Zinc Recovery from Lead-Zinc-Copper Complex Ores ...

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Zinc Recovery from a Lead-Zinc-Copper Ore by Ultrasonically Assisted Column Flotation a

Hulya Kursun & Ugur Ulusoy a

b

Department of Material and Metallurgical Engineering, Cumhuriyet University, Sivas, Turkey

b

Department of Mining Engineering, Cumhuriyet University, Sivas, Turkey Accepted author version posted online: 20 Oct 2014.

Click for updates To cite this article: Hulya Kursun & Ugur Ulusoy (2014): Zinc Recovery from a Lead-Zinc-Copper Ore by Ultrasonically Assisted Column Flotation, Particulate Science and Technology: An International Journal, DOI: 10.1080/02726351.2014.970314 To link to this article: http://dx.doi.org/10.1080/02726351.2014.970314

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Zinc Recovery from a Lead-Zinc-Copper Ore by Ultrasonically Assisted Column Flotation

Hulya Kursun1, Ugur Ulusoy2 1

Department of Material and Metallurgical Engineering, Cumhuriyet University, Sivas, Turkey, 2 Department of Mining Engineering, Cumhuriyet University, Sivas, Turkey

Downloaded by [Cumhuriyet University] at 01:14 15 June 2015

Corresponding author: E-mail address: [email protected].

Abstract In this study, zinc recovery from lead-zinc-copper ore was performed by column flotation with and without ultrasonic pre-treatment. Firstly, optimization of operational parameters was carried out by only single stage column flotation without ultrasonic pretreatment. A zinc concentrate containing 16.93 % Zn was obtained from the feed containing 2.71 % Zn with 29.41 % recovery using single stage column flotation. Secondly, a concentrate containing 24.51 % Zn was obtained with a recovery of 39.97 % when ultrasonic pretreatment was applied to zinc beneficiation by single stage column flotation at these optimized conditions. Thirdly, a zinc concentrate having 53.41 % Zn was produced with a recovery of 71.48 % by using 3 stages of cleaning and 3 stages of scavenging flotation by column. Finally, a zinc concentrate containing 73.32 % Zn was received with a recovery of 76.44 % when the ultrasonic pre-treatment was used before column flotation by multiple stages. The results revealed that, zinc grade and recovery were increased by ultrasonically assisted column flotation tests. It may be due to the increasing dispersion of ultrasound, increasing adsorption of collectors and the hydrodynamic cavitation which

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produced small bubbles attaching to the hydrophobic particles thereby increasing contact angle and attachment.

KEYWORDS: Lead-zinc-copper complex ore, Zn flotation, column flotation, ultrasonic treatment


1. INTRODUCTION Sound waves having frequencies higher than those to which the human ear can show a response (about 16 kHz) are called ultrasound. Power ultrasound (20-100 kHz) creates its effect by way of cavitation bubbles. When power ultrasound is applied to a mixture of particles and liquid, the bubbles collapse near a solid surface, a high-speed jet of liquid is driven into the particles and this jet can deposit enormous energy densities at the site of impact (Leonelli and Mason, 2010). It plays dominant role in the mineral surface. One of the ways of applying ultrasonic energy into fluid is to use an ultrasonic cleaning bath (Teipel et al., 2004).

Flotation is the most widely used separation process for the concentration of low grade complex Pb-Cu-Zn ores. It plays an important role in the mineral economies of the world since global zinc production in 2012 was reached to approximately 13 million tons (U.S. Geological Survey, 2013). The pulp must be conditioned before flotation in order to make valuable mineral hydrophobic. Since conditioning has a direct impact on the pulp residence time and plant throughput, various ways of facilitating conditioning process

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were investigated (Stassen, 1991; Bulatovic and Salter, 1989; Rubio and Brum, 1994, Aldrich and Feng, 1999).

Recently, application of ultrasonic treatment in flotation was studied by many researchers using different minerals and coal. The effects of ultrasonic treatment on the flotation of calcite, barite (Slaczka, 1987), quartz (Gurpınar et al., 2004; Gontijo et al., 2007), galena


(Çelik, 1989), Merensky complex sulphide ore (Aldrich and Feng, 1999), magnesite slime (Ozkan (2002), iron ore (Franko and Klima, 2002; Pandey et al. 2010), arsenopyrite (Misra et al., 2003), fine silica (Zhou, 1996; Zhou et al., 1994; 1997; 2009) and chalcopyrite (Çilek and Ozgen, 2010) were extensively studied. They reported that ultrasonic treatment has positive effect on the flotation performance and sometimes it may reduce reagents consumption. Ultrasonic pre-treatment used in the flotation of coal (Nicol et al., 1986; Celik, 1989; Buttermore and Slomka, 1991; Attalla et al., 2000; Jun et al., 2002; Ozkan and Kuyumcu, 2006, 2007; Kang et al., 2008; Ozkan, 2012; Tao et al., 2006; Qi and Aldrich, 2002) and oil shale (Altun et al., 2009) was also investigated by numerous researchers. They found that, it improved concentrate yield and reduced the ash content.

Column flotation provides higher concentration, more productivity, less cost of production, and better control of plant than the conventional flotation mainly due to the long retention time of the solid particles, countercurrent flow, contact pattern and the wash water added at the top of the froth (Finch and Dobby, 1990; Somasundaran, 1986;

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Kawatra and Eisele, 1987). Moreover, column flotation has an advantage in recovering of fine particles than conventional flotation.

In the recent study (Kursun and Ulusoy, 2012) positive effect of column flotation cell on the zinc recovery from lead-zinc-copper ore by comparing with the results of conventional flotation was reported. The effect of ultrasonic pre-treatment on the zinc


recovery from the same ore using column flotation was not studied yet. Therefore, the aim of this work is to investigate the effect of ultrasonic pre-treatment on the column flotation performances by single and multiple stages.

2. MATERIALS AND METHODS In this study, the same zinc ore (Kursun and Ulusoy, 2012) (Balıkesir–İvrindi) from Turkey was used in order to investigate the effect of ultrasonic pre-treatment on column flotation performance. It was taken from zinc feed of the selective zinc flotation circuit in a plant (GESOM A.Ş.) treating lead-zinc-copper complex ore. It contains Pb, Cu and Zn as 3.23%, 0.52% and 2.71%, respectively. The XRD of the ore was given previously by work of Kursun (2014). The particle size of the whole sample was below 74 micrometer as given in Figure 1.

Column flotation tests were accomplished in a tubular flotation column cell (Ünal Mühendislik A.Ş., Turkey) having a diameter of 5 cm and a height of 75 cm. Plexiglas (transparent) column which was assembled on a chassis, was used to observe the pulp/froth interface and control the flow conditions easily. A universal shower mounted

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on the top was used as the washing system. Peristaltic pumps (Watson Marlow 323U/D, England) were used for feeding and tailing discharge. The wash water was transferred to the column surface by a trunk working with a shower system. Pulp solid content was kept constant by preliminary tests. Bubbles were produced by air spargers (Ünal Mühendislik A.Ş.) with a pump having a maximum pressure greater than 0.012 MPa with 1.8 rpm. The air feed to column was adjusted by a flow meter (Ünal Mühendislik A.Ş.) at different air


rates. Wash water was added 2 cm above the froth surface. During the experiments, extra care was taken in order not to disturb the froth by the wash water added. The volume of the feed tank was measured as five times of the column volume.

Conditioning of the pulp was accomplished in a 12 liter laboratory-scale ultrasonic cleaning bath (United Ultrasonic Cleaner) which is capable of 40 kHz and a power of 600 watt. A mechanical stirrer (Heidolph RZR 2021, Germany) was attached to the top of the cleaning bath in order to stir the pulp. The pH of the pulp in the ultrasonic cleaning bath was controlled using a pH meter (WTW INO LAB 740, Germany) at about 25 °C. The experimental set-up used for the column flotation experiments was shown in Figure 2.

Experiments were performed firstly with single stage column flotation in order to optimize the selected flotation variables. Then, ultrasound assisted column flotation were tested at the optimized conditions. The pulp density was kept constant as 30% during the tests. After the optimization tests, KAX (Dow Chemical), CuSO4 (Merck), Aerofloat 211 (Cyanamid), 2-Ethyl hexanol (Merck) and Na2SiO3 (Merck) were used as collector, activator for sphalerite, collector for selective sphalerite flotation, frother and gangue

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depressant, respectively. They were allowed to be conditioned in ultrasonic cleaning bath for 5 min. before being fed into the column. When the column was filled with water and peristaltic pumps were started, the superficial air rate was determined. Then, the conditioned pulps and wash water were fed to the column. In order to keep the frother concentration constant the same amount of frother was added to the wash water tank as to the feeding tank. Otherwise, wash water will dilute the frother concentration in the


column. Pulp/water interface was kept constant during the tests. Tailing flow rate and superficial wash water rate were used as 0.437 cm/sec and 0.170 cm/sec, respectively. On the other hand, bias flow rate, superficial feed rate and superficial air rate was fixed as 0.0123 cm/sec, 0.425 cm/sec and 1.5 cm/sec, respectively.

Tap water (pH: 8.2) was used for the experiments and pH was set to approximately 11.5 by using lime (Merck). After a certain period of time the system was reached to steady state and became ready for column flotation experiments. Collected tailings and concentrates were weighed and analyzed. Experiments were repeated until the consistent grade and recovery values were obtained as 3 repetitions. After single stage column flotation with and without ultrasonic pre-treatment, multiple stages (3 stages of cleaning and 3 stages of scavenging) of column flotation tests were implemented with and without ultrasonic pre-treatment. Finally, results obtained by both flotation methods were compared.

Bubble diameters were measured by recording the bubbles for 40 sec. from the air-water phases (45 cm above the column base) using a camera (CANON EOS 5D-Mark II,

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Japan). Images were captured by illuminating the column and putting a black panel behind the wall. Camera was focused on midpoints of (both height and width) the front cross section of the column. Bubble diameters were measured on the milli-metric scale using a capture program running on the media player.

3. RESULTS AND DISCUSSION


3.1. Optimization Of The Column Flotation Conditions Effects of KAX dosage, 2-ethyl hexanol dosage, residence time, stirring speed, Na 2 SiO3 dosage, superficial air rate, superficial wash water rate and superficial feed rate were tested by the column flotation experiments to obtain optimum conditions. The fixed parameters for the effects of each variable (KAX dosage, 2-ethyl hexanol dosage, CuSO4 dosage, Aerofloat 211 dosage, Na 2SiO3 dosage, stirring speed, superficial wash water rate, superficial feed rate, superficial air rate and residence time) on the column flotation performance were given in Table 1.

3.1.1. Effect Of KAX Dosage Figure 3 (a) shows the variation of collector dosage with zinc grade and recovery. The highest values of grade and recovery were obtained at 90 g/t of KAX dosage as 17.13% and 30.48%, respectively. Further increase in the KAX dosage decreased zinc grade and recovery. It may be due to the decreasing adsorption of KAX onto zinc particles. Decreased zinc grade may also be attributed to the entrainment of gangue particles to the concentrate.

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3.1.2. Effect Of 2-Ethyl Hexanol Dosage Frother dosage which affects bubble size distribution and mean bubble size, determines the metallurgical performance since it changes surface tension of the liquid. The effect of 2-ethyl hexanol dosage on the zinc flotation performance was shown in Figure 3 (b). The optimum frother dosage was determined as 15 g/t, since the highest zinc grade and


recovery values were obtained at this dosage.

Increasing frother dosage caused the smaller bubbles which had lower rise velocity hence increased the gas hold up in the collection zone (Finch and Dobby, 1990; Goodall and O’Connor, 1992). Increasing superficial air rate increased the gas hold-up in the column. However, beyond a certain value of superficial air rate the bubbly flow regime in the column distorted and the churn-turbulent flow condition which is not desired for column operation were formed due to coalescence (Finch and Dobby, 1990; Hoffert, 1987; Kosick et al., 1988). Decreases in the zinc grade and recovery above the frother dosage of 15 g/t may be responsible for the churn-turbulent flow.

3.1.3. Effect Of Residence Time Figure 4 (a) illustrates the variation of flotation residence time with zinc grade and recovery. Zinc grade and recovery values were increased by increasing the residence time up to 4 min. Since the highest zinc grade (18.03%) and recovery (30.87%) were obtained, 4 min. was determined as optimum residence time. Further increments in residence time decreased the grade of concentrate. It may be due to increasing of gangue particles in the froth and increasing of distorted conditions related to froth-particle contact.

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3.1.4. Effect Of Stirring Speed The effect of stirring speed on the zinc flotation performance was given in Figure 4 (b). The optimum mechanical stirring speed was determined as 160 rpm, since the highest zinc grade and recovery were obtained at this speed. Above this value, grade was decreased much, but the recovery less. Decrease in the recovery may be due to the froth damaging which leads to the detachment of the particles from the froth. On the other


hand, decrease in the grade may be due to the entrainment of water (Akdemir and Güler, 2000; Deglon, 2005).

3.1.5. Effect Of Na2 SiO3 Dosage The effect of gangue depressant on the column flotation performance was given in Figure 5 (a). Increasing amount of Na2 SiO3 increased the zinc grade and recovery up to the 50 g/t. Further increase in Na2 SiO3 dosage decreased the grade much, but decreased the recovery little due to the less depressing effect of Na2SiO3. The highest values of zinc grade and recovery were obtained as 17.92% and 31.04%, respectively. Therefore, 50 g/t of Na2 SiO3 was determined as optimum dosage.

3.1.6. Effect Of Superficial Air Rate Figure 5 (b) illustrates the effect of superficial air rate on the column flotation performance. The superficial air rate controls the bubble size and gas holdup as well as turbulence created by the bubbles in the column. Increase in the superficial air rate increased the recovery, but decreased the zinc grade beyond the superficial air rate of 1.5 cm/sec. Bubbles were growth due to the coalescence, intensive slurry mixing and

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bursting. The bubbly flow conditions which were favored in column flotation were lost and turned to the churn-turbulent flow conditions. It was accompanied by large bubbles leading to the deterioration of flotation process (Burstein and Filippov, 2010). Decrease in the zinc grade was also attributed to the transition to churn-turbulent flow as evident by Fig. 6, which shows air bubble images captured at different air rates.


3.1.7. Effect Of Superficial Wash Water Rate The highest grade and recovery values were obtained at 0.170 cm/sec as seen from Figure 7 (a) for the investigation of the effect of superficial wash water rate on the column flotation performance. Both grade and recovery were decreased slightly beyond this level due to contamination of the concentrate by increasing of the mixed froth zone. This is in good agreement with the previously reported studies (Finch and Dobby, 1990; Coldea et al., 1996; Dalahmetoglu and Kemal, 1996; Yianatos et al., 1997; Tao et al., 2000a, b).

3.1.8. Effect Of Superficial Feed Rate The variation of superficial feed rate with column flotation performance was given in Figure 7 (b). As clearly seen from the Figure 7 (b), the highest zinc grade and recovery were obtained at 0.425 cm/sec. Zinc grade and flotation recovery were decreased beyond this optimum value of superficial feed rate. Reduced retention time may be responsible for the low recovery. Increasing feed rate created to the turbulence in the system flow and would contaminate the concentrate.

3.2. Effect Of Ultrasonic Pre-Treatment On The Column Flotation

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Ultrasonically assisted column flotation experiments were implemented for both single stage and multiple stages at the optimized flotation conditions (CuSO4 dosage: 400 g/t, Aerofloat 211 dosage: 100 g/t, 2-ethyl hexanol dosage: 15 g/t, Na2 SiO3 dosage: 50 g/t, KAX dosage: 90 g/t, stirring speed: 160 rpm, superficial wash water rate: 0.170 cm/sec, superficial feed rate: 0.425 cm/sec, superficial air rate: 1.5 cm/sec and residence time: 4


min.).

3.2.1. Single Stage Test Comparing the zinc grade and recovery values by single stage column flotation with and without ultrasonic pretreatment (Figure 8 (a)), the zinc grade was increased 7.58 units (from 16.93% to 24.51%) while the recovery was increased 10.56 units (from 29.41% to 39.97%).

3.2.2. Multiple Stages Test When 3 stages of cleaning and 3 stages of scavenging (Figure 8 (b)) flotation experiments carried out, zinc grade of the final concentrate was increased from 53.41% to 73.32% (19.91 units). On the other hand, zinc recovery was increased from 71.48% to 76.44% (4.96 units). These findings are in good agreement with the previously reported studies (Qi and Aldrich, 2002; Zhou et al., 1994; Gontijo et al., 2007; Ozkan and Kuyumcu, 2007).

Both improvements in the zinc grade and recovery may be attributed to the dispersing effects of ultrasound, increasing adsorption of collectors on the particle

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surfaces. It may also be due to the hydrodynamic cavitation which produced small bubbles (Qi and Aldrich, 2002; Zhou et al., 1994; Gontijo et al., 2007) attaching to the hydrophobic particles and leading to the agglomeration of ultrafine particles by bubble bridging, making them as if they were larger particles of higher probability of attachment to the large bubbles in a flotation cell thereby increasing contact angle, attachment forces, the bubble-particle collision efficiency and better flotation


recovery (Zhou et al., 1994; 1997; Misra et al., 2003). Fig. 9 shows bubble-particle aggregates formed by attachment of the small bubbles on the hydrophobic particles. It supports the improvements in flotation performance (Zhou et al., 2009; Gontijo et al., 2007).

It should be noted that, when the same ore was beneficiated by conventional flotation without ultrasonic pretreatment, zinc concentrate having 52.77% Zn was produced with a 61.38% recovery (Kursun and Ulusoy, 2012). After the same ore was concentrated by multiple stages (3 stages of cleaning and 3 stages of scavenging) of column flotation, zinc grade and recovery were raised only to 58.81% and 74.21%, respectively.

In the recent study (Kursun, 2014) the effect of ultrasonic pretreatment on the conventional flotation of the same ore was investigated. A zinc concentrate containing 8.52 % Zn was obtained from feed containing 1.60 %Zn with 24.64 % recovery using mechanical flotation method without ultrasonic pretreatment. On the other hand, a concentrate containing 18.73 %Zn was obtained with 33.18 %

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recovery using flotation with ultrasonic pretreatment. This study has also emphasized the positive effect of ultrasonic pre-treatment on the conventional flotation.

In the light of the findings above, the highest zinc grade and flotation recovery for the same ore was obtained by ultrasonically assisted column flotation method. The


reason for this improvement is the positive effect of ultrasonic pretreatment on the flotation. Whatever the reasons, the findings from this work strongly suggests that the ultrasonic pre-treatment is vital for the column flotation.

4. CONCLUSIONS Operational parameters which affect column flotation were optimized by single stage column flotation without ultrasonic pre-treatment. After the optimization tests, CuSO 4 dosage, Aerofloat 211 dosage, 2-ethyl hexanol dosage, Na2SiO3 dosage, KAX dosage, stirring speed, superficial wash water rate, superficial feed rate, superficial air rate and residence time were determined as optimum at 400 g/t, 100 g/t, 15 g/t, 50 g/t, 90 g/t, 160 rpm, 0.170 cm/sec, 0.425 cm/sec, 1.5 cm/sec and 4 min., respectively.

When single stage column flotation with ultrasonic pre-treatment was performed, zinc grade was increased from 16.93 to 24.51% while the recovery was increased from 29.41% to 39.97%.

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When multiple stages of column flotation (3 stages of cleaning and 3 stages of scavenging) with ultrasonic pre-treatment were done, the zinc grade was increased from 53.41% to 73.32%. But, the recovery was increased only from 71.48% to 76.44%.

Ultrasound pre-treatment has improved column flotation performance with respect to zinc grade and recovery in both single stage and multiple stages of column flotation. It may be


due to the increasing dispersion, adsorption of collectors and the hydrodynamic cavitation which produced small bubbles attaching to the hydrophobic particles thereby increasing contact angle and attachment forces causing bubble-particle collision efficiency and better flotation recovery.

Future feasibility studies and scale-up works are recommended for the application of ultrasonic equipment in industrial flotation plants.

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Table 1. The fixed flotation variables for the optimization. Variable

a

b

c

d

e

f

g

h

KAX

-

90

90

90

90

90

90

90

CuSO4 (g/t)

400

400

400

400

400

400

400

400

Aerofloat 211 (g/t)

100

100

100

100

100

100

100

100

Na2SiO3 (g/t)

50

50

50

50

-

50

50

50

2-ethyl hexanol (g/t)

15

-

15

15

15

15

15

15

Stirring speed (rpm)

160

160

160

-

160

160

160

160

Superficial wash water rate

0.170

0.170

0.170

0.170

0.170

0.170

-

0.170

Superficial feed rate (cm/sec)

0.425

0.425

0.425

0.425

0.425

0.425

0.425 -

Superficial air rate (cm/sec)

1.5

1.5

1.5

1.5

1.5

-

1.5

1.5

Residence time (min.)

4

4

-

4

4

4

4

4

(cm/sec)

a: effect of KAX dosage, b: effect of 2-ethyl hexanol, c: effect of residence time, d: effect of stirring speed, e: effect of Na2 SiO3 dosage, f: effect of superficial air rate, g: effect of superficial wash water rate, h: effect of superficial feed rate

20


Figure 1. The particle size distribution of the sample used in column flotation test s.

21


Figure 2. The experimental set-up used in this study.

22

Figure 3. Effects of KAX (a) and 2 -ethyl hexanol (b) dosages on the zinc grade and


recovery.

23

Figure 4. Effects of residence time (a) and stirring speed (b) on the zinc grade and


recovery.

24

Figure 5. Effects of Na 2 SiO 3 dosage (a) and superficial air rate (b) on the zinc grade


and recovery.

25

Figure 6. Bubble pictures photographed at different air rates a) 0.5 cm/sec, b) 1


cm/sec, c) 1.5 cm/sec, d) 2 cm/sec, e) greater than 2 cm/sec.

26

Figure 7. Effect of superficial wash water rate (a) and superficial feed rate (b) on the


zinc grade and recovery.

27

Figure 8. Effect of ultrasonic treatment on the performance of single stage (a) and


multiple stages (b) zinc column flotation.

28

Figure 9. The bubble-particle aggregates observed by column flotation with


ultrasonic pre-treatment.

29