Sustainable Recovery of Silver from Deactivated Catalysts Using a

Subscriber access provided by UNIV OF LOUISIANA

Separations

Sustainable Recovery of Silver from Deactivated Catalysts Using a Novel Process Combining Leaching and Emulsion Liquid Membrane Techniques Saeed Laki, Ahmad Arabi Shamsabadi, Farzad Seidi, and Masoud Soroush Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b02933 • Publication Date (Web): 24 Sep 2018 Downloaded from http://pubs.acs.org on September 27, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Sustainable Recovery of Silver from Deactivated Catalysts Using a Novel Process Combining Leaching and Emulsion Liquid Membrane Techniques

Saeed Laki1†, Ahmad Arabi Shamsabadi1†, Farzad Seidi2, and Masoud Soroush1,*

September 17, 2018

REVISED VERSION

Submitted for Publication in Industrial & Engineering Chemistry Research

Keywords: Deactivated catalyst, Silver, Leaching, Emulsion liquid membrane, Surfactant

1

Department of Chemical and Biological Engineering, Drexel University, Philadelphia, USA

2

Department of Material Science and Engineering, School of Molecular Science and Engineering, Vidyasirimedhi Institute of Science and Technology, Rayong 21210, Thailand †

These authors contributed equally to this work.

*Corresponding author: Email:[email protected], Tel: +1-215-895-1710

ACS Paragon Plus Environment

Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract Industrial deactivated Ag/alumina catalysts contain an appreciable amount of silver. As silver is a precious metal, it is of great economic and environmental interest to recover silver from the catalysts before disposing them. This paper introduces a novel hybrid process for efficient silver recovery from deactivated catalysts. The process combines leaching and emulsion liquid membrane (ELM) techniques. Leaching first transfers silver from catalyst particles to an aqueous solution. An ELM then extracts silver ions from the leach solution in a single separation step. To prevent emulsion instability in the ELM, a new surfactant, a relatively-low number-average-molecular-weight ( n-hexane > cyclohexane > benzene > toluene > carbon tetrachloride47-50. Compared to aliphatic diluents, in general, aromatic diluents have higher specific gravity, inhibiting dispersion and coalescence of the emulsion51. This paper introduces a novel process for efficient recovery of silver from deactivated Ag/alumina industrial catalysts. The process combines leaching and ELM techniques. This combination lowers the number of middle operating steps and the consumption of chemicals such as solvents, carriers and organic and inorganic acids. Leaching first transfers silver from deactivated catalyst particles to an aqueous solution. In a single separation step, an ELM then extracts silver ions from the leach solution. For the first time, 2-ethyl hexyl phosphoric acid (MEHPA) is used as the carrier in an ELM to extract silver ions from aqueous solutions. MEHPA has phosphorous in its structure (Scheme S1). Phosphorus is a soft Lewis base

52

,

while silver is a soft Lewis acid. Due to the soft-soft interactions, we anticipate MEHPA to have higher affinity towards silver ions than other metal ions

53-56

. A mixture of paraffinic

and naphthenic hydrocarbons with no aromatic components is used as a diluent. To address 3


Page 5 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the well-known instability of ELMs, which results from the low efficacy of common surfactants like Span 80, a new surfactant, a relatively low number-average-molecular-weight ( 1 M

(2)

3Ag (s) + 4HNO3 (l) → 3AgNO3 (l) + NO (g) +2H2O (l),

[HNO3] ≤1 M

(3)

The first reaction is first-order but the second is second-order 68. After attaining the desired acidity level of the feed phase and mixing the feed phase with the emulsion, the carrier facilitates transfer of silver ions through the liquid membrane via the formation of an Agcarrier complex (Scheme 2). Without a mobile carrier, the transfer of the silver ions through an organic phase is difficult. The role of the carrier in an ELM is facile transport of the silver ions through the membrane phase to improve the ELM efficiency. 7


Page 9 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 2. Schematic of the silver ions transport in the ELM. To understand the mechanism of the Ag–carrier complex formation, an ideal extraction system is assumed (liquid phase activity = 1)28. Generally, the following reaction can be proposed for the Ag–carrier formation: Ag+ (l) + m(HL)x (l) → AgL(HL)(mx-1) (l) + H+ (l)

(4)

where (HL)x is the carrier, AgL(HL)(mx-1) is the Ag-carrier complex, H+ is the hydrogen ion released during formation of the Ag-carrier complex, x is the degree of aggregation of the carrier70-71, and m is the coordination number28, 72. Our previous study on solvent extraction had shown that the coordination number for the formation of Ag-MEHPA complex is 4 28. 3. Results and Discussion 3.1. Characterization of P5000 To confirm the surfactant structure,

13

C NMR, 1H NMR and FTIR spectroscopies

were conducted. 13C NMR spectrum of P5000 is shown in Figure 1a. The CH2 carbon signal of PEG is at 70.45 ppm. The signals at 17.23, 73.24, and 75.19 ppm are related to the carbons of CH3, CH, and CH2 groups of PPGs, respectively. Figure 1b presents 1H NMR spectrum of P5000. As can be seen, PEG’s CH2 groups signal is at 3.65 ppm. The signals at 1.14, 3.40, and 3.55 ppm are associated with the CH3, CH, and CH2 groups of PPGs, respectively. A comparison of the integrals related to the CH3

8



of PPG (at 1.14 ppm) with CH2 of PEG (at 3.65 ppm) revealed that the ratio of PPG repeating units to

Figure 1. (a) 13C NMR and (b) 1H NMR spectra of P5000. the PEG ones are 2.1 to 1.0. This means that each PEG block included around 34 repeating units whereas each PPG block in each side composed of around 36 repeating units. This number agrees with the number-average molecular weight and polydispersity index (PDI) of P5000 measured using a GPC (Mn = ~ 5650 and PDI = ~1.8). In FTIR spectrum (Figure 2), the strong peak at 1108 cm‒1 is related to etheric C–O bonds. The strong peaks in the range of 2870 and 2970 cm‒1 are ascribed to stretching vibration of aliphatic C–H bonds and the peaks at 1374 and 1458 cm‒1 are due to aliphatic C–H bending vibrations. Also, the small peak at 3490 cm‒1 corresponds to the terminal hydroxyl groups of the terpolymer.

9


Page 10 of 28

Page 11 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. FTIR spectrum of P5000.

3.2. Leaching Technique To maximize the recovery of silver from the deactivated catalyst, the effects of the HNO3 concentration, temperature, solid/liquid (S/L) ratio and stirring speed on the performance of the leaching technique were investigated. Silver extraction efficiencies obtained using different HNO3 solutions (0.6–3 M) with a S/L ratio of 50 g/L at 70°C are presented in Figure 3a. As shown, the HNO3 concentration had a negligible effect on the extraction efficiency of Ti and K ions because of their low concentrations in the leach solution and the low affinity of nitric acid (≤1 M) towards these ions. This behavior had also been observed in Ref. [57]. The leaching efficiencies of Al, Si, and Ca increased with the acid concentration. Also, a 97.7% leaching efficiency was achieved for Ag with a 1 M HNO3 solution. However, higher acid concentrations did not improve the leaching efficiency of silver substantially and leached other metal ions (Al, Si and Ca ions) more into the solution. Higher silver recovery is anticipated at higher acid concentrations. However, as explained in Section 2.7, at HNO3 concentrations above 1 M the governing leaching mechanism is the one in Eq.2, leading to the removal of less silver. Thus, the 1 M HNO3 concentration maximized the recovery efficiency of silver but minimize the recovery efficiencies of other metal ions. Temperature is another key parameter in leaching19, 73-74. We conducted the leaching at 50 to 80 °C (Figure 3b). We found that the temperature has no noticeable effects on the leaching extraction efficiencies of Ti and K ions, due to the low concentrations of these ions in the leach solution. However, leaching extraction efficiencies of the other metals increased with temperature, because of the endothermicity of metal leaching techniques20, 75. 98% of silver was recovered from the deactivated catalyst at 70 ºC. Increasing the temperature from 70 to 80 °C enhanced the extraction efficiency of Al, Si and Ca by 16, 12 and 13 %, respectively, and the leaching efficiency of silver improved negligibly. Since the increases in the extraction efficiencies of other metals with the temperature change were much more than the increase in that of silver, 70 °C was selected as the optimal leaching temperature.

10



Figure 3. Effects on the leaching extraction efficiency. (a) HNO3 concentration (S/L ratio = 50 g/L; mixing speed = 500 rpm; temperature = 70°C); (b) temperature (S/L ratio = 50 g/L; mixing speed = 500 rpm; [ HNO3 ] = 1 M); (c) S/L ratio (temperature = 70°C; mixing speed = 500 rpm; [ HNO3 ] = 1 M), and (d) mixing speed (S/L ratio = 50 g/L; temperature = 70°C; [ HNO3 ] = 1 M).

From an economic point of view, it is important to optimize the S/L ratio in leaching. The effect of the S/L ratio on the leaching efficiency of metals is presented in Figure 3c. The results show that increasing the S/L ratio decreased the Ag leaching efficiency. The leaching mechanism is partly controlled by the concentration gradient of the metal ions in the system 76

. Although the driving force increases with the S/L ratio, a high solid content raises the

solution density, leading to a decline in the leaching efficiency24. The S/L ratio up to 50 g/L did not induce considerable decrease in the leaching efficiency of the silver because of a balance between the driving force, solution density, and solubility of the silver in the solution. However, a further increase in the S/L ratio (beyond 50 g/L) declines the leaching 11


Page 12 of 28

Page 13 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


efficiency, as at the higher S/L ratios the solution density is higher and the silver solubility is lower. By increasing the S/L ratio to 30 g/L, the leaching efficiency of other metals decreased slightly (Al: 55 to 44%, Si: 65 to 63%, Ti: 25 to 21% and Ca: 77 to 72%). A further increase in the S/L ratio to 50 g/L led to a significant decrease in the leaching efficiency of the metals (Al: 44 to 22%, Si: 63 to 34%, Ti: 21 to 6% and Ca: 72 to 55%). As beyond 50 g/L the silver recovery efficiency decreased, this value was selected as the optimal S/L ratio. Figure 3d shows the effect of the mixing speed in the range of 300 to 600 rpm on the metals leaching efficiencies. The results show that increasing of the stirring speed resulted in an improvement metals recovery due to larger Reynold numbers

and mass transfer

coefficients at higher speeds77-78. Consequently, the amount of silver ions in the leach solution increased. Silver extraction efficiencies of 98% and 99% were achieved at 500 and 600 rpm, respectively. On the other hand, extraction efficiencies of other metals remained constant at mixing speeds of up to 500 rpm, and beyond 500 rpm their extraction efficiency increased sharply. Since the increases in the extraction efficiencies of other metals with the stirring speed increase were much more than the increase in that of silver, 500 rpm was selected as the optimal stirring speed. The optimal leaching conditions are given in Table S2, and the compositions of the leach solutions obtained at these conditions are presented in Table 2. While the high silver recovery was achieved at these conditions, an efficient complementary method is needed to separate silver from other metal ions in the leach solution.

Table 2. Composition of the obtained leach solution. Metal ion

Ag+

Al3+

K+

Ti4+

Si4+

Ca2+

Concentration (ppm)

5782.0

3052.6

1.3

12.0

225.5

11.9

3.3. ELM Technique 3.3.1. ELM Stability Stability is of great importance in an ELM operation, as it affects the operation efficiency strongly. Membrane break-up causes a decrease in the ELM separation efficiency 12



due to leakage of separated ions from the internal phase to the external phase4. We first used Method I to understand the compatibility of the emulsion components and obtain preliminary conditions such as dilution type, surfactant and acid concentrations, and homogenizing speed for emulsion preparation. To investigate the influence of the diluent on the membrane stability three diluents (industrial solvent, kerosene and chloroform) were tested. Method I showed that the industrial solvent formed more stable emulsions than chloroform and kerosene. This is probably due to the long chain (greater than C10) aliphatic hydrocarbons of the industrial solvent79-80. Preparing numerous emulsions with different surfactant concentrations and homogenizing speeds revealed that the emulsion containing 6% (w/v) surfactant and 0.6 M HNO3 prepared using homogenizing speed of 7000 rpm is the most stable one, which was considered as the starting emulsion for Method II stability tests. The effect of emulsification time on the emulsion stability was investigated during 30 min using Method II (Figure 4a). For emulsification time of less than 7 min, the emulsion globules are quite large for the droplets coalescence, which led to the globules breakage29. The lowest breakages were obtained for 10 to 15 min emulsification time. However, further increase in the emulsification time to 20 min decreased the membrane stability due to an increase in the frequency contact between small droplets, and internal shearing imposed to the small droplets with thinner membrane layer8. Accordingly, to ensure the stability of the ELM, 10 min emulsification was selected. The effect of the stirring speed on the ELM stability was explored for 30 minutes (Figure 4b). High mixing speeds lead to the formation of small size distribution of globules providing a large interfacial contact area between the feed and the membrane phases, and consequently high mass transfer81. However, high mixing speeds result in globule swelling and rupture. The rapture of the emulsion globules leads to leakage of the internal phase to the external phase and consequently separation loss. As Figure 4b shows, increasing mixing speed from 400 to 500 rpm did not significantly affect the ELM stability during 20 min. But after 20 min, the ELM stability deteriorated. A further increase in the mixing speed to 600 and 700 rpm made the ELM unstable during the first 5 minutes. This instability is due to an increase in shear stress on the emulsion globules leading to the emulsion breakage and finally gradual reduction in extraction efficiency43. Also, to guarantee the ELM stability, 10 min extraction was performed. Based on Method I and Method II stability analyses, the surfactant and acid concentrations, the extraction and emulsification times, the striping and homogenizing speeds, and the diluent type were obtained (Table S3). The carrier concentration, volume ratio, and pH were selected based on 13


Page 14 of 28

Page 15 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the solvent extraction results

28

. Also, we chose 50.0/500.0 as the treatment ratio based on

previous studies47-48, 82-85.

Figure 4. Effects on emulsion globules break-up (stability of the ELM). (a) Emulsification time (mixing speed = 500 rpm), and (b) mixing speed (emulsification time = 10 min). [Surfactant concentration = 6% g/L; homogenizing speed = 7000 rpm; MEHPA concentration = 10 v/v %; feed phase pH = 6.5; volume ratio = 5.0/5.0; treatment ratio = 50.0/500.0; [ HNO3 ] = 0.6 M].

3.3.2. Recovery of Silver from a Synthetic Solution To maximize the silver ion recovery from the leach solution, the ELM capability was assessed for silver recovery from a synthetic external phase with a concentration of 5000 mg. L−1 silver ions (according to the silver concentration in the leach solution). ELM Components. In addition to the ELM stability, the concentrations of the surfactant, carrier, and internal phase were adjusted to optimize the silver recovery. The effect of the surfactant concentration on the silver recovery was probed while considering the ELM stability (Figure 5a). With a surfactant concentration of 4 % (w/v), approximately 82% of silver ions were separated within 2.5 min. However, after 2.5 min the quantity of the extracted silver ions decreased sharply due to the instability of the emulsion. With surfactant concentrations of 5 and 6 %, a silver extraction efficiency of ~ 98% was achieved. The extraction efficiency was decreased surprisingly by further increasing the surfactant concentration to 7%. Excessive surfactant increases the mass transfer resistance at the membrane/external phase interfaces caused by high surfactant occupancy and high interfacial viscosity29,

47, 86

. Therefore, a decrease in movement of inner droplets in the emulsion

globules resulted in low silver ions extraction at the interface29-30,

35

. Considering ELM

stability and extraction efficiency, the surfactant concentration of 6% was used. 14



Figure 5. Effects on the extraction efficiency. (a) Surfactant concentration (MEHPA = 10.0% (v/v); internal phase = 0.6 M HNO3), (b) internal phase concentration (P5000 = 6% g/L; MEHPA: 10.0% v/v), and (c) carrier concentration (P5000 = 6% g/L; stripping solution = 0.6 M HNO3). [Mixing speed = 500 rpm; Ag concentration of the feed solution = 5000 mg/L; feed solution pH = 6.5; phase ratio = 6/5; treatment ratio = 1/10].

The main driving force in an ELM with a counter-transport mechanism is the difference between chemical potential of two aqueous phases related to their hydrogen ions concentrations47,

87

. The metal recovery efficiency of the ELM increases with the HNO3

concentration of the internal phase. However, the HNO3 concentration above a threshold causes the ELM instability47,

88

. To determine the maximum HNO3 concentration for the

ELM operation, the influence of acid concentration in the internal phase on silver ions recovery was investigated (Figure 5b). As can be seen, the silver extraction efficiency improved, the HNO3 concentration increased from 0.4 to 0.6 M. However, at the concentration of 0.7 M, the emulsion swelled up due to the osmotic phenomenon, leading to a 15


Page 16 of 28

Page 17 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


lower silver recovery. In addition to the dilution of the internal phase, at longer times the osmotic effect caused an increase in the silver concentration of the external phase due to rupture of the swelled globules, resulting in a low extraction efficiency89. The effect of MEHPA concentration on the extraction efficiency of silver ions is presented in Figure 5c. As can be seen, the transport of silver ions was insignificant without the carrier. This showed that the presence of the surfactant did not affect the silver ions transport. By increasing MEHPA concentration, the extraction efficiency of the silver ions was enhanced. A rise in the extraction efficiency from 90 to 98% was observed with an increase in the MEHPA concentration from 5 to 10 v/v %. The extraction enhancement was due to the higher carrier concentration at the interface, promoting the transport of the silver ions. As shown in Scheme S1, MEHPA has phosphorous in its structure. Phosphorus is a soft Lewis base 52, silver is a soft Lewis acid, and Al and K are hard Lewis acids. Due to the softsoft interactions, phosphorous has a higher affinity towards silver ions than other metal ions 53-56

. In addition, the concentration of Ag+ in the leach solution was higher than other metal

ions, increasing the possibility of Ag ions interactions with the carrier. The same behavior (more affinity towards silver ions) was observed when di(2-ethylhexyl) phosphoric acid (D2EHPA) was used as the carrier72,

90-92

. Nevertheless, a further increase in the MEHPA

concentration to 12.5% reduced the extraction efficiency due to more a viscous membrane phase and larger globules47, 87. Therefore, the carrier concentration of 10% was selected as the optimum value, which also meets the ELM stability requirements. ELM Technique. As transport of metal ions through an ELM depends on the H+ concentration in the external phase, the influence of pH on the silver extraction efficiency was investigated (Figure 6a)35. More silver was extracted when pH was increased from 5 to 6.5. At a low pH; i.e., ≤5, hydrogen ions highly compete with the silver ions at the membrane–feed interface, which decreases the recovery of silver ions. However, at a high pH; i.e., >5, more recovery of silver ions is anticipated due to lower hydrogen ion concentrations, which leads to the formation of

more metal-silver complexes at the

membrane–feed interface. This increases the concentration gradient of the complex in the membrane phase resulting in the enhancement of the silver recovery 82. A further pH increase to 7 lowers the extraction efficiency because of the emulsion swelling and instability 47. The pH difference between the internal and external phases causes a rise in the osmotic pressure and therefore emulsion swelling and lower extraction efficiency 29, 47. In our previous study, 16



100% silver ions had been recovered at this pH using solvent extraction 28. The highest silver recovery was achieved at the pH of 6.5. The mixing speed affected the ELM performance strongly. As can be seen in Figure 6b, the performance of the ELM improved, as the mixing speed was increases up to 500 rpm. The highest silver extraction efficiency (98%) was obtained with the mixing speed of 500 rpm after 10 min. This is due to an increase in the number of the emulsion globules and in the surface area, allowing for an enhancement in mass transfer. However, at 600 rpm, the extraction efficiency sharply declined after 5 min, because high mixing speeds add high shear energy to the system, leading to the globules breakage, and thereby the emulsion instability6667, 93-94

. The volume ratio of the internal phase (stripping phase) to the membrane phase has a

significant effect on the performance of an ELM. The effect of the volume ratio on the efficiency of silver recovery is shown in Figure 6c. Up to 6.0/5.0, the extraction efficiency was enhanced due to an increase in the emulsion capacity. The higher emulsion capacity is due to an enhancement in the internal phase volume, leading to the formation of a thinner membrane and a better dispersion of the internal phase in the membrane phase66, 81,67. This is favorable to transport of the silver ions to the internal phase and consequently higher extraction of the ions. A further increase in the volume ratio to 7.0/5.0 led to a decrease in the extraction efficiency after 7.5 min. This is most likely related to the formation of bigger droplets in a more viscous emulsion29,

67, 94

. A growth in the droplets diameter of internal

phase not only leads to declines the interfacial contact area between the external phase and emulsion, but also results in a decrease of emulsion stability, thereby decreases the extraction efficiency. In addition, the emulsion stability was in danger when the volume ratio increased from 6.0/5.0 to 7.0/5.0. At higher internal phase volume, the emulsion was more unstable due to the leakage of the internal phase into the external phase. Thus, the volume ratio of 6.0/5.0 maximizes the Ag extraction efficiency. The treatment ratio (emulsion phase holdup) is the ratio of the emulsion volume to the external phase (feed solution) volume. It affects the interfacial mass transfer across an ELM. Increasing the treatment ratio increases the extraction capacity of an ELM. The influence of the treatment ratio on the extraction efficiency of silver is illustrated in Figure 6d. The lowest extraction efficiency was obtained at the treatment ratio of 50/500. Increasing the treatment ratio to 75/500 slightly improved the extraction efficiency. Furthermore, at treatment ratios higher than 75/500 the extraction efficiency declined. This behavior can be explained via two 17


Page 18 of 28

Page 19 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


competing phenomena occurring simultaneously. Growing the treatment ratio increases the emulsion volume, the quantity of carrier and the surface area of the membrane, allowing for higher silver extraction38, 46. However, increasing the emulsion volume resulted in a decrease in the mass transfer area and therefore lower extraction efficiency. Also, high emulsion volumes prolong the life of the extraction process to achieve a specific efficiency, which increases the possibility of the emulsion breakage and decrease the transfer of the silver ions67, 89. Therefore, the treatment ratio of 75/500 was recognized as the optimum value.

Figure 6. Effects on the silver extraction efficiency. (a) acidity of feed solution (mixing speed = 500 rpm; phase ratio = 6/5; treatment ratio = 1/10), (b) mixing speed (pH = 6.5; phase ratio = 6/5; treatment ratio = 1/10), (c) phase ratio (pH = 6.5; mixing speed = 500 rpm; treatment ratio = 1/10), and (d) treatment ratio (pH = 6.5; mixing speed = 500 rpm; phase ratio = 6/5). [P5000 = 6% g/L, MEHPA = 10.0% v/v; Ag concentration of feed solution = 5000 mg/L; internal phase = 0.6 M HNO3]. 18



3.3.3. Recovery of Silver from the Leach Solution The optimum conditions for the extraction of silver ions from the synthetic solution using the ELM are summarized in Table S4. Figure 7 shows the Ag extraction efficiency of the ELM with the optimal conditions when the leach solution containing Ag, Al, Ca, Ti, Si and K ions was used. It can be seen that the 97% Ag extraction efficiency was attained in 7.5 min and the emulsion stability was maintained throughout the operation. However, the concentrations of the other metal ions in the internal phase increased with the extraction duration. Interestingly, this is most likely due to the highest carrier affinity toward the silver ions compared to the associated metal ions. After 10 min, while silver was almost completely extracted, the carrier started to interact with other metal ions. Therefore, to achieve the highest purity for the silver, the extraction should be stopped after 7.5 min.

Figure 7. Silver recovery from the leach solution when the optimum conditions in Table S4 were used [P5000 = 6% g/L; MEHPA = 10.00% v/v; stripping solution = 0.6 M HNO3; pH = 6.5; mixing speed = 500 rpm; phase ratio = 6/5; treatment ratio = 1/10].

4. Conclusions This paper presented a novel hybrid process for efficient silver recovery from industrial deactivated Ag/alumina catalysts. The process combines leaching and ELM techniques. The results showed that the nitric acid concentration, S/L ratio, mixing speed and temperature have strong effects on the leaching eﬃciencies of the metals, especially on Ag. More than 97.7% of Ag can be leached from spent Ag/alumina catalyst under the optimum leaching conditions: nitric acid concentration of 1.0 mol·L−1, solid/liquid ratio of 50 g·L−1, mixing speed of 500 rpm, and leaching temperature of 70 °C. A new PPG36-PEG34-PPG36 19


Page 20 of 28

Page 21 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


surfactant was synthesized, characterized and used to prepare stable ELMs. Two stability methods showed excellent compatibilities of the surfactant with the ELM components. Extraction of silver from the leach solution was successfully achieved using a novel stable ELM. ELM design parameters such as the surfactant and carrier concentrations, internal phase volume ratio and internal phase acidity, and ELM operating conditions such as the treatment volume ratio, feed-phase pH and mixing speed were optimized. With a P5000 concentration of 6% (w/v), a strip phase concentration of 0.6 M HNO3, a feed phase pH of 6.5, a mixing speed of 500 rpm, a treatment ratio of 75/500, and a phase ratio of 6/5, a 97% recovery of silver from the leach solution was attained after just 7.5 min. The achieved high silver recovery points to the potential of the leaching-ELM hybrid process for recovery of metals from deactivated catalysts.

Reference 1. Park, Y. J.; Fray, D. J., Recovery of high purity precious metals from printed circuit boards. Journal of Hazardous Materials 2009, 164 (2-3), 1152-1158. 2. Zirehpour, A.; Rahimpour, A.; Arabi Shamsabadi, A.; Sharifian Gh, M.; Soroush, M., Mitigation of thin-film composite membrane biofouling via immobilizing nano-sized biocidal reservoirs in the membrane active layer. Environmental Science & Technology 2017, 51 (10), 5511-5522. 3. Firouzjaei, M. D.; Shamsabadi, A. A.; Sharifian Gh, M.; Rahimpour, A.; Soroush, M., A Novel Nanocomposite with Superior Antibacterial Activity: A Silver‐Based Metal Organic Framework Embellished with Graphene Oxide. Advanced Materials Interfaces 2018, 1701365. 4. Ajiwe, V.; Anyadiegwu, I., Recovery of silver from industrial wastes, cassava solution effects. Separation and Purification Technology 2000, 18 (2), 89-92. 5. Nasser, I. I.; Amor, F. I. E. H.; Donato, L.; Algieri, C.; Garofalo, A.; Drioli, E.; Ahmed, C., Removal and recovery of Ag (CN) 2-from synthetic electroplating baths by polymer inclusion membrane containing Aliquat 336 as a carrier. Chemical Engineering Journal 2016, 295, 207-217. 6. Desai, K. R.; Murthy, Z., Removal of silver from aqueous solutions by complexation– ultrafiltration using anionic polyacrylamide. Chemical Engineering Journal 2012, 185, 187192. 7. El-Shafey, E.; Al-Hashmi, A., Sorption of lead and silver from aqueous solution on phosphoric acid dehydrated carbon. Journal of Environmental Chemical Engineering 2013, 1 (4), 934-944. 8. Ahmad, A.; Kusumastuti, A.; Derek, C.; Ooi, B., Emulsion liquid membrane for heavy metal removal: An overview on emulsion stabilization and destabilization. Chemical engineering journal 2011, 171 (3), 870-882. 9. Pillai, K. C.; Chung, S. J.; Moon, I.-S., Studies on electrochemical recovery of silver from simulated waste water from Ag (II)/Ag (I) based mediated electrochemical oxidation process. Chemosphere 2008, 73 (9), 1505-1511.

20



10. Rivera, I.; Roca, A.; Cruells, M.; Patiño, F.; Salinas, E., Study of silver precipitation in thiosulfate solutions using sodium dithionite. Application to an industrial effluent. Hydrometallurgy 2007, 89 (1-2), 89-98. 11. Zouboulis, A., Silver recovery from aqueous streams using ion flotation. Minerals Engineering 1995, 8 (12), 1477-1488. 12. Wang, X.; Zhao, Y.; Li, X.; Ren, Y., Performance evaluation of a microfiltrationosmotic membrane bioreactor (MF-OMBR) during removing silver nanoparticles from simulated wastewater. Chemical Engineering Journal 2017, 313, 171-178. 13. Kononova, O.; Kholmogorov, A.; Danilenko, N.; Goryaeva, N.; Shatnykh, K.; Kachin, S., Recovery of silver from thiosulfate and thiocyanate leach solutions by adsorption on anion exchange resins and activated carbon. Hydrometallurgy 2007, 88 (1-4), 189-195. 14. Hu, Q.; Yang, G.; Zhao, Y.; Yin, J., Determination of copper, nickel, cobalt, silver, lead, cadmium, and mercury ions in water by solid-phase extraction and the RP-HPLC with UV-Vis detection. Analytical and bioanalytical chemistry 2003, 375 (6), 831-835. 15. Reyes-Cruz, V.; González, I.; Oropeza, M., Electro-recovery of gold and silver from a cyanide leaching solution using a three-dimensional reactor. Electrochimica Acta 2004, 49 (25), 4417-4423. 16. Khan, A.; Badshah, S.; Airoldi, C., Biosorption of some toxic metal ions by chitosan modified with glycidylmethacrylate and diethylenetriamine. Chemical engineering journal 2011, 171 (1), 159-166. 17. Alvarado-Macías, G.; Fuentes-Aceituno, J.; Nava-Alonso, F.; Lee, J.-c., Silver leaching with the nitrite–copper novel system: A kinetic study. Hydrometallurgy 2016, 160, 98-105. 18. Avraamides, J., Leaching of silver with various copper (II) salts in aqueous acetonitrile: solubility measurements and recovery of silver powders via distillation. Hydrometallurgy 1987, 18 (1), 55-64. 19. Wang, H.; Huang, K.; Zhang, Y.; Chen, X.; Jin, W.; Zhe, S., Recovery of lithium, nickel and cobalt from spent lithium-ion batteries powders by selective ammonia leaching and adsorption separation system. 20. He, L.-P.; Sun, S.-Y.; Mu, Y.-Y.; Song, X.-F.; Yu, J.-G., Recovery of lithium, nickel, cobalt, and manganese from spent lithium-ion batteries using L-tartaric acid as a leachant. ACS Sustainable Chemistry & Engineering 2016, 5 (1), 714-721. 21. Li, L.; Fan, E.; Guan, Y.; Zhang, X.; Xue, Q.; Wei, L.; Wu, F.; Chen, R., Sustainable recovery of cathode materials from spent lithium-ion batteries using lactic acid leaching system. ACS Sustainable Chemistry & Engineering 2017, 5 (6), 5224-5233. 22. Cuscusa, M.; Rigoldi, A.; Artizzu, F.; Cammi, R.; Fornasiero, P.; Deplano, P.; Marchiò, L.; Serpe, A., Ionic Couple-Driven Palladium Leaching by Organic Triiodide Solutions. ACS Sustainable Chemistry & Engineering 2017, 5 (5), 4359-4370. 23. Hu, P.; Zhang, Y.; Huang, J.; Liu, T.; Yuan, Y.; Xue, N., Eco-friendly leaching and separation of vanadium over iron impurity from vanadium-bearing shale using oxalic acid as a leachant. ACS Sustainable Chemistry & Engineering 2017. 24. Sun, P.-P.; Song, H.-I.; Kim, T.-Y.; Min, B.-J.; Cho, S.-Y., Recovery of Silver from the Nitrate Leaching Solution of the Spent Ag/α-Al2O3 Catalyst by Solvent Extraction. Industrial & Engineering Chemistry Research 2014, 53 (52), 20241-20246. 25. Shimojo, K.; Goto, M., Solvent extraction and stripping of silver ions in roomtemperature ionic liquids containing calixarenes. Analytical chemistry 2004, 76 (17), 50395044.

21


Page 22 of 28

Page 23 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


26. Yin, X.; Long, J.; Xi, Y.; Luo, X., Recovery of Silver from Wastewater Using a New Magnetic Photocatalytic Ion-Imprinted Polymer. ACS Sustainable Chemistry & Engineering 2017, 5 (3), 2090-2097. 27. Niroomanesh, M.; Ehsani, M. R.; Ghadiri, M.; Shamsabadi, A. A.; Laki, S., Solvent Extraction of Mn (II) by Mixture of MEHPA and DEHPA (MDEHPA) from Sulfate Solution. Transactions of the Indian Institute of Metals 2016, 69 (8), 1563-1569. 28. Laki, S.; Shamsabadi, A. A.; Kargari, A., Comparative solvent extraction study of silver (I) by MEHPA and Cyanex 302 as acidic extractants in a new industrial diluent (MIPS). Hydrometallurgy 2016, 160, 38-46. 29. Othman, N.; Mat, H.; Goto, M., Separation of silver from photographic wastes by emulsion liquid membrane system. Journal of membrane science 2006, 282 (1-2), 171-177. 30. Chakrabarty, K.; Saha, P.; Ghoshal, A. K., Separation of lignosulfonate from its aqueous solution using emulsion liquid membrane. Journal of Membrane Science 2010, 360 (1-2), 34-39. 31. Zeng, L.; Yang, L.; Liu, Q.; Li, W.; Yang, Y., Influences of axial mixing of continuous phase and polydispersity of emulsion drops on mass transfer performance in a modified rotating disc contactor for an emulsion liquid membrane system. Industrial & Engineering Chemistry Research 2015, 54 (40), 9832-9843. 32. Park, H.-J.; Chung, T.-S., Removal of phenol from aqueous solution by liquid emulsion membrane. Korean Journal of Chemical Engineering 2003, 20 (4), 731-735. 33. Madaeni, S. S.; Monfared, H. A.; Vatanpour, V.; Shamsabadi, A. A.; Salehi, E.; Daraei, P.; Laki, S.; Khatami, S. M., Coke removal from petrochemical oily wastewater using γ-Al2O3 based ceramic microfiltration membrane. Desalination 2012, 293, 87-93. 34. Madaeni, S. S.; Vatanpour, V.; Ahmadi Monfared, H.; Arabi Shamsabadi, A.; Majdian, K.; Laki, S., Removal of coke particles from oil contaminated marun petrochemical wastewater using PVDF microfiltration membrane. Industrial & Engineering Chemistry Research 2011, 50 (20), 11712-11719. 35. Laki, S.; Shamsabadi, A. A.; Madaeni, S. S.; Niroomanesh, M., Separation of manganese from aqueous solution using an emulsion liquid membrane. RSC Advances 2015, 5 (102), 84195-84206. 36. Feng-Jee, C.; Bao-Long, T.; Ming-Xia, X.; Qing-Jin, Q.; Lan-Ying, Z., A study on a two-component liquid membrane system. Journal of membrane science 1985, 23 (2), 137154. 37. Mohapatra, R.; Kanungo, S., Kinetics of Mn (II) transport from aqueous sulfate solution through a supported liquid membrane containing di (2-ethylhexyl) phosphoric acid in kerosene. Separation science and technology 1992, 27 (13), 1759-1773. 38. Boyadzhiev, L.; Bezenshek, E., Carrier mediated extraction: application of double emulsion technique for mercury removal from waste water. Journal of Membrane Science 1983, 14 (1), 13-18. 39. Devi, N.; Nathsarma, K.; Chakravortty, V., Extraction and separation of Mn (II) and Zn (II) from sulphate solutions by sodium salt of Cyanex 272. Hydrometallurgy 1997, 45 (12), 169-179. 40. Mane, C. P.; Anuse, M. A., Extraction behaviour of 2-octylaminopyridine towards lead (II) from succinate media and its separation from other toxic metals. Journal of hazardous materials 2008, 152 (3), 1146-1154. 41. Kolekar, S. S.; Anuse, M. A., Solvent extraction separation of rhodium (III) with Nnoctylaniline as an extractant. Talanta 2002, 58 (4), 761-771.

22



42. BABA, Y.; UMEZAKI, Y.; INOUE, K., Extraction equilibrium of silver (I) with triisobutylphosphine sulfide from nitrate media. Journal of chemical engineering of Japan 1986, 19 (1), 27-30. 43. Kulkarni, P. S.; Tiwari, K. K.; Mahajani, V. V., Membrane stability and enrichment of nickel in the liquid emulsion membrane process. Journal of Chemical Technology and Biotechnology 2000, 75 (7), 553-560. 44. Abou-Nemeh, I.; Van Peteghem, A., Sorbitan monooleate (Span 80) decomposition during membrane ageing. A kinetic study. Journal of membrane science 1992, 74 (1-2), 9-17. 45. Barad, J. M.; Chakraborty, M.; Bart, H.-J. r., Stability and performance study of water-in-oil-in-water emulsion: extraction of aromatic amines. Industrial & Engineering Chemistry Research 2010, 49 (12), 5808-5815. 46. El Aamrani, F.; Kumar, A.; Beyer, L.; Florido, A.; Sastre, A., Mechanistic study of active transport of silver (I) using sulfur containing novel carriers across a liquid membrane. Journal of membrane science 1999, 152 (2), 263-275. 47. Dâas, A.; Hamdaoui, O., Extraction of anionic dye from aqueous solutions by emulsion liquid membrane. Journal of Hazardous Materials 2010, 178 (1-3), 973-981. 48. Kumbasar, R. A., Selective extraction of chromium (VI) from multicomponent acidic solutions by emulsion liquid membranes using tributhylphosphate as carrier. Journal of hazardous materials 2010, 178 (1-3), 875-882. 49. Dâas, A.; Hamdaoui, O., Extraction of bisphenol A from aqueous solutions by emulsion liquid membrane. Journal of Membrane Science 2010, 348 (1-2), 360-368. 50. Datta, D.; Kumar, S., Reactive extraction of 2-methylidenebutanedioic acid with N, N-dioctyloctan-1-amine dissolved in six different diluents: experimental and theoretical equilibrium studies at (298±1) K. Journal of Chemical & Engineering Data 2011, 56 (5), 2574-2582. 51. Nguyen, D.; Balsamo, V.; Phan, J., Effect of diluents and asphaltenes on interfacial properties and steam-assisted gravity drainage emulsion stability: Interfacial rheology and wettability. Energy & Fuels 2013, 28 (3), 1641-1651. 52. Awad, F. S.; AbouZeid, K. M.; El-Maaty, W. M. A.; El-Wakil, A. M.; El-Shall, M. S., Efficient Removal of Heavy Metals from Polluted Water with High Selectivity for Mercury (II) by 2-Imino-4-thiobiuret–Partially Reduced Graphene Oxide (IT-PRGO). ACS applied materials & interfaces 2017, 9 (39), 34230-34242. 53. Ravishankar Rai, V.; Jamuna Bai, A., Nanoparticles and their potential application as antimicrobials. A Méndez-Vilas A, editor. Mysore: Formatex 2011. 54. Oh, Y.; Morris, C. D.; Kanatzidis, M. G., Polysulfide chalcogels with ion-exchange properties and highly efficient mercury vapor sorption. Journal of the American Chemical Society 2012, 134 (35), 14604-14608. 55. Chillemi, G.; Mancini, G.; Sanna, N.; Barone, V.; Della Longa, S.; Benfatto, M.; Pavel, N. V.; D'Angelo, P., Evidence for sevenfold coordination in the first solvation shell of Hg (II) aqua ion. Journal of the American Chemical Society 2007, 129 (17), 5430-5436. 56. El-Shishtawy, R. M.; Asiri, A. M.; Abdelwahed, N. A.; Al-Otaibi, M. M., In situ production of silver nanoparticle on cotton fabric and its antimicrobial evaluation. Cellulose 2011, 18 (1), 75-82. 57. Dutrizac, J. E.; MacDonald, R., Ferric ion as a leaching medium. Minerals Science and Engineering 1974, 6 (2), 59-95. 58. Akretche, D.-E.; Slimane, S. K.; Kerdjoudj, H., Selective leaching of a polymetallic complex ore by sulphuric acid and thiourea mixed with sea water. Hydrometallurgy 1995, 38 (2), 189-204. 23


Page 24 of 28

Page 25 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


59. Sandberg, R.; Huiatt, J., Ferric chloride, thiourea and brine leach recovery of Ag, Au and Pb from complex sulfides. JOM 1986, 38 (6), 18-22. 60. Gašpar, V.; Mejerovich, A.; Meretukov, M.; Schmiedl, J., Practical application of potential-pH diagrams for Au-CS (NH2) 2-H2O and Ag-CS (NH2) 2-H2O systems for leaching gold and silver with acidic thiourea solution. Hydrometallurgy 1994, 34 (3), 369381. 61. Won, C.; Cho, T., The Dissolution of Gold and Silver in Acidic Solutions of Thiourea. J. Korean Inst. Met. 1985, 23 (5), 495-500. 62. Dutrizac, J., DISSOLUTION OF SILVER-CHLORIDE IN FERRIC-CHLORIDE HYDROCHLORIC-ACID MEDIA. TRANSACTIONS OF THE INSTITUTION OF MINING AND METALLURGY SECTION C-MINERAL PROCESSING AND EXTRACTIVE METALLURGY 1987, 96, C79-C86. 63. Nuñez, C.; Roca, A.; Espiell, F., IMPROVED GOLD AND SILVER RECOVERY FROM SPANISH GOSSAN ORES BY SULFIDIZATION PRIOR TO CYANIDATION. TRANSACTIONS OF THE INSTITUTION OF MINING AND METALLURGY SECTION CMINERAL PROCESSING AND EXTRACTIVE METALLURGY 1986, 95, C195-C198. 64. Acma, E.; Arslan, F.; Wuth, W., Silver extraction from a refractory type ore by thiourea leaching. Hydrometallurgy 1993, 34 (2), 263-274. 65. Dutrizac, J., The leaching of silver sulphide in ferric ion media. Hydrometallurgy 1994, 35 (3), 275-292. 66. Das, C.; Rungta, M.; Arya, G.; DasGupta, S.; De, S., Removal of dyes and their mixtures from aqueous solution using liquid emulsion membrane. Journal of hazardous materials 2008, 159 (2-3), 365-371. 67. Tang, B.; Yu, G.; Fang, J.; Shi, T., Recovery of high-purity silver directly from dilute effluents by an emulsion liquid membrane-crystallization process. Journal of hazardous materials 2010, 177 (1-3), 377-383. 68. Özmetin, C.; Çopur, M.; Yartasi, A.; Muhtar Kocakerim, M., Kinetic investigation of reaction between metallic silver and nitric acid solutions in the range 7.22− 14.44 M. Industrial & engineering chemistry research 1998, 37 (12), 4641-4645. 69. Ozmetin, C., A Rotating Disc Study on Silver Dissolution in Concentrate HNO~ 3 Solutions. Chemical and biochemical engineering quarterly 2003, 17 (2), 165-169. 70. Ritcey, G. M.; Ashbrook, A., Solvent Extraction. Principles and Applications to Process Metallurgy. Part I. 1984. 71. Musikas, C.; Choppin, G. R.; Rydberg, J., Principles and practices of solvent extraction. Marcel Dekker: 1992. 72. Gamino Arroyo, Z.; Stambouli, M.; Pareau, D.; Buch, A.; Durand, G.; Avila Rodriguez, M., Thiosubstituted organophosphorus acids as selective extractants for Ag (I) from acidic thiourea solutions. Solvent Extraction and Ion Exchange 2008, 26 (2), 128-144. 73. Yin, X.; Wu, Y.; Tian, X.; Yu, J.; Zhang, Y.-N.; Zuo, T., Green Recovery of Rare Earths from Waste Cathode Ray Tube Phosphors: Oxidative Leaching and Kinetic Aspects. ACS Sustainable Chemistry & Engineering 2016, 4 (12), 7080-7089. 74. Li, H.; Xing, S.; Liu, Y.; Li, F.; Guo, H.; Kuang, G., Recovery of Lithium, Iron, and Phosphorus from Spent LiFePO4 Batteries Using Stoichiometric Sulfuric Acid Leaching System. ACS Sustainable Chemistry & Engineering 2017, 5 (9), 8017-8024. 75. Trinh, H. B.; Lee, J.-c.; Srivastava, R. R.; Kim, S.; Ilyas, S., Eco-threat Minimization in HCl Leaching of PGMs from Spent Automobile Catalysts by Formic Acid Prereduction. ACS Sustainable Chemistry & Engineering 2017, 5 (8), 7302-7309.

24



76. Li, Q.; Liu, Z.; Liu, Q., Kinetics of vanadium leaching from a spent industrial V2O5/TiO2 catalyst by sulfuric acid. Industrial & Engineering Chemistry Research 2014, 53 (8), 2956-2962. 77. Geankoplis, C., J1 T ransport Processes and Unit Operations. 3rd ed1 Englewood Cliffs. NJ: Prentice Hall: 1993. 78. Levenspiel, O., Chemical reaction engineering. Industrial & engineering chemistry research 1999, 38 (11), 4140-4143. 79. Stankiewicz, A.; Moulijn, J. A., Re-engineering the chemical processing plant: process intensification. CRC Press: 2003. 80. Laki, S.; Kargari, A., Extraction of Silver Ions from Aqueous Solutions by Emulsion Liquid Membrane. Journal of Membrane Science and Research 2016, 2 (1), 33-40. 81. Hirato, T.; Kishigami, I.; Awakura, Y.; Majima, H., Concentration of uranyl sulfate solution by an emulsion-type liquid membrane process. Hydrometallurgy 1991, 26 (1), 19-33. 82. Hasan, M.; Selim, Y.; Mohamed, K., Removal of chromium from aqueous waste solution using liquid emulsion membrane. Journal of hazardous materials 2009, 168 (2-3), 1537-1541. 83. Ng, Y. S.; Jayakumar, N. S.; Hashim, M. A., Performance evaluation of organic emulsion liquid membrane on phenol removal. Journal of hazardous materials 2010, 184 (13), 255-260. 84. Zhao, L.; Fei, D.; Dang, Y.; Zhou, X.; Xiao, J., Studies on the extraction of chromium (III) by emulsion liquid membrane. Journal of hazardous materials 2010, 178 (1-3), 130-135. 85. Othman, N.; Zailani, S.; Mili, N., Recovery of synthetic dye from simulated wastewater using emulsion liquid membrane process containing tri-dodecyl amine as a mobile carrier. Journal of hazardous materials 2011, 198, 103-112. 86. Uddin, M. S.; Kathiresan, M., Extraction of metal ions by emulsion liquid membrane using bi-functional surfactant: equilibrium and kinetic studies. Separation and purification Technology 2000, 19 (1-2), 3-9. 87. Davoodi-Nasab, P.; Rahbar-Kelishami, A.; Safdari, J.; Abolghasemi, H., Evaluation of the emulsion liquid membrane performance on the removal of gadolinium from acidic solutions. Journal of Molecular Liquids 2018. 88. Schmidts, T.; Dobler, D.; Guldan, A.-C.; Paulus, N.; Runkel, F., Multiple W/O/W emulsions—Using the required HLB for emulsifier evaluation. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2010, 372 (1-3), 48-54. 89. Teresa, M.; Reis, A.; Carvalho, J. M., Recovery of zinc from an industrial effluent by emulsion liquid membranes. Journal of membrane science 1993, 84 (3), 201-211. 90. Men’shikov, V.; Voronova, I. Y.; Proidakova, O.; Malysheva, S.; Ivanova, N.; Belogorlova, N.; Gusarova, N.; Trofimov, B., Preconcentration of gold, silver, palladium, platinum, and ruthenium with organophosphorus extractants. Russian journal of applied chemistry 2009, 82 (2), 183-189. 91. Gherrou, A.; Kerdjoudj, H.; Molinari, R.; Drioli, E., Removal of silver and copper ions from acidic thiourea solutions with a supported liquid membrane containing D2EHPA as carrier. Separation and Purification Technology 2002, 28 (3), 235-244. 92. Bromberg, L.; Lewin, I.; Warshawsky, A., Membrane extraction of silver by di (2ethylhexyl) dithiophosphoric acid. Journal of membrane science 1992, 70 (1), 31-39. 93. Kumbasar, R. A.; Tutkun, O., Separation of cobalt and nickel from acidic leach solutions by emulsion liquid membranes using Alamine 300 (TOA) as a mobile carrier. Desalination 2008, 224 (1-3), 201-208.

25


Page 26 of 28

Page 27 of 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


94. Kumbasar, R. A., Extraction and concentration study of cadmium from zinc plant leach solutions by emulsion liquid membrane using trioctylamine as extractant. Hydrometallurgy 2009, 95 (3-4), 290-296.

26


Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25


Page 28 of 28

Sustainable Recovery of Silver from Deactivated Catalysts Using a

Recommend Documents