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Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process
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Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process Norul Fatiha Mohamed Noah a, Norasikin Othman a,b,∗, Norela Jusoh a a
Department of Chemical Engineering, Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bharu, Johor, Malaysia Centre of Lipids Engineering & Applied Research (CLEAR), Ibnu Sina Institute for Scientific and Industrial Research (Ibnu Sina ISIR), Universiti Teknologi Malaysia, 81310 UTM Johor Bharu, Johor, Malaysia
b
a r t i c l e
i n f o
Article history: Received 23 August 2015 Revised 22 February 2016 Accepted 24 March 2016 Available online xxx Keywords: Emulsion liquid membrane Palladium Chromium Electroplating wastewater
a b s t r a c t A new liquid membrane formulation containing phosphinic acid groups as a carrier was developed for the selective extraction of palladium (Pd) from electroplating wastewater using emulsion liquid membrane (ELM) process. The important parameters that affect the membrane stability and the recovery of Pd were investigated, such as extraction time, concentrations of carrier and stripping agents, pH of feed phase, and treat ratio. Furthermore, at the optimum condition, the performance of Pd extraction was evaluated using real matrices solution. All experiments were carried out using batch extraction process and the recovery stage at high voltage demulsifier was employed. The results showed that the favorable conditions obtained for the extraction and the recovery processes were at 0.2 M of Cyanex 302, 1.0 M thiourea in 1.0 M H2 SO4 of stripping agent, 1:3 treat ratio, pH 3 of feed phase, and 5 mins of extraction time. At these conditions, the maximum extraction and recovery of the Pd was 97% and 40%, respectively. Moreover, the result from the real matrices showed that almost 100% of Pd was extracted selectively over chromium at these conditions. © 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Recovery of electroplating wastewaters is an important subject not only from the view of waste treatment but also from the recovery of valuable metals that is Pd. Exposure of Pd can cause acute toxicity or hypersensitivity with respiratory symptoms, urticaria and less frequently, contact dermatitis. The epidemiological studies have demonstrated that the Pd ions are one of the most frequent reacting sensitizers, which affect the immune system that represents the most important health hazard to humans [1]. Pd with unique physical properties has been used in diverse industrial applications such as jewelry, semiconductors and connectors. These applications take benefit of Pd’s lower cost and its material properties that are superior to gold. Due to its economic value and its limited natural resources, Pd recovery from the secondary resources is significant. According to the invention [2], the amount of Pd used in Pd exchange bath is 0.150–0.25 g/L [2]. Out of the total amount of precious metals used in electroplating, 4% goes as waste in the sludge spent wash and the electroplating solution [3]. Hence, it can be concluded that the Pd composition in the electroplating wastewater is in the range of 6–10 ppm.
∗
Corresponding author. Tel: +6 07 5535561; fax: +6 07 5581463. E-mail address: [email protected] (N. Othman).
In order to separate the Pd from aqueous solutions, various studies have been recently focused on conventional methods. For example, an ion exchange is one of the simple ways to separate Pd [4]. A disadvantage of this treatment is the method involves high operating costs for the ion exchange unit due to the resin costs. Biosorption is another efficient low cost process of Pd ions recovery from aqueous solutions. Since the biosorption frequently employs dead biomass, it can eliminate the problem of toxicity environments and the need of nutrient requirement [5]. Solvent extraction has become an effective technique in the recovery and separation of Pd [6,7]. However, various problems have been associated with the solvent extraction systems, such as the corresponding hydrodynamics related problems, third phase problems, and compatibility issues with the diluent. In 1968, emulsion liquid membranes (ELMs) were first applied to the separation of hydrocarbons [8]. Recently, the ELM technology has become a promising method to recover precious metals, even in a very low concentration from the industrial wastes [9,10]. Since the ELM process combines the extraction and recovery process, this method does not need the second treatment like electrowinning that needs cementation or chemical precipitation process [11,12]. Due to its high surface area to volume ratio compared to solid membranes, it has high solute transfer flux and selectivity as well as low contacting equipment volume and cost [11,13], and it is chosen as the suitable method to extract and recover Pd
http://dx.doi.org/10.1016/j.jtice.2016.03.047 1876-1070/© 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article as: N.F.M. Noah et al., Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.03.047
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Table 1 Experimental conditions used for the preparations of ELMs.
Pre-treatment
Solvent
Kerosene
Homogenizer speed (HS) Emulsifying time Agitation speed (AS) Surfactant Carrier Stripping agent (SA)
12,0 0 0 rpm 3 mins 200 rpm 2% (w/v) Span 80 0.001–0.7 M Cyanex 302 0.3, 0.5, 1.0, and 1.5 M Thiourea in 0.3, 0.5, 1.0 and 1.5 M H2 SO4 1:3, 1:5, 1:7, 1:10 1, 3, 5, 7 1, 3,5, 7, 10 mins
Treat ratio (TR) pH feed phase Extraction time
First Plating
Second Plating
Entry waste (Waste 1)
Exit waste (Waste 2)
Oxidation/ Neutralizatio
Wastewater
Kualiti Alam Schedule
Fig. 3. Electroplating wastewater process flow diagrams.
the internal phase and the carriers diffuse back to the membraneexternal interphase to react with other Pds
PdR2 (org) + 2[CS + (RH)2 (org)
(NH2 )2 H]+ (aq)
→
Pd[(CS
(NH2 )2 )2 ]2+ (aq) (2)
3. Materials and methods 3.1. Materials Fig. 1. Schematic transport mechanism of Pd by ELM from the aqueous solution using Cyanex 302 as carrier.
Fig. 2. Structure of Cyanex 302.
from the electroplating wastewater. ELM has been intensively investigated and demonstrated as an effective alternative technology for the separation and purification process for precious metal extraction such as silver [14], gold [15] and Pd [16]. Hence, in this research, the ELM process was utilized for the recovery of Pd from the electroplating wastewater. The ranges of parameters used in the ELM extraction of Pd from the simulated liquid waste are listed in Table 1. The liquid membrane components such as type of diluents and stripping agent and its concentration for the Pd extraction are taken from the previous studies [17].
There are four components in the ELM system namely carrier, surfactant, stripping agent and diluent. All four components are manufactured for laboratory grade and were used as received. The Cyanex 302 (85% purity) as a carrier for Pd was obtained from Sigma. The kerosene (99% purity) and span 80 (99% purity) as a diluent and surfactant respectively were purchased from Fluka Chemika. The thiourea (99% purity) and sulfuric acid (99% purity) were purchased from Merck (M) Sdn. Bhd. An aqueous solution of Pd was prepared using palladium (II) nitrate (Pd(NO3 )2 ) obtained from Merck (M) Sdn. Bhd. The water used in this research was distilled water. 3.2. Electroplating waste sample and characterization process The real electroplating wastewater sample was obtained from the Electroplating Company at Masai, Johor. Ion chromatography (IC) model LC20 with electric chemical detector model ED40 was used to measure anion contents in the sample. Contents of metals in the electroplating wastewaters were measured using an atomic absorption spectrometer (AAS) (PerkinElmer, model: Analyst 400). A Cyber scan 100 pH meter model was used to measure the pH measurements. A hydrometer was used to measure the densities (ρ ) of the samples. A programmable Rheometer Brookfield Model DV-III was used to determine the kinematic viscosity, v [14].
2. Extraction mechanism of palladium 3.3. Palladium in simulated electroplating wastewater The transport mechanism of Pd by the ELM process using Cyanex 302 as a carrier is shown in Fig. 1. In this mechanism, the selected carrier, Cyanex 302 (Fig. 2) chemically reacts with the cationic Pd in kerosene to form complexes of Pd–Cyanex 302 at the membrane-external interphase as represented by Eq. (1).
Pd2+ (aq) +(RH)2 (org) → PdR2 (org) +2(H+ )(aq)
(1)
After that, the Pd–Cyanex 302 complexes diffuse through the membrane phase from the membrane-external interphase to the membrane-internal interphase. Then, the Pd–Cyanex 302 complexes at the membrane-internal interphase undergo the stripping process by reacting with the acidic thiourea from the internal phase as shown in Eq. (2). The Pd–thiourea complexes released to
The palladium (II) nitrate was dissolved into real electroplating wastewater in the concentration range of 1–15 ppm. Then, the initial pH of the feed phase was measured. The pH for each sample was adjusted in the range of 3.0–3.5. In this preparation, two types of waste solutions were considered in the electroplating process, which were Waste 1 and Waste 2 for entry and exit effluents, respectively, as shown in Fig. 3. 3.4. Water in oil (W/O) emulsion preparation The organic solution was prepared by dissolving an appropriate concentration of the carrier (Cyanex 302) and the surfactant (Span 80) in a diluent (kerosene). The internal aqueous stripping phase
Please cite this article as: N.F.M. Noah et al., Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.03.047
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Fig. 4. Schematic diagrams of ELM process for Pd extraction and recovery process [18]. Fig. 5. Primary emulsions at 400x magnification under microscope. [19].
was a thiourea in H2 SO4 solution. An equal volume of 5 mL portions of organic phase and aqueous stripping phase were stirred continuously at 12,0 0 0 rpm for about 3 mins to obtain stable water in oil emulsion. The emulsion must be freshly prepared before each experiment of extraction study. 3.5. Extraction and recovery process The ELM extraction of Pd was carried out by dispersing the W/O emulsion into the external phase containing Pd ions. The water in oil in water (W/O/W) emulsion was agitated using a fourblade stirrer (Cole-Parmer, model: 50,0 06-0 0). Several parameters such as carrier concentration, internal phase concentration, treat ratio, pH of external phase, and extraction time were varied during the Pd extraction experiments. One-factor-at-a-time method was applied. The volume of emulsion before and after extraction was measured for emulsion stability study. After the extraction process, the sample mixture of W/O emulsion and external phase was separated using the separating funnel. The aqueous external samples were analyzed using the AAS for Pd removal extraction performance while the remaining emulsion will undergo the demulsification process. Pulsed AC field with 20 kV electric potential at 300 Hz frequency across the outer and inner electrode probe was used to demulsify the emulsion in order to recover Pd in the internal stripping phase. The recovered Pd solution was collected and analyzed using the AAS. The recovery of Pd was calculated based on mass balance principal. At these favorable conditions, the performance of Pd extraction from real matrices solution was studied. The experiment was carried out using different initial Pd concentrations from 1 to 15 ppm. The schematic diagram of the ELM process is shown in Fig. 4. 3.6. Determination and calculation of ELM performance The percentage of Pd extraction, recovery and swelling or breakage was determined by using Eqs. (3)–(5), respectively:
Extraction (% ) = Recovery (% ) =
[Pd]i − [Pd]f × 100% [Pd]i
[Pd]int × 100% 2TR[Pd]i
Swelling/Breakage (% ) =
Vf − Vi × 100% Vi
(3)
(4)
(5)
where, [Pd]i is the initial concentration of Pd ion in aqueous before extraction, [Pd]f represents the final concentration of Pd ion in aqueous after extraction, [Pd]int is the concentration of Pd in internal phase after extraction, Vi is the initial volume of emulsion
Fig. 6. Percentages of Pd extraction, recovery and swelling/breakage at various Cyanex 302 concentration (Experimental conditions: [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
before extraction, Vf is the final volume of emulsion after extraction, and TR is the treat ratio. 4. Results and discussion 4.1. Primary emulsion droplet size From the previous study [19], the stability of emulsion was studied. Fig. 5 shows the image of emulsion droplet. The most stable emulsion was observed at 2% (w/v) of span 80 concentration, 12,0 0 0 rpm homogenizer speed, 3 mins emulsifying time and 200 rpm agitation speed. At the optimum condition, the average droplet size was 3 μm, which is accepted as stable emulsions. 4.2. Effect of carrier concentration The proper selection of carrier concentration always exerts a significant influence on the ELM system [20]. The effect of carrier concentration on the extraction of Pd is presented in Fig. 6. Fig. 7 shows the effects of carrier concentration on viscosity of liquid membrane. The results showed that a very small amount of Pd was extracted at 0.001–0.01 M of Cyanex 302. This is due to the inability of the carrier concentration to selectively transport the solute throughout the membrane phase into the internal phase. Therefore, it gives a low extraction performance. Meanwhile, the extraction performance drastically increased from 11% to 65% when the concentration of Cyanex 302 is increased from 0.01 to 0.05 M. As can be seen at 0.01 and 0.05 M Cyanex 302, the viscosity of liquid membrane is almost equal (2.2 cp) and it provides the same extraction rate. This means that the increase in Pd extraction depends on the amount of carrier compound that existed in the liquid membrane. Hence, more formation of Pd–carrier complexes
Please cite this article as: N.F.M. Noah et al., Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.03.047
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% Swelling % Pd extracon % Pd recovery
0.3
0.5
1
1.5
Concentraon H2SO4 in 1 M Thiourea (M)
Fig. 7. Effect of carrier concentration on viscosity of liquid membrane (Experimental conditions: [Span 80] = 2% w/v, Diluent = kerosene).
can occur at the membrane-external aqueous interphase, resulting in increases in diffusion rates of Pd ion from the external phase into the membrane phase. Further increases of the Cyanex 302 concentration up to 0.3 M significantly increased the Pd extraction rate, which was around 95%. It is indicated that the bigger the amount of carrier compounds existed in the membrane phase, the larger amount of Pd is extracted. This finding is in line with Fouad [21] who discovered that the extraction percentages increased with an increase in the membrane’s carrier concentration. Further increases of the Cyanex 302 concentration up to 0.7 M decreased the extraction rate to 90%. This is due to high concentration of carrier resulted in a decrease of Pd extraction due to the increase in the viscosity of the membrane phase as shown in Fig. 7. This indicated that 0.3 M is enough for the facilitated transport of Pd. The result also shows that from 0.001 to 0.005 M Cyanex 302, the recovery percentage of Pd was increased. The recovery performance remained constant as further increases up to 0.05 M Cyanex 302 were made due to small formations of Pd–carrier complexes in the membrane phase. Further increasing of concentrations up to 0.2 M significantly increased the percentage of recovery. Meanwhile, although the extraction percentage increased when the carrier concentration was increased up to 0.3 M, the recovery performances decreased due to accumulation of Pd–carrier complexes in the membrane phase. Further increases up to 0.7 M significantly decreased the percentage of recovery. It can be seen that the more concentrated the carrier concentration is, the more viscous the membrane phase, as illustrated in Fig. 7. This effect resists the diffusion of solute into the internal phase, which reduces the mass transfer of Pd–carrier complexes. Therefore, the recovery percentage of Pd was decreased. Meanwhile, by increasing the concentration of Cyanex 302 from 0.001 to 0.1 M, the emulsion swelling had decreased. This is due to the high viscosity of liquid membrane that led to resistance for the water transport. This is in agreement with Kulkarni et al. [22] who indicated that high viscosities of liquid membrane increased the emulsion stability by inhibiting water transportation into the internal phase, leading to emulsion swelling. This result is supported by Fig. 7 that shows the viscosity of emulsion increasing from 1.5 to 3.0 cP when the carrier concentration was increased from 0.001 to 0.7 M. The emulsion swelling began to plateau with further increases of the carrier concentration over 0.7 M Cyanex 302. This indicates that some globules tend to swell and break at the same time. Therefore, there exists a trade-off between these two effects. In addition, the result showed that increasing of the carrier concentration from 0.1 to 0.7 M results in the increase of liquid membrane viscosity. High viscosity will reduce water molecule transport from the external phase into the internal phase. Based on the results of the extraction performance, the recovery of Pd and the
Fig. 8. Percentages of Pd extraction, recovery and swelling/breakage at various H2 SO4 concentrations (Experimental conditions: [Cyanex 302] = 0.2 M; [Thiourea] = 1.0 M; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
swelling condition, 0.2 M of Cyanex 302 is recommended as a suitable amount of concentration for Pd extraction. 4.3. Effect of H2 SO4 concentration in internal phase As depicted in Fig. 8, the concentrations of H2 SO4 apparently affect the extraction and recovery of Pd and the emulsion swelling. It can be seen that by increasing the H2 SO4 concentration from 0.3 to 1 M, the extraction percentage of Pd increased from 75% to 96%. At low pH values (high hydrogen ion concentration), there is competition between the positively charged ions, Pd and hydrogen at the membrane feed interphase. Meanwhile, further increases in the H2 SO4 concentration from 1.0 to 1.5 M tend to decrease the Pd extraction percentage to 91%. If the acidity of the solution is high, more thiourea is needed to ensure that the acidic thiourea acts as an excellent stripping agent for Cyanex 302 [23]. Fig. 8 also shows that by increasing the H2 SO4 concentration from 0.3 to 1.0 M, the Pd recovery increased from 40% to 56% but emulsion swelling remained constant. As the system’s pH moved toward the acidic range, stronger complexation of extract–carrier complex is carried out, hence the percentage of recovery is high. However, with further increases in the H2 SO4 concentration from 1.0 to 1.5 M, the extraction and recovery of Pd was found to decrease due to the swelling of emulsion. This can be explained by the increase of hydrogen ion concentrations giving a higher pH difference between the external phase and internal phase. This condition might lead to a high osmotic pressure gradient between the internal and external phases. Therefore, more water molecules were transported from the external phase into the internal phase. The suitable concentration of H2 SO4 as a stripping agent was obtained at 1.0 M, which provides the highest degree of Pd extraction and recovery and a minimum percentage of swelling. 4.4. Effect of thiourea concentration in internal phase Fig. 9 shows the effects of thiourea concentration on Pd recovery, extraction and emulsion swelling. The results showed that the extraction percentage increased from 86% to 96% when the thiourea concentration was increased from 0.3 to 0.5 M, and then the extraction percentage remained constant with addition of thiourea concentrations up to 1.5 M. Increments of thiourea concentration in the internal phase increased the size of Pd ion strip due to the formation of more complexes. Hence, the extraction percentage increased. On the other hand, the recovery of Pd remained constant at 44% when the thiourea concentration was increased from 0.3 to 0.5 M although the extraction rate had increased. This is due to insufficient thiourea concentrations to strip the Pd ions from the membrane phase into the internal phase. Further increases of the
Please cite this article as: N.F.M. Noah et al., Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.03.047
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% Swelling % Pd extracon % Pd recovery
Percentage (%)
Percentage (%)
N.F.M. Noah et al. / Journal of the Taiwan Institute of Chemical Engineers 000 (2016) 1–8
100 90 80 70 60 50 40 30 20 10 0
% Pd Extracon % Pd recovery % Swelling
1
0.3
0.5
1
1.5
5
3
5
7
pH feed phase
Concentraon Thiourea in 1 M H2SO4 (M)
Percentage (%)
Fig. 9. Percentages of Pd extraction, recovery and swelling/breakage at various thiourea concentrations (Experimental conditions: [Cyanex 302] = 0.2 M; [H2 SO4 ] = 1.0 M; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
100 90 80 70 60 50 40 30 20 10 0
% Pd Extracon % Pd Recovery % Swelling
1:03
1:05
1:07
Fig. 11. Percentages of Pd extraction, recovery and swelling/breakage at various pH of external phase (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min).
tance between the emulsion droplets. Therefore, the interfacial areas between both phases decreased, resulting in extraction and recovery decrease. Mortaheb et al. [24] and Kumbasar and Sahin [25] had discussed that an increase in the volume of external phase will decrease the recovery performance. Further increases of the external phase up to 1:10 resulted in no significant effects on the recovery percentage. The results showed that the percentage of swelling occurring at 1:3 to 1:10 treat ratio was around 10%. By increasing the volume of external phase, no significant effects on swelling was observed. This indicates that the treat ratio does not give any significant effects on the emulsion stability in this process.
1:10
Treat rao Fig. 10. Percentages of Pd extraction, recovery and swelling/breakage at various treat ratio (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; [Pd] = 10 ppm; extraction time = 5 min; pH of external phase = 3).
thiourea concentration up to 1.0 M resulted in increases of the recovery percentage up to 56%. This is owing to the increase in thiourea concentration of the internal phase. Meanwhile, at 1.5 M thiourea, the recovery percentage slightly decreased to 46%. This is due to an excess of thiourea in the internal phase. Therefore, a 1.0 M H2 SO4 concentration only needs 1.0 M thiourea concentration to ensure that the acidic thiourea acts as an excellent stripping agent for Cyanex 302. However, the degree of break-up is found to be scarcely dependent as the thiourea added as a stripping reagent in the internal phase does not affect the stability of liquid membranes because it is not a surface active agent. 4.5. Effect of treat ratio Treat ratio plays an important role on selective parameters for ELM. The effects of treat ratio on Pd extraction, recovery and emulsion swelling are exhibited in Fig. 10. Decreasing the treat ratio from 1:3 to 1:7 tend to reduce the extraction performance. This is because the decrease in the capacity of the emulsion phase in contact with the external phase reduced the extraction and stripping of Pd ions into the internal phase. Further increase of the external phase volume from 1:7 to 1:10 gave same extraction and recovery percentage of around 80% and 16% respectively. This result indicated that the saturation of complexes at the internal interphase occurred because of the amount of Pd in the external phase increased, while the amounts of thiourea in internal phase to form complexes with Pd remained constant during the process. The results also exhibited that the recovery percentage decreased from 37% to 16% when the treat ratio was decreased from 1:3 to 1:7. By increasing the amount of external phase, the distribution of the emulsion became broader, hence increased the dis-
4.6. Effect of pH of external phase The external phase pH plays an important role in the recovery of Pd ions and stability of emulsion up to optimum conditions. Fig. 11 demonstrates the pH external phase effects toward the extraction and recovery of Pd and membrane swelling percentage. It can be inferred from Fig. 11 that the extraction and recovery efficiency of Pd was maximum around pH 3 with 93% and 59% respectively. Decreases in H+ ion concentration (high pH value) will cause a decrease in the rate of association of Pd with Cyanex 302 as a result of hydrolysis of Pd (Eq. 6). Lower external phase pH values will provide high concentrations of hydrogen ions. Since the Cyanex 302 is an acidic carrier, it tends to release hydrogen ions into the external phase, so there is competition with Pd ions to be attracted by the carriers in the membrane-external interphase. As reported by Kumbasar [26], the poor performance of solute extraction occurs at low pH owing to the competition of hydrogen ions with the solute, which is due to the release of hydrogen ions from the acidic carrier to the external solution.
Pd2+ +H2 O→PdOH+H+
(6)
After reaching the maximum value, further increases of pH up to 7 resulted in decreases in Pd recovery rates and no significant effects on Pd extraction. This indicates that a pH of around 3 is enough for Pd extraction. The results also showed that the increase in emulsion swelling from 5% to 25% with increases of external phase pH from 1 to 7. This is owing to the osmotic pressure difference resulting due to the pH increase of the external phase, driving water into the internal phase and thereby causing swelling. If the pH of external phase remains low, the extraction rate will be more rapid and more extraction will occur. 4.7. Effect of extraction time Fig. 12 shows the recovery, extraction and emulsion swelling percentages at various extraction times. It was observed that by
Please cite this article as: N.F.M. Noah et al., Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.03.047
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Table 3 Physical and chemical properties of real electroplating wastes solution, Waste 2 (exit waste).
100 90 80 70 60 50 40 30 20 10 0
Cations
% Pd Extracon % Pd Recovery % Swelling Pd
1
3
5
7
10
Concentration (ppm)
Anions
Concentration (ppm)
As Fe Cd Cr
0.14 0.027 0.04 42.62
SO4 2−
4.45
1 ppm 10 ppm 15 ppm
1.60 9.33 16.03
Physical properties pH
3
Density Viscosity
1.008 g/mL 0.83 cP
Fig. 12. Percentages of Pd extraction, recovery and swelling/breakage at various extraction time (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min; pH of external phase = 3). Table 2 Physical and chemical properties of real electroplating wastes solution, Waste 1 (entry waste).
Pd
Concentration (ppm)
Anions
Concentration (ppm)
Pb As Cu Fe Ni Cd
0.01 0.3 0.02 0.04 0.01 0.01
SO4 2− Cl−
9.0 50.0
Physical properties pH Density
14 1.004 g/mL
1 ppm 10 ppm 15 ppm
1.04 6.64 9.35
Viscosity
0.81 cP
100 90 80 70 60 50 40 30 20 10 0
% Extracon % Recovery
1
10
15
Pd inial concentraon (ppm)
increasing the extraction time from 1 to 5 mins, the extraction and recovery percentage increases. When the contact of emulsion onto the impeller and the vessel wall is longer, the emulsion droplets split into smaller emulsion and form larger surface area. Therefore, the mass transfer of Pd ions from the external phase into the internal phase increased. In addition, the emulsion was stable with below than 10% of swelling when the extraction time was increased from 1 to 5 mins. Small amounts of swelling indicate that the emulsion is stable enough to sustain the stability of the ELM system. Further increases up to 10 mins provide no significant effects on the extraction and recovery percentages, but the swelling percentage had gradually increased. This is due to the fact that by extending the extraction time, the emulsion promotes more entrainment of water into the internal phase of emulsion. This was in agreement with Chiha et al. [27] who indicated that increasing the extraction time will increase the emulsion breakage. Therefore, 5 mins of extraction time was chosen for the next experiment. Therefore, it can be concluded that the ELM process has received considerable attention because of its potential in extracting almost 100% of Pd in aqueous solutions with stable emulsion and 8% swelling. 4.8. Recovery study of real matrices The results from the characterization of the electroplating waste effluents are presented in Tables 2 and 3 respectively. The physical and chemical characterizations of the electroplating waste were carried out in order to determine the cations and anions compositions, density, pH, and viscosity. The results showed that only chromium existed in high concentrations in the electroplating waste while the other metals existed in less than 0.5 ppm. On the other hand the anion contents were 50 ppm chloride and 9 ppm
Fig. 13. Percentages of Pd extraction and recovery at various initial feed solution from aqueous solution (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
Percentage (%)
Cations
Percentage (%)
Extracon me (minutes)
100 90 80 70 60 50 40 30 20 10 0
% Extracon % Recovery
1
10
15
Pd inial concentraon (ppm) Fig. 14. Percentages of Pd extraction and recovery at various initial feed solutions from simulated electroplating solutions Waste 1 (entry) (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
sulfate in the entry waste. Low concentrations of sulfate ions at 4.45 ppm in the exit waste indicated that it may not compete with metal extraction in the ELM system. The removal efficiency of Pd was further examined by dissolving the metal in an aqueous and simulated electroplating solution (entry waste), as depicted in Figs. 13 and 14 respectively. The results showed that at low initial Pd concentrations (1 ppm), the percentage of extraction and recovery was high. This is owing to the low Pd ion concentration as compared to the larger amounts of carrier. But when the initial concentration of Pd is increased, the degree of metal extraction decreased slightly, which is coherent with the necessary amount of carrier to transport a larger quantity of metal. Its decrement might be attributed to the possible swelling of emulsion due to the differences in the ion strength and the osmotic pressure between the two phases that were partly hindered against solute transfer. In addition, the saturation of internal droplets in the peripheral region of the emulsion is achieved faster for high concentrations in the external solution. Hence, the
Please cite this article as: N.F.M. Noah et al., Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.03.047
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Palladium
20
Chromium
0 1 10 15 Inial feed concentraon (ppm)
Recovery percentage (%)
Percentage extracon( %)
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7
100 80 60 40
Palladium
20
Chromium
0 1 10 15 Inial feed concentraon (ppm)
(a) Metals Extraction
(b) Metals recovery
Fig. 15. Extraction and recovery percentage of Pd and chromium at various initial feed solutions from simulated electroplating solutions Waste 2 (exit) (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
diffused Pd–Cyanex 302 complexes cannot be stripped in the internal phase. As a result, the extracted Pd (Pd–Cyanex 302 complexes) had accumulated in the membrane phase and no carrier had diffused back to react with the Pd. The solute moves toward the emulsion globules by diffusion. At low initial solute concentrations, since driving force for the mass transfer is low, the molecules take longer time to reach the emulsion globules. However, this is compensated by the increased distribution coefficient by increasing the initial Pd concentration. Thus, the Pd dissolves rapidly in the membrane phase, resulting in faster extraction. Conversely, although the increased Pd concentration results in faster diffusion toward the emulsion globules, the extraction rate decreases owing to a decreased distribution coefficient. The results also showed that by increasing initial Pd concentration from 1 to 15 ppm, the recovery rate decreased from 53% to 25%. This is mostly due to the reduced capacity of the internal phase to strip the transported Pd. Moreover, at high Pd concentrations, the internal droplets in the peripheral region are more readily saturated with the solute. In order to investigate the selectivity of Pd from other metals, various initial concentrations of Pd in simulated electroplating wastewater (exit waste) were used and the results were obtained as shown in Fig. 15. The results showed that the Cyanex 302 was very selective to Pd over chromium. The chromate ion may exist in the liquid phase in different ionic forms (HCr2 O7 − , CrO4 2− , Cr2 O7 2− , HCrO4 − ). The Cr2 O7 2 – anions dominate in acidic chromium (VI) water solutions. According to Lewis acid base theory, soft acid–soft base (Pd-Cyanex 302) interactions are stronger than hard acid–soft base (Cr-Cyanex 302) interactions. In addition, the sulfur substitution of Cyanex 302 has higher acidic properties and was categorized as soft base. This makes them particularly suitable for the extraction of soft (Lewis) acid metal ions such as Pd (II), which are in accordance with the HSAB principle [28]. Therefore, reagents containing sulfur donor atoms (Cyanex 302) was expected to be strong carrier for soft metals ions, such as Pd compared to hard metal ions such as chromium. The removal and recovery efficiency decreases with the increase of Pd concentration from 1 to 15 ppm. It is because the internal droplets achieved its saturation conditions. When the initial Pd concentration increased, the peripheral droplets were exhausted faster, requiring the Pd to permeate deeper within the globule prior to being stripped. Since the degree of extraction and recovery increases with the decrease in Pd concentration it may be concluded that the formulation for Pd ELM is more suitable for Pd removal and recovery selectively from dilute aqueous solutions within 1–10 ppm and from the real matrices solutions with chromium.
5. Conclusion As a conclusion, the maximum extraction of Pd from aqueous waste solutions can be achieved at 0.2 M of Cyanex 302 as a carrier, 1.0 M of thiourea in 1.0 M of H2 SO4 as the stripping agent, 5 mins extraction time, pH 3 of external phase and 1:3 of treat ratio. The ELM process has received considerable attention because of its potential in extracting almost 100% of Pd in aqueous solutions. At these conditions, the extraction and recovery of Pd from matrices solutions were successful and the Cyanex 302 was found to be very selective toward Pd over chromium. Acknowledgment The authors would like to acknowledge the Ministry of Higher Education (MOHE) (Research Grant: Vot 4F450), Centre of Lipids Engineering and Applied Research (CLEAR), and Universiti Teknologi Malaysia (UTM) for facilities support to make this research possible. References [1] Lavicoli I, Fontana L. Palladium: exposure uses, and human health effects. In: O N, editor. Encyclopedia of environmental health. Jerome Burlington: Elsevier; 2011. Editor in Chief: p. 307–14. [2] Jochen H, Erwin M, Walter M and Silke O. Method for depositing a palladium layer suitable for wire bonding on conductors of a printed circuit board, and palladium bath for use in said method. U.S. Patent No. 2012/0244276 A1. [3] TIPAC, Technology Information. Forecasting and assessment council. Recovery from electroplating industry waste. India: Technology Information, Forecasting and assessment council; 2009. [4] Hubicki Z, Wołowicz A, Leszcznska M. Studies of removal of palladium(II) ions from chloride solutions on weakly and strongly basic anion exchangers. J Hazard Mater 2008;159:280–6. [5] Volesky B. Biosorption of heavy metals. Boca Raton, FL, USA: CRC Press; 1990. [6] Rydberg J, Cox M, Musikas C, Choppin GR. Solvent extraction principles and practice. 2nd ed. Marcel Dekker, Inc; 2004. p. 480–93. [7] Swain B, Jeong J, Kim S, Lee JA. Separation of platinum and palladium from chloride solution by solvent extraction using Alamine 300. Hydrometallurgy 2010;104:1–7. [8] Li NN. Separating hydrocarbons with liquid membranes. US3410794 A. 1968. [9] Othman N, Chan KH, Goto M, Mat H. Emulsion liquid membrane extraction of silver from photographic waste using CYANEX 302 as the mobile carrier. Solvent Extr Res Dev 2006;13:191–202. [10] Rajasimman M, Karthic P. Application of response surface methodology for the extraction of chromium (VI) by emulsion liquid membrane. J Taiwan Inst Chem Eng 2001;41(1):105–10. [11] Zing-Yi O, Othman N, Mohamad M, Rashid R. Removal performance of lignin compound from simulated pulping wastewater using emulsion liquid membrane process. Int J Global Warm 2014;6:270–83. [12] Sulaiman RNR, Othman N, Amin NAS. Emulsion liquid membrane stability in the extraction of ionized nanosilver from wash water. J Ind Eng Chem 2014;20:3243–50. [13] Chakraborty M, Bhattacharya C, Datta S, Kislik VS. Liquid membranes. Amsterdam: Elsevier; 2010. p. 141–99.
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[14] Othman N, Mat H, Goto M. Separation of silver from photographic wastes by emulsion liquid membrane system. J Membr Sci 2006;282:171–7. [15] Kargari A, Kaghazchi T, Soleimani M. Experimental and modeling of selective separation of gold(III) ions from aqueous solutions by emulsion liquid membrane system membrane technique. Desalination 2006;279: 389–393. [16] Kakoi T, Horinouchi N, Goto M, Nakashio F. Selective recovery of palladium from simulated industrial waste water by liquid surfactant membrane process. J Membr Sci 1996;118:63–71. [17] Othman N, Noah NFM, Sulaiman RNR, Abdullah NA, Bachok SK. Liquid-liquid extraction of palladium from simulated liquid waste using phosphinic acid as a carrier. J Teknol 2014;68:41–5. [18] Othman N, Noah NFM, Harruddin N, Abdullah NA, Bachok SK. Selective extraction of palladium from simulated liquid waste solution by emulsion liquid membrane process using D2EHPA as a mobile carrier. J Teknol 2014;69:1–4. [19] Noah NFM, Othman N, Bachok SK, Abdullah NA. Palladium extraction using emulsion liquid membrane process – stability study. Adv Mater Res 2014;1113:376–81. [20] Malik MA, Hashim MA, Nabi F. Extraction of metal ions by ELM separation technology. J Dispers Sci Technol 2012;33:346–56.
[21] Fouad EA. Zinc and copper separation through an emulsion liquid membrane containing di-(2-ethylhexyl) phosphoric acid as a carrier. Chem Eng Technol 2008;31:370–6. [22] Kulkarni PS, Tiwari KK,Mahajani VV. Membrane stability and enrichment of nickel in the liquid emulsion membrane process. Chem Technol Biot 20 0 0;75:553–60. [23] Othman N, Mat H, Goto M. Selective extraction of silver from liquid photographic waste. Solvent Extr Res Dev 2005;12:27–34. [24] Mortaheb HR, Kosuge H, Mokhtarani B. Study on removal of cadmium from wastewater by emulsion liquid membrane. J Hazard Mater 2009;165:1–3. [25] Kumbasar RA, Sahin I. Separation and concentration of cobalt from ammoniacal solutions containing cobalt and nickel by emulsion liquid membranes using 5, 7-dibromo-8-hydroxyquinoline (DBHQ). J Membr Sci 2008;164:712–18. [26] Kumbasar RA. Extraction of chromium (VI) from multicomponent acidic solutions by emulsion liquid membranes using TOPO as extractant. J Hazard Mater 2009;67:1141–8. [27] Chiha M, Samar MH, Hamdaoui O. Extraction of chromium (VI) from sulphuric acid aqueous solutions by a liquid surfactant membrane (LSM). Desalination 2006;194:69–80. [28] Pearson RG. Hard and soft acids and bases. J Am Chem Soc 1963;85:3533–43.
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Journal of the Taiwan Institute of Chemical Engineers 0 0 0 (2016) 1–8
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Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process Norul Fatiha Mohamed Noah a, Norasikin Othman a,b,∗, Norela Jusoh a a
Department of Chemical Engineering, Faculty of Chemical and Energy Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bharu, Johor, Malaysia Centre of Lipids Engineering & Applied Research (CLEAR), Ibnu Sina Institute for Scientific and Industrial Research (Ibnu Sina ISIR), Universiti Teknologi Malaysia, 81310 UTM Johor Bharu, Johor, Malaysia
b
a r t i c l e
i n f o
Article history: Received 23 August 2015 Revised 22 February 2016 Accepted 24 March 2016 Available online xxx Keywords: Emulsion liquid membrane Palladium Chromium Electroplating wastewater
a b s t r a c t A new liquid membrane formulation containing phosphinic acid groups as a carrier was developed for the selective extraction of palladium (Pd) from electroplating wastewater using emulsion liquid membrane (ELM) process. The important parameters that affect the membrane stability and the recovery of Pd were investigated, such as extraction time, concentrations of carrier and stripping agents, pH of feed phase, and treat ratio. Furthermore, at the optimum condition, the performance of Pd extraction was evaluated using real matrices solution. All experiments were carried out using batch extraction process and the recovery stage at high voltage demulsifier was employed. The results showed that the favorable conditions obtained for the extraction and the recovery processes were at 0.2 M of Cyanex 302, 1.0 M thiourea in 1.0 M H2 SO4 of stripping agent, 1:3 treat ratio, pH 3 of feed phase, and 5 mins of extraction time. At these conditions, the maximum extraction and recovery of the Pd was 97% and 40%, respectively. Moreover, the result from the real matrices showed that almost 100% of Pd was extracted selectively over chromium at these conditions. © 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Recovery of electroplating wastewaters is an important subject not only from the view of waste treatment but also from the recovery of valuable metals that is Pd. Exposure of Pd can cause acute toxicity or hypersensitivity with respiratory symptoms, urticaria and less frequently, contact dermatitis. The epidemiological studies have demonstrated that the Pd ions are one of the most frequent reacting sensitizers, which affect the immune system that represents the most important health hazard to humans [1]. Pd with unique physical properties has been used in diverse industrial applications such as jewelry, semiconductors and connectors. These applications take benefit of Pd’s lower cost and its material properties that are superior to gold. Due to its economic value and its limited natural resources, Pd recovery from the secondary resources is significant. According to the invention [2], the amount of Pd used in Pd exchange bath is 0.150–0.25 g/L [2]. Out of the total amount of precious metals used in electroplating, 4% goes as waste in the sludge spent wash and the electroplating solution [3]. Hence, it can be concluded that the Pd composition in the electroplating wastewater is in the range of 6–10 ppm.
∗
Corresponding author. Tel: +6 07 5535561; fax: +6 07 5581463. E-mail address: [email protected] (N. Othman).
In order to separate the Pd from aqueous solutions, various studies have been recently focused on conventional methods. For example, an ion exchange is one of the simple ways to separate Pd [4]. A disadvantage of this treatment is the method involves high operating costs for the ion exchange unit due to the resin costs. Biosorption is another efficient low cost process of Pd ions recovery from aqueous solutions. Since the biosorption frequently employs dead biomass, it can eliminate the problem of toxicity environments and the need of nutrient requirement [5]. Solvent extraction has become an effective technique in the recovery and separation of Pd [6,7]. However, various problems have been associated with the solvent extraction systems, such as the corresponding hydrodynamics related problems, third phase problems, and compatibility issues with the diluent. In 1968, emulsion liquid membranes (ELMs) were first applied to the separation of hydrocarbons [8]. Recently, the ELM technology has become a promising method to recover precious metals, even in a very low concentration from the industrial wastes [9,10]. Since the ELM process combines the extraction and recovery process, this method does not need the second treatment like electrowinning that needs cementation or chemical precipitation process [11,12]. Due to its high surface area to volume ratio compared to solid membranes, it has high solute transfer flux and selectivity as well as low contacting equipment volume and cost [11,13], and it is chosen as the suitable method to extract and recover Pd
http://dx.doi.org/10.1016/j.jtice.2016.03.047 1876-1070/© 2016 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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Table 1 Experimental conditions used for the preparations of ELMs.
Pre-treatment
Solvent
Kerosene
Homogenizer speed (HS) Emulsifying time Agitation speed (AS) Surfactant Carrier Stripping agent (SA)
12,0 0 0 rpm 3 mins 200 rpm 2% (w/v) Span 80 0.001–0.7 M Cyanex 302 0.3, 0.5, 1.0, and 1.5 M Thiourea in 0.3, 0.5, 1.0 and 1.5 M H2 SO4 1:3, 1:5, 1:7, 1:10 1, 3, 5, 7 1, 3,5, 7, 10 mins
Treat ratio (TR) pH feed phase Extraction time
First Plating
Second Plating
Entry waste (Waste 1)
Exit waste (Waste 2)
Oxidation/ Neutralizatio
Wastewater
Kualiti Alam Schedule
Fig. 3. Electroplating wastewater process flow diagrams.
the internal phase and the carriers diffuse back to the membraneexternal interphase to react with other Pds
PdR2 (org) + 2[CS + (RH)2 (org)
(NH2 )2 H]+ (aq)
→
Pd[(CS
(NH2 )2 )2 ]2+ (aq) (2)
3. Materials and methods 3.1. Materials Fig. 1. Schematic transport mechanism of Pd by ELM from the aqueous solution using Cyanex 302 as carrier.
Fig. 2. Structure of Cyanex 302.
from the electroplating wastewater. ELM has been intensively investigated and demonstrated as an effective alternative technology for the separation and purification process for precious metal extraction such as silver [14], gold [15] and Pd [16]. Hence, in this research, the ELM process was utilized for the recovery of Pd from the electroplating wastewater. The ranges of parameters used in the ELM extraction of Pd from the simulated liquid waste are listed in Table 1. The liquid membrane components such as type of diluents and stripping agent and its concentration for the Pd extraction are taken from the previous studies [17].
There are four components in the ELM system namely carrier, surfactant, stripping agent and diluent. All four components are manufactured for laboratory grade and were used as received. The Cyanex 302 (85% purity) as a carrier for Pd was obtained from Sigma. The kerosene (99% purity) and span 80 (99% purity) as a diluent and surfactant respectively were purchased from Fluka Chemika. The thiourea (99% purity) and sulfuric acid (99% purity) were purchased from Merck (M) Sdn. Bhd. An aqueous solution of Pd was prepared using palladium (II) nitrate (Pd(NO3 )2 ) obtained from Merck (M) Sdn. Bhd. The water used in this research was distilled water. 3.2. Electroplating waste sample and characterization process The real electroplating wastewater sample was obtained from the Electroplating Company at Masai, Johor. Ion chromatography (IC) model LC20 with electric chemical detector model ED40 was used to measure anion contents in the sample. Contents of metals in the electroplating wastewaters were measured using an atomic absorption spectrometer (AAS) (PerkinElmer, model: Analyst 400). A Cyber scan 100 pH meter model was used to measure the pH measurements. A hydrometer was used to measure the densities (ρ ) of the samples. A programmable Rheometer Brookfield Model DV-III was used to determine the kinematic viscosity, v [14].
2. Extraction mechanism of palladium 3.3. Palladium in simulated electroplating wastewater The transport mechanism of Pd by the ELM process using Cyanex 302 as a carrier is shown in Fig. 1. In this mechanism, the selected carrier, Cyanex 302 (Fig. 2) chemically reacts with the cationic Pd in kerosene to form complexes of Pd–Cyanex 302 at the membrane-external interphase as represented by Eq. (1).
Pd2+ (aq) +(RH)2 (org) → PdR2 (org) +2(H+ )(aq)
(1)
After that, the Pd–Cyanex 302 complexes diffuse through the membrane phase from the membrane-external interphase to the membrane-internal interphase. Then, the Pd–Cyanex 302 complexes at the membrane-internal interphase undergo the stripping process by reacting with the acidic thiourea from the internal phase as shown in Eq. (2). The Pd–thiourea complexes released to
The palladium (II) nitrate was dissolved into real electroplating wastewater in the concentration range of 1–15 ppm. Then, the initial pH of the feed phase was measured. The pH for each sample was adjusted in the range of 3.0–3.5. In this preparation, two types of waste solutions were considered in the electroplating process, which were Waste 1 and Waste 2 for entry and exit effluents, respectively, as shown in Fig. 3. 3.4. Water in oil (W/O) emulsion preparation The organic solution was prepared by dissolving an appropriate concentration of the carrier (Cyanex 302) and the surfactant (Span 80) in a diluent (kerosene). The internal aqueous stripping phase
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3
Fig. 4. Schematic diagrams of ELM process for Pd extraction and recovery process [18]. Fig. 5. Primary emulsions at 400x magnification under microscope. [19].
was a thiourea in H2 SO4 solution. An equal volume of 5 mL portions of organic phase and aqueous stripping phase were stirred continuously at 12,0 0 0 rpm for about 3 mins to obtain stable water in oil emulsion. The emulsion must be freshly prepared before each experiment of extraction study. 3.5. Extraction and recovery process The ELM extraction of Pd was carried out by dispersing the W/O emulsion into the external phase containing Pd ions. The water in oil in water (W/O/W) emulsion was agitated using a fourblade stirrer (Cole-Parmer, model: 50,0 06-0 0). Several parameters such as carrier concentration, internal phase concentration, treat ratio, pH of external phase, and extraction time were varied during the Pd extraction experiments. One-factor-at-a-time method was applied. The volume of emulsion before and after extraction was measured for emulsion stability study. After the extraction process, the sample mixture of W/O emulsion and external phase was separated using the separating funnel. The aqueous external samples were analyzed using the AAS for Pd removal extraction performance while the remaining emulsion will undergo the demulsification process. Pulsed AC field with 20 kV electric potential at 300 Hz frequency across the outer and inner electrode probe was used to demulsify the emulsion in order to recover Pd in the internal stripping phase. The recovered Pd solution was collected and analyzed using the AAS. The recovery of Pd was calculated based on mass balance principal. At these favorable conditions, the performance of Pd extraction from real matrices solution was studied. The experiment was carried out using different initial Pd concentrations from 1 to 15 ppm. The schematic diagram of the ELM process is shown in Fig. 4. 3.6. Determination and calculation of ELM performance The percentage of Pd extraction, recovery and swelling or breakage was determined by using Eqs. (3)–(5), respectively:
Extraction (% ) = Recovery (% ) =
[Pd]i − [Pd]f × 100% [Pd]i
[Pd]int × 100% 2TR[Pd]i
Swelling/Breakage (% ) =
Vf − Vi × 100% Vi
(3)
(4)
(5)
where, [Pd]i is the initial concentration of Pd ion in aqueous before extraction, [Pd]f represents the final concentration of Pd ion in aqueous after extraction, [Pd]int is the concentration of Pd in internal phase after extraction, Vi is the initial volume of emulsion
Fig. 6. Percentages of Pd extraction, recovery and swelling/breakage at various Cyanex 302 concentration (Experimental conditions: [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
before extraction, Vf is the final volume of emulsion after extraction, and TR is the treat ratio. 4. Results and discussion 4.1. Primary emulsion droplet size From the previous study [19], the stability of emulsion was studied. Fig. 5 shows the image of emulsion droplet. The most stable emulsion was observed at 2% (w/v) of span 80 concentration, 12,0 0 0 rpm homogenizer speed, 3 mins emulsifying time and 200 rpm agitation speed. At the optimum condition, the average droplet size was 3 μm, which is accepted as stable emulsions. 4.2. Effect of carrier concentration The proper selection of carrier concentration always exerts a significant influence on the ELM system [20]. The effect of carrier concentration on the extraction of Pd is presented in Fig. 6. Fig. 7 shows the effects of carrier concentration on viscosity of liquid membrane. The results showed that a very small amount of Pd was extracted at 0.001–0.01 M of Cyanex 302. This is due to the inability of the carrier concentration to selectively transport the solute throughout the membrane phase into the internal phase. Therefore, it gives a low extraction performance. Meanwhile, the extraction performance drastically increased from 11% to 65% when the concentration of Cyanex 302 is increased from 0.01 to 0.05 M. As can be seen at 0.01 and 0.05 M Cyanex 302, the viscosity of liquid membrane is almost equal (2.2 cp) and it provides the same extraction rate. This means that the increase in Pd extraction depends on the amount of carrier compound that existed in the liquid membrane. Hence, more formation of Pd–carrier complexes
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Percentage (%)
4
ARTICLE IN PRESS 100 90 80 70 60 50 40 30 20 10 0
% Swelling % Pd extracon % Pd recovery
0.3
0.5
1
1.5
Concentraon H2SO4 in 1 M Thiourea (M)
Fig. 7. Effect of carrier concentration on viscosity of liquid membrane (Experimental conditions: [Span 80] = 2% w/v, Diluent = kerosene).
can occur at the membrane-external aqueous interphase, resulting in increases in diffusion rates of Pd ion from the external phase into the membrane phase. Further increases of the Cyanex 302 concentration up to 0.3 M significantly increased the Pd extraction rate, which was around 95%. It is indicated that the bigger the amount of carrier compounds existed in the membrane phase, the larger amount of Pd is extracted. This finding is in line with Fouad [21] who discovered that the extraction percentages increased with an increase in the membrane’s carrier concentration. Further increases of the Cyanex 302 concentration up to 0.7 M decreased the extraction rate to 90%. This is due to high concentration of carrier resulted in a decrease of Pd extraction due to the increase in the viscosity of the membrane phase as shown in Fig. 7. This indicated that 0.3 M is enough for the facilitated transport of Pd. The result also shows that from 0.001 to 0.005 M Cyanex 302, the recovery percentage of Pd was increased. The recovery performance remained constant as further increases up to 0.05 M Cyanex 302 were made due to small formations of Pd–carrier complexes in the membrane phase. Further increasing of concentrations up to 0.2 M significantly increased the percentage of recovery. Meanwhile, although the extraction percentage increased when the carrier concentration was increased up to 0.3 M, the recovery performances decreased due to accumulation of Pd–carrier complexes in the membrane phase. Further increases up to 0.7 M significantly decreased the percentage of recovery. It can be seen that the more concentrated the carrier concentration is, the more viscous the membrane phase, as illustrated in Fig. 7. This effect resists the diffusion of solute into the internal phase, which reduces the mass transfer of Pd–carrier complexes. Therefore, the recovery percentage of Pd was decreased. Meanwhile, by increasing the concentration of Cyanex 302 from 0.001 to 0.1 M, the emulsion swelling had decreased. This is due to the high viscosity of liquid membrane that led to resistance for the water transport. This is in agreement with Kulkarni et al. [22] who indicated that high viscosities of liquid membrane increased the emulsion stability by inhibiting water transportation into the internal phase, leading to emulsion swelling. This result is supported by Fig. 7 that shows the viscosity of emulsion increasing from 1.5 to 3.0 cP when the carrier concentration was increased from 0.001 to 0.7 M. The emulsion swelling began to plateau with further increases of the carrier concentration over 0.7 M Cyanex 302. This indicates that some globules tend to swell and break at the same time. Therefore, there exists a trade-off between these two effects. In addition, the result showed that increasing of the carrier concentration from 0.1 to 0.7 M results in the increase of liquid membrane viscosity. High viscosity will reduce water molecule transport from the external phase into the internal phase. Based on the results of the extraction performance, the recovery of Pd and the
Fig. 8. Percentages of Pd extraction, recovery and swelling/breakage at various H2 SO4 concentrations (Experimental conditions: [Cyanex 302] = 0.2 M; [Thiourea] = 1.0 M; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
swelling condition, 0.2 M of Cyanex 302 is recommended as a suitable amount of concentration for Pd extraction. 4.3. Effect of H2 SO4 concentration in internal phase As depicted in Fig. 8, the concentrations of H2 SO4 apparently affect the extraction and recovery of Pd and the emulsion swelling. It can be seen that by increasing the H2 SO4 concentration from 0.3 to 1 M, the extraction percentage of Pd increased from 75% to 96%. At low pH values (high hydrogen ion concentration), there is competition between the positively charged ions, Pd and hydrogen at the membrane feed interphase. Meanwhile, further increases in the H2 SO4 concentration from 1.0 to 1.5 M tend to decrease the Pd extraction percentage to 91%. If the acidity of the solution is high, more thiourea is needed to ensure that the acidic thiourea acts as an excellent stripping agent for Cyanex 302 [23]. Fig. 8 also shows that by increasing the H2 SO4 concentration from 0.3 to 1.0 M, the Pd recovery increased from 40% to 56% but emulsion swelling remained constant. As the system’s pH moved toward the acidic range, stronger complexation of extract–carrier complex is carried out, hence the percentage of recovery is high. However, with further increases in the H2 SO4 concentration from 1.0 to 1.5 M, the extraction and recovery of Pd was found to decrease due to the swelling of emulsion. This can be explained by the increase of hydrogen ion concentrations giving a higher pH difference between the external phase and internal phase. This condition might lead to a high osmotic pressure gradient between the internal and external phases. Therefore, more water molecules were transported from the external phase into the internal phase. The suitable concentration of H2 SO4 as a stripping agent was obtained at 1.0 M, which provides the highest degree of Pd extraction and recovery and a minimum percentage of swelling. 4.4. Effect of thiourea concentration in internal phase Fig. 9 shows the effects of thiourea concentration on Pd recovery, extraction and emulsion swelling. The results showed that the extraction percentage increased from 86% to 96% when the thiourea concentration was increased from 0.3 to 0.5 M, and then the extraction percentage remained constant with addition of thiourea concentrations up to 1.5 M. Increments of thiourea concentration in the internal phase increased the size of Pd ion strip due to the formation of more complexes. Hence, the extraction percentage increased. On the other hand, the recovery of Pd remained constant at 44% when the thiourea concentration was increased from 0.3 to 0.5 M although the extraction rate had increased. This is due to insufficient thiourea concentrations to strip the Pd ions from the membrane phase into the internal phase. Further increases of the
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% Swelling % Pd extracon % Pd recovery
Percentage (%)
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100 90 80 70 60 50 40 30 20 10 0
% Pd Extracon % Pd recovery % Swelling
1
0.3
0.5
1
1.5
5
3
5
7
pH feed phase
Concentraon Thiourea in 1 M H2SO4 (M)
Percentage (%)
Fig. 9. Percentages of Pd extraction, recovery and swelling/breakage at various thiourea concentrations (Experimental conditions: [Cyanex 302] = 0.2 M; [H2 SO4 ] = 1.0 M; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
100 90 80 70 60 50 40 30 20 10 0
% Pd Extracon % Pd Recovery % Swelling
1:03
1:05
1:07
Fig. 11. Percentages of Pd extraction, recovery and swelling/breakage at various pH of external phase (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min).
tance between the emulsion droplets. Therefore, the interfacial areas between both phases decreased, resulting in extraction and recovery decrease. Mortaheb et al. [24] and Kumbasar and Sahin [25] had discussed that an increase in the volume of external phase will decrease the recovery performance. Further increases of the external phase up to 1:10 resulted in no significant effects on the recovery percentage. The results showed that the percentage of swelling occurring at 1:3 to 1:10 treat ratio was around 10%. By increasing the volume of external phase, no significant effects on swelling was observed. This indicates that the treat ratio does not give any significant effects on the emulsion stability in this process.
1:10
Treat rao Fig. 10. Percentages of Pd extraction, recovery and swelling/breakage at various treat ratio (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; [Pd] = 10 ppm; extraction time = 5 min; pH of external phase = 3).
thiourea concentration up to 1.0 M resulted in increases of the recovery percentage up to 56%. This is owing to the increase in thiourea concentration of the internal phase. Meanwhile, at 1.5 M thiourea, the recovery percentage slightly decreased to 46%. This is due to an excess of thiourea in the internal phase. Therefore, a 1.0 M H2 SO4 concentration only needs 1.0 M thiourea concentration to ensure that the acidic thiourea acts as an excellent stripping agent for Cyanex 302. However, the degree of break-up is found to be scarcely dependent as the thiourea added as a stripping reagent in the internal phase does not affect the stability of liquid membranes because it is not a surface active agent. 4.5. Effect of treat ratio Treat ratio plays an important role on selective parameters for ELM. The effects of treat ratio on Pd extraction, recovery and emulsion swelling are exhibited in Fig. 10. Decreasing the treat ratio from 1:3 to 1:7 tend to reduce the extraction performance. This is because the decrease in the capacity of the emulsion phase in contact with the external phase reduced the extraction and stripping of Pd ions into the internal phase. Further increase of the external phase volume from 1:7 to 1:10 gave same extraction and recovery percentage of around 80% and 16% respectively. This result indicated that the saturation of complexes at the internal interphase occurred because of the amount of Pd in the external phase increased, while the amounts of thiourea in internal phase to form complexes with Pd remained constant during the process. The results also exhibited that the recovery percentage decreased from 37% to 16% when the treat ratio was decreased from 1:3 to 1:7. By increasing the amount of external phase, the distribution of the emulsion became broader, hence increased the dis-
4.6. Effect of pH of external phase The external phase pH plays an important role in the recovery of Pd ions and stability of emulsion up to optimum conditions. Fig. 11 demonstrates the pH external phase effects toward the extraction and recovery of Pd and membrane swelling percentage. It can be inferred from Fig. 11 that the extraction and recovery efficiency of Pd was maximum around pH 3 with 93% and 59% respectively. Decreases in H+ ion concentration (high pH value) will cause a decrease in the rate of association of Pd with Cyanex 302 as a result of hydrolysis of Pd (Eq. 6). Lower external phase pH values will provide high concentrations of hydrogen ions. Since the Cyanex 302 is an acidic carrier, it tends to release hydrogen ions into the external phase, so there is competition with Pd ions to be attracted by the carriers in the membrane-external interphase. As reported by Kumbasar [26], the poor performance of solute extraction occurs at low pH owing to the competition of hydrogen ions with the solute, which is due to the release of hydrogen ions from the acidic carrier to the external solution.
Pd2+ +H2 O→PdOH+H+
(6)
After reaching the maximum value, further increases of pH up to 7 resulted in decreases in Pd recovery rates and no significant effects on Pd extraction. This indicates that a pH of around 3 is enough for Pd extraction. The results also showed that the increase in emulsion swelling from 5% to 25% with increases of external phase pH from 1 to 7. This is owing to the osmotic pressure difference resulting due to the pH increase of the external phase, driving water into the internal phase and thereby causing swelling. If the pH of external phase remains low, the extraction rate will be more rapid and more extraction will occur. 4.7. Effect of extraction time Fig. 12 shows the recovery, extraction and emulsion swelling percentages at various extraction times. It was observed that by
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Table 3 Physical and chemical properties of real electroplating wastes solution, Waste 2 (exit waste).
100 90 80 70 60 50 40 30 20 10 0
Cations
% Pd Extracon % Pd Recovery % Swelling Pd
1
3
5
7
10
Concentration (ppm)
Anions
Concentration (ppm)
As Fe Cd Cr
0.14 0.027 0.04 42.62
SO4 2−
4.45
1 ppm 10 ppm 15 ppm
1.60 9.33 16.03
Physical properties pH
3
Density Viscosity
1.008 g/mL 0.83 cP
Fig. 12. Percentages of Pd extraction, recovery and swelling/breakage at various extraction time (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; [Pd] = 10 ppm; TR = 1:3; extraction time = 5 min; pH of external phase = 3). Table 2 Physical and chemical properties of real electroplating wastes solution, Waste 1 (entry waste).
Pd
Concentration (ppm)
Anions
Concentration (ppm)
Pb As Cu Fe Ni Cd
0.01 0.3 0.02 0.04 0.01 0.01
SO4 2− Cl−
9.0 50.0
Physical properties pH Density
14 1.004 g/mL
1 ppm 10 ppm 15 ppm
1.04 6.64 9.35
Viscosity
0.81 cP
100 90 80 70 60 50 40 30 20 10 0
% Extracon % Recovery
1
10
15
Pd inial concentraon (ppm)
increasing the extraction time from 1 to 5 mins, the extraction and recovery percentage increases. When the contact of emulsion onto the impeller and the vessel wall is longer, the emulsion droplets split into smaller emulsion and form larger surface area. Therefore, the mass transfer of Pd ions from the external phase into the internal phase increased. In addition, the emulsion was stable with below than 10% of swelling when the extraction time was increased from 1 to 5 mins. Small amounts of swelling indicate that the emulsion is stable enough to sustain the stability of the ELM system. Further increases up to 10 mins provide no significant effects on the extraction and recovery percentages, but the swelling percentage had gradually increased. This is due to the fact that by extending the extraction time, the emulsion promotes more entrainment of water into the internal phase of emulsion. This was in agreement with Chiha et al. [27] who indicated that increasing the extraction time will increase the emulsion breakage. Therefore, 5 mins of extraction time was chosen for the next experiment. Therefore, it can be concluded that the ELM process has received considerable attention because of its potential in extracting almost 100% of Pd in aqueous solutions with stable emulsion and 8% swelling. 4.8. Recovery study of real matrices The results from the characterization of the electroplating waste effluents are presented in Tables 2 and 3 respectively. The physical and chemical characterizations of the electroplating waste were carried out in order to determine the cations and anions compositions, density, pH, and viscosity. The results showed that only chromium existed in high concentrations in the electroplating waste while the other metals existed in less than 0.5 ppm. On the other hand the anion contents were 50 ppm chloride and 9 ppm
Fig. 13. Percentages of Pd extraction and recovery at various initial feed solution from aqueous solution (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
Percentage (%)
Cations
Percentage (%)
Extracon me (minutes)
100 90 80 70 60 50 40 30 20 10 0
% Extracon % Recovery
1
10
15
Pd inial concentraon (ppm) Fig. 14. Percentages of Pd extraction and recovery at various initial feed solutions from simulated electroplating solutions Waste 1 (entry) (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
sulfate in the entry waste. Low concentrations of sulfate ions at 4.45 ppm in the exit waste indicated that it may not compete with metal extraction in the ELM system. The removal efficiency of Pd was further examined by dissolving the metal in an aqueous and simulated electroplating solution (entry waste), as depicted in Figs. 13 and 14 respectively. The results showed that at low initial Pd concentrations (1 ppm), the percentage of extraction and recovery was high. This is owing to the low Pd ion concentration as compared to the larger amounts of carrier. But when the initial concentration of Pd is increased, the degree of metal extraction decreased slightly, which is coherent with the necessary amount of carrier to transport a larger quantity of metal. Its decrement might be attributed to the possible swelling of emulsion due to the differences in the ion strength and the osmotic pressure between the two phases that were partly hindered against solute transfer. In addition, the saturation of internal droplets in the peripheral region of the emulsion is achieved faster for high concentrations in the external solution. Hence, the
Please cite this article as: N.F.M. Noah et al., Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.03.047
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100 80 60 40
Palladium
20
Chromium
0 1 10 15 Inial feed concentraon (ppm)
Recovery percentage (%)
Percentage extracon( %)
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7
100 80 60 40
Palladium
20
Chromium
0 1 10 15 Inial feed concentraon (ppm)
(a) Metals Extraction
(b) Metals recovery
Fig. 15. Extraction and recovery percentage of Pd and chromium at various initial feed solutions from simulated electroplating solutions Waste 2 (exit) (Experimental conditions: [Cyanex 302] = 0.2 M; [SA] = 1.0 M thiourea in 1.0 M H2 SO4 ; TR = 1:3; extraction time = 5 min; pH of external phase = 3).
diffused Pd–Cyanex 302 complexes cannot be stripped in the internal phase. As a result, the extracted Pd (Pd–Cyanex 302 complexes) had accumulated in the membrane phase and no carrier had diffused back to react with the Pd. The solute moves toward the emulsion globules by diffusion. At low initial solute concentrations, since driving force for the mass transfer is low, the molecules take longer time to reach the emulsion globules. However, this is compensated by the increased distribution coefficient by increasing the initial Pd concentration. Thus, the Pd dissolves rapidly in the membrane phase, resulting in faster extraction. Conversely, although the increased Pd concentration results in faster diffusion toward the emulsion globules, the extraction rate decreases owing to a decreased distribution coefficient. The results also showed that by increasing initial Pd concentration from 1 to 15 ppm, the recovery rate decreased from 53% to 25%. This is mostly due to the reduced capacity of the internal phase to strip the transported Pd. Moreover, at high Pd concentrations, the internal droplets in the peripheral region are more readily saturated with the solute. In order to investigate the selectivity of Pd from other metals, various initial concentrations of Pd in simulated electroplating wastewater (exit waste) were used and the results were obtained as shown in Fig. 15. The results showed that the Cyanex 302 was very selective to Pd over chromium. The chromate ion may exist in the liquid phase in different ionic forms (HCr2 O7 − , CrO4 2− , Cr2 O7 2− , HCrO4 − ). The Cr2 O7 2 – anions dominate in acidic chromium (VI) water solutions. According to Lewis acid base theory, soft acid–soft base (Pd-Cyanex 302) interactions are stronger than hard acid–soft base (Cr-Cyanex 302) interactions. In addition, the sulfur substitution of Cyanex 302 has higher acidic properties and was categorized as soft base. This makes them particularly suitable for the extraction of soft (Lewis) acid metal ions such as Pd (II), which are in accordance with the HSAB principle [28]. Therefore, reagents containing sulfur donor atoms (Cyanex 302) was expected to be strong carrier for soft metals ions, such as Pd compared to hard metal ions such as chromium. The removal and recovery efficiency decreases with the increase of Pd concentration from 1 to 15 ppm. It is because the internal droplets achieved its saturation conditions. When the initial Pd concentration increased, the peripheral droplets were exhausted faster, requiring the Pd to permeate deeper within the globule prior to being stripped. Since the degree of extraction and recovery increases with the decrease in Pd concentration it may be concluded that the formulation for Pd ELM is more suitable for Pd removal and recovery selectively from dilute aqueous solutions within 1–10 ppm and from the real matrices solutions with chromium.
5. Conclusion As a conclusion, the maximum extraction of Pd from aqueous waste solutions can be achieved at 0.2 M of Cyanex 302 as a carrier, 1.0 M of thiourea in 1.0 M of H2 SO4 as the stripping agent, 5 mins extraction time, pH 3 of external phase and 1:3 of treat ratio. The ELM process has received considerable attention because of its potential in extracting almost 100% of Pd in aqueous solutions. At these conditions, the extraction and recovery of Pd from matrices solutions were successful and the Cyanex 302 was found to be very selective toward Pd over chromium. Acknowledgment The authors would like to acknowledge the Ministry of Higher Education (MOHE) (Research Grant: Vot 4F450), Centre of Lipids Engineering and Applied Research (CLEAR), and Universiti Teknologi Malaysia (UTM) for facilities support to make this research possible. References [1] Lavicoli I, Fontana L. Palladium: exposure uses, and human health effects. In: O N, editor. Encyclopedia of environmental health. Jerome Burlington: Elsevier; 2011. Editor in Chief: p. 307–14. [2] Jochen H, Erwin M, Walter M and Silke O. Method for depositing a palladium layer suitable for wire bonding on conductors of a printed circuit board, and palladium bath for use in said method. U.S. Patent No. 2012/0244276 A1. [3] TIPAC, Technology Information. Forecasting and assessment council. Recovery from electroplating industry waste. India: Technology Information, Forecasting and assessment council; 2009. [4] Hubicki Z, Wołowicz A, Leszcznska M. Studies of removal of palladium(II) ions from chloride solutions on weakly and strongly basic anion exchangers. J Hazard Mater 2008;159:280–6. [5] Volesky B. Biosorption of heavy metals. Boca Raton, FL, USA: CRC Press; 1990. [6] Rydberg J, Cox M, Musikas C, Choppin GR. Solvent extraction principles and practice. 2nd ed. Marcel Dekker, Inc; 2004. p. 480–93. [7] Swain B, Jeong J, Kim S, Lee JA. Separation of platinum and palladium from chloride solution by solvent extraction using Alamine 300. Hydrometallurgy 2010;104:1–7. [8] Li NN. Separating hydrocarbons with liquid membranes. US3410794 A. 1968. [9] Othman N, Chan KH, Goto M, Mat H. Emulsion liquid membrane extraction of silver from photographic waste using CYANEX 302 as the mobile carrier. Solvent Extr Res Dev 2006;13:191–202. [10] Rajasimman M, Karthic P. Application of response surface methodology for the extraction of chromium (VI) by emulsion liquid membrane. J Taiwan Inst Chem Eng 2001;41(1):105–10. [11] Zing-Yi O, Othman N, Mohamad M, Rashid R. Removal performance of lignin compound from simulated pulping wastewater using emulsion liquid membrane process. Int J Global Warm 2014;6:270–83. [12] Sulaiman RNR, Othman N, Amin NAS. Emulsion liquid membrane stability in the extraction of ionized nanosilver from wash water. J Ind Eng Chem 2014;20:3243–50. [13] Chakraborty M, Bhattacharya C, Datta S, Kislik VS. Liquid membranes. Amsterdam: Elsevier; 2010. p. 141–99.
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Please cite this article as: N.F.M. Noah et al., Highly selective transport of palladium from electroplating wastewater using emulsion liquid membrane process, Journal of the Taiwan Institute of Chemical Engineers (2016), http://dx.doi.org/10.1016/j.jtice.2016.03.047