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Treatment of wastewaters from cyanide-free plating process by electrodialysis
Journal of Cleaner Production 91 (2015) 241e250
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Treatment of wastewaters from cyanide-free plating process by electrodialysis a Moura Bernardes b, Tatiana Scarazzato a, *, Daniella Cardoso Buzzi a, Andre Denise Crocce Romano Espinosa a a b
~o Paulo, Chemical Engineering Department, Av. Prof. Lineu Prestes, 580, Bloco 18, CEP 05424-970, Sa ~o Paulo, Brazil University of Sa Federal University of Rio Grande do Sul, Department of Materials Engineering, Av. Bento Gonçalves, 9500, CEP 91509-900, Rio Grande do Sul, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 June 2014 Received in revised form 5 December 2014 Accepted 12 December 2014 Available online 20 December 2014
Cyanidric compounds are used in certain stages of electroplating processes. However, the toxicity of the cyanide stimulates the development of alternative raw materials. Therefore, the utilization of cyanidefree compounds requires the consolidation of treatment methodologies for this novel type of wastewater generated. One of the alternatives that is currently available consists of the replacement of the cyanide by 1-hydroxyethane 1,1-diphosphonic acid (HEDP). In this study it was employed an HEDP based electrolyte, which was used to produce solutions that simulate the rinse waters of copper strike baths. The application of electrodialysis (ED) in a closed system was evaluated by considering the recovery of the copper, the HEDP and the water. The trials were carried out in an ED cell which contains five compartments. The results showed the extraction of up to 99.7% of the copper and up to 94.4% of the HEDP from the working solution. By varying the pH values, along with the construction of speciation diagrams, it was achieved a separation of the Cu(II)-HEDP complexes. While the characteristics of the treated solutions enabled their reutilization in the rinse tanks, the concentrated solutions can be reused in the electrolyte in order to replace ions lost by drag-out. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Electrodialysis HEDP Electroplating Rinse waters
1. Introduction A common application of copper in electroplating processes is as an intermediate layer in systems of two or more coatings, which increases other metals adherence to the substrates, facilitates polishing of parts and improves the substrate corrosion resistance. Moreover, the addition of cyanide to alkaline copper baths, called strike baths, are used industrially to form complexes with copper, reducing its equilibrium potential and enabling an adhesive layer to be deposited on less-noble substrates than copper (Panossian, 1993). The attractive cost, uniformity and adhesion of the deposit, coupled with the utilization of relatively simple equipment boosted the use of cyanide based raw materials for many years. In addition to this, the technologies for process control and treatment of wastewater are already well known and widely used among the majority of companies (Piccinini et al., 2000). However, cyanide
* Corresponding author. Tel.: þ55 11 30915240. E-mail address: [email protected] (T. Scarazzato). http://dx.doi.org/10.1016/j.jclepro.2014.12.046 0959-6526/© 2014 Elsevier Ltd. All rights reserved.
salts are linked to the chemical risks that are involved in any electroplating operation, in addition to representing an important type of pollution of natural resources (Dash et al., 2009). Therefore, cyanide toxicity rised the need to replace it by other raw materials that are equally competitive in terms of costs and quality. One study (Vargas, 2008) evaluated the modification of cyanidefree commercial bath for copper-plating processes on Zamak substrates using a bath based on based on 1-hydroxyethane 1,1diphosphonic acid (HEDP), which is an organic phosphonate capable of forming stables complexes with metallic ions. This study led to the determination of the operational parameters and formulation of baths for obtaining deposits with a comparable level of adherence and shine to that produced by cyanide based baths, as shown in Table 1 (Vargas, 2008). Due to its chelating properties, HEDP has industrial applications as a corrosion inhibitor and antioxidant, in treatments of bone diseases, in cleaning agents and in treatment of water in cooling systems (Nowack, 2003; Fischer, 1993). The diversity of applications of HEDP promoted research (Nowack, 2003; Fischer, 1993; Knepper, 2003; Jaworska et al., 2002) on the use of this substance in natural environments. According to Steber and Wierich, 1986 one
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Table 1 Operating parameters and composition of the HEDP based bath (Vargas, 2008). Cuþ2 ions HEDP Potassium chloride Salicyl sulphonic acid (optional) Potassium sulfate (optional) pH Density of current applied Temperature of the bath Agitation
4.5 g L1 105 g L1 4 a 10 g L1 4 g L1 4 g L1 10 From 0.2 to 0.5 A dm2 From 25 to 60 C Present
characteristic of HEDP is its photodegradability in sunlight wavelengths, giving rise to acetate and orthophosphate byproducts. Photodegradation of HEDP in the presence of metals was analyzed by Fischer (Fischer, 1993) and the results indicated that the presence of Cu2þ ions increased the oxidation of HEDP by 199% (Fischer, 1993). In electroplating operations, the diluted wastewater produced by the washing of the parts accounts for the greatest consumption of water, which calls attention for the development of methods to recover and recycle most of the water used in such processes (Mclay and Reinhard, 2002). The immersion of parts in one or more water tanks results in the dilution of substances carried from a previous bath, minimizing the contamination of the next process. As a consequence, the concentration of contaminants in rinse waters increases gradually over time due to the drag-out (Evans et al., 2009). Conventional wastewater treatments containing cyanide use oxidizing agents to convert it into a less toxic form, namely cyanate (CNO). The stages that follow the cyanide oxidization are wastewater neutralization and formation of insoluble hydroxides followed by flocculation and precipitation reactions, which results in the production of galvanic sludge (Roy, 1996). The replacement of cyanide by HEDP gives rise to changes in the composition of the effluents produced. In order to make HEDP based compounds technically and economically viable, it is necessary to consolidate a methodology for treatment of wastewater, recovery of the components and reutilization of the water in the industrial flow. Electrodialysis (ED) has been explored in the treatment of wastewater resulting from electroplating operations. Electrodialysis (ED) is a membrane separation process which uses an electric potential difference as the driving force to promote ionic transport from different solutions. Semi-permeable anionic and cationic membranes are set correspondingly between two poles e cathode and anode e forming individual compartments, as shown in Fig. 1 (Strathmann, 2004). Its attraction lies in the possibility of recovery of the water and of the ions contained therein, without any need for phase changes or addition of extra components for oxidative processes (Rodrigues et al., 2007). This technique was developed for desalination of brackish waters and for separation and concentration of acids and salts from aqueous solutions. Nevertheless, modifications in classic procedures of electrodialysis allowed its use in a new range of applications, such as treatment of industrial wastewaters (Strathmann, 2004). The application of ED was evaluated for the treatment of rinse waters from plating processes of metals such as nickel (Benvenuti et al., 2014), cadmium (Marder et al., 2003) and chromium (Nataraj et al., 2007). Studies were developed involving the application of the ED (Chiapello and Gal, 1992; Zuoa et al., 2008; Cifuentes et al., 2009), or ED along with electro-recovery (Peng et al., 2011) or ionic exchange processes (Mahmoud and Hoadley, 2012) for copper recovery. The formation of complexes between metals and chelating agents in ED processes has been studied. The separation between
nickel and cobalt by the addition of EDTA has been examined, aiming at the formation of stable anionic complexes between EDTA and nickel (Chaudhary et al., 2000). The same principle was used to study the transport of silver, zinc and copper cations with EDTA, assessing the selective separation of silver (Cherif et al., 1993). Moreover, the selective separation capacity of nickel and copper by the chelating agents oxalic acid and glycine were studied (Huang et al., 1988). However, there are a number of problems associated with the presence of complexes in solution in ED because it may alter the ionic transport in solutions and affect the properties of membranes (Aouad et al., 1999). It was noted that the low mobility of complexes reduces the current efficiency of ion transport (Cherif et al., 1993). In addition, the presence of complexes can increase the resistance of the membranes. Complexes located in the interior of the matrix can result in interactions with sites of the membrane and alter its permselectivity (Aouad et al., 1999, 1997). In a previous study (Aouad et al., 1997), the transport of Cl by an anionic exchange membrane (AEM) was reduced in the presence of zinc complexes, while the flow of Naþ cations was increased, suggesting that complexes of a certain type neutralize part of the fixed sites of the membrane. The rate of complexes in relation to the free ions is important for transport through membranes, as well as the concentration of the species and the pH values of the solution (Huang et al., 1988; Aouad et al., 1999, 1997). Industrial application of electrodialysis are related to operational costs of the process, specially the energy consumption. The total energy consumption of the system is usually defined as function of the characteristics of every application. An important parcel of the energy is used to transport the ions through the solutions and the membranes. It is also important to highlight that, in practice, hundreds of membranes pairs can be settled between the electrode compartments (Strathmann, 1995). The fraction of the current that is effectively used to separate the ion of interest is called current efficiency. The current efficiency (f) is related to the imposed current to the system through the Equation (1) and it is directly proportional to the concentration of ions in the central compartment (Martí-Calatayud et al., 2014).
fðtÞ ¼
n$F$V$ðCt C0 Þ 100 Z t Idt
(1)
0
Through the applied potencial between poles, it is also possible to estimate the specific energy consumption to transport an ion in a given moment. The specific energy consumption is related to the applied potential and depends on the ion concentration in the diluted compartment and on its molar mass (Equation (2)) (MartíCalatayud et al., 2014).
Z EðtÞ ¼
0
t
UðtÞ $Idt
3600$M$V$ðCt C0 Þ
(2)
In this study, it was employed the electrolyte described in Table 1 to produce synthetic solutions that simulate the rinse waters of HEDP-based strike baths. The aim of this study was to evaluate the application of ED for copper, HEDP and water recovery. The influence of the type of trial (galvanostatic and potentiostatic) and pH values in the percentage extraction of ions from the wastewater were analyzed. The ionic transport in presence of Cu(II)-HEDP complexes was assessed. The chemical characteristics of the diluted and concentrated solutions generated as a result of the ED process were determined. Due to photodegradation
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Fig. 1. Typical electrodialysis system containing cation exchange membranes and anion exchange membranes.
properties of HEDP, it was also investigated a possible reduction in HEDP recovery possibility caused by oxidization during ED. The ED system and the membranes used in the experiments are detailed in Section 2 e Materials and Methods. The solutions used in the system are described in item 2.2. The current density to be applied in the system was determined through currentevoltage curves. ED tests were performed for evaluating the percent extraction of copper and HEDP, the influence of the pH and the control mode e potentiostatic or galvanostatic. After the experiments, the samples were characterized using ICP-OES, UVeVis
spectrophotometry and turbidimetric method. Finally, it was evaluated the possibility of photodegradation of HEDP during the ED process through orthophosphate analysis. 2. Materials and methods 2.1. Electrodialysis apparatus The experiments were carried out in an ED cell with five compartments made out of acrylic, separated by cationic and anionic
Fig. 2. Schematic representation of the ED cell used.
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T. Scarazzato et al. / Journal of Cleaner Production 91 (2015) 241e250 Table 2 Characteristics of the cationic (HDX100) and anionic membranes (HDX200) (Buzzi et al., 2013). Parameter
Unit
Ionic group attached e Water content % Ionic exchange capacity mol.kg1 (dry) Ohm.cm2 Membrane surface resistance (0.1 mol NaCl) % Permselectivity (0.1 mol KCl/0.2 mol KCl) Burst strength MPa Dimension change rate % (longitudinal, lateral) Water permeability mL.h.cm2 Fig. 3. Electrodialysis cell with five compartments.
membranes with an area of 16 cm2 arranged alternatively in an assembly of the press-filter type. Each compartment has a tank with a 1000 mL capacity. The central compartment was labeled diluted and received 1000 mL of the working solution. Conductive solutions were placed in the other compartments (1000 mL in each one) e the cathode compartment, the anode compartment, the cation concentrate compartment and the anion concentrate compartment e in order to maintain the conductivity of the system. Centrifugal electro-pumps connected independently to each compartment produced the circulation of the solutions. A schematic representation of the electrodialysis system employed in this study is presented in Fig. 2. Titanium electrodes coated with titanium oxide and ruthenium oxide (70TiO2/30RuO2) were positioned at the extremities of the cell. Continuous current power supplies were used to apply the electric current. During the experiments, samples were collected in order to evaluate the extraction percentage. The ED cell, with five compartments (1 e cathode compartment; 2 e cation concentrate compartment; 3 e diluted compartment; 4 e anion concentrate compartment; 5 e anode compartment), is presented in Fig. 3.
Cationic membrane Anionic membrane (HDX 100) (HDX 200) eSO3 35e50 2.0
eNR3 þ 30e45 1.8
20
20
90
89
0.6 2
0.6 2
0.1 (below 0.2 MPa)
0.2 (below 0.035 MPa)
2.4. Current-voltage curves In order to construct the current voltage curves and determine the limiting current density, the system described in item 2.1, was used. In the central compartment, called diluted, were placed 1000 mL of working solution. The other compartments received 1000 mL of potassium chloride conductive solution. Platinum wires were positioned at the interfaces of a cationic membrane and an anionic membrane, both adjacent to the diluted compartment. The potential of the membranes was ascertained by means of direct readings using multimeters connected to the platinum wires. Initially a current of 5 mA was applied for a period of 5 minutes. After this, the amount of the current was gradually increased at a rate of 2 mA each 2 minutes, with intervals of 3 minutes without the application of any current. After each interval, the current values, the total voltage measured between the electrodes and the potential difference of the membranes were recorded. Once the figures for the current and the potential difference of the membranes had been obtained, polarization curves were constructed in triplicate.
2.2. Working solutions
2.5. Electrodialysis
The synthetic solutions were produced from the dilution of the electrolyte, the composition of which is shown in Table 1. The concentration of the working solutions was set at 1% of the concentration of the bath, simulating the rinse waters of the HEDP based baths. The working solutions were prepared immediately before the start of each experiment, in order to avoid photodegradation of the HEDP. The working solution was placed in the supply tank of the diluted compartment. Solutions of KCl 0.01 M or K2SO4 0.004 M were placed in the concentrate tanks and the electrode tanks. In order to study the effect of the pH, the working solution had its pH decreased to approximately 2.0 using concentrated H2SO4. For these trials, in pH equal to 2.0, the concentration of the KCl and K2SO4 solutions was altered to 0.018 M and 0.019 M, respectively, for the purpose of maintaining the conductivity of the system.
The ED trials were also carried out on ED cell with the configuration described in item 2.1 in duplicate. In the same way as done for the polarization curves, before starting the trials, the membranes were balanced in the working solution for periods of between 18 and 24 hours. During the experiments, samples with volumes of between 15 and 20 mL were collected, in order to study the ionic movement and the extraction percentage. The aliquots were removed from all the solutions every hour for trials lasting 8.5 hours, and each 1.5 hours for trials lasting 10.5 hours. The pH and conductivity were monitored every hour, as were the current applied and the total voltage from the system. The percent extraction was assessed on the basis of trial time, pH value of the trial environment and the type of trial, whether galvanostatic or potentiostatic A summary of the ED trials performed is presented in Table 3.
2.3. Ion-exchange membranes
2.6. Sample characterization
The commercial ion-exchange membranes used in this study, both cationic (HDX 100) and anionic (HDX 200), were provided by Hydrodex®, with an effective area of 16 cm2. Table 2 presents the characteristics of the membranes.
The concentration of Cu2þ and Kþ were ascertained by atomic emission spectrometry by coupled plasma (ICP-OES). This technique is used to determine different metals in aqueous solutions. However, the use of solutions containing organic components can
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Table 3 Parameters used during the electrodialysis experiments. Parameters
POH8
POH10
GOH8
GOH10
GOH10
GH27
Operation time (h) pH Operation control
8.5 10 potentiostatic
10.5 10 potentiostatic
8.5 10 galvanostatic
10.5 10 galvanostatic
12.0 10 galvanostatic
27.0 2 galvanostatic
give rise to difficulties in the sample feed and interference in some spectra. This is due to the physical properties and the carbon content of the organic matrix (McCurdy and Potter, 2002). The digestion of the organic components and the breakdown of complexes are some of the alternatives for the analysis of samples containing these compounds (McCurdy and Potter, 2002; Schmidt et al., 2014). For this reason, each sample collected underwent a process of conversion from the organic forms of phosphorus to orthophosphate prior to the analysis by ICP. The conversion of the organic phosphorus was carried out by means of the persulfate digestion method (American public health association et al., 1998a). The analyses to ascertain the HEDP and orthophosphate were done using the colorimetric method by reduction with ascorbic acid and visible reading region (880 nm). The sulfate analyses were accomplished via the turbidimetric method (American public health association et al., 1998b). The conductivity and pH of the solutions from all of the compartments were monitored every hour, as was the potential difference between electrodes and the current applied. 2.7. Photodegradation of HEDP The possibility of the photodegradation of the HEDP during the application of the electrodialysis was evaluated. It is known that the HEDP can be degraded in acetate and orthophosphate (Steber and Wierich, 1986). Samples of the initial diluted, final diluted and final anion concentrated compartments were analyzed using the Ascorbic Acid Method (American public health association et al., 1998b). The results were expressed in terms of percentage of HEDP in the form of orthophosphate.
in relation to the other samples. This change is due to the acidification of the GHK solution by means of concentrated H2SO4. A variation was noted in the concentration of copper and HEDP in the samples analyzed, caused by the conversion of the organic forms of phosphorus prior to the actual analysis. The process of conversion of the organic forms of phosphorus consists of the following stages (American public health association et al., 1998b): 1. Dilution of the samples, so that the estimated concentration of total phosphorus is consistent with the method's application range; 2. Addition of 0.4 g of ammonium persulfate and of 1 mL of H2SO4 30% v/v to the sample; 3. Heating for a period of at least 30 minutes. This can be done on a heating plate or in an autoclave under a pressure of between 98 and 137 kPa; 4. Neutralization of the pH using NaOH 1 M solution, followed by an adjustment in the volume to 50 mL, whenever necessary. The sensitivity of the ICP-OES and UVeVis spectrophotometry analysis methods, coupled with the possible variations of the factors mentioned can alter the conversion of the organophosphate compounds and the breakdown of the Cu(II)-HEDP complexes. As a result, a number of strategies were employed to reduce the error associated with the stages prior to chemical analysis: the digestion of the phosphorus was carried out in batches, with samples from a single experiment. The stages listed were carried out in periods not exceeding 24 hours. The glassware used was washed with hydrochloric acid (American public health association et al., 1998b). The samples analyzed were diluted in the same proportion. The average concentration values obtained for copper and HEDP were 41.8 mg L1 and 944 mg L1, respectively.
3. Results and discussion 3.2. Determination of currentevoltage curves
3.1. Characterization of working solutions The working solutions were obtained by means of the dilution of the electrolyte developed for an alkaline copper strike bath (Vargas, 2008). Due to the photodegradative properties of HEDP listed by a number of authors (Fischer, 1993; Steber and Wierich, 1986), it was decided to store the electrolyte solution protected from the light and to prepare the working solutions immediately before the start of each trial. A characterization of the working solutions was performed and it is presented in Table 4. According to Table 4, differences can be observed in the pH value (2.2) and the conductivity value (4500 mS cm1) of the GHK sample Table 4 Characterization of the working solutions studied. Parameters
Samples
pH Conductivity (mS.cm1) Cu2þ (mg.L1) HEDP (mg.L1) Cu2þ: HEDP ratio
10.3 1650 32 683 1:21
POH8 POH10 GOH8 GOH10 GOHK GHK Average 10.5 1610 43 890 1:21
10.3 1691 39 926 1:24
10.5 1664 41 1281 1:31
10.6 1535 48 983 1:20
2.2 4500 48 901 1:19
e e 41.8 944 1:23
The trials to obtain the polarization curves in order to determine the limiting current density to be used in the electrodialysis experiments were carried out in triplicate. The overlapping of the current curves versus the potential of the anionic exchange membrane (AEM) and of the cationic exchange membrane (CEM) are presented in Fig. 4. For the anionic membrane (a), it is observed a linear region followed by an alteration in the slope of the curves, indicating the existence of the limiting current region. In the curves constructed for the cationic membrane (b), only the ohmic region seems to have been reached. The maximum current applied in the system should remain between 70 and 80% of the limiting current density (Meng et al., 2005) of the membrane that presented the lowest limiting current. Therefore, the curve of the anionic membrane was chosen as representative (Fig. 5) and the current density to be applied was set at 2.1 mA cm2. 3.3. Electrodialysis Based on the results of the polarization curves, ED experiments were carried out in potentiostatic and galvanostatic mode for 8.5 h
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Fig. 4. Polarization curves in triplicate constructed for the anionic membrane (a) and the cationic membrane (b).
and 10.5 h. In the trials using galvanostatic mode, the current density applied was fixed according to the results of the polarization curves, at 2.1 mA cm2. In the potentiostatic trials, the potential was set at 16.9 V, a value which corresponds to an initial current density of 2.1 mA cm2. The pH and the conductivity of the solutions of all the compartments were monitored every hour. The table shows the variation in the parameters monitored.Table 5. The reactions that occur in the electrodes are responsible for the variation in the pH value and of the conductivity in the anode, cathode, anion concentrate and cation concentrate compartments. The increase in the pH value on the cathode side is due to the release of hydroxyl ions, while the decrease in the pH on the anode side is the result of the formation of Hþ. The reduction in the conductivity of the diluted compartment is attributed to the extraction of ions from the working solution. Over the course of the experiments, the removal of the number of ions available in the diluted compartment caused an increase in the total resistance of the system. This increase can be seen from the reduction in the value of the current applied for the potentiostatic trials, or from the increase in the total potential for the galvanostatic trials. Fig. 6 shows the changes of the potential and of the current in the potentiostatic and galvanostatic trials carried out over the course of 8.5 h (a) and 10.5 h (b). During the first 3 hours of trial, there is a decrease in the total resistance of the system, both in galvanostatic mode as well as in the potentiostatic mode. This behavior is observed in Fig. 6, by means of the increase in the initial current value (in potentiostatic mode) and the decrease in initial value of the potential (in
Fig. 5. Polarization curve of the anionic membrane.
galvanostatic mode). After 3 hours of trial, the resistance of the system started to increase, due to the extraction of ions from the diluted compartment. In potentiostatic mode, the electric current reached 55% and 54% of the value initially applied in 8.5 and 10.5 hours, respectively. In galvanostatic mode, the potential values registered after the same periods were 27.2 V and 23.6 V. 3.3.1. Effect of pH Depending upon the pH value of the bath, as well as of the rinsing method and of the frequency of disposal of diluted wastewater, the rinse waters can drop to pH values of less than 2. In order to evaluate the effect of the change in pH value, the working solutions were submitted to trials in an acid environment (pH z 2). The pH of the working solutions was adjusted by means of addition of 345 mL of concentrated sulphuric acid. After the addition of the acid, the variation in volume of the working solution was less than 0.05%. The study of the pH variation was carried out along with the construction of the speciation diagrams of the working solutions, because of the influence of Cu(II)HEDP complexes on ionic migration. Fig. 7 shows the speciation diagram of the working solution, composed of copper, HEDP and potassium chloride. As it can be seen in Fig. 7, in an alkaline environment, the copper cations are complexed by the HEDP. It is noted that when the pH value is in between 5.2 and 9.4, 100% of the copper ions form complexes with the HEDP, predominantly in the CuHHEDP and CuHEDP2 anionic specimens. In an acidic environment, a trend toward the separation of the complexes is observed, given that at a pH equal to 2, 81.5% of the Cu2þ ions are free. The acidification of the working solution by means of the addition of sulphuric acid modifies the composition of the specimens, due to the formation of copper sulfate with a pH of between 0 and 5.4, as shown in Fig. 8. Nevertheless, the existence of 54.6% of free copper cations with a pH equal to 2 indicates the possibility of separation of the complexes. The concentration of copper and of HEDP in the concentrated cation and concentrated anion compartments after the ED is shown in Table 6. In the case of the experiments that were carried out in an alkaline environment, the transport of the copper and HEDP ions occurred predominantly from the diluted compartment to the anion concentrated compartment. The results suggest the presence of anionic complexes between the copper and the HEDP in the working solution. In the experiment with acidified solution, indicated by the acronym GH27, the copper ions were transported from the diluted compartment to the cation concentrated one. The HEDP
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Table 5 Variation in the pH and in the conductivity during the electrodialysis trials. Parameter
Anode Anode concentrate Diluted Cathode concentrate Cathode
POH8
pH Conductivity pH Conductivity pH Conductivity pH Conductivity pH Conductivity
(mS cm1) (mS cm1) (mS cm1) (mS cm1) (mS cm1)
POH10
GOH8
GOH10
GOH12
GH27
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
5.2 1532 5.2 1532 10.3 1650 5.2 1532 5.2 1532
2.6 2230 3.3 2570 5.4 227 10.9 3590 10.9 2090
7.2 1574 7.2 1574 10.5 1610 7.2 1574 7.2 1574
2.3 2330 2.8 2660 4.0 193 11.0 4100 11.0 2280
6.2 1536 6.2 1536 10.3 1691 6.2 1536 6.2 1536
2.4 2160 3.1 2410 3.8 265 11.6 3730 11.7 2120
5.7 1560 5.7 1560 10.5 1664 5.7 1560 5.7 1560
3.3 2250 4.0 2450 4.3 277 12.8 3760 13.0 2180
6.2 1631 6.2 1631 10.6 1535 6.2 1631 6.2 1631
2.3 2590 3.3 2420 3.4 192 11.2 3460 11.6 2390
5.3 4310 5.3 4310 2.2 4500 5.3 4310 5.3 4310
1.8 6800 2.3 7300 3.2 198 2.2 7600 12.2 6600
Fig. 6. Variation of the potential and of the current in the system during trial lasting 8.5 h (a) and trial lasting 10.5 h (b).
anions moved toward the anion concentrated compartment, indicating the separation of the complex.
3.4. Percent extraction Fig. 9 presents the results in terms of percent extraction of copper and HEDP in the experiments carried out. The experiment that produced the greatest removal of copper from the diluted compartment was trial GH27, in which a 92% rate was achieved in relation to the removal of the copper ions. The greatest extraction of
Fig. 7. Speciation diagram of the copper complexes formed in the alkaline working solution. The diagram was constructed with the help of the Hydra-Medusa software.
HEDP from the diluted compartment was obtained with the experiment GOH12, with 94.4% of the acid being removed. The analysis of the tests POH8 and GOH8 shows that, in the galvanostatic control (GOH8), the percent extraction of copper was 34% greater when compared to the potentiostatic control (POH8). The percent extraction of HEDP was 4e9% higher in the galvanostatic control. The tests done for 10e5 hours, POH10 and GOH10, showed that the removal of copper in the galvanostatic control experiment (GOH10) was 8e9% greater than in the potentiostatic control (POH10) and the removal of HEDP was 4e3% higher in the
Fig. 8. Speciation diagram of the copper complexes formed in the working solution acidified with sulphuric acid. The diagram was constructed with the help of the HydraMedusa software.
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Table 6 Concentration of copper and of HEDP after the ED experiments, in the anion concentrated and cation concentrated compartments. POH8 POH10 GOH8 GOH10 GOH12 GH27 Cu2þ (mg L1) HEDP (mg L1)
Anode concentrated 21 Cathode concentrated 3 Anode concentrated 583 Cathode concentrated 0
24 0 646 0
19 0 582 0
21 0 695 1
33 4 683 21
8 45 550 10
Fig. 10. Percentage extraction of the HxHEDPy and SO4 2 anions as a result of the trial time.
Table 7 Concentration of sulfate in the diluted and concentrated anion compartments, at the start of the experiment and after 27 h. SO4 2 (mg L1)
Diluted compartment Anode concentrated
Initial
After 27 h
1288 446
1596 2229
Fig. 9. Percentage extraction obtained for copper and for HEDP in the electrodialysis trials.
galvanostatic control tests. It is observed that the higher index of percent extraction was given in the galvanostatic control experiments. Besides that, the extraction of copper was more influenced by the mode of the experiment than the extraction of HEDP. For industrial operations of electrodialysis, other factors than the extraction should be considered, such as economical issues and operational safety. The utilization of the potentiostatic control may avoid the concentration polarization phenomenon, since the current density remains constantly under the limit determined by the currentevoltage curve. Furthermore, the process can be economically beneficial in certain cases in which different stages of treatment are operated in different potential (Strathmann, 2004; Costa et al., 2002). The acidification of the solution by addition of H2SO4 caused a reduction in the speed of HEDP extraction. This behavior is attributed to the existence of SO4 2 anions in the same compartment as the HxHEDPy anions, causing a migratory competition between the ionic specimens. The extraction percentage of HEDP and SO4 2 as a result of the duration of trials is presented in Fig. 10. It can be observed that the extraction of the two anions occurs simultaneously, with the extraction of HEDP being greater than that of sulfate. An analysis of sulfate in the initial and final samples of the anion concentrated compartment was carried out. The results indicate that the movement of the anions takes place in the same direction, as shown in Table 7. After a trial of 27 hours, the sulfate concentration in the concentrated anion compartment increased 40%, which can be attributed to the presence of an anionic membrane between the diluted and concentrated anion compartments.
3.5. Chemical characterization of solutions after ED The concentrated and diluted solutions produced by the application of the ED had their characteristics determined. The pH value and conductivity of all the solutions were measured and analyses
were carried out to determine the concentration of copper, potassium, HEDP and sulfate. The results are presented in Table 8. The results presented in Table 8 indicate that the diluted solutions obtained can be reutilized by integrating them into the electroplating rinse tanks. At the same time, the recovery of the copper and HEDP ions in the concentrated compartment indicates the possibility of reusing these components in the electrolyte, offsetting possible losses caused by drag-out. 3.6. Current efficiency and energy consumption In the evaluation of the strike bath containing copper and HEDP, it is considered that the applied electric current will be used to transport the following ions: Cuhedp2, CuHhedp, Cu2þ (acid environment), Kþ, Cl e SO4 2 (acid environment). The reactions that involve HEDP and Cu2þ in the working solutions are: Cu2þ þ hedp4 4 Cuhedp2Hþ þ Cu2þ þ hedp4 4 CuHhedpHþ þ hedp4 4 Hhedp32Hþ þ hedp4 4 H2hedp2Electroplating baths containing complexant agents are used to decrease the activity of the metal cations in the bath. Therefore, it is assumed that all cupreous ions will be complexed by the HEDP and
Table 8 Chemical characteristics of the concentrated and diluted solutions. Concentration after ED tests (mg.L1) pH Cu2þ
Kþ
HxHEDPy- SO4 2
Conductivity (mS.cm1)
Concentrated 19e45 50e193 550e695 634e2564 2.2e4.0 2410e7600 solutions Diluted solutions 4e18 9e29 55e357 10e446 3.2e5.4 193e277
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that each mol of Cu2þ reacts with one mol of hedp4 to form one mol of complex. Since the molar concentration of the HEDP in the bath is higher than the molar concentration of the copper, it is possible to deduce that there are free HEDP ions in the solution, which can present valence of 2 or 3, depending on the pH of the solution. It is expected that the current efficiency of Cuhedp2 and CuHhedp complexes would be lower than the current efficiency of free HEDP ions e hedp2 and Hhedp3 e because in the strike bath, the molar concentration of copper is about 7 times smaller than the molar concentration of HEDP. Likewise, the specific consumption of energy to transport the complexes shall be higher. According to McGovern et al., 2014, the effective cost of an ED system should consider the ratio between the ionic concentrations of the diluted and concentrated compartments, so as the conductivity of the solutions involved in the process. In this sense, the limiting current density is a fundamental factor in the operation and may influence the system characteristics (e.g. the size and the number of cell pairs) and the energy consumption. In stages of the process in which the conductivity is low, the ohmic drop of the solutions starts to play an important role in the energy consumption of the system, because the electrical resistance of the solution can outgrow the electrical resistance of the membrane (McGovern et al., 2014). In this situation, one can evaluate the possibility of using a hybrid system that allows the reduction of the energy consumption (Mahmoud and Hoadley, 2012).
direction of the anion concentrated compartment. In an acidic environment, it is possible to bring about the separation of the Cu(II)-HEDP complexes and the recovery of copper and HEDP in separate compartments. However, HEDP extraction was slower in an acidic environment due to the simultaneous transport between the HxHEDPy and SO4 2 anions. In industrial processes, the pH value of the rinse waters depends on the pH value of the bath applied, on the type of rinse and on the frequency of disposal of the wastewater. The experiments carried out indicated that in an environment with a pH of more than 5.4, it is preferable to recover the complexes in the same compartment, avoiding the addition of reagents in order to adjust the pH value of the system. The presence of inorganic phosphorus in the samples of the trial in an acidic environment also suggests the viability of the process in neutral or alkaline solutions.
3.7. Photodegradation of HEDP
American public health association, American water works association, Water environmnet federation, 1998a. Standard Methods for the Examination of Water and Wastewater, 20. ed. In: Ascorbic Acid Method, pp. 4e146 American public health association, American water works association, Water environmnet federation, 1998b. Standard Methods for the Examination of Water and Wastewater, 20. ed. In: SO24 Turbidimetric Method, pp. 4e178 Aouad, F., Lindheimer, A., Gavach, C., 1997. Transport properties of electrodialysis membranes in the presence of Zn2þ complexes with Cl. J. Membr. Sci. 123, 207e223. Aouad, F., Lindheimer, A., Chaouky, M., Gavach, C., 1999. Loss of permselectivity of anion exchange membranes in contact with zinc chloride complexes. Desalination. 121, 13e22. Benvenuti, T., Siqueira, M.A.S., Bernardes, A.M.B., Ferreira, J.Z., 2014. Electrodialysis Treatment of Nickel Wastewater. In: Topics in Mining, Metallurgy and Materials Engineering, pp. 133e144. Buzzi, D.C., Viegas, L.S., Rodrigues, M.A.S., Bernardes, A.M., Tenorio, J.A.S., 2013. Water recovery from acid mine drainage by electrodialysis. Min. Eng. 40, 82e89. Chaudhary, A.J., Donaldson, J.D., Grimes, S.M., Yasri, N.G., 2000. Separation of nickel from cobalt using electrodialysis in the presence of EDTA. J. Appl. Electrochem. 30, 439e445. Cherif, T., Elmidaoui, A., Gavach, C., 1993. Separation of Agþ, Zn2þ and Cu2þ ions by electrodialysis with a monovalent cation specific membrane and EDTA. J. Membr. Sci. 76 (1), 39e49. Chiapello, J.M., Gal, J.Y., 1992. Recovery by electrodialysis of cyanide electroplating rinse waters. J. Membr. Sci. 68 (3), 283e291. Cifuentes, L., García, I., Arriagada, P., Casas, J.M., 2009. The use of electrodialysis for metal separation and water recovery from CuSO4-H2SO4-Fe solutions. Sep. Purif. Technol. 68 (1), 105e108. Costa, R.F.D., Klein, C.W., Bernardes, A.M., Ferreira, J.Z., 2002. Evaluation of the electrodialysis process for the treatment of metal finishing wastewater. J. Braz. Chem. Soc. 13, 540e547. Dash, R.R., Gaur, A., Balomajumder, C., 2009. Cyanide in industrial wastewaters and its removal: a review on biotreatment. J. Hazard. Mater. 163 (1), 1e11. Evans, T., Lorenz, A., Peukert, L., 2009. Drag-out reduction techniques using barrel blow-down and DSC dip-spin-tilt technology. Met. Finish. 107 (12), 35e37. Fischer, K., 1993. Distribution and elimination of HEDP in aquatic systems. Water Res. 27 (3), 485e493. Huang, T.C., Lin, Y.K., Chen, C.Y., 1988. Selective separation of nickel and copper from a complexing solution by a cation-exchange membrane. J. Membr. Sci. 37, 131e144. Jaworska, J., Genderen-Takken, H.V., Hanstveit, A., Plasshe, E., Feijtel, T., 2002. Environmental risk assessment of phosphonates, used in domestic laundry and cleaning agents in the Netherlands. Chemosphere 47 (6), 655e665. Knepper, T.P., 2003. Synthetic chelating agents and compounds exhibiting complexing properties in the aquatic environment. Trends Anal. Chem. 22 (10), 1e17. Mahmoud, A., Hoadley, A.F., 2012. An evaluation of a hybrid ion exchange electrodialysis process in the recovery of heavy metals from simulated dilute industrial wastewater. Water Res. 46 (10), 3364e3376.
Samples from the initial diluted, final diluted and final anion concentrated compartments of three trials, GOH10, GOH12 and GH27 were analyzed. Analysis was carried out based on the orthophosphate fraction present in the samples before digestion of the organic phosphorus. The presence of inorganic phosphorus in the samples without prior conversion of the organic forms indicates the occurrence of photo-oxidation of the HEDP. As a result, the presence of inorganic phosphorus was not observed in the samples from the trials in an alkaline environment. For the trial in an acidic environment, GH27, there was a 0.6% degradation of the HEDP in the sample from the initial diluted compartment and a 7% degradation in the sample from the final anion concentrated compartment. 4. Conclusions It was evaluated the application of electrodialysis for the treatment of an effluent simulating rinse waters from HEDP based strike baths, aiming to recover the copper, the HEDP and the water. The chemical analyses performed on the solutions produced after the application of ED indicated a concentration of copper of between 4 and 18 mg L1 in the diluted solutions and one of between 19 and 45 mg L1 in the concentrated solutions. The concentration of HEDP in the diluted solutions varied from 55 to 373 mg L1 and, in the concentrated solutions, between 550 and 695 mg L1. The greatest extraction percentage obtained was one of 99.7% for copper and 94.4% for HEDP. The experiments performed under galvanostatic control presented a higher percentage extraction of ions from the working solution when compared to the potentiostatic tests. The results suggest the possibility of reutilization of the concentrated solutions in replacing the ions of the electrolyte lost by drag-out. At the same time, the characteristics of the diluted solution allow it to be incorporated into the rinse tanks. It was observed that in an alkaline environment the copper cations form anionic complexes, migrating predominantly in the
Acknowledgments The authors would like to thank the Laboratory of Corrosion, Protection and Recycling of Materials of the Federal University of Rio Grande do Sul for the technical assistance and the CAPES and the FAPESP 12/51871-9 for their financial support.
References
250
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Marder, L., Sulzbach, G.O., Bernardes, A.M.B., Ferreira, J.Z., 2003. Removal of cadmium and cyanide from aqueous solutions through electrodialysis. J. Braz. Chem. Soc. 14 (4), 610e615. n, M., Ortega, E., Bernardes, A.M., Martí-Calatayud, M.C., Buzzi, D.C., García-Gabaldo rio, J.A.S., Pe rez-Herranz, V., 2014. Sulfuric acid recovery from acid mine Teno drainage by means of electrodialysis. Desalination. 343, 120e127. McCurdy, E., Potter, D., 2002. Techniques for the Analysis of Organic Chemicals by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). McGovern, R.K., Zubair, S.M., Lienhard V, J.H., 2014. The cost effectiveness of electrodialysis for diverse salinity applications. Desalination 348, 57e65. Mclay, W.J., Reinhard, F. P, 2002. Waste minimization and recovery technologies. Met. Finish. 100 (1), 798e829. Meng, H., Deng, D., Chen, S., Zhang, G., 2005. A new method to determine the optimal operating current (Ilim') in the electrodialysis process. Desalination. 181, 101e108. Nataraj, S.K., Hosamani, K.M., Aminabhavi, T.M., 2007. Potential application of an electrodialysis pilot plant containing ion-exchange membranes in chromium removal. Desalination 217 (1e3), 181e190. Nowack, B., 2003. Environmental chemistry of phosphonates. Water Res. 37 (11), 2533e2546. ~o e proteç~ ~o em equipamentos e Panossian, Z., 1993 Corrosa ao contra corrosa licas, First ed., vol. 2. IPT, Sa ~o Paulo. estruturas meta Peng, C., Liu, Y., Bi, J., Xu, H., Ahmed, A.S., 2011. Recovery of copper and water from copper-electroplating wastewater by the combination process of electrolysis and electrodialysis. J. Hazard. Mater. 189 (3), 814e820.
Piccinini, N., Ruggiero, G.N., Baldi, G., Robotto, A., 2000. Risk of hydrocyanic acid release in the electroplating industry. J. Hazard. Mater. 71 (1e3), 395e407. Rodrigues, M.A.S., Amado, F.D.R., Xavier, J.L.N., Streit, K.F., Bernardes, A.M., Ferreira, J.Z., 2007. Application of photoelectrochemical-electrodialysis treatment for the recovery and reuse of water from tannery effluents. J. Clean. Prod. 16, 605e611. Roy, C.H., 1996. Wastewater control and treatment. In: Durney, L.J. (Ed.), Electroplating Engineering Handbook, Four ed. Chapman & Hall, Londres. Schmidt, C.K., Raue, B., Brauch, H.J., Sacher, F., 2014. Trace-level analysis of phosphonates in environmental waters by ion chromatography and inductively coupled plasma mass spectrometry. Intern. J. Environ. Anal. Chem. 94 (4), 385e398. Steber, J., Wierich, P., 1986. Properties of hydroxyethane diphosphonate affecting its environmental fate: degradability, sludge adsorption, mobility in soils, and bioconcentration. Chemosphere 15 (7), 929e945. Strathmann, H., 1995. Membrane Separation Technology. Elsevier, Amsterdan. Strathmann, H., 2004. Ion-exchange Membrane Separation Processes. Elsevier, Amsterdan. Vargas, C., 2008. Estudo da eletrodeposiç~ ao do cobre a partir de banhos alcalinos cnisentos de cianetos. Dissertaç~ ao. (Mestrado em Engenharia) e Escola Polite ~o Paulo, p. 221. ica, Universidade de S~ ao Paulo, Sa Zuoa, W., Zhanga, G., Mengb, Q., Zhangb, H., 2008. Characteristics and application of multiple membrane process in plating wastewater reutilization. Desalination. 222 (1e3), 187e196.
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Treatment of wastewaters from cyanide-free plating process by electrodialysis a Moura Bernardes b, Tatiana Scarazzato a, *, Daniella Cardoso Buzzi a, Andre Denise Crocce Romano Espinosa a a b
~o Paulo, Chemical Engineering Department, Av. Prof. Lineu Prestes, 580, Bloco 18, CEP 05424-970, Sa ~o Paulo, Brazil University of Sa Federal University of Rio Grande do Sul, Department of Materials Engineering, Av. Bento Gonçalves, 9500, CEP 91509-900, Rio Grande do Sul, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 June 2014 Received in revised form 5 December 2014 Accepted 12 December 2014 Available online 20 December 2014
Cyanidric compounds are used in certain stages of electroplating processes. However, the toxicity of the cyanide stimulates the development of alternative raw materials. Therefore, the utilization of cyanidefree compounds requires the consolidation of treatment methodologies for this novel type of wastewater generated. One of the alternatives that is currently available consists of the replacement of the cyanide by 1-hydroxyethane 1,1-diphosphonic acid (HEDP). In this study it was employed an HEDP based electrolyte, which was used to produce solutions that simulate the rinse waters of copper strike baths. The application of electrodialysis (ED) in a closed system was evaluated by considering the recovery of the copper, the HEDP and the water. The trials were carried out in an ED cell which contains five compartments. The results showed the extraction of up to 99.7% of the copper and up to 94.4% of the HEDP from the working solution. By varying the pH values, along with the construction of speciation diagrams, it was achieved a separation of the Cu(II)-HEDP complexes. While the characteristics of the treated solutions enabled their reutilization in the rinse tanks, the concentrated solutions can be reused in the electrolyte in order to replace ions lost by drag-out. © 2014 Elsevier Ltd. All rights reserved.
Keywords: Electrodialysis HEDP Electroplating Rinse waters
1. Introduction A common application of copper in electroplating processes is as an intermediate layer in systems of two or more coatings, which increases other metals adherence to the substrates, facilitates polishing of parts and improves the substrate corrosion resistance. Moreover, the addition of cyanide to alkaline copper baths, called strike baths, are used industrially to form complexes with copper, reducing its equilibrium potential and enabling an adhesive layer to be deposited on less-noble substrates than copper (Panossian, 1993). The attractive cost, uniformity and adhesion of the deposit, coupled with the utilization of relatively simple equipment boosted the use of cyanide based raw materials for many years. In addition to this, the technologies for process control and treatment of wastewater are already well known and widely used among the majority of companies (Piccinini et al., 2000). However, cyanide
* Corresponding author. Tel.: þ55 11 30915240. E-mail address: [email protected] (T. Scarazzato). http://dx.doi.org/10.1016/j.jclepro.2014.12.046 0959-6526/© 2014 Elsevier Ltd. All rights reserved.
salts are linked to the chemical risks that are involved in any electroplating operation, in addition to representing an important type of pollution of natural resources (Dash et al., 2009). Therefore, cyanide toxicity rised the need to replace it by other raw materials that are equally competitive in terms of costs and quality. One study (Vargas, 2008) evaluated the modification of cyanidefree commercial bath for copper-plating processes on Zamak substrates using a bath based on based on 1-hydroxyethane 1,1diphosphonic acid (HEDP), which is an organic phosphonate capable of forming stables complexes with metallic ions. This study led to the determination of the operational parameters and formulation of baths for obtaining deposits with a comparable level of adherence and shine to that produced by cyanide based baths, as shown in Table 1 (Vargas, 2008). Due to its chelating properties, HEDP has industrial applications as a corrosion inhibitor and antioxidant, in treatments of bone diseases, in cleaning agents and in treatment of water in cooling systems (Nowack, 2003; Fischer, 1993). The diversity of applications of HEDP promoted research (Nowack, 2003; Fischer, 1993; Knepper, 2003; Jaworska et al., 2002) on the use of this substance in natural environments. According to Steber and Wierich, 1986 one
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Table 1 Operating parameters and composition of the HEDP based bath (Vargas, 2008). Cuþ2 ions HEDP Potassium chloride Salicyl sulphonic acid (optional) Potassium sulfate (optional) pH Density of current applied Temperature of the bath Agitation
4.5 g L1 105 g L1 4 a 10 g L1 4 g L1 4 g L1 10 From 0.2 to 0.5 A dm2 From 25 to 60 C Present
characteristic of HEDP is its photodegradability in sunlight wavelengths, giving rise to acetate and orthophosphate byproducts. Photodegradation of HEDP in the presence of metals was analyzed by Fischer (Fischer, 1993) and the results indicated that the presence of Cu2þ ions increased the oxidation of HEDP by 199% (Fischer, 1993). In electroplating operations, the diluted wastewater produced by the washing of the parts accounts for the greatest consumption of water, which calls attention for the development of methods to recover and recycle most of the water used in such processes (Mclay and Reinhard, 2002). The immersion of parts in one or more water tanks results in the dilution of substances carried from a previous bath, minimizing the contamination of the next process. As a consequence, the concentration of contaminants in rinse waters increases gradually over time due to the drag-out (Evans et al., 2009). Conventional wastewater treatments containing cyanide use oxidizing agents to convert it into a less toxic form, namely cyanate (CNO). The stages that follow the cyanide oxidization are wastewater neutralization and formation of insoluble hydroxides followed by flocculation and precipitation reactions, which results in the production of galvanic sludge (Roy, 1996). The replacement of cyanide by HEDP gives rise to changes in the composition of the effluents produced. In order to make HEDP based compounds technically and economically viable, it is necessary to consolidate a methodology for treatment of wastewater, recovery of the components and reutilization of the water in the industrial flow. Electrodialysis (ED) has been explored in the treatment of wastewater resulting from electroplating operations. Electrodialysis (ED) is a membrane separation process which uses an electric potential difference as the driving force to promote ionic transport from different solutions. Semi-permeable anionic and cationic membranes are set correspondingly between two poles e cathode and anode e forming individual compartments, as shown in Fig. 1 (Strathmann, 2004). Its attraction lies in the possibility of recovery of the water and of the ions contained therein, without any need for phase changes or addition of extra components for oxidative processes (Rodrigues et al., 2007). This technique was developed for desalination of brackish waters and for separation and concentration of acids and salts from aqueous solutions. Nevertheless, modifications in classic procedures of electrodialysis allowed its use in a new range of applications, such as treatment of industrial wastewaters (Strathmann, 2004). The application of ED was evaluated for the treatment of rinse waters from plating processes of metals such as nickel (Benvenuti et al., 2014), cadmium (Marder et al., 2003) and chromium (Nataraj et al., 2007). Studies were developed involving the application of the ED (Chiapello and Gal, 1992; Zuoa et al., 2008; Cifuentes et al., 2009), or ED along with electro-recovery (Peng et al., 2011) or ionic exchange processes (Mahmoud and Hoadley, 2012) for copper recovery. The formation of complexes between metals and chelating agents in ED processes has been studied. The separation between
nickel and cobalt by the addition of EDTA has been examined, aiming at the formation of stable anionic complexes between EDTA and nickel (Chaudhary et al., 2000). The same principle was used to study the transport of silver, zinc and copper cations with EDTA, assessing the selective separation of silver (Cherif et al., 1993). Moreover, the selective separation capacity of nickel and copper by the chelating agents oxalic acid and glycine were studied (Huang et al., 1988). However, there are a number of problems associated with the presence of complexes in solution in ED because it may alter the ionic transport in solutions and affect the properties of membranes (Aouad et al., 1999). It was noted that the low mobility of complexes reduces the current efficiency of ion transport (Cherif et al., 1993). In addition, the presence of complexes can increase the resistance of the membranes. Complexes located in the interior of the matrix can result in interactions with sites of the membrane and alter its permselectivity (Aouad et al., 1999, 1997). In a previous study (Aouad et al., 1997), the transport of Cl by an anionic exchange membrane (AEM) was reduced in the presence of zinc complexes, while the flow of Naþ cations was increased, suggesting that complexes of a certain type neutralize part of the fixed sites of the membrane. The rate of complexes in relation to the free ions is important for transport through membranes, as well as the concentration of the species and the pH values of the solution (Huang et al., 1988; Aouad et al., 1999, 1997). Industrial application of electrodialysis are related to operational costs of the process, specially the energy consumption. The total energy consumption of the system is usually defined as function of the characteristics of every application. An important parcel of the energy is used to transport the ions through the solutions and the membranes. It is also important to highlight that, in practice, hundreds of membranes pairs can be settled between the electrode compartments (Strathmann, 1995). The fraction of the current that is effectively used to separate the ion of interest is called current efficiency. The current efficiency (f) is related to the imposed current to the system through the Equation (1) and it is directly proportional to the concentration of ions in the central compartment (Martí-Calatayud et al., 2014).
fðtÞ ¼
n$F$V$ðCt C0 Þ 100 Z t Idt
(1)
0
Through the applied potencial between poles, it is also possible to estimate the specific energy consumption to transport an ion in a given moment. The specific energy consumption is related to the applied potential and depends on the ion concentration in the diluted compartment and on its molar mass (Equation (2)) (MartíCalatayud et al., 2014).
Z EðtÞ ¼
0
t
UðtÞ $Idt
3600$M$V$ðCt C0 Þ
(2)
In this study, it was employed the electrolyte described in Table 1 to produce synthetic solutions that simulate the rinse waters of HEDP-based strike baths. The aim of this study was to evaluate the application of ED for copper, HEDP and water recovery. The influence of the type of trial (galvanostatic and potentiostatic) and pH values in the percentage extraction of ions from the wastewater were analyzed. The ionic transport in presence of Cu(II)-HEDP complexes was assessed. The chemical characteristics of the diluted and concentrated solutions generated as a result of the ED process were determined. Due to photodegradation
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Fig. 1. Typical electrodialysis system containing cation exchange membranes and anion exchange membranes.
properties of HEDP, it was also investigated a possible reduction in HEDP recovery possibility caused by oxidization during ED. The ED system and the membranes used in the experiments are detailed in Section 2 e Materials and Methods. The solutions used in the system are described in item 2.2. The current density to be applied in the system was determined through currentevoltage curves. ED tests were performed for evaluating the percent extraction of copper and HEDP, the influence of the pH and the control mode e potentiostatic or galvanostatic. After the experiments, the samples were characterized using ICP-OES, UVeVis
spectrophotometry and turbidimetric method. Finally, it was evaluated the possibility of photodegradation of HEDP during the ED process through orthophosphate analysis. 2. Materials and methods 2.1. Electrodialysis apparatus The experiments were carried out in an ED cell with five compartments made out of acrylic, separated by cationic and anionic
Fig. 2. Schematic representation of the ED cell used.
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T. Scarazzato et al. / Journal of Cleaner Production 91 (2015) 241e250 Table 2 Characteristics of the cationic (HDX100) and anionic membranes (HDX200) (Buzzi et al., 2013). Parameter
Unit
Ionic group attached e Water content % Ionic exchange capacity mol.kg1 (dry) Ohm.cm2 Membrane surface resistance (0.1 mol NaCl) % Permselectivity (0.1 mol KCl/0.2 mol KCl) Burst strength MPa Dimension change rate % (longitudinal, lateral) Water permeability mL.h.cm2 Fig. 3. Electrodialysis cell with five compartments.
membranes with an area of 16 cm2 arranged alternatively in an assembly of the press-filter type. Each compartment has a tank with a 1000 mL capacity. The central compartment was labeled diluted and received 1000 mL of the working solution. Conductive solutions were placed in the other compartments (1000 mL in each one) e the cathode compartment, the anode compartment, the cation concentrate compartment and the anion concentrate compartment e in order to maintain the conductivity of the system. Centrifugal electro-pumps connected independently to each compartment produced the circulation of the solutions. A schematic representation of the electrodialysis system employed in this study is presented in Fig. 2. Titanium electrodes coated with titanium oxide and ruthenium oxide (70TiO2/30RuO2) were positioned at the extremities of the cell. Continuous current power supplies were used to apply the electric current. During the experiments, samples were collected in order to evaluate the extraction percentage. The ED cell, with five compartments (1 e cathode compartment; 2 e cation concentrate compartment; 3 e diluted compartment; 4 e anion concentrate compartment; 5 e anode compartment), is presented in Fig. 3.
Cationic membrane Anionic membrane (HDX 100) (HDX 200) eSO3 35e50 2.0
eNR3 þ 30e45 1.8
20
20
90
89
0.6 2
0.6 2
0.1 (below 0.2 MPa)
0.2 (below 0.035 MPa)
2.4. Current-voltage curves In order to construct the current voltage curves and determine the limiting current density, the system described in item 2.1, was used. In the central compartment, called diluted, were placed 1000 mL of working solution. The other compartments received 1000 mL of potassium chloride conductive solution. Platinum wires were positioned at the interfaces of a cationic membrane and an anionic membrane, both adjacent to the diluted compartment. The potential of the membranes was ascertained by means of direct readings using multimeters connected to the platinum wires. Initially a current of 5 mA was applied for a period of 5 minutes. After this, the amount of the current was gradually increased at a rate of 2 mA each 2 minutes, with intervals of 3 minutes without the application of any current. After each interval, the current values, the total voltage measured between the electrodes and the potential difference of the membranes were recorded. Once the figures for the current and the potential difference of the membranes had been obtained, polarization curves were constructed in triplicate.
2.2. Working solutions
2.5. Electrodialysis
The synthetic solutions were produced from the dilution of the electrolyte, the composition of which is shown in Table 1. The concentration of the working solutions was set at 1% of the concentration of the bath, simulating the rinse waters of the HEDP based baths. The working solutions were prepared immediately before the start of each experiment, in order to avoid photodegradation of the HEDP. The working solution was placed in the supply tank of the diluted compartment. Solutions of KCl 0.01 M or K2SO4 0.004 M were placed in the concentrate tanks and the electrode tanks. In order to study the effect of the pH, the working solution had its pH decreased to approximately 2.0 using concentrated H2SO4. For these trials, in pH equal to 2.0, the concentration of the KCl and K2SO4 solutions was altered to 0.018 M and 0.019 M, respectively, for the purpose of maintaining the conductivity of the system.
The ED trials were also carried out on ED cell with the configuration described in item 2.1 in duplicate. In the same way as done for the polarization curves, before starting the trials, the membranes were balanced in the working solution for periods of between 18 and 24 hours. During the experiments, samples with volumes of between 15 and 20 mL were collected, in order to study the ionic movement and the extraction percentage. The aliquots were removed from all the solutions every hour for trials lasting 8.5 hours, and each 1.5 hours for trials lasting 10.5 hours. The pH and conductivity were monitored every hour, as were the current applied and the total voltage from the system. The percent extraction was assessed on the basis of trial time, pH value of the trial environment and the type of trial, whether galvanostatic or potentiostatic A summary of the ED trials performed is presented in Table 3.
2.3. Ion-exchange membranes
2.6. Sample characterization
The commercial ion-exchange membranes used in this study, both cationic (HDX 100) and anionic (HDX 200), were provided by Hydrodex®, with an effective area of 16 cm2. Table 2 presents the characteristics of the membranes.
The concentration of Cu2þ and Kþ were ascertained by atomic emission spectrometry by coupled plasma (ICP-OES). This technique is used to determine different metals in aqueous solutions. However, the use of solutions containing organic components can
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Table 3 Parameters used during the electrodialysis experiments. Parameters
POH8
POH10
GOH8
GOH10
GOH10
GH27
Operation time (h) pH Operation control
8.5 10 potentiostatic
10.5 10 potentiostatic
8.5 10 galvanostatic
10.5 10 galvanostatic
12.0 10 galvanostatic
27.0 2 galvanostatic
give rise to difficulties in the sample feed and interference in some spectra. This is due to the physical properties and the carbon content of the organic matrix (McCurdy and Potter, 2002). The digestion of the organic components and the breakdown of complexes are some of the alternatives for the analysis of samples containing these compounds (McCurdy and Potter, 2002; Schmidt et al., 2014). For this reason, each sample collected underwent a process of conversion from the organic forms of phosphorus to orthophosphate prior to the analysis by ICP. The conversion of the organic phosphorus was carried out by means of the persulfate digestion method (American public health association et al., 1998a). The analyses to ascertain the HEDP and orthophosphate were done using the colorimetric method by reduction with ascorbic acid and visible reading region (880 nm). The sulfate analyses were accomplished via the turbidimetric method (American public health association et al., 1998b). The conductivity and pH of the solutions from all of the compartments were monitored every hour, as was the potential difference between electrodes and the current applied. 2.7. Photodegradation of HEDP The possibility of the photodegradation of the HEDP during the application of the electrodialysis was evaluated. It is known that the HEDP can be degraded in acetate and orthophosphate (Steber and Wierich, 1986). Samples of the initial diluted, final diluted and final anion concentrated compartments were analyzed using the Ascorbic Acid Method (American public health association et al., 1998b). The results were expressed in terms of percentage of HEDP in the form of orthophosphate.
in relation to the other samples. This change is due to the acidification of the GHK solution by means of concentrated H2SO4. A variation was noted in the concentration of copper and HEDP in the samples analyzed, caused by the conversion of the organic forms of phosphorus prior to the actual analysis. The process of conversion of the organic forms of phosphorus consists of the following stages (American public health association et al., 1998b): 1. Dilution of the samples, so that the estimated concentration of total phosphorus is consistent with the method's application range; 2. Addition of 0.4 g of ammonium persulfate and of 1 mL of H2SO4 30% v/v to the sample; 3. Heating for a period of at least 30 minutes. This can be done on a heating plate or in an autoclave under a pressure of between 98 and 137 kPa; 4. Neutralization of the pH using NaOH 1 M solution, followed by an adjustment in the volume to 50 mL, whenever necessary. The sensitivity of the ICP-OES and UVeVis spectrophotometry analysis methods, coupled with the possible variations of the factors mentioned can alter the conversion of the organophosphate compounds and the breakdown of the Cu(II)-HEDP complexes. As a result, a number of strategies were employed to reduce the error associated with the stages prior to chemical analysis: the digestion of the phosphorus was carried out in batches, with samples from a single experiment. The stages listed were carried out in periods not exceeding 24 hours. The glassware used was washed with hydrochloric acid (American public health association et al., 1998b). The samples analyzed were diluted in the same proportion. The average concentration values obtained for copper and HEDP were 41.8 mg L1 and 944 mg L1, respectively.
3. Results and discussion 3.2. Determination of currentevoltage curves
3.1. Characterization of working solutions The working solutions were obtained by means of the dilution of the electrolyte developed for an alkaline copper strike bath (Vargas, 2008). Due to the photodegradative properties of HEDP listed by a number of authors (Fischer, 1993; Steber and Wierich, 1986), it was decided to store the electrolyte solution protected from the light and to prepare the working solutions immediately before the start of each trial. A characterization of the working solutions was performed and it is presented in Table 4. According to Table 4, differences can be observed in the pH value (2.2) and the conductivity value (4500 mS cm1) of the GHK sample Table 4 Characterization of the working solutions studied. Parameters
Samples
pH Conductivity (mS.cm1) Cu2þ (mg.L1) HEDP (mg.L1) Cu2þ: HEDP ratio
10.3 1650 32 683 1:21
POH8 POH10 GOH8 GOH10 GOHK GHK Average 10.5 1610 43 890 1:21
10.3 1691 39 926 1:24
10.5 1664 41 1281 1:31
10.6 1535 48 983 1:20
2.2 4500 48 901 1:19
e e 41.8 944 1:23
The trials to obtain the polarization curves in order to determine the limiting current density to be used in the electrodialysis experiments were carried out in triplicate. The overlapping of the current curves versus the potential of the anionic exchange membrane (AEM) and of the cationic exchange membrane (CEM) are presented in Fig. 4. For the anionic membrane (a), it is observed a linear region followed by an alteration in the slope of the curves, indicating the existence of the limiting current region. In the curves constructed for the cationic membrane (b), only the ohmic region seems to have been reached. The maximum current applied in the system should remain between 70 and 80% of the limiting current density (Meng et al., 2005) of the membrane that presented the lowest limiting current. Therefore, the curve of the anionic membrane was chosen as representative (Fig. 5) and the current density to be applied was set at 2.1 mA cm2. 3.3. Electrodialysis Based on the results of the polarization curves, ED experiments were carried out in potentiostatic and galvanostatic mode for 8.5 h
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Fig. 4. Polarization curves in triplicate constructed for the anionic membrane (a) and the cationic membrane (b).
and 10.5 h. In the trials using galvanostatic mode, the current density applied was fixed according to the results of the polarization curves, at 2.1 mA cm2. In the potentiostatic trials, the potential was set at 16.9 V, a value which corresponds to an initial current density of 2.1 mA cm2. The pH and the conductivity of the solutions of all the compartments were monitored every hour. The table shows the variation in the parameters monitored.Table 5. The reactions that occur in the electrodes are responsible for the variation in the pH value and of the conductivity in the anode, cathode, anion concentrate and cation concentrate compartments. The increase in the pH value on the cathode side is due to the release of hydroxyl ions, while the decrease in the pH on the anode side is the result of the formation of Hþ. The reduction in the conductivity of the diluted compartment is attributed to the extraction of ions from the working solution. Over the course of the experiments, the removal of the number of ions available in the diluted compartment caused an increase in the total resistance of the system. This increase can be seen from the reduction in the value of the current applied for the potentiostatic trials, or from the increase in the total potential for the galvanostatic trials. Fig. 6 shows the changes of the potential and of the current in the potentiostatic and galvanostatic trials carried out over the course of 8.5 h (a) and 10.5 h (b). During the first 3 hours of trial, there is a decrease in the total resistance of the system, both in galvanostatic mode as well as in the potentiostatic mode. This behavior is observed in Fig. 6, by means of the increase in the initial current value (in potentiostatic mode) and the decrease in initial value of the potential (in
Fig. 5. Polarization curve of the anionic membrane.
galvanostatic mode). After 3 hours of trial, the resistance of the system started to increase, due to the extraction of ions from the diluted compartment. In potentiostatic mode, the electric current reached 55% and 54% of the value initially applied in 8.5 and 10.5 hours, respectively. In galvanostatic mode, the potential values registered after the same periods were 27.2 V and 23.6 V. 3.3.1. Effect of pH Depending upon the pH value of the bath, as well as of the rinsing method and of the frequency of disposal of diluted wastewater, the rinse waters can drop to pH values of less than 2. In order to evaluate the effect of the change in pH value, the working solutions were submitted to trials in an acid environment (pH z 2). The pH of the working solutions was adjusted by means of addition of 345 mL of concentrated sulphuric acid. After the addition of the acid, the variation in volume of the working solution was less than 0.05%. The study of the pH variation was carried out along with the construction of the speciation diagrams of the working solutions, because of the influence of Cu(II)HEDP complexes on ionic migration. Fig. 7 shows the speciation diagram of the working solution, composed of copper, HEDP and potassium chloride. As it can be seen in Fig. 7, in an alkaline environment, the copper cations are complexed by the HEDP. It is noted that when the pH value is in between 5.2 and 9.4, 100% of the copper ions form complexes with the HEDP, predominantly in the CuHHEDP and CuHEDP2 anionic specimens. In an acidic environment, a trend toward the separation of the complexes is observed, given that at a pH equal to 2, 81.5% of the Cu2þ ions are free. The acidification of the working solution by means of the addition of sulphuric acid modifies the composition of the specimens, due to the formation of copper sulfate with a pH of between 0 and 5.4, as shown in Fig. 8. Nevertheless, the existence of 54.6% of free copper cations with a pH equal to 2 indicates the possibility of separation of the complexes. The concentration of copper and of HEDP in the concentrated cation and concentrated anion compartments after the ED is shown in Table 6. In the case of the experiments that were carried out in an alkaline environment, the transport of the copper and HEDP ions occurred predominantly from the diluted compartment to the anion concentrated compartment. The results suggest the presence of anionic complexes between the copper and the HEDP in the working solution. In the experiment with acidified solution, indicated by the acronym GH27, the copper ions were transported from the diluted compartment to the cation concentrated one. The HEDP
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Table 5 Variation in the pH and in the conductivity during the electrodialysis trials. Parameter
Anode Anode concentrate Diluted Cathode concentrate Cathode
POH8
pH Conductivity pH Conductivity pH Conductivity pH Conductivity pH Conductivity
(mS cm1) (mS cm1) (mS cm1) (mS cm1) (mS cm1)
POH10
GOH8
GOH10
GOH12
GH27
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
Initial
Final
5.2 1532 5.2 1532 10.3 1650 5.2 1532 5.2 1532
2.6 2230 3.3 2570 5.4 227 10.9 3590 10.9 2090
7.2 1574 7.2 1574 10.5 1610 7.2 1574 7.2 1574
2.3 2330 2.8 2660 4.0 193 11.0 4100 11.0 2280
6.2 1536 6.2 1536 10.3 1691 6.2 1536 6.2 1536
2.4 2160 3.1 2410 3.8 265 11.6 3730 11.7 2120
5.7 1560 5.7 1560 10.5 1664 5.7 1560 5.7 1560
3.3 2250 4.0 2450 4.3 277 12.8 3760 13.0 2180
6.2 1631 6.2 1631 10.6 1535 6.2 1631 6.2 1631
2.3 2590 3.3 2420 3.4 192 11.2 3460 11.6 2390
5.3 4310 5.3 4310 2.2 4500 5.3 4310 5.3 4310
1.8 6800 2.3 7300 3.2 198 2.2 7600 12.2 6600
Fig. 6. Variation of the potential and of the current in the system during trial lasting 8.5 h (a) and trial lasting 10.5 h (b).
anions moved toward the anion concentrated compartment, indicating the separation of the complex.
3.4. Percent extraction Fig. 9 presents the results in terms of percent extraction of copper and HEDP in the experiments carried out. The experiment that produced the greatest removal of copper from the diluted compartment was trial GH27, in which a 92% rate was achieved in relation to the removal of the copper ions. The greatest extraction of
Fig. 7. Speciation diagram of the copper complexes formed in the alkaline working solution. The diagram was constructed with the help of the Hydra-Medusa software.
HEDP from the diluted compartment was obtained with the experiment GOH12, with 94.4% of the acid being removed. The analysis of the tests POH8 and GOH8 shows that, in the galvanostatic control (GOH8), the percent extraction of copper was 34% greater when compared to the potentiostatic control (POH8). The percent extraction of HEDP was 4e9% higher in the galvanostatic control. The tests done for 10e5 hours, POH10 and GOH10, showed that the removal of copper in the galvanostatic control experiment (GOH10) was 8e9% greater than in the potentiostatic control (POH10) and the removal of HEDP was 4e3% higher in the
Fig. 8. Speciation diagram of the copper complexes formed in the working solution acidified with sulphuric acid. The diagram was constructed with the help of the HydraMedusa software.
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Table 6 Concentration of copper and of HEDP after the ED experiments, in the anion concentrated and cation concentrated compartments. POH8 POH10 GOH8 GOH10 GOH12 GH27 Cu2þ (mg L1) HEDP (mg L1)
Anode concentrated 21 Cathode concentrated 3 Anode concentrated 583 Cathode concentrated 0
24 0 646 0
19 0 582 0
21 0 695 1
33 4 683 21
8 45 550 10
Fig. 10. Percentage extraction of the HxHEDPy and SO4 2 anions as a result of the trial time.
Table 7 Concentration of sulfate in the diluted and concentrated anion compartments, at the start of the experiment and after 27 h. SO4 2 (mg L1)
Diluted compartment Anode concentrated
Initial
After 27 h
1288 446
1596 2229
Fig. 9. Percentage extraction obtained for copper and for HEDP in the electrodialysis trials.
galvanostatic control tests. It is observed that the higher index of percent extraction was given in the galvanostatic control experiments. Besides that, the extraction of copper was more influenced by the mode of the experiment than the extraction of HEDP. For industrial operations of electrodialysis, other factors than the extraction should be considered, such as economical issues and operational safety. The utilization of the potentiostatic control may avoid the concentration polarization phenomenon, since the current density remains constantly under the limit determined by the currentevoltage curve. Furthermore, the process can be economically beneficial in certain cases in which different stages of treatment are operated in different potential (Strathmann, 2004; Costa et al., 2002). The acidification of the solution by addition of H2SO4 caused a reduction in the speed of HEDP extraction. This behavior is attributed to the existence of SO4 2 anions in the same compartment as the HxHEDPy anions, causing a migratory competition between the ionic specimens. The extraction percentage of HEDP and SO4 2 as a result of the duration of trials is presented in Fig. 10. It can be observed that the extraction of the two anions occurs simultaneously, with the extraction of HEDP being greater than that of sulfate. An analysis of sulfate in the initial and final samples of the anion concentrated compartment was carried out. The results indicate that the movement of the anions takes place in the same direction, as shown in Table 7. After a trial of 27 hours, the sulfate concentration in the concentrated anion compartment increased 40%, which can be attributed to the presence of an anionic membrane between the diluted and concentrated anion compartments.
3.5. Chemical characterization of solutions after ED The concentrated and diluted solutions produced by the application of the ED had their characteristics determined. The pH value and conductivity of all the solutions were measured and analyses
were carried out to determine the concentration of copper, potassium, HEDP and sulfate. The results are presented in Table 8. The results presented in Table 8 indicate that the diluted solutions obtained can be reutilized by integrating them into the electroplating rinse tanks. At the same time, the recovery of the copper and HEDP ions in the concentrated compartment indicates the possibility of reusing these components in the electrolyte, offsetting possible losses caused by drag-out. 3.6. Current efficiency and energy consumption In the evaluation of the strike bath containing copper and HEDP, it is considered that the applied electric current will be used to transport the following ions: Cuhedp2, CuHhedp, Cu2þ (acid environment), Kþ, Cl e SO4 2 (acid environment). The reactions that involve HEDP and Cu2þ in the working solutions are: Cu2þ þ hedp4 4 Cuhedp2Hþ þ Cu2þ þ hedp4 4 CuHhedpHþ þ hedp4 4 Hhedp32Hþ þ hedp4 4 H2hedp2Electroplating baths containing complexant agents are used to decrease the activity of the metal cations in the bath. Therefore, it is assumed that all cupreous ions will be complexed by the HEDP and
Table 8 Chemical characteristics of the concentrated and diluted solutions. Concentration after ED tests (mg.L1) pH Cu2þ
Kþ
HxHEDPy- SO4 2
Conductivity (mS.cm1)
Concentrated 19e45 50e193 550e695 634e2564 2.2e4.0 2410e7600 solutions Diluted solutions 4e18 9e29 55e357 10e446 3.2e5.4 193e277
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that each mol of Cu2þ reacts with one mol of hedp4 to form one mol of complex. Since the molar concentration of the HEDP in the bath is higher than the molar concentration of the copper, it is possible to deduce that there are free HEDP ions in the solution, which can present valence of 2 or 3, depending on the pH of the solution. It is expected that the current efficiency of Cuhedp2 and CuHhedp complexes would be lower than the current efficiency of free HEDP ions e hedp2 and Hhedp3 e because in the strike bath, the molar concentration of copper is about 7 times smaller than the molar concentration of HEDP. Likewise, the specific consumption of energy to transport the complexes shall be higher. According to McGovern et al., 2014, the effective cost of an ED system should consider the ratio between the ionic concentrations of the diluted and concentrated compartments, so as the conductivity of the solutions involved in the process. In this sense, the limiting current density is a fundamental factor in the operation and may influence the system characteristics (e.g. the size and the number of cell pairs) and the energy consumption. In stages of the process in which the conductivity is low, the ohmic drop of the solutions starts to play an important role in the energy consumption of the system, because the electrical resistance of the solution can outgrow the electrical resistance of the membrane (McGovern et al., 2014). In this situation, one can evaluate the possibility of using a hybrid system that allows the reduction of the energy consumption (Mahmoud and Hoadley, 2012).
direction of the anion concentrated compartment. In an acidic environment, it is possible to bring about the separation of the Cu(II)-HEDP complexes and the recovery of copper and HEDP in separate compartments. However, HEDP extraction was slower in an acidic environment due to the simultaneous transport between the HxHEDPy and SO4 2 anions. In industrial processes, the pH value of the rinse waters depends on the pH value of the bath applied, on the type of rinse and on the frequency of disposal of the wastewater. The experiments carried out indicated that in an environment with a pH of more than 5.4, it is preferable to recover the complexes in the same compartment, avoiding the addition of reagents in order to adjust the pH value of the system. The presence of inorganic phosphorus in the samples of the trial in an acidic environment also suggests the viability of the process in neutral or alkaline solutions.
3.7. Photodegradation of HEDP
American public health association, American water works association, Water environmnet federation, 1998a. Standard Methods for the Examination of Water and Wastewater, 20. ed. In: Ascorbic Acid Method, pp. 4e146 American public health association, American water works association, Water environmnet federation, 1998b. Standard Methods for the Examination of Water and Wastewater, 20. ed. In: SO24 Turbidimetric Method, pp. 4e178 Aouad, F., Lindheimer, A., Gavach, C., 1997. Transport properties of electrodialysis membranes in the presence of Zn2þ complexes with Cl. J. Membr. Sci. 123, 207e223. Aouad, F., Lindheimer, A., Chaouky, M., Gavach, C., 1999. Loss of permselectivity of anion exchange membranes in contact with zinc chloride complexes. Desalination. 121, 13e22. Benvenuti, T., Siqueira, M.A.S., Bernardes, A.M.B., Ferreira, J.Z., 2014. Electrodialysis Treatment of Nickel Wastewater. In: Topics in Mining, Metallurgy and Materials Engineering, pp. 133e144. Buzzi, D.C., Viegas, L.S., Rodrigues, M.A.S., Bernardes, A.M., Tenorio, J.A.S., 2013. Water recovery from acid mine drainage by electrodialysis. Min. Eng. 40, 82e89. Chaudhary, A.J., Donaldson, J.D., Grimes, S.M., Yasri, N.G., 2000. Separation of nickel from cobalt using electrodialysis in the presence of EDTA. J. Appl. Electrochem. 30, 439e445. Cherif, T., Elmidaoui, A., Gavach, C., 1993. Separation of Agþ, Zn2þ and Cu2þ ions by electrodialysis with a monovalent cation specific membrane and EDTA. J. Membr. Sci. 76 (1), 39e49. Chiapello, J.M., Gal, J.Y., 1992. Recovery by electrodialysis of cyanide electroplating rinse waters. J. Membr. Sci. 68 (3), 283e291. Cifuentes, L., García, I., Arriagada, P., Casas, J.M., 2009. The use of electrodialysis for metal separation and water recovery from CuSO4-H2SO4-Fe solutions. Sep. Purif. Technol. 68 (1), 105e108. Costa, R.F.D., Klein, C.W., Bernardes, A.M., Ferreira, J.Z., 2002. Evaluation of the electrodialysis process for the treatment of metal finishing wastewater. J. Braz. Chem. Soc. 13, 540e547. Dash, R.R., Gaur, A., Balomajumder, C., 2009. Cyanide in industrial wastewaters and its removal: a review on biotreatment. J. Hazard. Mater. 163 (1), 1e11. Evans, T., Lorenz, A., Peukert, L., 2009. Drag-out reduction techniques using barrel blow-down and DSC dip-spin-tilt technology. Met. Finish. 107 (12), 35e37. Fischer, K., 1993. Distribution and elimination of HEDP in aquatic systems. Water Res. 27 (3), 485e493. Huang, T.C., Lin, Y.K., Chen, C.Y., 1988. Selective separation of nickel and copper from a complexing solution by a cation-exchange membrane. J. Membr. Sci. 37, 131e144. Jaworska, J., Genderen-Takken, H.V., Hanstveit, A., Plasshe, E., Feijtel, T., 2002. Environmental risk assessment of phosphonates, used in domestic laundry and cleaning agents in the Netherlands. Chemosphere 47 (6), 655e665. Knepper, T.P., 2003. Synthetic chelating agents and compounds exhibiting complexing properties in the aquatic environment. Trends Anal. Chem. 22 (10), 1e17. Mahmoud, A., Hoadley, A.F., 2012. An evaluation of a hybrid ion exchange electrodialysis process in the recovery of heavy metals from simulated dilute industrial wastewater. Water Res. 46 (10), 3364e3376.
Samples from the initial diluted, final diluted and final anion concentrated compartments of three trials, GOH10, GOH12 and GH27 were analyzed. Analysis was carried out based on the orthophosphate fraction present in the samples before digestion of the organic phosphorus. The presence of inorganic phosphorus in the samples without prior conversion of the organic forms indicates the occurrence of photo-oxidation of the HEDP. As a result, the presence of inorganic phosphorus was not observed in the samples from the trials in an alkaline environment. For the trial in an acidic environment, GH27, there was a 0.6% degradation of the HEDP in the sample from the initial diluted compartment and a 7% degradation in the sample from the final anion concentrated compartment. 4. Conclusions It was evaluated the application of electrodialysis for the treatment of an effluent simulating rinse waters from HEDP based strike baths, aiming to recover the copper, the HEDP and the water. The chemical analyses performed on the solutions produced after the application of ED indicated a concentration of copper of between 4 and 18 mg L1 in the diluted solutions and one of between 19 and 45 mg L1 in the concentrated solutions. The concentration of HEDP in the diluted solutions varied from 55 to 373 mg L1 and, in the concentrated solutions, between 550 and 695 mg L1. The greatest extraction percentage obtained was one of 99.7% for copper and 94.4% for HEDP. The experiments performed under galvanostatic control presented a higher percentage extraction of ions from the working solution when compared to the potentiostatic tests. The results suggest the possibility of reutilization of the concentrated solutions in replacing the ions of the electrolyte lost by drag-out. At the same time, the characteristics of the diluted solution allow it to be incorporated into the rinse tanks. It was observed that in an alkaline environment the copper cations form anionic complexes, migrating predominantly in the
Acknowledgments The authors would like to thank the Laboratory of Corrosion, Protection and Recycling of Materials of the Federal University of Rio Grande do Sul for the technical assistance and the CAPES and the FAPESP 12/51871-9 for their financial support.
References
250
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Marder, L., Sulzbach, G.O., Bernardes, A.M.B., Ferreira, J.Z., 2003. Removal of cadmium and cyanide from aqueous solutions through electrodialysis. J. Braz. Chem. Soc. 14 (4), 610e615. n, M., Ortega, E., Bernardes, A.M., Martí-Calatayud, M.C., Buzzi, D.C., García-Gabaldo rio, J.A.S., Pe rez-Herranz, V., 2014. Sulfuric acid recovery from acid mine Teno drainage by means of electrodialysis. Desalination. 343, 120e127. McCurdy, E., Potter, D., 2002. Techniques for the Analysis of Organic Chemicals by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). McGovern, R.K., Zubair, S.M., Lienhard V, J.H., 2014. The cost effectiveness of electrodialysis for diverse salinity applications. Desalination 348, 57e65. Mclay, W.J., Reinhard, F. P, 2002. Waste minimization and recovery technologies. Met. Finish. 100 (1), 798e829. Meng, H., Deng, D., Chen, S., Zhang, G., 2005. A new method to determine the optimal operating current (Ilim') in the electrodialysis process. Desalination. 181, 101e108. Nataraj, S.K., Hosamani, K.M., Aminabhavi, T.M., 2007. Potential application of an electrodialysis pilot plant containing ion-exchange membranes in chromium removal. Desalination 217 (1e3), 181e190. Nowack, B., 2003. Environmental chemistry of phosphonates. Water Res. 37 (11), 2533e2546. ~o e proteç~ ~o em equipamentos e Panossian, Z., 1993 Corrosa ao contra corrosa licas, First ed., vol. 2. IPT, Sa ~o Paulo. estruturas meta Peng, C., Liu, Y., Bi, J., Xu, H., Ahmed, A.S., 2011. Recovery of copper and water from copper-electroplating wastewater by the combination process of electrolysis and electrodialysis. J. Hazard. Mater. 189 (3), 814e820.
Piccinini, N., Ruggiero, G.N., Baldi, G., Robotto, A., 2000. Risk of hydrocyanic acid release in the electroplating industry. J. Hazard. Mater. 71 (1e3), 395e407. Rodrigues, M.A.S., Amado, F.D.R., Xavier, J.L.N., Streit, K.F., Bernardes, A.M., Ferreira, J.Z., 2007. Application of photoelectrochemical-electrodialysis treatment for the recovery and reuse of water from tannery effluents. J. Clean. Prod. 16, 605e611. Roy, C.H., 1996. Wastewater control and treatment. In: Durney, L.J. (Ed.), Electroplating Engineering Handbook, Four ed. Chapman & Hall, Londres. Schmidt, C.K., Raue, B., Brauch, H.J., Sacher, F., 2014. Trace-level analysis of phosphonates in environmental waters by ion chromatography and inductively coupled plasma mass spectrometry. Intern. J. Environ. Anal. Chem. 94 (4), 385e398. Steber, J., Wierich, P., 1986. Properties of hydroxyethane diphosphonate affecting its environmental fate: degradability, sludge adsorption, mobility in soils, and bioconcentration. Chemosphere 15 (7), 929e945. Strathmann, H., 1995. Membrane Separation Technology. Elsevier, Amsterdan. Strathmann, H., 2004. Ion-exchange Membrane Separation Processes. Elsevier, Amsterdan. Vargas, C., 2008. Estudo da eletrodeposiç~ ao do cobre a partir de banhos alcalinos cnisentos de cianetos. Dissertaç~ ao. (Mestrado em Engenharia) e Escola Polite ~o Paulo, p. 221. ica, Universidade de S~ ao Paulo, Sa Zuoa, W., Zhanga, G., Mengb, Q., Zhangb, H., 2008. Characteristics and application of multiple membrane process in plating wastewater reutilization. Desalination. 222 (1e3), 187e196.