-ionised and saline water
Minerals Engineering 24 (2011) 479–481
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Technical Note
The flotation of slime–fine fractions of Mt. Keith pentlandite ore in de-ionised and saline water Y. Peng a,b,⇑, D. Seaman b,c a
School of Chemical Engineering, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia Formerly BHP Billiton Perth Technology Centre, 26 Dick Perry Avenue, Kensington, Perth, WA 6845, Australia c Newcrest Mining Limited, 193 Great Eastern Highway, Belmont, WA 6104, Australia b
a r t i c l e
i n f o
Article history: Received 1 December 2010 Accepted 31 December 2010 Available online 26 January 2011 Keywords: Slime and fine flotation Pentlandite Serpentine Saline water Dispersion
a b s t r a c t In this work, the flotation of slime–fine fractions of Mt. Keith pentlandite ore was studied in de-ionised water, and bore water with high ionic strength. Compared with de-ionised water, bore water increased pentlandite flotation significantly while decreasing serpentine flotation. Carboxymethyl cellulose (CMC) was tested as a dispersant to improve pentlandite flotation in both de-ionised and bore water. The degree of substitute (DS) of CMC, an indication of the charge density, was found to be an important parameter. In de-ionised water, the higher the DS of CMC, the better the pentlandite flotation, while in bore water, the lower the DS of CMC, the better the pentlandite flotation. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction The flotation of nickel sulphides in saline water at Mt. Keith has historically been difficult due to a low nickel grade and large amounts of serpentine minerals. A unique process, the split flotation, has been implemented at Mt. Keith to optimise pentlandite flotation. The grinding discharge is pumped to a two-stage cyclone classification. The underflows from the first and second stages of cyclones pass to rougher–scavenger flotation of coarse (160 lm) and fine streams (25 lm), respectively, while the overflows of the second stage of cyclones pass to rougher–scavenger flotation of a slime stream (8 lm). The overall nickel recovery at Mt. Keith is about 60%. The low nickel recovery in the flotation of the coarse stream has been mainly attributed to composite pentlandite– serpentine particles, while the low nickel recovery in the flotation of slime and fine streams has been mainly attributed to serpentine coating on pentlandite particles (Senior and Thomas, 2005). Some studies have been conducted to disperse serpentine coating from pentlandite surfaces in the flotation of Mt. Keith and other nickel ores from Western Australia by using CMC. Pietrobon et al. (1997) demonstrated that the addition of soda ash and CMC improved pentlandite flotation rate and recovery in the laboratory. However, when CMC and soda ash were tested in slime and fine ⇑ Corresponding author at: School of Chemical Engineering, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia. Tel.: +61 7 3365 7156; fax: +61 7 3365 3888. E-mail address: [email protected] (Y. Peng). 0892-6875/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2010.12.014
flotation streams at Mt. Keith, the improvement of pentlandite flotation obtained in the laboratory was not translated in the plant. This discrepancy may be attributed to different water used in the laboratory and in the plant. In the laboratory, tap water was used, while in the plant, bore water with high ionic strength was used. Wellham et al. (1992) investigated the effect of CMC on the dispersion of serpentine coating in the flotation of a nickel ore in salt solutions. They found that CMC was ineffective. In this study, CMC with different DS was tested in the flotation of slime–fine fractions of Mt. Keith ore in de-ionised and bore water. The DS of CMC is the average of the hydroxyl groups that have taken part in the substitution reaction (the number of original H atoms of cellulose hydroxyl groups that are replaced by carboxymethyl substituent) on each glucose unit (Husband, 1998). As a result, the DS is linked with the charge density of CMC. The greater the DS, the more negatively charged the CMC.
2. Experimental 2.1. Materials and reagents The pentlandite ore sample with 0.6% Ni, 41.5% MgO, 0.5% S and 4.7% Fe was obtained from Mt. Keith and crushed to a size of 2.36 mm before grinding and flotation. Pentlandite is the main nickel mineral with small amounts of millerite, violarite and heazlewoodite while chrysotile, antigorite and lizardite are the main serpentine minerals. The properties of this ore have been described
Y. Peng, D. Seaman / Minerals Engineering 24 (2011) 479–481
elsewhere (Senior and Thomas, 2005). The bore water was obtained from Mt. Keith as well. The compositions of the main ions, Na+, K+, Ca2+, Mg2+, Cl and SO2 are 20,000, 940, 400, 5100, 4 32,000 and 23,000 mg/L, respectively. Sodium ethyl xanthate and H407 (polypropylene glycol ether blend), industrial grade, were used as collector and frother, respectively. They are used at Mt. Keith. CMCs with the DS of 0.4, 0.6 and 0.9 were obtained from Akzo Nobel. 2.2. Grinding and flotation One kilogram crushed sample was ground in a laboratory stainless steel rod mill at 40% solids to obtain 80% particles passing 125 lm to match the nickel distribution produced in the plant. The mill discharge was then transferred and run through a 100 Mozley cyclone. The overflow stream with about 400 g solids was filtered and then floated. It is a combination of the slime and fine flotation feeds in Mt. Keith plant and referred to as the ‘‘slime–fine fraction’’ in this study. The P80 of this fraction is 25 lm, while the P50 is 8 lm. The compositions of Ni, MgO, S and Fe in this fraction are 0.4%, 41.8%, 0.5% and 4.3%, respectively. Flotation was carried out in a 2.5 L Agitair flotation cell using an agitation speed of 750 rpm. The solid density in the flotation cell was 15%. During the conditioning, CMC (100 g/t), collector (150 g/t) and frother (20 g/t) were added. Flotation was performed for 32 min and six concentrates were collected after cumulative times of 1, 2, 4, 8, 16 and 32 min. Both de-ionised and bore water were tested in this study. The chosen water type was utilised in all stages of grinding, cycloning and flotation. The pH during grinding and flotation was constant, about 8.9 due to the buffering effect of the ore.
100
Cumulative MgO or Ni recovery (%)
480
MgO recover, bore water MgO recovery, de-ionised water Ni recovery, bore water Ni recovery, de-ionised water
80 60 40 20 0 0
5
10
15
20
Cumulative water recovery (%) Fig. 2. Ni and MgO recovery as a function of water recovery in de-ionised and bore water.
water recovery, indicating that the collection of serpentine gangue minerals to the concentrates was through water entrainment (Warren, 1985). George et al. (2004) proposed a method to determine the true flotation of the hydrophobic minerals by the difference in recovery between hydrophobic and hydrophilic minerals versus water recovered. Based on this method, a low level of true flotation of pentlandite occurred in de-ionised water, but the true flotation of pentlandite was increased significantly in bore water. This is because the relationship between Ni recovery and water recovery deviated from the MgO–water recovery line slightly in de-ionised water but remarkably in bore water.
3. Results
3.2. Mineral dispersion by CMC
3.1. Flotation in de-ionised and bore water
Fig. 3 shows flotation results with the addition of 100 g/t CMC with different DS in de-ionised and bore water. As can be seen, in bore water CMC improved pentlandite flotation and its separation from serpentine to some extent. The lower the DS of CMC, the greater the improvement. With the DS 0.4, Ni recovery was increased from 69% to 75%, while MgO recovery was reduced from 17% to 13%. In de-ionised water, CMC also improved pentlandite flotation and its separation from serpentine. However, DS had an opposite effect. The higher the DS, the better the flotation separation. Pentlandite flotation in the presence of CMC in de-ionised water was still lower than that in the absence of CMC in bore water.
28
Cumulative MgO recovery (%)
Cumulative MgO recovery (%)
Fig. 1 shows repeat flotation tests on pentlandite separation from serpentine in de-ionised and bore water. As can be seen, in de-ionised water, Ni recovery was low but MgO recovery was high. At the completion of 32 min of flotation, they were 38% and 24%, respectively. In bore water, Ni recovery was increased to 69% while MgO recovery was decreased to 17%. As a result, bore water with high ionic strength increased pentlandite flotation and its selectivity against serpentine significantly. Fig. 2 shows MgO and Ni recovery as a function of water recovery in de-ionised and bore water. In both de-ionised and bore water, a linear relationship existed between MgO recovery and
Bore water 1 Bore water 2 De-ionised water 1 De-ionised water 2
24 20 16 12 8 4 0 0
20
40
60
80
25 Without CMC CMC DS 0.4 CMC DS 0.6 CMC DS 0.9
20 15
De-ionised water
10 5
Bore water
0 0
20
40
60
80
Cumulative Ni recovery (%)
Cumulative Ni recovery (%) Fig. 1. Pentlandite flotation against serpentine in de-ionised and bore water with repeat tests of each.
Fig. 3. Pentlandite flotation and separation from serpentine with the addition of 100 g/t CMC in de-ionised and bore water: empty symbols (bore water); solid symbols (de-ionised water).
Y. Peng, D. Seaman / Minerals Engineering 24 (2011) 479–481
4. Discussion and conclusions In de-ionised water, the flotation of the slime–fine fraction of Mt. Keith ore was poor with low Ni recovery and high MgO gangue entrainment. Edwards et al. (1980) demonstrated that serpentine particles were positively charged and pentlandite particles were negatively charged in neutral and alkaline pH solutions resulting in the coating of serpentine particles on the pentlandite surface and the subsequent depression of pentlandite flotation. In bore water, Ni recovery was increased significantly while MgO recovery was decreased. In electrolyte solutions the electrical double layers surrounding the particles are collapsed (Rattanakawin and Hogg, 2001). This is supported by our zeta potential measurements showing that the zeta potentials of both pentlandite and serpentine were close to zero in a solution with only 2% bore water. The reduced electrostatic attraction between serpentine and pentlandite particles may mitigate the serpentine coating on the pentlandite surface resulting in the improved pentlandite flotation. In bore water, water recovery was decreased as well (Fig. 2) indicating the decreased froth stability corresponding to the decreased MgO recovery. The reason why the froth stability was decreased in bore water is under investigation. It seems that the significantly increased surface hydrophobicity on pentlandite after the mitigation of serpentine coating destabilised the froth. In fact, Schwarz and Grano (2005) observed a decrease in the concentrate flow rate of water and froth stability with increasing particle contact angle. CMC is an anionic dispersant providing steric stabilisation. It increased pentlandite flotation in both de-ionised and bore water. In de-ionised water, a higher DS with the higher charge density corresponded to the higher pentlandite flotation. This may be due to the higher adsorption of CMC on the positively charged serpentine particles and more reduction of the charge of serpentine particles. In contrast, a lower DS with the lower charge density corresponded to the better pentlandite flotation in bore water. Koopal et al.
481
(1995) observed that an increase in ionic strength of bulk solutions caused a screening of the columbic attraction between the head group of ionic dispersants and the oppositely charged mineral surface, leading to a decrease in adsorption. It seems that CMC with the lower charge density is less sensitive to the charged electrolytes in bore water. Detailed mechanisms are under investigation. Acknowledgment The authors gratefully acknowledge the approval of publication of this paper by BHP Billiton. References Edwards, G.R., Kipkie, W.B., Agar, G.E., 1980. The effect of slime coatings of the serpentine minerals, chrysotile and lizardite on pentlandite flotation. Int. J. Miner. Process. 7, 33–42. George, P., Nguyen, A.V., Jameson, G.J., 2004. Assessment of true flotation and entrainment in the flotation of submicron particles by fine bubbles. Miner. Eng. 17, 847–853. Husband, J.C., 1998. Adsorption and rheological studies of sodium carboxymethyl cellulose onto kaolin: effect of degree of substitution. Colloids Surf. A: Physicochem. Eng. Aspects 134, 349–358. Koopal, L.K., Lee, E.M., Bohmer, M.R., 1995. Adsorption of cationic and anionic surfactants on charged metal oxide surfaces. J. Colloid Interface Sci. 170, 85–97. Pietrobon, M.C., Grano, S.R., Sobieraj, S., Ralston, J., 1997. Recovery mechanisms for pentlandite and MgO-bearing gangue minerals in nickel ores from Western Australia. Miner. Eng. 10, 775–786. Rattanakawin, C., Hogg, H., 2001. Aggregate size distributions in flocculation. Colloids Surf. A: Physicochem. Eng. Aspects 177, 87–98. Schwarz, S., Grano, S., 2005. Effect of particle hydrophobicity on particle and water transport across a flotation froth. Colloids Surf. A: Physicochem. Eng. Aspects 256, 157–164. Senior, G.D., Thomas, S.A., 2005. Development and implementation of a new flowsheet for the flotation of a low grade nickel ore. Int. J. Miner. Process. 78, 49–61. Warren, L.J., 1985. Determination of the contributions of true flotation and entrainment in batch flotation tests. Int. J. Miner. Process. 14, 33–44. Wellham, E.J., Elber, I., Yan, D.S., 1992. The role of carboxymethyl cellulose in the flotation of a nickel sulphide transition ore. Miner. Eng. 5, 381–395.
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Technical Note
The flotation of slime–fine fractions of Mt. Keith pentlandite ore in de-ionised and saline water Y. Peng a,b,⇑, D. Seaman b,c a
School of Chemical Engineering, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia Formerly BHP Billiton Perth Technology Centre, 26 Dick Perry Avenue, Kensington, Perth, WA 6845, Australia c Newcrest Mining Limited, 193 Great Eastern Highway, Belmont, WA 6104, Australia b
a r t i c l e
i n f o
Article history: Received 1 December 2010 Accepted 31 December 2010 Available online 26 January 2011 Keywords: Slime and fine flotation Pentlandite Serpentine Saline water Dispersion
a b s t r a c t In this work, the flotation of slime–fine fractions of Mt. Keith pentlandite ore was studied in de-ionised water, and bore water with high ionic strength. Compared with de-ionised water, bore water increased pentlandite flotation significantly while decreasing serpentine flotation. Carboxymethyl cellulose (CMC) was tested as a dispersant to improve pentlandite flotation in both de-ionised and bore water. The degree of substitute (DS) of CMC, an indication of the charge density, was found to be an important parameter. In de-ionised water, the higher the DS of CMC, the better the pentlandite flotation, while in bore water, the lower the DS of CMC, the better the pentlandite flotation. Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction The flotation of nickel sulphides in saline water at Mt. Keith has historically been difficult due to a low nickel grade and large amounts of serpentine minerals. A unique process, the split flotation, has been implemented at Mt. Keith to optimise pentlandite flotation. The grinding discharge is pumped to a two-stage cyclone classification. The underflows from the first and second stages of cyclones pass to rougher–scavenger flotation of coarse (160 lm) and fine streams (25 lm), respectively, while the overflows of the second stage of cyclones pass to rougher–scavenger flotation of a slime stream (8 lm). The overall nickel recovery at Mt. Keith is about 60%. The low nickel recovery in the flotation of the coarse stream has been mainly attributed to composite pentlandite– serpentine particles, while the low nickel recovery in the flotation of slime and fine streams has been mainly attributed to serpentine coating on pentlandite particles (Senior and Thomas, 2005). Some studies have been conducted to disperse serpentine coating from pentlandite surfaces in the flotation of Mt. Keith and other nickel ores from Western Australia by using CMC. Pietrobon et al. (1997) demonstrated that the addition of soda ash and CMC improved pentlandite flotation rate and recovery in the laboratory. However, when CMC and soda ash were tested in slime and fine ⇑ Corresponding author at: School of Chemical Engineering, University of Queensland, St. Lucia, Brisbane, QLD 4072, Australia. Tel.: +61 7 3365 7156; fax: +61 7 3365 3888. E-mail address: [email protected] (Y. Peng). 0892-6875/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.mineng.2010.12.014
flotation streams at Mt. Keith, the improvement of pentlandite flotation obtained in the laboratory was not translated in the plant. This discrepancy may be attributed to different water used in the laboratory and in the plant. In the laboratory, tap water was used, while in the plant, bore water with high ionic strength was used. Wellham et al. (1992) investigated the effect of CMC on the dispersion of serpentine coating in the flotation of a nickel ore in salt solutions. They found that CMC was ineffective. In this study, CMC with different DS was tested in the flotation of slime–fine fractions of Mt. Keith ore in de-ionised and bore water. The DS of CMC is the average of the hydroxyl groups that have taken part in the substitution reaction (the number of original H atoms of cellulose hydroxyl groups that are replaced by carboxymethyl substituent) on each glucose unit (Husband, 1998). As a result, the DS is linked with the charge density of CMC. The greater the DS, the more negatively charged the CMC.
2. Experimental 2.1. Materials and reagents The pentlandite ore sample with 0.6% Ni, 41.5% MgO, 0.5% S and 4.7% Fe was obtained from Mt. Keith and crushed to a size of 2.36 mm before grinding and flotation. Pentlandite is the main nickel mineral with small amounts of millerite, violarite and heazlewoodite while chrysotile, antigorite and lizardite are the main serpentine minerals. The properties of this ore have been described
Y. Peng, D. Seaman / Minerals Engineering 24 (2011) 479–481
elsewhere (Senior and Thomas, 2005). The bore water was obtained from Mt. Keith as well. The compositions of the main ions, Na+, K+, Ca2+, Mg2+, Cl and SO2 are 20,000, 940, 400, 5100, 4 32,000 and 23,000 mg/L, respectively. Sodium ethyl xanthate and H407 (polypropylene glycol ether blend), industrial grade, were used as collector and frother, respectively. They are used at Mt. Keith. CMCs with the DS of 0.4, 0.6 and 0.9 were obtained from Akzo Nobel. 2.2. Grinding and flotation One kilogram crushed sample was ground in a laboratory stainless steel rod mill at 40% solids to obtain 80% particles passing 125 lm to match the nickel distribution produced in the plant. The mill discharge was then transferred and run through a 100 Mozley cyclone. The overflow stream with about 400 g solids was filtered and then floated. It is a combination of the slime and fine flotation feeds in Mt. Keith plant and referred to as the ‘‘slime–fine fraction’’ in this study. The P80 of this fraction is 25 lm, while the P50 is 8 lm. The compositions of Ni, MgO, S and Fe in this fraction are 0.4%, 41.8%, 0.5% and 4.3%, respectively. Flotation was carried out in a 2.5 L Agitair flotation cell using an agitation speed of 750 rpm. The solid density in the flotation cell was 15%. During the conditioning, CMC (100 g/t), collector (150 g/t) and frother (20 g/t) were added. Flotation was performed for 32 min and six concentrates were collected after cumulative times of 1, 2, 4, 8, 16 and 32 min. Both de-ionised and bore water were tested in this study. The chosen water type was utilised in all stages of grinding, cycloning and flotation. The pH during grinding and flotation was constant, about 8.9 due to the buffering effect of the ore.
100
Cumulative MgO or Ni recovery (%)
480
MgO recover, bore water MgO recovery, de-ionised water Ni recovery, bore water Ni recovery, de-ionised water
80 60 40 20 0 0
5
10
15
20
Cumulative water recovery (%) Fig. 2. Ni and MgO recovery as a function of water recovery in de-ionised and bore water.
water recovery, indicating that the collection of serpentine gangue minerals to the concentrates was through water entrainment (Warren, 1985). George et al. (2004) proposed a method to determine the true flotation of the hydrophobic minerals by the difference in recovery between hydrophobic and hydrophilic minerals versus water recovered. Based on this method, a low level of true flotation of pentlandite occurred in de-ionised water, but the true flotation of pentlandite was increased significantly in bore water. This is because the relationship between Ni recovery and water recovery deviated from the MgO–water recovery line slightly in de-ionised water but remarkably in bore water.
3. Results
3.2. Mineral dispersion by CMC
3.1. Flotation in de-ionised and bore water
Fig. 3 shows flotation results with the addition of 100 g/t CMC with different DS in de-ionised and bore water. As can be seen, in bore water CMC improved pentlandite flotation and its separation from serpentine to some extent. The lower the DS of CMC, the greater the improvement. With the DS 0.4, Ni recovery was increased from 69% to 75%, while MgO recovery was reduced from 17% to 13%. In de-ionised water, CMC also improved pentlandite flotation and its separation from serpentine. However, DS had an opposite effect. The higher the DS, the better the flotation separation. Pentlandite flotation in the presence of CMC in de-ionised water was still lower than that in the absence of CMC in bore water.
28
Cumulative MgO recovery (%)
Cumulative MgO recovery (%)
Fig. 1 shows repeat flotation tests on pentlandite separation from serpentine in de-ionised and bore water. As can be seen, in de-ionised water, Ni recovery was low but MgO recovery was high. At the completion of 32 min of flotation, they were 38% and 24%, respectively. In bore water, Ni recovery was increased to 69% while MgO recovery was decreased to 17%. As a result, bore water with high ionic strength increased pentlandite flotation and its selectivity against serpentine significantly. Fig. 2 shows MgO and Ni recovery as a function of water recovery in de-ionised and bore water. In both de-ionised and bore water, a linear relationship existed between MgO recovery and
Bore water 1 Bore water 2 De-ionised water 1 De-ionised water 2
24 20 16 12 8 4 0 0
20
40
60
80
25 Without CMC CMC DS 0.4 CMC DS 0.6 CMC DS 0.9
20 15
De-ionised water
10 5
Bore water
0 0
20
40
60
80
Cumulative Ni recovery (%)
Cumulative Ni recovery (%) Fig. 1. Pentlandite flotation against serpentine in de-ionised and bore water with repeat tests of each.
Fig. 3. Pentlandite flotation and separation from serpentine with the addition of 100 g/t CMC in de-ionised and bore water: empty symbols (bore water); solid symbols (de-ionised water).
Y. Peng, D. Seaman / Minerals Engineering 24 (2011) 479–481
4. Discussion and conclusions In de-ionised water, the flotation of the slime–fine fraction of Mt. Keith ore was poor with low Ni recovery and high MgO gangue entrainment. Edwards et al. (1980) demonstrated that serpentine particles were positively charged and pentlandite particles were negatively charged in neutral and alkaline pH solutions resulting in the coating of serpentine particles on the pentlandite surface and the subsequent depression of pentlandite flotation. In bore water, Ni recovery was increased significantly while MgO recovery was decreased. In electrolyte solutions the electrical double layers surrounding the particles are collapsed (Rattanakawin and Hogg, 2001). This is supported by our zeta potential measurements showing that the zeta potentials of both pentlandite and serpentine were close to zero in a solution with only 2% bore water. The reduced electrostatic attraction between serpentine and pentlandite particles may mitigate the serpentine coating on the pentlandite surface resulting in the improved pentlandite flotation. In bore water, water recovery was decreased as well (Fig. 2) indicating the decreased froth stability corresponding to the decreased MgO recovery. The reason why the froth stability was decreased in bore water is under investigation. It seems that the significantly increased surface hydrophobicity on pentlandite after the mitigation of serpentine coating destabilised the froth. In fact, Schwarz and Grano (2005) observed a decrease in the concentrate flow rate of water and froth stability with increasing particle contact angle. CMC is an anionic dispersant providing steric stabilisation. It increased pentlandite flotation in both de-ionised and bore water. In de-ionised water, a higher DS with the higher charge density corresponded to the higher pentlandite flotation. This may be due to the higher adsorption of CMC on the positively charged serpentine particles and more reduction of the charge of serpentine particles. In contrast, a lower DS with the lower charge density corresponded to the better pentlandite flotation in bore water. Koopal et al.
481
(1995) observed that an increase in ionic strength of bulk solutions caused a screening of the columbic attraction between the head group of ionic dispersants and the oppositely charged mineral surface, leading to a decrease in adsorption. It seems that CMC with the lower charge density is less sensitive to the charged electrolytes in bore water. Detailed mechanisms are under investigation. Acknowledgment The authors gratefully acknowledge the approval of publication of this paper by BHP Billiton. References Edwards, G.R., Kipkie, W.B., Agar, G.E., 1980. The effect of slime coatings of the serpentine minerals, chrysotile and lizardite on pentlandite flotation. Int. J. Miner. Process. 7, 33–42. George, P., Nguyen, A.V., Jameson, G.J., 2004. Assessment of true flotation and entrainment in the flotation of submicron particles by fine bubbles. Miner. Eng. 17, 847–853. Husband, J.C., 1998. Adsorption and rheological studies of sodium carboxymethyl cellulose onto kaolin: effect of degree of substitution. Colloids Surf. A: Physicochem. Eng. Aspects 134, 349–358. Koopal, L.K., Lee, E.M., Bohmer, M.R., 1995. Adsorption of cationic and anionic surfactants on charged metal oxide surfaces. J. Colloid Interface Sci. 170, 85–97. Pietrobon, M.C., Grano, S.R., Sobieraj, S., Ralston, J., 1997. Recovery mechanisms for pentlandite and MgO-bearing gangue minerals in nickel ores from Western Australia. Miner. Eng. 10, 775–786. Rattanakawin, C., Hogg, H., 2001. Aggregate size distributions in flocculation. Colloids Surf. A: Physicochem. Eng. Aspects 177, 87–98. Schwarz, S., Grano, S., 2005. Effect of particle hydrophobicity on particle and water transport across a flotation froth. Colloids Surf. A: Physicochem. Eng. Aspects 256, 157–164. Senior, G.D., Thomas, S.A., 2005. Development and implementation of a new flowsheet for the flotation of a low grade nickel ore. Int. J. Miner. Process. 78, 49–61. Warren, L.J., 1985. Determination of the contributions of true flotation and entrainment in batch flotation tests. Int. J. Miner. Process. 14, 33–44. Wellham, E.J., Elber, I., Yan, D.S., 1992. The role of carboxymethyl cellulose in the flotation of a nickel sulphide transition ore. Miner. Eng. 5, 381–395.