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Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys
Journal of Cleaner Production xxx (2016) 1e7
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Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys sio Flore ^ncio de Almeida Neto* Mariana Borges Porto, Lucas Barbosa Alvim, Ambro University of Campinas, School of Chemical Engineering, Department of Products and Processes Design, Albert Einstein Avenue, 500, Campinas, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 September 2015 Received in revised form 23 October 2016 Accepted 24 October 2016 Available online xxx
In this work, nickel was removed from industrial effluent by an electrodeposition process and the alloy obtained with this metal was characterized. The removal tests occurred in optimized conditions, under those occurred the formation of Ni-W alloy from synthetic baths prepared in laboratory. Thus, an experimental planning was performed in order to investigate the variation of nickel concentration in the bath, temperature and density of the current applied. The variable of response considered was the faradic efficiency. The metallic alloy obtained through the nickel removal of an electroplating wastewater was characterized by X-ray Diffraction, Infrared Spectroscopy and Scanning Electron Microscope with chemical analysis by Dispersive Energy of X-rays. The faradic efficiency was strongly influenced by the nickel concentration, achieving a value of 51.4%. In the test of nickel removal from a real wastewater, the faradic efficiency registered was approximately 90% and the nickel removal was 38.76%. The coating obtained from the real wastewater was characterized by a high level of crystallinity and pureness. The Scanning Electron Microscope images showed that the metallic alloy of Ni-W was cracked, which may be related to its crystallinity. Ni and W contents in the alloy were approximately of 73 and 27%, respectively. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Nickel removal Electrodeposition Tungsten alloys
1. Introduction Electroplating is a process presented in innumerous industries that generate wastewater contaminated with metals. In industrial facilities that require metal surface coatings, electroplating of metals and alloys is used as a good way to protect and inhibit corrosion of materials (Wu et al., 2003). One of the co-deposition activities that has grown in recent years is called branch-plated jewelry (imitation jewelry). This activity greatly increases discharges of highly concentrated toxic metal wastewater into Brazil's water bodies, representing revenues of U$ 1572.3 million per year. The Southeast region of Brazil is responsible for the production of 37% of the veneers sector. The companies that generate and release wastewater containing metals are mostly small ones. The steps of the surface treatment processes involved in electroplating imitation jewelry are metal deposition, alkaline copper, acid, nickel bath and pre-gold, gold and color. The metal deposition is the initial deposition of a thin copper layer on the piece. The alkaline copper is obtained from copper cyanide, which avoids acidity in the product.
* Corresponding author. E-mail address: [email protected] (A.F. de Almeida Neto).
The acid copper is the deposition of a copper layer with increased thickness, which fills the piece holes. The nickel bath is prepared with nickel sulfate and evens the imperfections of the piece. Finally, the baths and the final gold color are performed, and the color baths are made of nickel salts, copper, silver or cobalt. Imitation jewelry industries also use large amounts of fresh water in the production process for washing the blanks before the electroplating process. As a result, the water used for this purpose is also contaminated with residues, such as iron and organic matter. Thus, copper, nickel, iron and cobalt are the non-precious metals discharged by imitation jewelry industries. These metals have produced a concentration of sewage-diluted ions, which is above the legal discharge limits, leading to the need of using a tertiary polishing process. Tungsten, that makes very hard alloys, is used in the manufacture of steel for cutting tools, operational machinery and coatings in general. The electrodeposition of tungsten in its pure form, starting from aqueous or organic solutions, has not achieved success (Devis and Gentry, 1956). However, there is no experimental difficulty in electrodeposition of tungsten with iron group metals. It has been deposited in either acid baths or alkali. According to Brenner (1963), in cases in which a metal cannot be electrodeposited from aqueous monolithic, but is alloyed in the presence of a metal, it has
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Please cite this article in press as: Porto, M.B., et al., Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.10.140
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an “induced co-deposition”. Tungsten is co-deposited in alloys with iron and non-ferrous metals. The baths contain tungsten in the form of salts along with the iron group metal and a complexing agent. It was observed that the variation in the bath pH has a significant effect on the amount of tungsten in the electroplated alloy. Some researchers have tried to explain this effect by correlating it to the formation of different complexes by iron group metals (Wu et al., 2003), but little effort has been made to study the polymer species of tungstate anions. We do not have yet a technique that enables the control of all parameters that interfere in the electroplating metal layers, whose characteristics are defined only by optimization of operating and bath parameters. The processes employed in producing electrodeposited amorphous metal alloys are still characterized by empiricism. Several investigators have studied the effects of the electric current density, temperature and concentration of tungsten on the tungsten alloys passive behavior. In a study of Ni-W alloy, Ahmadi and Guinel (2013) showed that the increase of concentration tungstate also increases resistance to charge transfer in 1.2 times. These authors reported that when using an appropriate concentration of tungsten, all types of nickel were removed from aqueous solutions. Lima-Neto et al. (2010) obtained uniform deposits, presenting a surface morphology that has evolved from fine globular grains to rough polycrystalline with decreasing electrodeposition current density. The authors stated that all studied coatings corroded in a chloride medium, and this phenomenon was not uniform for the Ni-W alloy. According to Alimadadi et al. (2009), the formation of two phases in the Ni-W alloy structure drastically reduces anticorrosive properties. From the first dual phase, Alimadadi et al. (2009) reported the occurrence of a reduction in grain size and density of cracks in all Ni-W amorphous alloy with increasing the corrosion resistance. However, if tungsten is present in higher quantity than nickel, more cracks and defects will occur, which increases the corrosion rate. Conversely, the phase of nanocrystalline Ni-W alloy carrying higher quantity of tungsten, having the best anticorrosion properties. With changing parameters such as mechanical stirring, electric current density, temperature, concentration of reactants, pH and the presence of other transition metals, the characteristics of the electroplated layer (adhesion to the substrate, hardness, uniformity, corrosion resistance and embrittlement) can be modified and improved, which is very important for industrial applications. It is very important to highlight that from an environmental perspective, wastewater generated from the baths of the electroplating process jewelry will be used as basis for tungsten alloy electroplating, which stands out the recyclable nature of the process, as well as the reduction of waste generated. Moreover, the process also has the advantage in obtaining electroplated alloy with good appearance and high quality by removing metals from the water that once released into the environment represents a serious problem due to its toxicity and non-degradability. In this study, we evaluated the nickel removal from electroplating wastewater through electrochemical co-deposition with tungsten to form corrosion-resistant alloys, featuring deposition results with other studies involving the electrodeposition of Ni-W alloy and others nickel removal processes. Thus, the importance of this work is linked to the relevance of the topic and the development of an alternative alloy, obtained from effluents, whose results contribute to technical and economic information appropriate to the improvement of production systems. The study reports the use of sustainable natural resources, minimizing loss of socio-economic aspects and environmental impact, as a function of the electrochemical efficiency of the method applied, the surface coating recovering the metals in the elemental state, minimizes the quantities waste to be treated, and can add value to waste which
become raw materials for another product, in this case the Ni-W alloy. 2. Materials and methods 2.1. Electrolytic baths The electrodepositions of this work were performed using two different electrolytic baths. The first one is a synthetic electrolytic bath prepared in our laboratory. The other electrolytic bath is a real effluent sample generated in electroplating jewelry during the nickel bath step. Sodium tungstate, Na2WO4, 0.3 mol L1 was added to this effluent. The nickel concentration of the effluent was determined by atomic absorption spectrophotometry. Synthetic electrolytic baths were prepared with sodium tungstate, Na2WO4, 0.3 mol L1, nickel sulfate, NiSO4, and ammonium citrate, (NH4)2C6H6O7, 0.3 mol L1, which was used in the bath as a Ni complexing agent. The concentration of NiSO4 ranged from 0.1 to 0.3 mol L1. Other reagents were used for specific purposes, for example: Na2B4O7 3.75 102 mol L1 as the boron source to obtain an amorphous alloy; sodium 1-dodecylsulfate 1.04 104 mol L1, so that the H2 released during electrodeposition is detached with higher speed avoiding the formation of bubbles in the bonded alloy; and (NH4)2SO4 1.287 101 mol L1, responsible for providing greater bath stability. Nickel and tungsten speciation diagrams were simulated using Hydra and Medusa software (Puigdomenech, 2004) to identify the different species in bath. These diagrams were plotted for electrodeposition at concentrations that correspond to concentrations of chemical species in ionic solution. Speciation was investigated considering the used stoichiometric ratio of nickel and tungsten salts. 2.2. Electrodeposition The substrate used was a copper plate in 2 cm square. This was initially polished with 220 and 320 mesh sandpaper and then immersed in 10% NaOH solutions, to perform degreasing and 1% H2SO4 for surface activation. The electrodeposition experiments were performed using a rotating electrode, a potentiostat/amperostat, that controlled the electrical potential difference between the working electrode and the counter electrode, a thermostatic bath for temperature control and a pH meter. The electric current density ranged from 10 to 50 mA cm2 and the temperature between 25 and 60 C. The electrodepositions were performed using cathode rotation in a speed of 30 rpm. The potentiostat was used in electroplating way and the bath pH was approximately 6. The counter electrode used was a hollow cylindrical platinum mesh. The faradic efficiency (ε) was calculated from the mass obtained by the load used and the chemical composition of the coating obtained by EDX according to Eq. (1):
ε¼
m$F X ni $wi I$t Mi
(1)
where m is the measured mass of coating (g), t is the deposition time (s), I is the total current passed (A), wi is the weight fraction of the element in the coating obtained by EDX, ni is the number of electrons transferred per atom of each metal, Mi is the atomic mass of that element (g mol1), and F is the Faraday's constant (96,485 C mol1). The experimental design methodology was used to evaluate the electrodeposition process in which the electrolytic bath was the one prepared at the laboratory. The influence of the initial
Please cite this article in press as: Porto, M.B., et al., Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.10.140
M.B. Porto et al. / Journal of Cleaner Production xxx (2016) 1e7
concentration of nickel in the bath (CNi), the electric current density (I) and the bath temperature (T) on faradic efficiency (ε) were analyzed. The method involved 23 ¼ 8 experiments with 3 experimental replicates in the central point, a total of 11 trials. Table 1 shows the input variables used in experimental design, their coding and actual levels of each variable electrodeposition system for the Ni-W alloy on the copper substrate. The experimental data regression analyzes were performed to estimate the faradic efficiency from the input variables. 2.3. Characterization X-ray Diffraction (XRD), Infrared Spectroscopy Fourier Transform (FTIR), and scanning electron microscopy with Chemical Analysis by Energy Dispersive X-ray (EDX) characterized the substrate samples containing Ni-W alloys. The XRD was obtained with a Philips device, model X'PERT with copper Ka radiation, voltage 40 kV, current 40 mA, wavelength 1.52 Å, 0.02 2q step size and a time per step of 1 s. The FTIR spectrum was determined in Infrared Spectrometer from the brand Thermo Scientific; model 6700 Nicolet (Madison/USA). FTIR analyses were performed in the reflectance mode with range of 4000e650 cm1 and 4 cm1 resolution. The micrographs of the copper substrates containing metal alloys of tungsten were obtained in the scanning electronic microscope (SEM) from LEO brand, LEO 440i model with Energy Dispersive X-ray detector (EDX).
3
Table 1 Actual and coded values of variables in the 23 experimental design. Variables
Level (1)
Level (0)
Level (þ1)
CNi (mol L1) I (mA cm2) T ( C)
0.1 10 25
0.2 30 42.5
0.3 50 60
Table 2 Matrix of 23 factorial experimental design plus faradic efficiency. Exp.
CNi (mol L1)
I (mA cm2)
T ( C)
mNi (g)
mW (g)
ε (%)
1 2 3 4 5 6 7 8 9 10 11
0.1 0.3 0.1 0.3 0.1 0.3 0.1 0.3 0.2 0.2 0.2
10 10 50 50 10 10 50 50 30 30 30
25 (1) 25 (1) 25 (1) 25 (1) 60 (þ1) 60 (þ1) 60 (þ1) 60 (þ1) 42.5 (0) 42.5 (0) 42.5 (0)
0.012 0.016 0.071 0.105 0.006 0.030 0.047 0.166 0.065 0.056 0.053
0.008 0.006 0.044 0.039 0.004 0.011 0.029 0.061 0.031 0.026 0.025
22.24 24.49 25.84 32.55 10.56 46.16 17.14 51.40 35.85 30.71 29.06
(1) (þ1) (1) (þ1) (1) (þ1) (1) (þ1) (0) (0) (0)
(1) (1) (þ1) (þ1) (1) (1) (þ1) (þ1) (0) (0) (0)
3. Results and discussion 3.1. Electrodeposition using synthetic bath The results from faradic efficiency (ε) obtained for the 23 experimental design matrix used in the study of synthesized electrolytic bath prepared in the laboratory are shown in Table 2. These results were analyzed by no-linear regression. The faradic efficiency (ε) can be estimated by Eq. (2) with 95% confidence level, and regression coefficient (R2) obtained was 0.9646, which means that 96.46% of the variation around average may be estimated by Eq. (2).
ε ¼ 98:5$CNi þ 1:79$CNi $T 3:04
(2)
CNi is nickel concentration in mol L1, and T is bath temperature in C. The analysis of variance (ANOVA) for Eq. (2) allowed us to obtain a line that describes the relationship between the predicted and obtained yield for the set of experiments in the 23 experimental design, as shown in Fig. 1. The experimental points of Fig. 1 performed satisfactory linearity according to the straight line expected by the linear adjustment that in turn, is fundamental to verify if the given model was appropriate to interpret the data set. Admitting that the errors follow a regular distribution, the model of Eq. (2) proves to be adequate. The statistic evaluation of the model was determined by
Fig. 1. Representative graph of the relation between the obtained and the predict incomes.
the Fisher test for the variance analysis, presented on Table 3. The results of ANOVA listed in Table 3 indicate that both the nickel concentration (CNi) and its interaction with the temperature (T) are statistically significant, with a confidence level of 95%. Fig. 2 shows the response surface for the faradic efficiency as a result of the interaction between the nickel concentration and bath temperature. As the nickel concentration and the bath temperature increases, so does the faradic efficiency of the process. That makes a clear evidence that the nickel complexes formed during the bath are decisive factors for an efficient deposition process. The specie
Table 3 Results of ANOVA for deposition efficiency. Source
Sum of squares
Degree of freedom
F
P
Concentration of Nickel Sulfate (1) Current Density (2) Temperature (3) Interaction between 1 and 2 Interaction between 1 and 3 Interaction between 2 and 3
19.70 5.87 5.03 0.78 15.22 0.04
1 1 1 1 1 1
7.88 2.34 0.31 2.02 6.09 0.01
0.001 0.079 0.114 0.770 0.004 0.988
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electrolysis. Thus, there is an increase of complex mobility, transport number, conductance and, consequently, faradic efficiency. 3.2. Effects of synthetic electrolytic bath composition
Fig. 2. Response surface for the faradic efficiency.
Ni(cit)- is much more interesting for the electrodeposition, because, according to the metallic speciation diagrams, that was the kind of nickel with higher nickel sulfate concentration. The increase of temperature causes ions loss that hydrates the metallic complex and, therefore, reduces the mass transported during the
The citrate ion is a complex agent that forms different kinds of nickel complexes according to pH of the bath. Thus, the citrate and the pH are essential for obtaining the Ni-W alloy. The bath with the optimum pH and the addition of citrate in appropriate concentration improves the deposition efficiency, the metallic ions solubility, the adherent deposits, homogeneous and the larger amount of Ni removed from an industrial wastewater. Speciation diagrams (Fig. 3) show the distribution of metallic species of Ni, depending on the pH and the aqueous solution. According to these diagrams, it can be noticed that the chemical species Ni2þ form complexes with the citrate anions on the pH range that goes from 4, and 5 to 7. With the higher concentration of nickel used, the complex formed is almost exclusively the form of Ni(cit)-. The nickel complex formation is important, because it is the precursor for Ni-W alloy deposition. According to the experimental planning, the increase of the nickel concentration in bath promotes the faradic efficiency. That is a marked indication that the nickel complexes
Fig. 3. Nickel species at concentrations of (A) 0.1 mol L1, (B) 0.2 mol L1 and (C) 0.3 mol L1.
Please cite this article in press as: Porto, M.B., et al., Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.10.140
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Fig. 4. Tungsten species in the electrolytic bath with nickel (A) 0.1 mol L1 and (B) 0.3 mol L1.
1.50 1.35 1.20
Ni in bath
Ni mass (g)
1.05 0.90 0.75 0.60 0.45
Ni in alloy
0.30 0.15 0.00 0
50
100
150
200
250
300
t (min) Fig. 5. Ni removal from a real wastewater.
3.3. Ni removal of a real wastewater According to the experimental planning, the electrodeposition of Ni-W was more efficient in current density conditions of 50 mA cm2, temperature 60 C and nickel sulfate concentration of 0.3 mol L1. Therefore, the nickel removal of an electroplating wastewater, by electrodeposition, was accomplished in these conditions. By the atomic absorption analysis, the total of nickel concentration in the wastewater was 0.256 mol L1. The sodium tungstate was added to the bath at a concentration of 0.05 mol L1, maximum solubility permitted for the bath supplied by the industry. The pH measured in the nickel wastewater containing the
Fig. 6. Ni-W metallic alloys diffractogram.
104 102
Absorbance (u. a.)
formed in bath are decisive factors for an efficient process, in which case, Ni(cit)- is more interesting for the electrodeposition. The chemical species of tungsten, which arise in the pH range of the nickel complexes (pH ¼ 4, 5e7), are predominantly paratungstate A (Prasad et al., 2007), as shown in Fig. 4. In this isopolyanion the tungsten has oxidation number of þ5/2. Thus, the pH used in the electrolyte bath was 6, and this value is shown naturally by the electrolytic bath after its preparation with all the constituents of the bath.
100 98 96 94 92 90 4000
3500
3000
2500
2000
1500
1000
500
-1
Wave number (cm ) Fig. 7. Spectra for FTIR of Ni-W alloy.
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Fig. 8. Ni-W alloy micrographs with nickel and tungsten mapping.
sodium tungstate was 6, this being exactly the same to the pH of the synthetic bath prepared in the laboratory. Fig. 5 describes the exponential decay of the nickel amount in the electrolytic wastewater and the nickel increase in the alloy. The nickel removal took 300 min and the copper substrate was weighed every 20 min until the deposited mass of metallic alloy was constant. The faradic efficiency for this test was 89.95% and the metallic alloy obtained was shiny and adherent. The highest Faradic efficiency obtained in laboratory test was 51.4% and in the nickel removal test of a real wastewater showed an even greater efficiency. This was possibly due to low tungsten amount used in the bath containing the effluent. The ratio between the nickel mass in the alloy, during 300 min of the test, and the initial nickel mass of the wastewater, provided the nickel removal percentage of 36.78%. On others, nickel removal percentage are presented by adsorption processes (Almeida Neto et al., 2014), but in these processes nickel is only removed in low concentrations. 3.4. Crystallinity of Ni-W coating Fig. 6 shows the XRD of Ni-W metallic alloy supplied by the database of XRD equipment from the brand Philips Analytica X-Ray, model X'Pert-MPD, and the X-rays diffraction obtained for the NiW sample, which was deposited from the real wastewater. All Ni-
W alloy obtained from the electrolytic bath prepared in the laboratory showed similar diffraction patterns for the sample of Fig. 6. In the graph, it can be seen the peaks that characterize Ni-W metallic alloy in the range of 42 and 50 2q (degrees) at both presentations, confirming that the copper substrate was coated by NiW alloy and that is crystalline. Thus, in accordance with the nickel atomic rays, 124 p.m., and tungsten, 135 p.m., it is emphasized that the alloy obtained is the homogeneous and substitutional type, in which the tungsten is capable of replacing nickel in the crystalline lattice. 3.5. Ni-W alloy purity Carbon chemical species, such as citrates, cyanides and carbonates can be produced in secondary reactions during the electrodeposition process. The presence of these impurities in the alloy can damage the material, turning it to corrosion susceptible, which causes instability and compromise the coating quality. Fig. 7 shows the results of FTIR of the Ni-W alloy, obtained by the co-deposition of tungsten using real nickel effluent, indicating the absence of peaks or bands, typical of vibrations, stretches or angular deformations of chemical bonds from other species that could have been deposited as impurities in the alloy. Therefore, it emphasizes the coating purity that has not even vibrations,
Fig. 9. Micrographs of Ni-W alloy for Exps. 1 and 8 of Table 2.
Please cite this article in press as: Porto, M.B., et al., Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.10.140
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stretches or angular deformations of O-H alloys. This purity was also found for the Ni-W sample synthesized from the electrolyte bath prepared in the laboratory. 3.6. Coating morphology and Ni-W distribution in the alloy In Fig. 8, there are images obtained in SEM, with the increase of 1500 times and Ni distribution (green dots) and W (red dots) in the alloy obtained from bath containing effluent. This Ni-W coating showed cracks, which are associated with high crystallinity of the obtained alloy. For this sample, the content of Ni and W in the alloy was 73 and 27%, respectively. Fig. 9 shows the micrographs of Ni-W alloys of the Exp. 1 of Table 2 (image left) obtained with lower current density (10 mA cm2). A smaller amount of microcracks was detected. From the Exp. 8 of Table 2 (image right), which was conducted with a higher current density (50 mA cm2), a large amount of microcracks is observed. Both images are magnifications of 1500 times. Ghaferi et al. (2015) also concluded that the lower the density of the electric current more uniform the surfaces are. 4. Conclusions The results obtained in the present work showed that the nickel electrodeposition, as a metal inductor of tungsten deposition, has a significant potential in nickel removal from wastewater generated by the electroplating industry. It was verified that in the studied conditions, the metallic alloys of Ni-W presented adherence, shine and faradic efficiency, as in tests performed with the synthetic baths and as in a sample of real wastewater. The capacity of nickel removal was 36.78% in conditions of maximum faradic efficiency obtained for the electrodeposition of Ni-W, using synthetic baths. The maximum faradic efficiency was 89.9% to the electrodeposition of Ni-W using real wastewater, and 51.40% to the formation of Ni-W using the synthetic bath, in the temperature of 60 C and the electric current density of 50 mA cm2. According to the diagrams of speciation, the electrolytic baths could be used with pH achieved by these solutions after the salts dissolution, once this pH is about 6. The nickel formed crystalline metallic alloy with tungsten, like
7
proven by the XRD analyses, besides the purity indicated by FTIR. The micrographs showed uniformity of the coating and a regular distribution of kinds of nickel and tungsten on the deposit. Therefore, the nickel removal by co-deposition with the tungsten is an alternative to the reuse methods and a better use of wastewater, being economically beneficial and collaborating with the environment.
Acknowledgements The authors acknowledge the financial support received from ~o Paulo Research Foundation, FAPESP, for this study. State of Sa
References Ahmadi, M., Guinel, M.J.-F., 2013. Synthesis, characterization and understanding of the mechanisms of electroplating of nanocrystallineeamorphous nickeletungsten alloys using in situ electrochemical impedance spectroscopy. J. Alloys Compd. 574, 196e205. Alimadadi, H., Ahmadi, M., Aliofkhazraei, M., Younesi, S.R., 2009. Corrosion properties of electrodeposited nanocrystalline and amorphous patterned Ni-W alloy. Mater. Des. 30, 1356e1361. Almeida Neto, A.F., Vieira, M.G.A., Silva, M.G.C., 2014. Insight of the removal of nickel and copper ions in fixed bed through acid activation and treatment with sodium of clay. Braz. J. Chem. Eng. 31, 1047e1056. Brenner, A., 1963. Electrodeposition of Alloys, vol. 2. Academic Press, New York, USA. Devis, G.L., Gentry, C.H.R., 1956. The electrodeposition of tungsten. Metallurgia 53, 3e17. Ghaferi, Z., Sharafi, S., Bahrololoom, M.E., 2015. Effect of current density and bath composition on crystalline structure and magnetic properties of electrodeposited FeCoW alloy. Appl. Surf. Sci. 355, 766e773. Lima-Neto, P., Correia, A.N., Santana, R.A.C., Colares, R.P., Barros, E.B., Casciano, P.N.S., Vaz, G.L., 2010. Morphological, structural, microhardness and electrochemical characterizations of electrodeposited Cr and Ni-W coatings. Electrochim. Acta 55, 2078e2086. Prasad, S., Santana, R.A.C., Campos, A.R.N., Leite, V.D., 2007. Potentiometric and conductometric studies on the system acid-isopolytungstate and the formation t. Quím. 32, 71e78. of lanthanumtungstates. Ecle Puigdomenech, I., 2004. Chemical Equilibrium Diagrams, Inorganic Chemistry Royal Institute of Technology (KTH). Sweden, Stockholm. Wu, Y., Chang, D., Kim, D., Kwon, S., 2003. Effects of 2-butyne-1, 4-diol on structures and morphologies of electroplating Ni-W alloy. Surf. Coat. Technol. 162, 269e275.
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Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys sio Flore ^ncio de Almeida Neto* Mariana Borges Porto, Lucas Barbosa Alvim, Ambro University of Campinas, School of Chemical Engineering, Department of Products and Processes Design, Albert Einstein Avenue, 500, Campinas, SP, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 September 2015 Received in revised form 23 October 2016 Accepted 24 October 2016 Available online xxx
In this work, nickel was removed from industrial effluent by an electrodeposition process and the alloy obtained with this metal was characterized. The removal tests occurred in optimized conditions, under those occurred the formation of Ni-W alloy from synthetic baths prepared in laboratory. Thus, an experimental planning was performed in order to investigate the variation of nickel concentration in the bath, temperature and density of the current applied. The variable of response considered was the faradic efficiency. The metallic alloy obtained through the nickel removal of an electroplating wastewater was characterized by X-ray Diffraction, Infrared Spectroscopy and Scanning Electron Microscope with chemical analysis by Dispersive Energy of X-rays. The faradic efficiency was strongly influenced by the nickel concentration, achieving a value of 51.4%. In the test of nickel removal from a real wastewater, the faradic efficiency registered was approximately 90% and the nickel removal was 38.76%. The coating obtained from the real wastewater was characterized by a high level of crystallinity and pureness. The Scanning Electron Microscope images showed that the metallic alloy of Ni-W was cracked, which may be related to its crystallinity. Ni and W contents in the alloy were approximately of 73 and 27%, respectively. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Nickel removal Electrodeposition Tungsten alloys
1. Introduction Electroplating is a process presented in innumerous industries that generate wastewater contaminated with metals. In industrial facilities that require metal surface coatings, electroplating of metals and alloys is used as a good way to protect and inhibit corrosion of materials (Wu et al., 2003). One of the co-deposition activities that has grown in recent years is called branch-plated jewelry (imitation jewelry). This activity greatly increases discharges of highly concentrated toxic metal wastewater into Brazil's water bodies, representing revenues of U$ 1572.3 million per year. The Southeast region of Brazil is responsible for the production of 37% of the veneers sector. The companies that generate and release wastewater containing metals are mostly small ones. The steps of the surface treatment processes involved in electroplating imitation jewelry are metal deposition, alkaline copper, acid, nickel bath and pre-gold, gold and color. The metal deposition is the initial deposition of a thin copper layer on the piece. The alkaline copper is obtained from copper cyanide, which avoids acidity in the product.
* Corresponding author. E-mail address: [email protected] (A.F. de Almeida Neto).
The acid copper is the deposition of a copper layer with increased thickness, which fills the piece holes. The nickel bath is prepared with nickel sulfate and evens the imperfections of the piece. Finally, the baths and the final gold color are performed, and the color baths are made of nickel salts, copper, silver or cobalt. Imitation jewelry industries also use large amounts of fresh water in the production process for washing the blanks before the electroplating process. As a result, the water used for this purpose is also contaminated with residues, such as iron and organic matter. Thus, copper, nickel, iron and cobalt are the non-precious metals discharged by imitation jewelry industries. These metals have produced a concentration of sewage-diluted ions, which is above the legal discharge limits, leading to the need of using a tertiary polishing process. Tungsten, that makes very hard alloys, is used in the manufacture of steel for cutting tools, operational machinery and coatings in general. The electrodeposition of tungsten in its pure form, starting from aqueous or organic solutions, has not achieved success (Devis and Gentry, 1956). However, there is no experimental difficulty in electrodeposition of tungsten with iron group metals. It has been deposited in either acid baths or alkali. According to Brenner (1963), in cases in which a metal cannot be electrodeposited from aqueous monolithic, but is alloyed in the presence of a metal, it has
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Please cite this article in press as: Porto, M.B., et al., Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.10.140
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an “induced co-deposition”. Tungsten is co-deposited in alloys with iron and non-ferrous metals. The baths contain tungsten in the form of salts along with the iron group metal and a complexing agent. It was observed that the variation in the bath pH has a significant effect on the amount of tungsten in the electroplated alloy. Some researchers have tried to explain this effect by correlating it to the formation of different complexes by iron group metals (Wu et al., 2003), but little effort has been made to study the polymer species of tungstate anions. We do not have yet a technique that enables the control of all parameters that interfere in the electroplating metal layers, whose characteristics are defined only by optimization of operating and bath parameters. The processes employed in producing electrodeposited amorphous metal alloys are still characterized by empiricism. Several investigators have studied the effects of the electric current density, temperature and concentration of tungsten on the tungsten alloys passive behavior. In a study of Ni-W alloy, Ahmadi and Guinel (2013) showed that the increase of concentration tungstate also increases resistance to charge transfer in 1.2 times. These authors reported that when using an appropriate concentration of tungsten, all types of nickel were removed from aqueous solutions. Lima-Neto et al. (2010) obtained uniform deposits, presenting a surface morphology that has evolved from fine globular grains to rough polycrystalline with decreasing electrodeposition current density. The authors stated that all studied coatings corroded in a chloride medium, and this phenomenon was not uniform for the Ni-W alloy. According to Alimadadi et al. (2009), the formation of two phases in the Ni-W alloy structure drastically reduces anticorrosive properties. From the first dual phase, Alimadadi et al. (2009) reported the occurrence of a reduction in grain size and density of cracks in all Ni-W amorphous alloy with increasing the corrosion resistance. However, if tungsten is present in higher quantity than nickel, more cracks and defects will occur, which increases the corrosion rate. Conversely, the phase of nanocrystalline Ni-W alloy carrying higher quantity of tungsten, having the best anticorrosion properties. With changing parameters such as mechanical stirring, electric current density, temperature, concentration of reactants, pH and the presence of other transition metals, the characteristics of the electroplated layer (adhesion to the substrate, hardness, uniformity, corrosion resistance and embrittlement) can be modified and improved, which is very important for industrial applications. It is very important to highlight that from an environmental perspective, wastewater generated from the baths of the electroplating process jewelry will be used as basis for tungsten alloy electroplating, which stands out the recyclable nature of the process, as well as the reduction of waste generated. Moreover, the process also has the advantage in obtaining electroplated alloy with good appearance and high quality by removing metals from the water that once released into the environment represents a serious problem due to its toxicity and non-degradability. In this study, we evaluated the nickel removal from electroplating wastewater through electrochemical co-deposition with tungsten to form corrosion-resistant alloys, featuring deposition results with other studies involving the electrodeposition of Ni-W alloy and others nickel removal processes. Thus, the importance of this work is linked to the relevance of the topic and the development of an alternative alloy, obtained from effluents, whose results contribute to technical and economic information appropriate to the improvement of production systems. The study reports the use of sustainable natural resources, minimizing loss of socio-economic aspects and environmental impact, as a function of the electrochemical efficiency of the method applied, the surface coating recovering the metals in the elemental state, minimizes the quantities waste to be treated, and can add value to waste which
become raw materials for another product, in this case the Ni-W alloy. 2. Materials and methods 2.1. Electrolytic baths The electrodepositions of this work were performed using two different electrolytic baths. The first one is a synthetic electrolytic bath prepared in our laboratory. The other electrolytic bath is a real effluent sample generated in electroplating jewelry during the nickel bath step. Sodium tungstate, Na2WO4, 0.3 mol L1 was added to this effluent. The nickel concentration of the effluent was determined by atomic absorption spectrophotometry. Synthetic electrolytic baths were prepared with sodium tungstate, Na2WO4, 0.3 mol L1, nickel sulfate, NiSO4, and ammonium citrate, (NH4)2C6H6O7, 0.3 mol L1, which was used in the bath as a Ni complexing agent. The concentration of NiSO4 ranged from 0.1 to 0.3 mol L1. Other reagents were used for specific purposes, for example: Na2B4O7 3.75 102 mol L1 as the boron source to obtain an amorphous alloy; sodium 1-dodecylsulfate 1.04 104 mol L1, so that the H2 released during electrodeposition is detached with higher speed avoiding the formation of bubbles in the bonded alloy; and (NH4)2SO4 1.287 101 mol L1, responsible for providing greater bath stability. Nickel and tungsten speciation diagrams were simulated using Hydra and Medusa software (Puigdomenech, 2004) to identify the different species in bath. These diagrams were plotted for electrodeposition at concentrations that correspond to concentrations of chemical species in ionic solution. Speciation was investigated considering the used stoichiometric ratio of nickel and tungsten salts. 2.2. Electrodeposition The substrate used was a copper plate in 2 cm square. This was initially polished with 220 and 320 mesh sandpaper and then immersed in 10% NaOH solutions, to perform degreasing and 1% H2SO4 for surface activation. The electrodeposition experiments were performed using a rotating electrode, a potentiostat/amperostat, that controlled the electrical potential difference between the working electrode and the counter electrode, a thermostatic bath for temperature control and a pH meter. The electric current density ranged from 10 to 50 mA cm2 and the temperature between 25 and 60 C. The electrodepositions were performed using cathode rotation in a speed of 30 rpm. The potentiostat was used in electroplating way and the bath pH was approximately 6. The counter electrode used was a hollow cylindrical platinum mesh. The faradic efficiency (ε) was calculated from the mass obtained by the load used and the chemical composition of the coating obtained by EDX according to Eq. (1):
ε¼
m$F X ni $wi I$t Mi
(1)
where m is the measured mass of coating (g), t is the deposition time (s), I is the total current passed (A), wi is the weight fraction of the element in the coating obtained by EDX, ni is the number of electrons transferred per atom of each metal, Mi is the atomic mass of that element (g mol1), and F is the Faraday's constant (96,485 C mol1). The experimental design methodology was used to evaluate the electrodeposition process in which the electrolytic bath was the one prepared at the laboratory. The influence of the initial
Please cite this article in press as: Porto, M.B., et al., Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.10.140
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concentration of nickel in the bath (CNi), the electric current density (I) and the bath temperature (T) on faradic efficiency (ε) were analyzed. The method involved 23 ¼ 8 experiments with 3 experimental replicates in the central point, a total of 11 trials. Table 1 shows the input variables used in experimental design, their coding and actual levels of each variable electrodeposition system for the Ni-W alloy on the copper substrate. The experimental data regression analyzes were performed to estimate the faradic efficiency from the input variables. 2.3. Characterization X-ray Diffraction (XRD), Infrared Spectroscopy Fourier Transform (FTIR), and scanning electron microscopy with Chemical Analysis by Energy Dispersive X-ray (EDX) characterized the substrate samples containing Ni-W alloys. The XRD was obtained with a Philips device, model X'PERT with copper Ka radiation, voltage 40 kV, current 40 mA, wavelength 1.52 Å, 0.02 2q step size and a time per step of 1 s. The FTIR spectrum was determined in Infrared Spectrometer from the brand Thermo Scientific; model 6700 Nicolet (Madison/USA). FTIR analyses were performed in the reflectance mode with range of 4000e650 cm1 and 4 cm1 resolution. The micrographs of the copper substrates containing metal alloys of tungsten were obtained in the scanning electronic microscope (SEM) from LEO brand, LEO 440i model with Energy Dispersive X-ray detector (EDX).
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Table 1 Actual and coded values of variables in the 23 experimental design. Variables
Level (1)
Level (0)
Level (þ1)
CNi (mol L1) I (mA cm2) T ( C)
0.1 10 25
0.2 30 42.5
0.3 50 60
Table 2 Matrix of 23 factorial experimental design plus faradic efficiency. Exp.
CNi (mol L1)
I (mA cm2)
T ( C)
mNi (g)
mW (g)
ε (%)
1 2 3 4 5 6 7 8 9 10 11
0.1 0.3 0.1 0.3 0.1 0.3 0.1 0.3 0.2 0.2 0.2
10 10 50 50 10 10 50 50 30 30 30
25 (1) 25 (1) 25 (1) 25 (1) 60 (þ1) 60 (þ1) 60 (þ1) 60 (þ1) 42.5 (0) 42.5 (0) 42.5 (0)
0.012 0.016 0.071 0.105 0.006 0.030 0.047 0.166 0.065 0.056 0.053
0.008 0.006 0.044 0.039 0.004 0.011 0.029 0.061 0.031 0.026 0.025
22.24 24.49 25.84 32.55 10.56 46.16 17.14 51.40 35.85 30.71 29.06
(1) (þ1) (1) (þ1) (1) (þ1) (1) (þ1) (0) (0) (0)
(1) (1) (þ1) (þ1) (1) (1) (þ1) (þ1) (0) (0) (0)
3. Results and discussion 3.1. Electrodeposition using synthetic bath The results from faradic efficiency (ε) obtained for the 23 experimental design matrix used in the study of synthesized electrolytic bath prepared in the laboratory are shown in Table 2. These results were analyzed by no-linear regression. The faradic efficiency (ε) can be estimated by Eq. (2) with 95% confidence level, and regression coefficient (R2) obtained was 0.9646, which means that 96.46% of the variation around average may be estimated by Eq. (2).
ε ¼ 98:5$CNi þ 1:79$CNi $T 3:04
(2)
CNi is nickel concentration in mol L1, and T is bath temperature in C. The analysis of variance (ANOVA) for Eq. (2) allowed us to obtain a line that describes the relationship between the predicted and obtained yield for the set of experiments in the 23 experimental design, as shown in Fig. 1. The experimental points of Fig. 1 performed satisfactory linearity according to the straight line expected by the linear adjustment that in turn, is fundamental to verify if the given model was appropriate to interpret the data set. Admitting that the errors follow a regular distribution, the model of Eq. (2) proves to be adequate. The statistic evaluation of the model was determined by
Fig. 1. Representative graph of the relation between the obtained and the predict incomes.
the Fisher test for the variance analysis, presented on Table 3. The results of ANOVA listed in Table 3 indicate that both the nickel concentration (CNi) and its interaction with the temperature (T) are statistically significant, with a confidence level of 95%. Fig. 2 shows the response surface for the faradic efficiency as a result of the interaction between the nickel concentration and bath temperature. As the nickel concentration and the bath temperature increases, so does the faradic efficiency of the process. That makes a clear evidence that the nickel complexes formed during the bath are decisive factors for an efficient deposition process. The specie
Table 3 Results of ANOVA for deposition efficiency. Source
Sum of squares
Degree of freedom
F
P
Concentration of Nickel Sulfate (1) Current Density (2) Temperature (3) Interaction between 1 and 2 Interaction between 1 and 3 Interaction between 2 and 3
19.70 5.87 5.03 0.78 15.22 0.04
1 1 1 1 1 1
7.88 2.34 0.31 2.02 6.09 0.01
0.001 0.079 0.114 0.770 0.004 0.988
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electrolysis. Thus, there is an increase of complex mobility, transport number, conductance and, consequently, faradic efficiency. 3.2. Effects of synthetic electrolytic bath composition
Fig. 2. Response surface for the faradic efficiency.
Ni(cit)- is much more interesting for the electrodeposition, because, according to the metallic speciation diagrams, that was the kind of nickel with higher nickel sulfate concentration. The increase of temperature causes ions loss that hydrates the metallic complex and, therefore, reduces the mass transported during the
The citrate ion is a complex agent that forms different kinds of nickel complexes according to pH of the bath. Thus, the citrate and the pH are essential for obtaining the Ni-W alloy. The bath with the optimum pH and the addition of citrate in appropriate concentration improves the deposition efficiency, the metallic ions solubility, the adherent deposits, homogeneous and the larger amount of Ni removed from an industrial wastewater. Speciation diagrams (Fig. 3) show the distribution of metallic species of Ni, depending on the pH and the aqueous solution. According to these diagrams, it can be noticed that the chemical species Ni2þ form complexes with the citrate anions on the pH range that goes from 4, and 5 to 7. With the higher concentration of nickel used, the complex formed is almost exclusively the form of Ni(cit)-. The nickel complex formation is important, because it is the precursor for Ni-W alloy deposition. According to the experimental planning, the increase of the nickel concentration in bath promotes the faradic efficiency. That is a marked indication that the nickel complexes
Fig. 3. Nickel species at concentrations of (A) 0.1 mol L1, (B) 0.2 mol L1 and (C) 0.3 mol L1.
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Fig. 4. Tungsten species in the electrolytic bath with nickel (A) 0.1 mol L1 and (B) 0.3 mol L1.
1.50 1.35 1.20
Ni in bath
Ni mass (g)
1.05 0.90 0.75 0.60 0.45
Ni in alloy
0.30 0.15 0.00 0
50
100
150
200
250
300
t (min) Fig. 5. Ni removal from a real wastewater.
3.3. Ni removal of a real wastewater According to the experimental planning, the electrodeposition of Ni-W was more efficient in current density conditions of 50 mA cm2, temperature 60 C and nickel sulfate concentration of 0.3 mol L1. Therefore, the nickel removal of an electroplating wastewater, by electrodeposition, was accomplished in these conditions. By the atomic absorption analysis, the total of nickel concentration in the wastewater was 0.256 mol L1. The sodium tungstate was added to the bath at a concentration of 0.05 mol L1, maximum solubility permitted for the bath supplied by the industry. The pH measured in the nickel wastewater containing the
Fig. 6. Ni-W metallic alloys diffractogram.
104 102
Absorbance (u. a.)
formed in bath are decisive factors for an efficient process, in which case, Ni(cit)- is more interesting for the electrodeposition. The chemical species of tungsten, which arise in the pH range of the nickel complexes (pH ¼ 4, 5e7), are predominantly paratungstate A (Prasad et al., 2007), as shown in Fig. 4. In this isopolyanion the tungsten has oxidation number of þ5/2. Thus, the pH used in the electrolyte bath was 6, and this value is shown naturally by the electrolytic bath after its preparation with all the constituents of the bath.
100 98 96 94 92 90 4000
3500
3000
2500
2000
1500
1000
500
-1
Wave number (cm ) Fig. 7. Spectra for FTIR of Ni-W alloy.
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Fig. 8. Ni-W alloy micrographs with nickel and tungsten mapping.
sodium tungstate was 6, this being exactly the same to the pH of the synthetic bath prepared in the laboratory. Fig. 5 describes the exponential decay of the nickel amount in the electrolytic wastewater and the nickel increase in the alloy. The nickel removal took 300 min and the copper substrate was weighed every 20 min until the deposited mass of metallic alloy was constant. The faradic efficiency for this test was 89.95% and the metallic alloy obtained was shiny and adherent. The highest Faradic efficiency obtained in laboratory test was 51.4% and in the nickel removal test of a real wastewater showed an even greater efficiency. This was possibly due to low tungsten amount used in the bath containing the effluent. The ratio between the nickel mass in the alloy, during 300 min of the test, and the initial nickel mass of the wastewater, provided the nickel removal percentage of 36.78%. On others, nickel removal percentage are presented by adsorption processes (Almeida Neto et al., 2014), but in these processes nickel is only removed in low concentrations. 3.4. Crystallinity of Ni-W coating Fig. 6 shows the XRD of Ni-W metallic alloy supplied by the database of XRD equipment from the brand Philips Analytica X-Ray, model X'Pert-MPD, and the X-rays diffraction obtained for the NiW sample, which was deposited from the real wastewater. All Ni-
W alloy obtained from the electrolytic bath prepared in the laboratory showed similar diffraction patterns for the sample of Fig. 6. In the graph, it can be seen the peaks that characterize Ni-W metallic alloy in the range of 42 and 50 2q (degrees) at both presentations, confirming that the copper substrate was coated by NiW alloy and that is crystalline. Thus, in accordance with the nickel atomic rays, 124 p.m., and tungsten, 135 p.m., it is emphasized that the alloy obtained is the homogeneous and substitutional type, in which the tungsten is capable of replacing nickel in the crystalline lattice. 3.5. Ni-W alloy purity Carbon chemical species, such as citrates, cyanides and carbonates can be produced in secondary reactions during the electrodeposition process. The presence of these impurities in the alloy can damage the material, turning it to corrosion susceptible, which causes instability and compromise the coating quality. Fig. 7 shows the results of FTIR of the Ni-W alloy, obtained by the co-deposition of tungsten using real nickel effluent, indicating the absence of peaks or bands, typical of vibrations, stretches or angular deformations of chemical bonds from other species that could have been deposited as impurities in the alloy. Therefore, it emphasizes the coating purity that has not even vibrations,
Fig. 9. Micrographs of Ni-W alloy for Exps. 1 and 8 of Table 2.
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stretches or angular deformations of O-H alloys. This purity was also found for the Ni-W sample synthesized from the electrolyte bath prepared in the laboratory. 3.6. Coating morphology and Ni-W distribution in the alloy In Fig. 8, there are images obtained in SEM, with the increase of 1500 times and Ni distribution (green dots) and W (red dots) in the alloy obtained from bath containing effluent. This Ni-W coating showed cracks, which are associated with high crystallinity of the obtained alloy. For this sample, the content of Ni and W in the alloy was 73 and 27%, respectively. Fig. 9 shows the micrographs of Ni-W alloys of the Exp. 1 of Table 2 (image left) obtained with lower current density (10 mA cm2). A smaller amount of microcracks was detected. From the Exp. 8 of Table 2 (image right), which was conducted with a higher current density (50 mA cm2), a large amount of microcracks is observed. Both images are magnifications of 1500 times. Ghaferi et al. (2015) also concluded that the lower the density of the electric current more uniform the surfaces are. 4. Conclusions The results obtained in the present work showed that the nickel electrodeposition, as a metal inductor of tungsten deposition, has a significant potential in nickel removal from wastewater generated by the electroplating industry. It was verified that in the studied conditions, the metallic alloys of Ni-W presented adherence, shine and faradic efficiency, as in tests performed with the synthetic baths and as in a sample of real wastewater. The capacity of nickel removal was 36.78% in conditions of maximum faradic efficiency obtained for the electrodeposition of Ni-W, using synthetic baths. The maximum faradic efficiency was 89.9% to the electrodeposition of Ni-W using real wastewater, and 51.40% to the formation of Ni-W using the synthetic bath, in the temperature of 60 C and the electric current density of 50 mA cm2. According to the diagrams of speciation, the electrolytic baths could be used with pH achieved by these solutions after the salts dissolution, once this pH is about 6. The nickel formed crystalline metallic alloy with tungsten, like
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proven by the XRD analyses, besides the purity indicated by FTIR. The micrographs showed uniformity of the coating and a regular distribution of kinds of nickel and tungsten on the deposit. Therefore, the nickel removal by co-deposition with the tungsten is an alternative to the reuse methods and a better use of wastewater, being economically beneficial and collaborating with the environment.
Acknowledgements The authors acknowledge the financial support received from ~o Paulo Research Foundation, FAPESP, for this study. State of Sa
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Please cite this article in press as: Porto, M.B., et al., Nickel removal from wastewater by induced co-deposition using tungsten to formation of metallic alloys, Journal of Cleaner Production (2016), http://dx.doi.org/10.1016/j.jclepro.2016.10.140