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Froth flotation of sphalerite: Collector concentration, gas dispersion and particle size effects R. Pérez-Garibay a,, N. Ramírez-Aguilera a , J. Bouchard b , J. Rubio c a Cinvestav-IPN, Industria Metalúrgica 1062, Parque Industrial Ramos Arizpe-Saltillo, Ramos Arizpe, Coahuila, C.P. 25900, Mexico b LOOP (Laboratoire d’observation et d’optimisation des procédés), Département de génie des mines, de la métallurgie et des matériaux, Université Laval, Québec, Canada c Laboratório de Tecnologia Mineral e Ambiental (LTM), Departamento de Engenharia de Minas, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil article info Article history: Received 29 July 2013 Accepted 18 December 2013 Available online 11 January 2014 Keywords: Flotation Bubble-clusters Sphalerite Bubble size distribution Gas dispersion properties abstract This experimental work on sphalerite flotation investigated the effect on flotation performance of three particle size fractions, namely, coarse (d 80 = 100 lm), medium (d 80 = 39 lm) and fine (d 80 = 15 lm), bub- ble size distribution, superficial air velocity, and collector dosage. Bubble size distributions were charac- terized with the image analysis technique. The two-phase (liquid–gas) centrifugal pump and frother addition (MIBC, 5–30 ppm) allowed generating bubble diameters between 150 and 1050 lm, and air holdup ranging from 0.2% and 1.3%. Main results showed that each particle-size distribution required an optimal bubble-size profile, and that sphalerite recovery proceeded from mechanisms involving true flotation (when J g = 0.04 cm/s and 1.9 10 4 M SIPX). However, cluster-flotation occurs at high collector dosage (when J g = 0.04 cm/s and d 32 between 285 and 1030 lm), and requiring further investigation. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The future of mineral processing appears to be residing in treat- ing low-grade, multi-components, and complex mineral deposits, for which adjusting flotation operations for both coarse and fine particles at the same time becomes a forefront issue (Gontijo et al., 2007; Jameson, 2010). Fine grinding produces significant amounts of slimes (diameters of a few microns or less), thus result- ing in well-known issues in flotation recoveries (mainly low prob- ability of capture). Similarly, the flotation of coarse particles remains nowadays challenging, as it is extensively discussed and fairly well documented in several papers and theories (Jameson, 2010; Tao, 2005). Processing challenging ores through separate flotation circuits for coarse and fine particles would reduce the impact of the above- mentioned issues. This however, is generally not an option, and other options have to be explored such as optimizing operating conditions, or combining flotation with elutriation using an up- ward water flow, like in a hydroseparator (Mankosa et al., 2002; Kohmuench et al., 2007). On a surface area standpoint, the collector coverage may be uni- form with fine and coarse particles, and with this regard, the poorer recovery of coarse particles may mean that larger particles need to be more hydrophobic than fine to be recovered (Trahar, 1981). It has also been postulated that slower kinetics for the upper end of the size distribution would likely result from detachment, rather than to a lower adhesion probability (Jameson, 2012). Con- sidering as well the simple issue of bubble lifting capacity, with re- spect to their size, the problem of determining adequate bubble diameters for the flotation of a population of particles exhibiting a broad size distribution is not a simple one. Rubio et al. (2003, 2006), investigated the effect of mixing bub- bles generated in conventional cells (600–2000 lm in diameter) with finer bubbles, ranging from 50 to 200 lm in diameter, pro- duced by drawing air through an aspiration nozzle with water. They concluded that: conventional flotation cells do not generate bubbles smaller than 600 lm, thus preferentially floating coarse particles, and widening the bubble size distribution in the cell, through the injection of small bubbles, increases the bubble sur- face flux, thus significantly improving fine particle collection (Hie- skanen, 2000; Waters et al., 2008). The authors also claim that the results are in accordance with most of the reported models showing that improved particle col- lection (magnitude and kinetics) is the main challenge in flotation of fine particles (Yoon, 1999, 2000; Franzidis and Manlapig, 1999). Liu and Schwarz (2009)studied the effect of particle size in con- ventional froth flotation using galena and quartz particles, observ- ing that the probability of particle-bubble collision decreases with the particle size, indicating that the use of small bubbles could im- prove recovery. Similarly, Yoon (2000) suggests that the ultrafine 0892-6875/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.mineng.2013.12.020 Corresponding author. Tel./fax: +52 844 4389600. E-mail address: [email protected] (R. Pérez-Garibay). Minerals Engineering 57 (2014) 72–78 Contents lists available at ScienceDirect Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
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Page 1: Froth flotation of sphalerite: Collector … flotation of...Froth flotation of sphalerite: Collector concentration, gas dispersion and particle size effects R. Pérez-Garibaya, ,

Minerals Engineering 57 (2014) 72–78

Contents lists available at ScienceDirect

Minerals Engineering

journal homepage: www.elsevier .com/ locate/mineng

Froth flotation of sphalerite: Collector concentration, gas dispersionand particle size effects

0892-6875/$ - see front matter � 2014 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.mineng.2013.12.020

⇑ Corresponding author. Tel./fax: +52 844 4389600.E-mail address: [email protected] (R. Pérez-Garibay).

R. Pérez-Garibay a,⇑, N. Ramírez-Aguilera a, J. Bouchard b, J. Rubio c

a Cinvestav-IPN, Industria Metalúrgica 1062, Parque Industrial Ramos Arizpe-Saltillo, Ramos Arizpe, Coahuila, C.P. 25900, Mexicob LOOP (Laboratoire d’observation et d’optimisation des procédés), Département de génie des mines, de la métallurgie et des matériaux, Université Laval, Québec, Canadac Laboratório de Tecnologia Mineral e Ambiental (LTM), Departamento de Engenharia de Minas, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil

a r t i c l e i n f o

Article history:Received 29 July 2013Accepted 18 December 2013Available online 11 January 2014

Keywords:FlotationBubble-clustersSphaleriteBubble size distributionGas dispersion properties

a b s t r a c t

This experimental work on sphalerite flotation investigated the effect on flotation performance of threeparticle size fractions, namely, coarse (d80 = 100 lm), medium (d80 = 39 lm) and fine (d80 = 15 lm), bub-ble size distribution, superficial air velocity, and collector dosage. Bubble size distributions were charac-terized with the image analysis technique. The two-phase (liquid–gas) centrifugal pump and frotheraddition (MIBC, 5–30 ppm) allowed generating bubble diameters between 150 and 1050 lm, and airholdup ranging from 0.2% and 1.3%. Main results showed that each particle-size distribution requiredan optimal bubble-size profile, and that sphalerite recovery proceeded from mechanisms involving trueflotation (when Jg = 0.04 cm/s and 1.9 � 10�4 M SIPX). However, cluster-flotation occurs at high collectordosage (when Jg = 0.04 cm/s and d32 between 285 and 1030 lm), and requiring further investigation.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

The future of mineral processing appears to be residing in treat-ing low-grade, multi-components, and complex mineral deposits,for which adjusting flotation operations for both coarse and fineparticles at the same time becomes a forefront issue (Gontijoet al., 2007; Jameson, 2010). Fine grinding produces significantamounts of slimes (diameters of a few microns or less), thus result-ing in well-known issues in flotation recoveries (mainly low prob-ability of capture). Similarly, the flotation of coarse particlesremains nowadays challenging, as it is extensively discussed andfairly well documented in several papers and theories (Jameson,2010; Tao, 2005).

Processing challenging ores through separate flotation circuitsfor coarse and fine particles would reduce the impact of the above-mentioned issues. This however, is generally not an option, andother options have to be explored such as optimizing operatingconditions, or combining flotation with elutriation using an up-ward water flow, like in a hydroseparator (Mankosa et al., 2002;Kohmuench et al., 2007).

On a surface area standpoint, the collector coverage may be uni-form with fine and coarse particles, and with this regard, thepoorer recovery of coarse particles may mean that larger particles

need to be more hydrophobic than fine to be recovered (Trahar,1981). It has also been postulated that slower kinetics for the upperend of the size distribution would likely result from detachment,rather than to a lower adhesion probability (Jameson, 2012). Con-sidering as well the simple issue of bubble lifting capacity, with re-spect to their size, the problem of determining adequate bubblediameters for the flotation of a population of particles exhibitinga broad size distribution is not a simple one.

Rubio et al. (2003, 2006), investigated the effect of mixing bub-bles generated in conventional cells (600–2000 lm in diameter)with finer bubbles, ranging from 50 to 200 lm in diameter, pro-duced by drawing air through an aspiration nozzle with water.They concluded that: conventional flotation cells do not generatebubbles smaller than 600 lm, thus preferentially floating coarseparticles, and widening the bubble size distribution in the cell,through the injection of small bubbles, increases the bubble sur-face flux, thus significantly improving fine particle collection (Hie-skanen, 2000; Waters et al., 2008).

The authors also claim that the results are in accordance withmost of the reported models showing that improved particle col-lection (magnitude and kinetics) is the main challenge in flotationof fine particles (Yoon, 1999, 2000; Franzidis and Manlapig, 1999).

Liu and Schwarz (2009)studied the effect of particle size in con-ventional froth flotation using galena and quartz particles, observ-ing that the probability of particle-bubble collision decreases withthe particle size, indicating that the use of small bubbles could im-prove recovery. Similarly, Yoon (2000) suggests that the ultrafine

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R. Pérez-Garibay et al. / Minerals Engineering 57 (2014) 72–78 73

particles might be floated with smaller bubbles and fine/mid-sizedparticles with the bigger bubbles.

Studying the effect of the bubble size in air dissolved flotation(DAF) using a mathematical model (trajectories analyses), Hanet al. (2007) showed that maximal collision efficiency is reachedwhen the bubble size and particle size are appropriated. Accordingto Pease et al. (2005), the adhesion of fine particles on bubbles in-creases with collector addition and mixing intensity, both promot-ing particle-bubble collision. The authors conducted someexperiments floating sphalerite at Mount Isa Mines (Australia),finding higher recoveries with particle size between 4 and38 lm. In conventional flotation, the collector addition is around30 g/ton of solids, while it can reach 1500 g/ton for fine particles(Duarte and Grano, 2007).

The objective of this paper is to study the flotation of coarse,medium and fine sphalerite particles with bubbles generated usinga two phases (liquid–gas) centrifugal pump, and assess the com-bined effect of the collector dosage, bubble/particle size distribu-tions, and gas dispersion properties.

0

20

40

60

80

100

100101

Cum

ulat

ive

volu

me

pass

ing,

%

Particle size, μm

FineMediumCoarse

d80 d

d80

80=15 μm. =100μm.

=39 μm.

Fig. 1. Size distribution of the sphalerite flotation feed material.

10

10

Tails

Pulp

Feed

Concentrated2

4

7

8

9

Fig. 2. Experimenta

2. Experimental

2.1. Material

The feed material, consisting in sphalerite lumps (enriched ore)from a Mexican plant (59.2% Zn, 6.2% Fe, 0.08% Cu, 0.03% Pb, 30.1%S, 4.4% ins.), was ground to obtain three sub-samples, each oneexhibiting a different size distribution (determined by laser diffrac-tion Coulter LS100), i.e. following Rubio et al. (2003): fine(d80 = 15 lm), medium (d80 = 39 lm), and coarse (d80 = 100 lm)(see Fig. 1).

2.2. Experimental set-up

Fig. 2 depicts the experimental set-up. A modulating peristalticpump adjusts the flotation column feed and tailings rates. The bub-ble dispersion is generated and transported by a centrifugal pump(Nikuni

�: 15 L/min, 3500 rpm and 0.25 hp). Both the slurry and bub-

ble dispersion are introduced together in the column through a sta-tic mixer to maximize the probability of bubble-particle contact.

Commercial spargers typically generate relatively coarse bub-bles (between 1 and 3 mm) (López-Saucedo et al., 2012) that arenot suitable for achieving high recovery of fine particles. Thisinvestigation required finer bubble size distributions, and thethree-phase centrifugal pump (Nikuni

�), able to produce bubble

ranging from 10 to 1200 lm, was selected for this purpose. It isworth mentioning that the centrifugal pump / bubble generatorhas a limited capacity to produce high superficial gas rate (Jg), evenat very high shear water flow rate. This however was not a limita-tion as the objective was to study the relationship between thebubble and particle size independently of the value of Jg. Moreover,operating at lower aeration conditions prevented introducing fastflotation kinetics for all particle size distributions, which wouldhave masked the main studied effects, namely the bubble sizeand collector dosage.

Inside the squared column (wide: 23.4 cm and height: 205 cm),a vertical wall splits the cell into two distinct compartments: one

11

5

3

A1

1. - Flotation column2. - Window3. - Centrifugal pump4. - Mixing thank5. - Air rotameter6. - Air rotameter7. - Temperature controller8. - Peristaltic pomp9. - Photographical camera10. - Static mixer11. - Froth breaker

6

l flotation rig.

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74 R. Pérez-Garibay et al. / Minerals Engineering 57 (2014) 72–78

for flotation (left hand side in Fig. 2), and the other for tailings sol-ids/liquid separation (right hand side in Fig. 2). Clear water result-ing from particle settling accumulates in the upper zone (zone A ofthe column; see Fig. 2), and is recycled as shear water for bubblegeneration using the centrifugal pump.

A three-way valve mounted on the feed line allows taking sam-ples for particle size analysis.

The bubble size distribution is measured by image analysis. Adigital camera (Canon

�model EOS Rebel Xi) equipped with a

high-resolution lens (Canon�

model MP-E 65 mm) captures the pic-tures through window allowing bubble visualization. Pérez-Gari-bay et al. (2012) describes the image acquisition and analysissystem with greater details.

The bubble size distribution was determined beforehand, i.e.the pre-characterization stage, for a given frother dosage (methylisobutyl carbinol, MIBC) in aqueous solution to avoid the problems,due to the turbidity, of bubble visualization in a slurry. Imageacquisition started after feeding the bubble-solution (2-phaseoperation) to the column for 15 min at given experimental condi-tions. The resulting computed bubble size distribution was as-sumed to remain the same for the slurry operation. The columnfeed temperature was kept constant at 30 �C during both the pre-characterization stage (2-phase) and normal operation.

The difference of pulp level between normal (hl+g, aerated slur-ry) and airless (hl, after stopping air injection) operations served toestimate the air holdup (eg) as

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0Cf (MIBC)10 ppm20 ppm30 ppm

Jg = 0.02 cm/s.

Jl = 1.02 cm/s.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0Cf (MIBC)10 ppm20 ppm30 ppm

Jg = 0.06 cm/s.Jl = 0.98 cm/s.

Den

sity

fun

ctio

n, %

/μm

Den

sity

fun

ctio

n, %

/μm

Bubble diameter (d32, μm)

0 200 400 600 800 1000 1200

0 200 400 600 800 1000 1200

(a)

(c)

Fig. 3. Effect of the frother concentration on the bubbles size distribution at four differens.

eg ¼ ½hlþg þ hl�=hl ð1Þ

Images require being pre-processed to update the format andresolution (using VSO Image Resizer). A specialised software pro-gram (Northern Eclipse

�) performs the bubble detection and diam-

eter measurement (di), and allows computing the Sauter diameter(d32), defined as

d32 ¼X

d3i

.Xd2

i ð2Þ

Flotation tests were conducted in a 23-cm square section per175-cm high laboratory flotation. Sodium isopropyl xanthate(SIPX) and copper sulfate (1.9 � 10�4 M) respectively served as col-lector and the activator.

Overflowing froth was broken with an auxiliary system forremoval or recycling to the feed tank (200 L), thus allowing aclosed-circuit operation. An electrical resistance combined to acontroller kept the temperature constant at 30 �C,approximately.

The trials were conducted with 2.5% (w/w) solids content andappropriate MIBC dosage (5, 10, 20, 30 and 40 ppm). Obtaining astable operation in the solids/liquid separation compartment re-quired running the column for an hour before initiating an actualtrial. The system was then operated for 30 min to ensure reachingsteady-state before sampling the feed, tailings and concentratestreams. Samples were filtrated, dried and assayed to assess themetallurgical performance.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0Cf (MIBC)10 ppm20 ppm30 ppm

Jg = 0.04 cm/s.Jl = 1.0 cm/s.

Bubble diameter (d32, μm)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 200 400 600 800 1000 1200

0 200 400 600 800 1000 1200

Cf (MIBC)10 ppm20 ppm30 ppm

Jg = 0.08 cm/sJl = 0.9 cm/s.

(b)

(d)

t air superficial velocities: (a) 0.02 cm/s, (b) 0.04 cm/s, (c) 0.06 cm/s and (d) 0.08 cm/

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R. Pérez-Garibay et al. / Minerals Engineering 57 (2014) 72–78 75

3. Results and discussion

3.1. Bubbles characterization

Fig. 3 shows the function density of the bubble size distribu-tions generated in the two-phase pre-characterization stage. In or-der to increase the precision in the bubble size determination, 250pictures were analyzed, accounting for nearly 700 bubbles, in eachexperiment. The figure shows the effects of frother concentration,decreasing the bubble size, and tightening the distribution.

Fig. 4a shows the air holdup (eg) as a function of the superficialair velocity (Jg) and the frother concentration. In all three frotherconcentrations, results show a nearly proportional variation of eg

with Jg for the tested range. This linear relationship between eg

and Jg is common in mechanical cells and industrial flotation col-umns. It is sometimes used to define the ‘operating Jg range’ of acell (Dahlke et al., 2005). Because air gas holdup is not always mea-sured on-line, the control of the superficial air velocity is a practicalform for manipulating the gas hodup and the bubble surface areaflux.

Fig. 4b shows the effect of three frother concentrations on theair holdup and the bubble surface area flux. The frother concentra-tion increases both the bubble surface area flux and air holdup, assmaller bubbles (high specific area) are created at higher frotherdosage (see Fig. 3). This is in accordance with general expectationsand other observations (Matiolo et al., 2011).

3.2. Sphalerite flotation

Flotation of sphalerite was studied as a function of bubblediameter, air superficial velocity, collector concentration, and par-ticle size (d80).

Results presented assume that the bubble size does not signifi-cantly change with solids content (Goodall and O’Connor, 1991;Zhang et al., 2002). The same hypothesis cannot be postulatedfor the air holdup since empirical evidence suggests that it canbe affected in presence of solids (loaded bubbles) (Yianatos et al.,1988; Pérez-Garibay et al., 2002).

Fig. 5 shows flotation recoveries for sphalerite at three differentSIPX concentrations (low, medium and high), two air superficialvelocities (0.04 cm/s and 0.08 cm/s), and as a function of bubble

0.0

0.3

0.6

0.9

1.2

1.5

1.8

Jg, cm/s

Cf (MIBC)

10 ppm20 ppm30 ppm

0.00 0.02 0.04 0.06 0.08 0.10

Air

hol

dup

( εg,

%)

(a)

Fig. 4. (a) Effect of the frother concentration and the superficial air velocity (Jg) on the aifrother concentrations (MIBC).

size distribution. Results show a maximum in particles recovery,which varies with the average bubble size (d32), average particlesize (d80) and superficial velocity (Jg). As expected, all these vari-ables highly influenced the recovery of sphalerite because of thevarious flotation mechanisms, e.g. particles capture by bubbles(collision and adhesion), collector adsorption and clusters-formation effects.

The following discussion is divided in three parts, according tothe SIPX concentration (low, medium, and high).

(1) Flotation at low collector concentration – 3.8 � 10�5 M SIPXHere, flotation recoveries were very poor and similar in allcases, slightly increasing with the superficial velocity andcoarser bubbles, probably due to higher probability of colli-sion. The low collector coverage, leading to low particleshydrophobicity, obviously plays a key role for this behavior(see Fig. 5a and b).

(2) Flotation at medium collector concentration – 6.3 � 10�5 MSIPX Recoveries were lower for all particles classes, espe-cially for the fine fractions, probably due to the effect ofinsufficient hydrophobicity (lower SIPX dosage) or lowerprobability of capture. In common understanding is itaccepted that fine particles are less influenced by collectordosage (Trahar, 1981). However this is not in accordancewith results presented in Fig. 5, showing a significant effecton fine particles. The high superficial area of fine particles,which would exhibit – or require – higher collector adsorp-tion rates could probably explain this result. The recovery ofthe medium sized sphalerite fractions is very poor at lowersuperficial velocities, but increases over 20 points for thehighest Jg values. Interestingly, the maximum yield in allcases was attained with larger bubbles, which may beexplained by a higher probability of collision-adhesion (fas-ter film thinning), and more particle entrainment.

(3) Flotation at high collector concentration – 1.9 � 10�4 M SIPXFor the lowest Jg (0.04 cm/s) the highest recovery is attainedwith relatively small bubbles (150–300 lm range) for allparticle size classes. It is still unclear at this stage whetherthis result is a ‘true’ maximum as finer bubbles were nottested. The actual trend below 200 lm remains to be deter-mined. Recoveries exceeded 95% for the coarser particles,

0

2

4

6

8

10

12

14

0.0 0.5 1.0 1.5

εg, %

Cf (MIBC)

10 ppm

20 ppm

30 ppm

Bub

ble

surf

ace

area

flu

x (S

b, s-1

)

(b)

r holdup (eg), (b) Effect of the air holdup on the bubble surface area flux (Sb) at three

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0

20

40

60

80

100

FinesMediumCoarse

Jg= 0.04 cm/s

Rec

over

y, %

0

20

40

60

80

100

FinesMediumCoarse

Jg = 0.08 cm/s

0 150 300 450 600 750 900 1050 0 150 300 450 600 750 900 1050

0 150 300 450 600 750 900 10500 150 300 450 600 750 900 1050

0 150 300 450 600 750 900 10500 150 300 450 600 750 900 1050

3.8x10-5 M SIPX (Low) 3.8x10-5 M SIPX (Low)

0

20

40

60

80

100

Rec

over

y, %

FinesMediumCoarse

Jg = 0.04 cm/s

0

20

40

60

80

100

FinesMedium

Coarse

Jg = 0.08 cm/s

6.3x10-5 M SIPX (Medium) 6.3x10-5 M SIPX (Medium)

0

20

40

60

80

100

Rec

over

y, %

Fines

MediumCoarse

Jg= 0.04 cm/s

0

20

40

60

80

100

FinesMedium

Coarse

Jg = 0.08 cm/s1.9x10-4 M SIPX (High) 1.9x10-4 M SIPX (High)

Bubble diameter (d32, μm) Bubble diameter (d32, μm)

Bubble diameter (d32, μm) Bubble diameter (d32, μm)

Bubble diameter (d32, μm) Bubble diameter (d32, μm)

(a) (b)

(c) (d)

(e) (f)

Fig. 5. Effect of the bubble diameter on concentrate recovery at three different collector concentration and two superficial velocities (T = 30 �C, pH = 10). (a) Jg = 0.04 cm/s and3.8 � 10�5 M SIPX, (b) Jg = 0.08 cm/s and 3.8 � 10�5 M SIPX. (c) Jg = 0.04 cm/s and 6.3 � 10�5 M SIPX, (d) Jg = 0.08 cm/s and 6.3 � 10�5 M SIPX. (e) Jg = 0.04 cm/s and 1.9 � 10�4

M SIPX. (f) Jg = 0.08 cm/s and 1.9 � 10�4 M Xanthate.

76 R. Pérez-Garibay et al. / Minerals Engineering 57 (2014) 72–78

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Fig. 6. Sphalerite cluster (bubbles-coarse particles) formed at high collectorconcentration – 1.9 � 10�4 M SIPX.

Cum

ulat

ive

volu

me

pass

ing,

%

0

20

40

60

80

100

1 10 100

1030285

d32 (μm)(a)

Particle size, μm

Medium

Bubble diameter

3.8x10-5 M SIPX

Fig. 7. Particle size distribution of concentrates floated with two bubble size distributionsand (b) coarse particles with 1.9 � 10�4 M SIPX.

0

200

400

600

800

1000

1200

0 20 40 60 80 100 120

Bub

ble

diam

eter

, (d 32

, μm

)

Particle size of concentrate (d80), μm

SIPX M, Jg cm/s

6.3X10-5 0.04

6.3X10-5 0.08

3.8X10-5 0.04

3.8X10-5 0.08

SphaleriteSphaleriteh

(a)

Fig. 8. (a) True flotation domains of sphalerite, as a function of the particle size of the conparticle size, bubble diameter and the domains of recovery.

R. Pérez-Garibay et al. / Minerals Engineering 57 (2014) 72–78 77

and around 50% for the medium and fines. It is worth men-tioning that the results exhibit a certain dispersion for the‘optimal’ mean bubble size diameter, which suggests to bein agreement with the premise ‘for each particle size distri-bution, there is an optimal bubble size distribution for amaximum flotation recovery’ (Han et al., 2007; Pease et al.,2005).

This situation slightly changes at higher Jg (0.08 cm/s), with themaximum recovery attained with 300 lm bubbles (for all classes).These recoveries were high in all cases, reaching almost 95% coar-ser sphalerite, compared to 55–58% for the medium and fines. Theeffect of the higher air superficial velocity clear (yielding higherrecoveries) is not surprising and follow the general understanding.

Fig. 6 shows a picture of sphalerite clusters (bubbles-coarse par-ticles) formed at high collector concentration. It must be empha-sised that the clusters appear only to occur with coarse particles

0

20

40

60

80

100

d32 (μm)(b)

Coarse

Bubble diameter

1 10 100

Particle size, μm

1.9x10-4 M SIPX

1030285

. (T = 30 �C, pH = 10 and Jg = 0.08 cm/s). (a) medium particles with 3.8 � 10�5 M SIPX

Rec

over

y, %

100

80

60

40

20

0

200400

600

8001000

1200

2040

6080

100

(b)

centrate (d80) bubble d32, and two SIPX concentrations. (b) Relationship between the

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78 R. Pérez-Garibay et al. / Minerals Engineering 57 (2014) 72–78

fully covered by collector. Bubble-particle clusters formation prob-ably proceeds according to the following mechanism:

(1) A bubble attaches to a coarse particle forming a primarynucleus.

(2) Other particles and bubbles colliding with the primarynucleus initiate the growth of the cluster.

(3) As the available area increases, all types of particles arebeing capture (attach or entrain) by the cluster.

Fig. 7 depicts the particle size distribution of concentrates ob-tained with two different bubble size distributions at high andmedium SIPX concentration.

Fig. 7a suggests that, for the medium feed size where no clus-ters were observed, the sphalerite particle size distribution in theconcentrates is not independent of the bubble size distribution(d32: 285 lm and 1030 lm), although the magnitude of the effectis not very high. As it is generally assumed for a true flotationmechanism (Warren, 1985), better the bubbles match the particlesize distribution (i.e. large/small bubbles for coarse/fine particles,respectively), better is the recovery.

On the other hand, Fig. 7b indicates that the size distribution ofsphalerite particles in the concentrates was not influenced by theaverage bubble size (d32: 285 lm and 1030 lm). This suggests thatfor coarse particle flotation, similar clusters are formed regardlessof the bubble size distribution.

Fig. 8a summarizes recovery results (domains) at 3.8 � 10�5

and 6.3 � 10�5 M SIPX (low and medium concentrations) as a func-tion of two variables: bubble size (d32) and particle size of the con-centrates (d80). It is assumed that in these cases, particles arerecovered only by true flotation, i.e. neither the cluster flotationmechanism discussed before at high SIPX dosage occurs, nor signif-icant mechanical entrainment. Empirical results suggest that coar-ser particle flotation requires bigger bubbles, which follows theconclusion of model-based investigations (Yoon, 1999, 2000). Sim-ilarly, Fig. 8b shows the relationship between bubble size, particlesize of the concentrates and the domains of recoveries.

4. Conclusions

This empirical study investigated the effect on sphalerite flota-tion of the feed and bubble size distributions, superficial air veloc-ity, and collector dosage. Results showed that the recovery highlydepends on these factors. The carrying capacity of the smaller bub-bles was found to be higher for the fine than for the coarser sphal-erite. This is explained by the reduced mass of individual particles,and higher bubble surface available.

At high SIPX concentration and low Jg (0.04 cm/s) there is a dif-ferent optimal bubble size distribution, leading to maximumrecovery, for each particle size distribution. Interestingly, this phe-nomenon did not occur at high Jg values (0.08 cm/s), and the max-imum was reached for the same d32 (300 lm), ranging from low(50–55%) for the fine and medium feed (15 6 d80 6 39 lm), to high(�95%) for the coarse particles (d80 = 100 lm). Under these condi-tions, the coarser particles formed bubble-particle clusters. Thebubbles (d32: 285 and 1030 lm) were found to be not selectiveand readily attach to these clusters, thus suggesting that uncon-ventional flotation mechanisms are present with the bubbles beingeither attached or trapped.

Acknowledgments

The authors are grateful to CONACYT (Mexico) for providing ascholarship and other financial support. Jorge Rubio wants toacknowledge CNPq for financial assistance.

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