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On the detachment of hydrophobic particles from the froth phase
Minerals Engineering 95 (2016) 113–115
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Short communication
On the detachment of hydrophobic particles from the froth phase Yesenia Saavedra Moreno, Seher Ata ⇑ School of Mining Engineering, University of New South Wales, Sydney, NSW 2052, Australia
a r t i c l e
i n f o
Article history: Received 3 March 2016 Revised 12 June 2016 Accepted 15 June 2016
Keywords: Froth flotation Froth Froth recovery
a b s t r a c t We conducted an experimental study to investigate the behaviour of hydrophobic particles in the froth phase of a laboratory column. A stable froth was formed by passing the air through a porous disk into the liquid containing frother. Individual bubbles were loaded with hydrophobic particles separately in a fluidised bed and allowed to rise into the froth layer. Particles dislodged from the froth were collected and measured. The effect of collector concentration and superficial gas velocity on the detachment of particles from the froth was studied. The results showed that fraction of particles detaching from the froth decreases exponentially with increase in the collector concentration and increases slightly with superficial gas velocity. In general, low froth dropback values were obtained for the conditions studied in the present system which are considerably lower than the previously reported values. Ó 2016 Published by Elsevier Ltd.
1. Introduction Froth phase is an essential part of froth flotation: not only it defines the quality of the concentrate produced but also imposes the greatest limit to the overall recovery. Froth performance is generally described by the term, froth recovery (Rf) which is given by the ratio of the mass flowrate of hydrophobic particles reported to the concentrate, to the mass flowrate of attached particles entering the froth across the pulp-froth interface. A number of authors have reported values of the froth recovery for industrial flotation machines and laboratory cells. Falutsu and Dobby (1989) measured Rf recovery directly in a laboratory column using pure silica with d80 of 35 lm and found it to be in the range 45–55%. Rf was independent of the froth height and had lower values in the less mineralised froth. Yianatos et al. (2008) found that the froth recovery varied from 20 to 70% in industrial flotation column processing copper mineral while Alexander et al. (2003) reported a froth recovery of 40% in a rougher cell in a lead/zinc concentrator. Seaman et al. (2006) calculated Rf based on the particle load of bubbles sampled from the pulp phase in a zinc concentrate. A strong dependency of Rf on the minerals type and particle size in the froth were found. Rf values were 20% for pyrite and 28% for galena. Rahman et al. (2012) conducted experiments in a laboratory cell using pure silica as feed, with a wide particle size range. The Rf values for fine particles, up to 60 lm, were very high, approaching 100%. However, above 60 lm the froth recovery declined rapidly, dropping to 25% at 175 lm and above. ⇑ Corresponding author. E-mail address: [email protected] (S. Ata). http://dx.doi.org/10.1016/j.mineng.2016.06.016 0892-6875/Ó 2016 Published by Elsevier Ltd.
It was also found that as the fraction of fine particles in the feed increases, the froth recovery of coarse particles increases proportionally, presumably due to the froth stabilizing effect imposed by the fine particles. High froth recovery values were also obtained in the plant size flotation cell (Rahman et al., 2015a,b). The froth recovery values reported in the literature vary significantly not only because of different ore systems used but also due to the different techniques employed in the calculation and estimation of Rf. In general, the previous studies suggest that the recovery in flotation cells is only up to a half to two-thirds of the maximum possible in a given cell due to losses in the froth phase. This note reports the results of well-controlled experiments which show that hydrophobic particles are not easily dislodged from the froth. 2. Experimental A sketch of the apparatus is shown in Fig. 1. A single bubble was introduced into the particle bed via a stainless steel capillary, where it collected one or more of the hydrophobic particles and rose through a conical neck (10 mm ID) into the froth formed above. Water containing reagents entered through a detachable porous frit in the base of the unit via a peristaltic pump to provide a uniform flow distribution to the particle bed. The liquid velocity in the column was adjusted such that the minimum fluidization velocity (0.027 cm/s) was achieved. The supply of liquid stream also prevented any particle that fell off the froth re-entering into the bed. The particles are contained in a cylindrical column with diameter of 32 mm and height of 150 mm (A). The airflow rate to the particle bed (0.09 ml/min) was controlled precisely using a
114
Y.S. Moreno, S. Ata / Minerals Engineering 95 (2016) 113–115
froth
E recovered particles
D
culated based on the fraction of the total flow of particles that is recovered as the product. High grade silica particles (Unimin Australia Ltd, Melbourne, Australia) in the range of 106–250 lm were used in the experiments. Dodecylamine (DDA) and methyl isobutyl carbinol (MIBC) were used as collector and frother, respectively and NaOH and HCl were used to adjust the pH of the solutions. Collector (DDA) concentration was varied from 10 5 mM to 0.1 mM. All the reagents used in sample preparation and measurements were of analytical grade and used without further purification. Tap water was used in all experiments. For each condition the experiments were repeated at least twice.
3. Results and discussion
C
dropback particles
A
air
particle bed water + frother
B
water to fluidise bed
air Fig. 1. Experimental set-up used in the study.
Mass Flow Control (MFC) connected to a computer running custom written software. In order to produce the froth, bubbles were produced in a separate column (B; 80 mm D 75 mm H) connected to the main cell with at an angle of 45° (C, 30 mm ID). The bubbles were generated by introducing air through a sintered glass frit positioned into the base of the cell. The liquid airflow rate to the column was 280 ml/min. The hydrophobic particles can either pass into the froth and be recovered in the flotation product, or they may detach and drop in the chamber located beneath the froth where they are collected. The diameter of the column that captures the dropback particles (D) and froth column (E) were 70 mm and 30 mm, respectively. The froth depth was 200 mm for all experiments. Since silica particles are naturally hydrophilic, it is important that they are thoroughly conditioned in solution such that their surface becomes coated with the collector and consistently hydrophobic. To effectively do this, particles were washed in concentrated acid in order to remove impurities from their surface. Acid washed particles were subjected to conditioning by stirring the particles in a beaker of collector solution at pH of 9 for one hour before immediately being added to the column that had been initially loaded with coarse sand (+1.7–2 mm) to a nominal height of 50 mm to reduce the minimum fluidization velocity. The test sample was then added, to a total height of approximately 18–20 mm. Single bubbles were introduced through the particle bed for at least 20 min after the froth reached steady state condition. Both the floated (concentrate) and dislodged particles from the froth were collected and dried in an oven to get the total mass. The total particle load delivered to the froth is simply the sum of the mass of particles in the product and dropback streams, and the froth recovery (and the fraction of particles detached from the froth) was cal-
Fig. 2 shows the variation of particle detachment from the froth as a function of collector concentration in the concentration range from 10 5 mM to 0.1 mM at Jg = 1.75 cm/s. Since Rf = C/(C + D) (C and D are the mass flowrate of the attached particles in the concentrate and dropback streams, respectively) the fraction of particles detaching from the froth is 1-Rf. It is seen from the figure that the fraction of particles leaving the froth decreased sharply with an increase in collector concentration reaching a semi-plateau after 0.02 mM. The higher concentration tests experienced significantly lower loss of particles: approximately 5% of the particles that entered into the froth dropback while the rest were recovered in the concentrate. The result from Fig. 2 implies that there exists a critical hydrophobicity below which particles start to drop from the froth. Interestingly, several studies (Gontijo et al., 2007; Chipfunhu et al., 2011) reported the existence of a critical contact angle for flotation to occur. The critical contact angle was found to be strongly dependent on particle size and material used in these studies. In the current work, no attempt was made to measure the contact angle of particles, so the corresponding contact angle is not known. Further study is required to fully explore this phenomenon. It is important to note that the bubble loading in these tests changed significantly. The individual bubbles were seen to be entirely coated at the highest collector concentration and interestingly visible to survive climbing through the froth column without coalescing. Being a cationic collector, dodecylamine also acts as a frother, which could affect the bubble size by absorbing at the air-water interface, thus leading to the froth of various stabilities to be formed. MIBC was therefore added at the concentration of
Fig. 2. Fraction of particles detached from the froth as a function of collector concentration.
Y.S. Moreno, S. Ata / Minerals Engineering 95 (2016) 113–115
50 ppm to the solutions to minimise the variation in the froth stability as well as in the bubble size formed in the fluidised bed. Fig. 3 shows the effect of superficial gas velocity (Jg) on the fraction of particles dislodging from the froth phase at collector concentration of 10 3 mM. It is seen that there is a slight increase in dropback over Jg’s studied. Overall the fraction of particles detached rose by 15% as Jg was increased from 1.4 cm/s to 2.5 cm/s. The increase was pronounced at higher Jg’s which may suggest that the flow in the column deviated from plug flow and became unsteady, thus causing detachment of the particles. Increasing Jg may also increase the size of the bubbles in the liquid and create turbulence at the pulp-froth interface which may lead more particles to leave the froth. It is noted that the minimum Jg was set at 1.4 cm/s in these experiments since it wasn’t possible to create a certain depth of froth at lower Jg’s in the current system. The results from the present study suggest that the particles did not leave the froth easily as suggested in the literature. The dropback observed in the current system is much lower than the most values reported by the previous studies including those were carried out in the lab environment with a single mineral and much smaller particle size (see for example Falutsu and Dobby, 1989). We note that the conditions in the present system are not considered favorable for a high froth recovery. The current system is based on a single bubble introducing into the two- phase froth. The froth is anticipated to have a poor stability due to the absence of hydrophobic particles which plays an active role in stabilizing the froth and provide a safe environment for the attached particles. The size of the particles is also at the end of the coarse range, so smaller hydrophobic particles are more likely to reach the concentrate relatively easier than their coarse counterparts. Thus, under the optimum conditions, lower particle detachment would be expected. On the other hand, the conditions present in the current work may be considered well-controlled compared to those present in industrial flotation cells. It is worth to mention that, our preliminary results with coarser fraction have showed that the dropback from the froth could be almost doubled as the particles get larger under the same experimental conditions. A number of techniques have been developed to study froth performance and measure froth recovery (Vera et al., 1999; Runge et al., 2010; Ata, 2012). Each of these techniques has its advantages and limitations. The current experimental device offers a clear advantage over the existing froth recovery measurement techniques. The device allows only the hydrophobic particles that are attached to bubbles to enter into the froth phase, thus eliminating entrainment problem completely. In addition, since the bubbles forming the froth are produced in a separate column, it is
Fig. 3. Effect of Jg on the fractional detachment of particles from the froth.
115
possible to modify the stability of froth independently by coating the bubbles to various surface coverages and particles of different sizes. This will allow one a thorough analysis of the relation between froth stability and dropback. In the present form, the system is however limited in terms of changing the froth height and using low superficial gas velocities. The device is currently under modification to handle these restrictions. 4. Conclusions We developed a technique that allows the hydrophobic particles returning from the froth phase to be determined precisely. Strong dependence of dropback on the collector concentration was observed. There seemed to be a critical surface hydrophobicity below which the particle recovery dropped significantly. Overall, the results showed that hydrophobic particles do not leave the froth despite the conditions in the present system were not favorable for achieving higher froth recovery. Acknowledgements The authors wish to thank Mr Keehan Oliver of McGill University and Mr. Reza Rahman for their contribution to the experimental part. References Ata, S., 2012. Phenomena in the froth phase of flotation – a review. Int. J. Miner. Process. 102–103, 1–12. Alexander, D.J., Franzidis, J.P., Manlapig, E.V., 2003. Froth recovery measurement in plant scale flotation cells. Miner. Eng. 16 (11), 1197–1203. Chipfunhu, D., Zanin, M., Grano, S.R., 2011. The dependency of the critical contact angle for flotation on particle size – modelling the flotation limits for fine particles. Miner. Eng. 24, 50–57. Falutsu, M., Dobby, G.S., 1989. Direct measurement of froth drop back and collection zone recovery in a laboratory flotation column. Miner. Eng. 2 (3), 377–386. Gontijo, C., Fornasiero, D., Ralston, J., 2007. The limits of fine and coarse particle flotation. Can. J. Chem. Eng. 85, 739–747. Rahman, R.M., Ata, S., Jameson, G.J., 2012. The effect of flotation variables on the recovery of different particle size fractions in the froth and the pulp. Int. J Miner. Process. 52 (106–109), 70–77. Rahman, R.M., Ata, S., Jameson, G.J., 2015a. Study of froth behaviour in a controlled plant environment – Part 1: Effect of air flow rate and froth depth. Miner. Eng. 81, 152–160. Rahman, R.M., Ata, S., Jameson, G.J., 2015b. Study of froth behaviour in a controlled plant environment – Part 2: Effect of collector and frother concentration. Miner. Eng. 81, 161–166. Runge, K., Crosbie, R., Rivett, T., McMaster, J., 2010. An evaluation of froth recovery measurement techniques. In: XXV International Mineral Processing Congress, Brisbane, Australia, Brisbane, Australia. Seaman, D.R., Manlapig, E.V., Franzidis, J.P., 2006. Selective transport of attached particles across the pulp-froth interface. Miner. Eng. 19 (6–8), 841–851. Vera, M.A., Franzidis, J.P., Manlapig, E.V., 1999. Simultaneous determination of collection zone rate constant and froth zone recovery in a mechanical flotation environment. Miner. Eng. 12 (10), 1163–1176. Yianatos, J.B., Moys, M.H., Contreras, F., Villanueva, A., 2008. Froth recovery of industrial flotation cells. Miner. Eng. 21 (12–14), 817–825.
Contents lists available at ScienceDirect
Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Short communication
On the detachment of hydrophobic particles from the froth phase Yesenia Saavedra Moreno, Seher Ata ⇑ School of Mining Engineering, University of New South Wales, Sydney, NSW 2052, Australia
a r t i c l e
i n f o
Article history: Received 3 March 2016 Revised 12 June 2016 Accepted 15 June 2016
Keywords: Froth flotation Froth Froth recovery
a b s t r a c t We conducted an experimental study to investigate the behaviour of hydrophobic particles in the froth phase of a laboratory column. A stable froth was formed by passing the air through a porous disk into the liquid containing frother. Individual bubbles were loaded with hydrophobic particles separately in a fluidised bed and allowed to rise into the froth layer. Particles dislodged from the froth were collected and measured. The effect of collector concentration and superficial gas velocity on the detachment of particles from the froth was studied. The results showed that fraction of particles detaching from the froth decreases exponentially with increase in the collector concentration and increases slightly with superficial gas velocity. In general, low froth dropback values were obtained for the conditions studied in the present system which are considerably lower than the previously reported values. Ó 2016 Published by Elsevier Ltd.
1. Introduction Froth phase is an essential part of froth flotation: not only it defines the quality of the concentrate produced but also imposes the greatest limit to the overall recovery. Froth performance is generally described by the term, froth recovery (Rf) which is given by the ratio of the mass flowrate of hydrophobic particles reported to the concentrate, to the mass flowrate of attached particles entering the froth across the pulp-froth interface. A number of authors have reported values of the froth recovery for industrial flotation machines and laboratory cells. Falutsu and Dobby (1989) measured Rf recovery directly in a laboratory column using pure silica with d80 of 35 lm and found it to be in the range 45–55%. Rf was independent of the froth height and had lower values in the less mineralised froth. Yianatos et al. (2008) found that the froth recovery varied from 20 to 70% in industrial flotation column processing copper mineral while Alexander et al. (2003) reported a froth recovery of 40% in a rougher cell in a lead/zinc concentrator. Seaman et al. (2006) calculated Rf based on the particle load of bubbles sampled from the pulp phase in a zinc concentrate. A strong dependency of Rf on the minerals type and particle size in the froth were found. Rf values were 20% for pyrite and 28% for galena. Rahman et al. (2012) conducted experiments in a laboratory cell using pure silica as feed, with a wide particle size range. The Rf values for fine particles, up to 60 lm, were very high, approaching 100%. However, above 60 lm the froth recovery declined rapidly, dropping to 25% at 175 lm and above. ⇑ Corresponding author. E-mail address: [email protected] (S. Ata). http://dx.doi.org/10.1016/j.mineng.2016.06.016 0892-6875/Ó 2016 Published by Elsevier Ltd.
It was also found that as the fraction of fine particles in the feed increases, the froth recovery of coarse particles increases proportionally, presumably due to the froth stabilizing effect imposed by the fine particles. High froth recovery values were also obtained in the plant size flotation cell (Rahman et al., 2015a,b). The froth recovery values reported in the literature vary significantly not only because of different ore systems used but also due to the different techniques employed in the calculation and estimation of Rf. In general, the previous studies suggest that the recovery in flotation cells is only up to a half to two-thirds of the maximum possible in a given cell due to losses in the froth phase. This note reports the results of well-controlled experiments which show that hydrophobic particles are not easily dislodged from the froth. 2. Experimental A sketch of the apparatus is shown in Fig. 1. A single bubble was introduced into the particle bed via a stainless steel capillary, where it collected one or more of the hydrophobic particles and rose through a conical neck (10 mm ID) into the froth formed above. Water containing reagents entered through a detachable porous frit in the base of the unit via a peristaltic pump to provide a uniform flow distribution to the particle bed. The liquid velocity in the column was adjusted such that the minimum fluidization velocity (0.027 cm/s) was achieved. The supply of liquid stream also prevented any particle that fell off the froth re-entering into the bed. The particles are contained in a cylindrical column with diameter of 32 mm and height of 150 mm (A). The airflow rate to the particle bed (0.09 ml/min) was controlled precisely using a
114
Y.S. Moreno, S. Ata / Minerals Engineering 95 (2016) 113–115
froth
E recovered particles
D
culated based on the fraction of the total flow of particles that is recovered as the product. High grade silica particles (Unimin Australia Ltd, Melbourne, Australia) in the range of 106–250 lm were used in the experiments. Dodecylamine (DDA) and methyl isobutyl carbinol (MIBC) were used as collector and frother, respectively and NaOH and HCl were used to adjust the pH of the solutions. Collector (DDA) concentration was varied from 10 5 mM to 0.1 mM. All the reagents used in sample preparation and measurements were of analytical grade and used without further purification. Tap water was used in all experiments. For each condition the experiments were repeated at least twice.
3. Results and discussion
C
dropback particles
A
air
particle bed water + frother
B
water to fluidise bed
air Fig. 1. Experimental set-up used in the study.
Mass Flow Control (MFC) connected to a computer running custom written software. In order to produce the froth, bubbles were produced in a separate column (B; 80 mm D 75 mm H) connected to the main cell with at an angle of 45° (C, 30 mm ID). The bubbles were generated by introducing air through a sintered glass frit positioned into the base of the cell. The liquid airflow rate to the column was 280 ml/min. The hydrophobic particles can either pass into the froth and be recovered in the flotation product, or they may detach and drop in the chamber located beneath the froth where they are collected. The diameter of the column that captures the dropback particles (D) and froth column (E) were 70 mm and 30 mm, respectively. The froth depth was 200 mm for all experiments. Since silica particles are naturally hydrophilic, it is important that they are thoroughly conditioned in solution such that their surface becomes coated with the collector and consistently hydrophobic. To effectively do this, particles were washed in concentrated acid in order to remove impurities from their surface. Acid washed particles were subjected to conditioning by stirring the particles in a beaker of collector solution at pH of 9 for one hour before immediately being added to the column that had been initially loaded with coarse sand (+1.7–2 mm) to a nominal height of 50 mm to reduce the minimum fluidization velocity. The test sample was then added, to a total height of approximately 18–20 mm. Single bubbles were introduced through the particle bed for at least 20 min after the froth reached steady state condition. Both the floated (concentrate) and dislodged particles from the froth were collected and dried in an oven to get the total mass. The total particle load delivered to the froth is simply the sum of the mass of particles in the product and dropback streams, and the froth recovery (and the fraction of particles detached from the froth) was cal-
Fig. 2 shows the variation of particle detachment from the froth as a function of collector concentration in the concentration range from 10 5 mM to 0.1 mM at Jg = 1.75 cm/s. Since Rf = C/(C + D) (C and D are the mass flowrate of the attached particles in the concentrate and dropback streams, respectively) the fraction of particles detaching from the froth is 1-Rf. It is seen from the figure that the fraction of particles leaving the froth decreased sharply with an increase in collector concentration reaching a semi-plateau after 0.02 mM. The higher concentration tests experienced significantly lower loss of particles: approximately 5% of the particles that entered into the froth dropback while the rest were recovered in the concentrate. The result from Fig. 2 implies that there exists a critical hydrophobicity below which particles start to drop from the froth. Interestingly, several studies (Gontijo et al., 2007; Chipfunhu et al., 2011) reported the existence of a critical contact angle for flotation to occur. The critical contact angle was found to be strongly dependent on particle size and material used in these studies. In the current work, no attempt was made to measure the contact angle of particles, so the corresponding contact angle is not known. Further study is required to fully explore this phenomenon. It is important to note that the bubble loading in these tests changed significantly. The individual bubbles were seen to be entirely coated at the highest collector concentration and interestingly visible to survive climbing through the froth column without coalescing. Being a cationic collector, dodecylamine also acts as a frother, which could affect the bubble size by absorbing at the air-water interface, thus leading to the froth of various stabilities to be formed. MIBC was therefore added at the concentration of
Fig. 2. Fraction of particles detached from the froth as a function of collector concentration.
Y.S. Moreno, S. Ata / Minerals Engineering 95 (2016) 113–115
50 ppm to the solutions to minimise the variation in the froth stability as well as in the bubble size formed in the fluidised bed. Fig. 3 shows the effect of superficial gas velocity (Jg) on the fraction of particles dislodging from the froth phase at collector concentration of 10 3 mM. It is seen that there is a slight increase in dropback over Jg’s studied. Overall the fraction of particles detached rose by 15% as Jg was increased from 1.4 cm/s to 2.5 cm/s. The increase was pronounced at higher Jg’s which may suggest that the flow in the column deviated from plug flow and became unsteady, thus causing detachment of the particles. Increasing Jg may also increase the size of the bubbles in the liquid and create turbulence at the pulp-froth interface which may lead more particles to leave the froth. It is noted that the minimum Jg was set at 1.4 cm/s in these experiments since it wasn’t possible to create a certain depth of froth at lower Jg’s in the current system. The results from the present study suggest that the particles did not leave the froth easily as suggested in the literature. The dropback observed in the current system is much lower than the most values reported by the previous studies including those were carried out in the lab environment with a single mineral and much smaller particle size (see for example Falutsu and Dobby, 1989). We note that the conditions in the present system are not considered favorable for a high froth recovery. The current system is based on a single bubble introducing into the two- phase froth. The froth is anticipated to have a poor stability due to the absence of hydrophobic particles which plays an active role in stabilizing the froth and provide a safe environment for the attached particles. The size of the particles is also at the end of the coarse range, so smaller hydrophobic particles are more likely to reach the concentrate relatively easier than their coarse counterparts. Thus, under the optimum conditions, lower particle detachment would be expected. On the other hand, the conditions present in the current work may be considered well-controlled compared to those present in industrial flotation cells. It is worth to mention that, our preliminary results with coarser fraction have showed that the dropback from the froth could be almost doubled as the particles get larger under the same experimental conditions. A number of techniques have been developed to study froth performance and measure froth recovery (Vera et al., 1999; Runge et al., 2010; Ata, 2012). Each of these techniques has its advantages and limitations. The current experimental device offers a clear advantage over the existing froth recovery measurement techniques. The device allows only the hydrophobic particles that are attached to bubbles to enter into the froth phase, thus eliminating entrainment problem completely. In addition, since the bubbles forming the froth are produced in a separate column, it is
Fig. 3. Effect of Jg on the fractional detachment of particles from the froth.
115
possible to modify the stability of froth independently by coating the bubbles to various surface coverages and particles of different sizes. This will allow one a thorough analysis of the relation between froth stability and dropback. In the present form, the system is however limited in terms of changing the froth height and using low superficial gas velocities. The device is currently under modification to handle these restrictions. 4. Conclusions We developed a technique that allows the hydrophobic particles returning from the froth phase to be determined precisely. Strong dependence of dropback on the collector concentration was observed. There seemed to be a critical surface hydrophobicity below which the particle recovery dropped significantly. Overall, the results showed that hydrophobic particles do not leave the froth despite the conditions in the present system were not favorable for achieving higher froth recovery. Acknowledgements The authors wish to thank Mr Keehan Oliver of McGill University and Mr. Reza Rahman for their contribution to the experimental part. References Ata, S., 2012. Phenomena in the froth phase of flotation – a review. Int. J. Miner. Process. 102–103, 1–12. Alexander, D.J., Franzidis, J.P., Manlapig, E.V., 2003. Froth recovery measurement in plant scale flotation cells. Miner. Eng. 16 (11), 1197–1203. Chipfunhu, D., Zanin, M., Grano, S.R., 2011. The dependency of the critical contact angle for flotation on particle size – modelling the flotation limits for fine particles. Miner. Eng. 24, 50–57. Falutsu, M., Dobby, G.S., 1989. Direct measurement of froth drop back and collection zone recovery in a laboratory flotation column. Miner. Eng. 2 (3), 377–386. Gontijo, C., Fornasiero, D., Ralston, J., 2007. The limits of fine and coarse particle flotation. Can. J. Chem. Eng. 85, 739–747. Rahman, R.M., Ata, S., Jameson, G.J., 2012. The effect of flotation variables on the recovery of different particle size fractions in the froth and the pulp. Int. J Miner. Process. 52 (106–109), 70–77. Rahman, R.M., Ata, S., Jameson, G.J., 2015a. Study of froth behaviour in a controlled plant environment – Part 1: Effect of air flow rate and froth depth. Miner. Eng. 81, 152–160. Rahman, R.M., Ata, S., Jameson, G.J., 2015b. Study of froth behaviour in a controlled plant environment – Part 2: Effect of collector and frother concentration. Miner. Eng. 81, 161–166. Runge, K., Crosbie, R., Rivett, T., McMaster, J., 2010. An evaluation of froth recovery measurement techniques. In: XXV International Mineral Processing Congress, Brisbane, Australia, Brisbane, Australia. Seaman, D.R., Manlapig, E.V., Franzidis, J.P., 2006. Selective transport of attached particles across the pulp-froth interface. Miner. Eng. 19 (6–8), 841–851. Vera, M.A., Franzidis, J.P., Manlapig, E.V., 1999. Simultaneous determination of collection zone rate constant and froth zone recovery in a mechanical flotation environment. Miner. Eng. 12 (10), 1163–1176. Yianatos, J.B., Moys, M.H., Contreras, F., Villanueva, A., 2008. Froth recovery of industrial flotation cells. Miner. Eng. 21 (12–14), 817–825.