Performance and selectivity of the new column flotoextraction method

Minerals Engineering 71 (2015) 27–33

Contents lists available at ScienceDirect

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

Performance and selectivity of the new column flotoextraction method M.R. Tavakoli Mohammadi a,⇑, S.M. Javad Koleini a, H. Abolghasemi b, M. Abdollahy a, B. Sedaghat a a b

Mineral Processing Dept., Tarbiat Modares University, Tehran, Iran Oil and Gas Engineering Dept., University of Tehran, Tehran, Iran

a r t i c l e

i n f o

Article history: Received 9 June 2014 Accepted 2 October 2014

Keywords: Column Flotoextraction (CFE) SPRAY SX Performance Selectivity

a b s t r a c t The main difference between the new Column Flotoextraction (CFE) method and the conventional SX and SPRAY methods is the substitution of organic phase bubble dispersion, instead of its drop dispersion into the aqueous phase. This substitution is intended to increase the contact area of phases and to enhance the buoyancy force of the organic phase. The main aims of this study are the introduction of the CFE method and the comparison of its performance and selectivity with SX and SPRAY methods. The results indicated 10% and 20% increase of cobalt (Co) extraction from dilute (100 mg Co/l) synthetic solution in A/O = 40 and 1% and 6% increase of Co extraction from concentrated (1000 mg Co/l) synthetic solution in A/O = 30 for the CFE method compared to SX and SPRAY methods, respectively, due to improved contact surface of the phases. In the same extraction time (1 min), the increase of Co extraction from dilute and concentrated solutions in the CFE method compared to the SX method were 16% and 4%, which demonstrate improved kinetics of the extraction process in CFE method. Improvement of separation factors in the CFE method relative to SX and SPRAY methods warrants the better performance of this innovative method. Ó 2014 Elsevier Ltd. All rights reserved.

1. Introduction Solvent extraction (SX) or liquid–liquid extraction is one of the most important hydrometallurgical methods for selective removal, purification and concentration of valuable ions from aqueous solutions using organic solvents. Successful performance of this method in mineral processing requires clear and concentrated pregnant solutions from ore leaching (Habashi, 1999). Reduced concentration of the solution demands increased agitation of the two phases and increased interfacial area between them in order to reach a suitable rate of mass transfer. Therefore, the power consumption would be high for a certain extent of extraction. In addition, formation of stable emulsions due to vigorous agitation would increase separation time and loss of organic phase due to entrainment. On the other hand, the increased volume of the organic phase for enhanced collision probability of trace metal ions with extractant agent and improved extraction kinetics would increase operating costs. Subsequently, this increase of consumption can be followed by environmental problems due to an increase of organic phase loss (Rydberg et al., 2004).

⇑ Corresponding author. Tel.: +98 21 82884352. E-mail address: Mohammadi).

[email protected]

http://dx.doi.org/10.1016/j.mineng.2014.10.003 0892-6875/Ó 2014 Elsevier Ltd. All rights reserved.

(M.R.

Tavakoli

Despite these limitations, two points are important to note. Firstly, continuous depletion of mineral deposits coupled with low grades of the minerals increase the operating costs in the production of concentrated pregnant solutions for extraction contactors. Secondly, the current environmental concern in the world is the increasing volume of dilute solutions containing valuable ions and heavy metals with the development of various industries such as mining, and the high costs for the removal of their environmental problems. Improved performance of extraction equipment for dilute solutions not only expands the usable reserves, but may also enable the use of wastewaters as new sources of feed solution to the SX process. This technological development is valuable for effective recovery of valuable ions from dilute solutions or elimination of environmental problems of toxic and heavy metals in wastewaters. Research efforts conducted to achieve this important aim have led to the invention of various extraction technologies such as Predispersed Solvent Extraction (PDSE) (Tarkan and Finch, 2005), froth flotoextraction (Sebba, 1987), solvent extraction with bottom gas injection without moving parts (Dibrov et al., 1998; Sohn and Doungdeethaveeratana, 1998), liquid membranes, nondispersive solvent extraction, microemulsions and reverse micelles (Rydberg et al., 2004), Air-Assisted Solvent Extraction (AASX) (Doungdeethaveeratana and Sohn, 1998; Tarkan and Finch, 2006), Compressed Air-Assisted Solvent Extraction (CASX)

28

M.R. Tavakoli Mohammadi et al. / Minerals Engineering 71 (2015) 27–33

(Li et al., 2008), etc. Enabling the satisfactory disengagement of phases, reducing the process time and increasing the extraction in high A/O ratios are the main objectives of the approaches proposed in these studies. Consistent with these technological developments, the new Dissolved Nitrogen Predispersed Solvent Extraction (DNPDSE) method was developed. The mixing operation of the two phases in this method was based on organic phase bubble dispersion, instead of its drop dispersion into the aqueous phase. This substitution was aimed at increasing the contact area of the two phases (to improve recovery of metal ions from dilute solutions) and to enhance the buoyancy force of the organic phase (to improve separation of the two phases). In this method, solvent-coated nitrogen bubbles smaller than 100 lm were produced during along and multi-step preparation process by applying a system under pressure similar to the Dissolved Air Flotation (DAF) method (Tavakoli Mohammadi et al., 2013a,b). The Column Flotoextraction (CFE) method is the modified DNPDSE method aiming to improve system performance (reducing the period of extraction process), better separating the two phases, facilitating the extraction process and improving the safety (removing the system under pressure of organic compounds) by making changes in the production system of solvent-coated bubbles. In this method, by applying the pumps and spargers similar to the downcomer of the Jameson Cell in the contactor structure, instead of the system under pressure in the DNPDSE contactor as well as production of solvent-coated air bubbles in a size range of 100–600 lm, the main in adequacies of the DNPDSE method have been overcome. In this study, major and minor aims have been pursued. The main aim of this research is introducing the new method of CFE and comparing its performance and selectivity with SX and SPRAY methods. The term SX method in this paper refers to conventional bulk mixing to the organic and aqueous phases. In order to eliminate the effect of unknown causes and chemical compounds in the solutions and real wastewaters on the extraction results, synthetic aqueous solutions have been used. To select the major and associated elements in these solutions, environmental problems of mines in Iran were addressed. The environmental study of zinc (Zn) production plants showed that the solid residues of leaching, neutralization, hot purification, cold purification and electrowinning processes in these plants contain valuable metals such as Zn, cobalt (Co), and manganese (Mn). These residues have been accumulated and stored in tailings dams due to lack of appropriate extraction technologies, and have caused environmental problems over time. Taking into account the high economic value of these metals and the mentioned reasons, the need to devise methods for extracting metals from these residues with maximum efficiency, based on modern methods with minimum environmental impacts is of the utmost importance. The secondary aim of this study is to investigate the potential of the new CFE method in extraction of valuable elements from these residues by examining synthetic solutions containing similar elements. Due to the high economic value (even in low concentration), Co has been selected as the major element, with Zn and Mn as associated elements in the synthetic solution.

concentration of dilute and concentrated solutions) and 9600 mg Na2SO4/l in the extraction stage as well as a synthetic aqueous solution containing 100 g H2SO4/l were used in the stripping stage of the pregnant organic phase, respectively. Na2SO4 reagent was used to remove the effect of ionic strength on extraction results, and its concentration was considered twice the ionic strength due to the presence of selected elements in the synthetic solution. Characteristics of the synthetic aqueous solutions used to evaluate the extraction performance and selectivity of SX, SPRAY and CFE methods are presented in Tables 1 and 2, respectively. According to Table 2, to provide the same conditions for extraction of the three elements and enable a correct selectivity comparison of the three methods, a similar concentration of elements in the synthetic solution was used. Dilute sulfuric acid (Merck, Germany) and ammonia (Merck, Germany) solutions were used for pH adjustment of the synthetic solution. The organic phase was a mixture of 10% v/v chelating type extractant D2EHPA (Cognis), 5% v/v modifier TBP and 85% v/v diluent kerosene. The extraction mechanisms of D2EHPA with Co, Mn and Zn cations (M2+), which leads to the transfer of their complexes from the aqueous phase (at their extraction pH) to the organic phase, are as follows (Rydberg et al., 2004):

½4ðROÞ2 POOHðorgÞ þ M2þ ðaqÞ $ ½ðROÞ2 POO2 M½HOPOðORÞ2 2 ðorgÞ þ 2Hþ ðaqÞ

ð1Þ

In the CFE method, 11.4 g/l dilute silicone oil was used in the organic phase to improve its foaming capacity to produce bubbles (Tarkan and Finch, 2005). 2.2. Methods 2.2.1. Foam stability measurement method To convert the organic phase into bubbles in the CFE contactor, the best conditions should be provided for its foaming. For this purpose, the first step is to select the appropriate surfactant and determine its optimum concentration to get the highest quantity of foam from the organic phase (Tarkan and Finch, 2005).The experimental set-up of the foam meter is shown in Fig. 1. The Baykerman method (Sebba, 1987) was used to measure the foam stability. The organic phase (5 ml) containing different amounts of silicone oil was transferred into the cylindrical part, and the air required to produce the solvent-coated bubbles was generated using a compressor with a constant flow rate of 200 ml/min. The air enabled foam production by passing through a sparger in the bottom part of the foam meter. The total height of foam and the organic phase (H) for each experiment was measured after a steady state was achieved after 2 min. The foaminess unit for the organic phase was calculated using Eqs. (2)–(4):

Hf ¼ H  H o

ð2Þ

V ¼ pr 2 H f

ð3Þ

X

¼ V=Q

ð4Þ

2. Materials and methods 2.1. Materials Reagent-grade CoSO47H2O (Fluka, Switzerland), ZnSO47H2O (Fluka, Switzerland), MnSO4H2O (Merck, Germany) and Na2SO4 (Merck, Germany) were used to prepare the synthetic aqueous solutions. To evaluate the surfactant effect of dilute silicone oil (Shin Etsu, Japan) on the SX method, a synthetic aqueous solution containing 500 mg Co/l (2381.4 mg CoSO47H2O/l) (the intermediate

Table 1 Specifications of synthetic aqueous solutions used in evaluation of extraction performance. Specification

mg CoSO47H2O/l mg Co/l mg Na2SO4/l

Solution type Dilute

Concentrated

476.30 100.00 1920.00

4762.70 1000.00 19200.00

M.R. Tavakoli Mohammadi et al. / Minerals Engineering 71 (2015) 27–33 Table 2 Specifications of synthetic aqueous solution used in evaluation of selectivity. Compositions

Concentration

mg mg mg mg mg

476.30 441.50 307.30 100.00 5682.00

CoSO47H2O/l ZnSO47H2O/l MnSO4H2O/l Co, Zn, Mn/l Na2SO4/l

29

cell. The control valve inserted in the recycle tube of the pump was used to regulate the flow rate. Downcomer is a vertical pipe blocked in the upper part except for two inlets: one for air (a tube with a diameter of 5 mm) and the other for the organic phase (a nozzle with a diameter of 2 mm). When the organic phase is pumped through the nozzle into the downcomer, the air tube inlet of the downcomer is closed. When the organic phase reaches the end of the mixing tube, a hydraulic cap is formed, and thus hydrostatic suction occurs because the pressure on top of the downcomer is less than the atmospheric pressure during this operation. Through contact between the organic phase and the air sucked into the downcomer upper space, fine bubbles of 100–600 lm are produced and injected into the cell by a mixing tube. Since the cell has a width higher than the mixing tube, downfall speed of the solvent-coated air bubbles is decreased by leaving the downcomer, and they rise to the surface and pool at the top of the column (About Jamesonn cell; Harbort et al., 2003). The raffinate sample was taken after this simultaneous extraction and separation operation, and the containing elements were analyzed. 3. Results and discussion

Fig. 1. Experimental set-up of the foam meter.

where Hf is the foam height, Ho, the organic phase height (0.55 cm), Q, the gas flow rate (200 cm3/min), V, the foam volume (cm3) and P , the foaminess unit (foam stability) of liquid (min). 2.2.2. SX method In this method, the phases of aqueous (with an appropriate pH) and organic in the volume (A/O) ratios desired were mixed using a magnetic stirrer (500 rpm) for 10 min, and were then separated by transferring into a separating funnel after 15 min. Afterward, the equilibrium pH of the aqueous phase was measured, and the containing elements were determined using Inductivity Coupled Plasma (ICP) analysis. Concentration of elements in the organic phase was calculated from the difference between the metal concentrations in the aqueous phase before and after extraction equilibrium. The stripping method was the inverse of the extraction method in similar operating conditions to a mixture of pregnant organic phase and aqueous phase containing100 g/l H2SO4. 2.2.3. SPRAY method The contactor with the schematic diagram shown in Fig. 2 was used to implement this method. The synthetic aqueous solution (1000 ml) was transferred into a glass column with a diameter and height of 4 and 120 cm, respectively. A certain volume of the organic phase was injected into the aqueous phase with a flow rate of 0.27 l/m. The injection operation was performed using a peristaltic pump and sparger embedded in the bottom of the column with a diameter of orifices of 0.4 mm. The simultaneous operations of extraction and separation were carried out with the passage of the organic phase drops through the aqueous phase and their transfer to the surface. Finally, aqueous phase samples were taken from the sampler at the top of the column, and the containing elements were analyzed. 2.2.4. CFE method The schematic diagram of the CFE contactor is shown in Fig. 3. In this method, the synthetic solution (1000 ml) was transferred into the cell and bubble injection of a certain volume of the organic phase was done using a centrifugal pump with a flow rate of 1.5 l/m through the mixing tube embedded in the bottom of the

3.1. Evaluation of performance 3.1.1. Determination of silicone oil optimum concentration Successful performance of the CFE method in generating solvent-coated bubbles requires providing a high foaming capacity for the organic phase. Fig. 4 shows the foaminess unit of the organic phase for different concentrations of silicone oil in foam stability measurement experiments. The highest amount of foam stability was achieved at 11.4 g/l concentration of silicone oil. 3.1.2. Suitable pH choice for Co extraction The results of SX experiments at A/O = 1 and pHs > 4.4 did not show any improvement in extraction of Co2+ for either dilute or concentrated aqueous solutions and hence pH 4.4 was chosen for subsequent tests. 3.1.3. Silicone oil effect on performance of the SX, SPRAY and CFE methods As it was necessary for the additives to have no negative effects on extraction rates (Tarkan and Finch, 2005), the effect of silicone oil on the performance of the three methods was investigated. Fig. 5 shows the results of extraction and stripping experiments in the SX method for different concentrations of silicone oil. The results show no effect of silicone oil on the Co extraction and stripping in the SX method, and the observed extraction variations are due to the systematic errors which occurred during the experiments such as human and analyzing instruments errors. To investigate the effect of surfactant on the performance of SPRAY and CFE methods, the dilute aqueous solution was used due to the impossibility of applying low A/O ratios. Fig. 6 shows the experimental results at A/O = 40. In the absence of silicone oil, the Co extraction in the CFE method is lower than the SPRAY method due to the presence of large drops and organic phase accumulations in the CFE method relative to smaller drops with a more uniform distribution in the SPRAY method. With the addition of silicone oil up to the optimum amount and providing the highest foaming capacity for the organic phase, the efficiency of the CFE method was significantly increased due to conversion of the organic phase drops into bubbles. Under these conditions, the efficiency of the SPRAY method was gradually increased probably due to the production of smaller and more uniform drops and improved contact surface. Increasing the amount of

30

M.R. Tavakoli Mohammadi et al. / Minerals Engineering 71 (2015) 27–33

Fig. 2. Schematic diagram of SPRAY contactor.

0.6 0.4 0.2 0

0

5

10

15

Silicone oil (g/l)

Co extraction/stripping (%)

Foaminess unit (min)

Fig. 3. Schematic diagram of CFE contactor.

100 95 90 85 80

Extraction 0

5

10

Stripping 15

20

25

Silicone oil (g/l)

Fig. 4. Foaminess unit of organic phase for various concentrations of silicone oil.

Fig. 5. Silicone oil effect on the Co extraction and striping in SX method.

silicone oil to twice the optimum amount gradually decreased the extraction efficiency of both methods. Decreased extraction in the CFE method is due to the emergence of anti-foaming effects of this surfactant and reduced conversion process of drops into bubbles (Tarkan and Finch, 2005), while this reduction in the SPRAY method is probably due to the dominance of the negative influence of mass transfer resistance over the positive effect of increased contact surface with increasing concentration of the surfactant.

3.1.4. Performance comparison of the SX, SPRAY and CFE methods As mentioned earlier, it is expected that mixing of the aqueous phase with bubble dispersion of the organic phase in the CFE method, instead of its drop dispersion in SX and SPRAY methods, has led to an increase in the contact area between the phases and improved the extraction process. To prove this claim, similar extraction experiments were conducted using the three methods based on changes in the two basic parameters of pH and A/O ratio.

31

M.R. Tavakoli Mohammadi et al. / Minerals Engineering 71 (2015) 27–33

100 CFE

80 60 40 20 0

CFE 0

5

SPRAY

10

15

20

25

Co extraction (%)

Co extraction (%)

100

80

SPRAY

60

SX (10 min) SX (1 min)

40 20 0

Silicone oil (g/l)

0

20

40

Fig. 6. Silicone oil effect on the Co extraction in SPRAY and CFE methods.

3.1.4.1. Co extraction at various A/O ratios and pH = 4.4. Diagrams of Co extraction from dilute and concentrated solutions at different A/O ratios and pH = 4.4 are shown in Figs. 7 and 8. Due to the limited height of the cell, it was impossible to apply A/O ratios lower than 30 to get better extraction results in CFE and SPRAY methods. In this research, the bubbles of 100–600 lm and the drops of 1000–2000 lm were produced in CFE and SPRAY contactors, respectively. Based on visual observations, the residence time of drops in the SPRAY method was shorter than the residence time of bubbles in the CFE method for a few seconds, and the extraction process in the two methods was done in less than one minute. On the other hand, according to the volumes of aqueous and organic phases used in the SX method, the agitation rate of 500 rpm was the highest possible rate of agitation. Also, according to Cheng’s (Cheng, 2000) research, the mixing time of 10 min was sufficient for the reactions in the chemical system used. Therefore, the experimental conditions used in the SX method provided high surface area of drops and sufficient contact time of phases in order to carry out a quantitative comparison of results with the results of CFE and SPRAY methods. A quantitative comparison of results showed that the degrees of Co extraction from the dilute solution at A/O = 40 were 61.89%, 51.98% and 71.2% and from the concentrated solution at A/O = 30, they were 11.12%, 6.18% and 11.98% in SX, SPRAY and CFE methods, respectively. Clearly, the probability of collision and reaction of metal ions with extraction agent decreases in the more dilute solutions; thus, increased extraction of Co (due to the increased surface area) was more conspicuous for the dilute solution than the concentrated solution in the CFE method. Lower extents of extraction obtained with the SPRAY method can be explained by smaller contact area of the organic droplets compared with the solvent-coated bubbles in the CFE method. Lesser degrees of extraction in the SPRAY method compared with the SX method can be explained by shorter residence times of the droplets in the SPRAY column, compared with the extraction time in the SX method. The results of SX experiments at 1 min showed that the Co extraction from dilute solution at A/O = 40 was 55.08% and from

SX (10 min)

60

SX (1 min) 40 20 0

0

50

100

150

200

A/O Fig. 7. Co extraction by three methods from dilute solution at various A/O ratios and pH = 4.4.

120

the concentrated solution at A/O = 30 it was 8.17%, which was 16.04% and 3.81% lower than the CFE method, respectively. Therefore, although increased extraction of Co from the concentrated solution is negligible in the CFE method compared to the SX method, kinetics of the extraction process and system performance has been improved with this new method.

3.1.4.2. Co extraction at various pH values and same A/O ratios. Diagrams of Co extraction from dilute and concentrated solutions at various pHs and the same A/O ratios are shown in Figs. 9 and 10. As expected, an upward trend is observed in the Co extraction with increasing pH in the three methods. The residence times of bubbles and drops in CFE and SPRAY methods are almost identical. Therefore, higher degrees of extraction in the CFE method relative to the SX method can be explained by larger contact surface of the solvent-coated bubbles in this method compared with the organic droplets in the SX method. Also, lesser degrees of extraction in the SPRAY method relative to the SX method can be explained by decreasing residence time of the drops in the column.

3.2. Evaluation of selectivity 3.2.1. Choice of associated elements According to Fig. 11 (Cheng, 2000), Zn was chosen to evaluate the total selectivity because of its quite distinct extraction pH range, relative to that of Co, Mn was used to assess the partial selectivity because of the overlap of its extraction pH range with that of Co. In addition, in most of the residues obtained from various processing stages in Zn production plants, these three elements exist together. Hence, the performance mode of the CFE method in the separation of these elements with pH changes is industrially important.

100

SPRAY

100

Fig. 8. Co extraction by three methods from concentrated solution at various A/O ratios and pH = 4.4.

CFE

80

80

A/O

Co extraction (%)

Co extraction (%)

100

60

SX

CFE

SPRAY

80 60 40 20 0

3

3.5

4

4.5

pH Fig. 9. Co extraction by three methods from dilute solution at various pHs and A/ O = 40.

32

M.R. Tavakoli Mohammadi et al. / Minerals Engineering 71 (2015) 27–33

Co extraction (%)

15

SX

CFE

SPRAY

12 9 6 3 0

3

3.5

4

4.5

pH Fig. 10. Co extraction by three methods from concentrated solution at various pHs and A/O = 30.

methods in distribution coefficients, separation factors and enrichment factors are apparent. Distribution coefficients of the elements were determined according to Table 3 by SX, SPRAY and CFE experiments at pHs under study and A/O = 40. Table 4 shows the separation factors obtained from the ratio of elements distribution coefficients. Separation factors of Zn/Co at extraction pH = 2 were used to examine the total selectivity, and separation factors of Zn/Mn at extraction pH = 2 and Mn/Co at extraction pH = 3 were used to evaluate the partial selectivity. According to Table 4, infinite separation factors of Zn/Co indicate no effect of the three methods on total selectivity. Also, an increase of partial selectivity in the CFE method shows a significant influence of process pH on the extraction results. In other words, although in the extraction pH of the main element, a simultaneous increase in extraction of the main and associated elements has occurred, this increase is higher for the main element since it lies in its maximum extraction pH range, leading to increased partial selectivity. A quantitative comparison of the elements extraction percentages in Table 5 shows the highest and lowest degrees of elements Table 3 Distribution coefficients of elements by SX, SPRAY and CFE methods at various pHs.

Fig. 11. D2EHPA pH-extraction isotherms for seven elements at 23 °C (Cheng, 2000).

3.2.2. Choice of extraction pHs Extraction pHs of Co (3.2–4.4) are higher than Mn (2.2–3.4) and Zn (0.8–2.4). If the extraction process is conducted at pH values where Co2+ extraction is high, higher amounts of Zn and Mn are extracted, and no separation occurs. Therefore, in the evaluation of selectivity, first Zn, then Mn and finally Co were extracted in suitable extraction pHs by each of the three methods, and then the separation factors obtained were compared. Due to limited height of the cell and the impossibility of using low A/O ratios, valuable ions could not be completely extracted from the concentrated solution, and thus the experiments of selectivity evaluation were only conducted for the dilute solution. D2EHPA pH-extraction isotherms for dilute solutions of Co (containing 1920 mg Na2SO4/l), Mn (containing 1739 mg Na2SO4/ l) and Zn (containing 2068 mg Na2SO4/l) are shown in Fig. 12. Considering the range of suitable extraction pHs for Zn (0.8–2.4), Mn (2.2–3.4) and Co (3.2–4.4), the extraction process was first performed at pH = 2 for Zn separation, then at pH = 3 for Mn separation and finally at pH = 4 for Co separation. 3.2.3. Comparison of SX, SPRAY and CFE methods In this research, the degrees of Co extraction in three methods may be not true equilibrium values. Therefore, differences of these

Methods

pH

Mn

Co

SX

2 3 4

339.15 – –

1.54 196.75 –

0.00 2.92 43.14

SPRAY

2 3 4

141.65 – –

0.86 102.50 –

0.00 1.80 28.94

CFE

2 3 4

4041.63 – –

2.15 657.72 –

0.00 3.53 62.88

Table 4 Separation factors of elements in SX, SPRAY and CFE methods. Methods

bZn/Mn (at pH 2)

bZn/Co (at pH 2)

bMn/Co (at pH 3)

SX SPRAY CFE

220.23 164.71 1879.83

1 1 1

67.38 56.94 186.32

Table 5 Degrees of elements extraction by SX, SPRAY and CFE methods at various pHs. Methods

pH

Zn

SX

2 3 4

89.45 100.00 –

3.70 83.10 0.00

0.00 6.80 51.89

SPRAY

2 3 4

77.98 100.00 –

2.10 71.93 100.00

0.00 4.30 41.97

CFE

2 3 4

99.02 100.00 –

5.11 94.27 100.00

0.00 8.20 61.12

Extraction (%)

100 99

Zn

98

Mn

Co

Zn

97

Mn 96 95

Table 6 Enrichment factors of elements in SX, SPRAY and CFE methods.

Co 0

1

2

3

4

5

pH Fig. 12. D2EHPA pH-extraction isotherms for dilute solutions of Co, Mn and Zn in SX method.

Methods

EZn/Mn (at pH 2)

EZn/Co (at pH 2)

EMn/Co (at pH 3)

SX SPRAY CFE

24.18 37.13 19.38

1 1 1

12.22 16.73 11.50

M.R. Tavakoli Mohammadi et al. / Minerals Engineering 71 (2015) 27–33

extraction for CFE and SPRAY methods, respectively. Furthermore, in the three methods, Co has not been extracted in the Zn extraction pHs range, indicating no effect of CFE and SPRAY methods on total selectivity, similar to the SX method. Table 6 indicates the enrichment factors obtained from the ratio of degrees of elements extraction. The highest value of this factor was obtained for the CFE method. The reason for this result is improved extraction of the associated elements in the extraction pHs range of the main element due to increased contact area.

33

relative to the associated elements with increased contact surface. In contrast, improved extraction of the associated elements in the extraction pHs range of the main element has led to decreased enrichment factors in the CFE method relative to SX and SPRAY methods. Acknowledgment The authors wish to thank Tarbiat Modares University for providing the possibility of conducting this research.

4. Conclusions References Column Flotoextraction (CFE) is an innovative method to simplify and improve performance of the DNPDSE method. Applying the centrifugal pump and spargers similar to the downcomer of the Jameson cell in the CFE contactor instead of the system under pressure in the DNPDSE contactor has eliminated the major defects of the DNPDSE method. Successful performance of this method requires providing high foaming capacity for the organic phase. 11.4 g/l dilute silicone oil provided the highest foaminess unit for the organic phase and was selected as the optimum concentration. Despite the insignificant effect of this surfactant on the performance of SX and SPRAY methods, the performance of the CFE method was improved by addition of this surfactant, and the best extraction performance was obtained for optimum concentration. This result is due to the improved conversion process of organic phase drops into the bubbles. The degrees of Co extraction of 61.89%, 51.98% and 71.12% from the dilute solution in A/O = 40 and11.12%, 6.8% and 11.98% from the concentrated solution in A/O = 30 in SX, SPRAY and CFE methods, respectively, indicated improved extraction performance in the CFE method. In the same extraction time as the CFE method (1 min), the degrees of Co extraction from dilute and concentrated solutions in the SX method were 55.08% and 8.17%, respectively, indicating improved kinetics of the process in the CFE method. In the study of selectivity, observing no extraction of Co at extraction pH of Zn did not indicate any effect of the three methods on total selectivity. Comparing the separation factors of Zn/Mn in extraction pH = 2 and Mn/Co in extraction pH = 3 showed that partial selectivity has been increased in the CFE method. This result is due to higher increase in the distribution coefficient of each element in its extraction pH

About Jameson cell, Major installation in solvent extraction – electrowinning, coal and base metal flotation, Xstrata Technology. Cheng, C.Y., 2000. Purification of synthetic laterite leach solution by solvent extraction using D2EHPA. Hydrometallurgy 56, 369–386. Dibrov, I.A., Vornin, N.N., Kiemyatov, A.A., 1998. Froth flotoextraction: a new method of metal separation from aqueous solution. Int. J. Miner. Process. 54 (1), 45–58. Doungdeethaveeratana, D., Sohn, H.Y., 1998. The kinetics of extraction in a novel solvent extraction process with bottom gas injection without moving parts. Hydrometallurgy 49 (3), 229–254. Habashi, F., 1999. Textbook of Hydrometallurgy, second ed. Metallurgie Extractive, Quebec, Canada. Harbort, G., De Bono, S., Carr, D., Lawson, V., 2003. Jameson cell fundamentals – a revised perspective. Miner. Eng. 16, 1091–1101. Li, C.W., Chen, Y.M., Hsiao, S.T., 2008. Compressed air-assisted solvent extraction (CASX) for metal removal. Chemosphere 71, 51–58. Rydberg, J., Cox, M., Musikas, C., Choppin, G.R., 2004. Solvent Extraction Principles and Practice, second ed. Marcel Dekker, Inc., New York. Sebba, F., 1987. Foams and Biliquid Foams, Aphrons. Wiley, Chichester, West Sussex, New York. Sohn, H.Y., Doungdeethaveeratana, D., 1998. A novel solvent extraction process with bottom gas injection without moving parts. Sep. Purif. Technol. 13 (3), 227–235. Tarkan, H.M., Finch, J.A., 2005. Foaming properties of solvent for use in air-assisted solvent extraction. Colloids Surf., A 264 (1–3), 126–132. Tarkan, H.M., Finch, J.A., 2005. Air-assisted solvent extraction: towards a novel extraction process. Miner. Eng. 18 (1), 83–88. Tarkan, H.M., Finch, J.A., 2006. Multi-bubble production in the air-assisted solvent extraction. In: Congress of XXIII International Mineral Processing. Promed Advertising Agency, Istanbul, pp. 1340–1345. Tavakoli Mohammadi, M.R., Javad Koleini, S.M., Abdollahy, M., 2013a. New dissolved nitrogen predispersed solvent extraction method, 1: Performance. Ind. Eng. Chem. Res. 52, 3842–3851. Tavakoli Mohammadi, M.R., Javad Koleini, S.M., Abdollahy, M., 2013b. New dissolved nitrogen predispersed solvent extraction method, 2: Selectivity. Ind. Eng. Chem. Res. 52, 3852–3857.