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Recycling of Zn-C and Ni-Cd spent batteries using Cyphos IL 104 via hydrometallurgical route
Accepted Manuscript Recycling of Zn-C and Ni-Cd spent batteries using Cyphos IL 104 via hydrometallurgical route Harshit Mahandra, Rashmi Singh, Bina Gupta PII:
S0959-6526(17)32429-0
DOI:
10.1016/j.jclepro.2017.10.129
Reference:
JCLP 10921
To appear in:
Journal of Cleaner Production
Received Date: 17 May 2017 Revised Date:
11 October 2017
Accepted Date: 11 October 2017
Please cite this article as: Mahandra H, Singh R, Gupta B, Recycling of Zn-C and Ni-Cd spent batteries using Cyphos IL 104 via hydrometallurgical route, Journal of Cleaner Production (2017), doi: 10.1016/ j.jclepro.2017.10.129. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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GRAPHICAL ABSTRACT
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Recycling of Zn-C and Ni-Cd spent batteries using Cyphos IL 104 via hydrometallurgical route
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Harshit Mahandra, Rashmi Singh and Bina Gupta* Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee -247667,
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Uttrakhand, India
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*Author for correspondence Prof. Bina Gupta Department of Chemistry Indian Institute of Technology Roorkee Roorkee- 247667 (U.K.), India [email protected] Phone: +91-1332-285326 (off.) Fax: +91-1332-273560
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ABSTRACT The study suggests hydrometallurgical routes for the recovery of zinc and cadmium from spent battery leachates using a novel extractant Cyphos IL 104 diluted in toluene and synthesis of zinc
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and cadmium oxides from the loaded organic phases. Leaching is carried out using 5 mol/L HCl and the composition of the leach liquors obtained from Zn-C and Ni-Cd spent batteries in g/L is Zn- 2.400, Mn - 4.870, Fe - 2.655×10-3, and Cd- 4.280, Ni- 89.60×10-3, Fe- 148.2×10-3, Co-
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3.765×10-3, respectively. McCabe Thiele diagrams are drawn to determine the number of theoretical stages required for the quantitative extraction and stripping of zinc and cadmium and
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the data has been confirmed by counter current simulation studies. McCabe Thiele diagrams indicate two extraction stages for both zinc and cadmium at A/O = 1/1 and A/O = 3/2, respectively. EDTA (0.1 mol/L) and HNO3 (1.0 mol/L) are used as strippant for zinc and cadmium, respectively. Quantitative stripping of zinc and cadmium requires two and three
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counter current stripping stages, respectively at O/A = 1/1. Results of counter current extraction and stripping show quantitative recovery (> 99%) of zinc and cadmium with high purity. Zinc and cadmium oxides have been synthesized from the loaded organic phase using precipitation
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followed by thermal decomposition of precursors at 400oC. Synthesized materials were characterized by XRD, FE-SEM and EDX techniques. Zinc and cadmium oxide particles
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correspond to hexagonal zincite and cubic monteponite structures, respectively. The average particle size of zinc and cadmium oxides is 43±13 nm and 55±14 nm, respectively. The morphology of zinc and cadmium oxide particles is considered to be globular with particle agglomeration. The proposed methods are selective for zinc and cadmium. Results of present study have been compared with the reported data. Keywords: Cyphos IL 104, McCabe-Thiele Diagrams, Ni-Cd batteries, Zn-C batteries
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1. INTRODUCTION Consumption of batteries in different electronic devices such as laptops, cell phones, watches, toys, calculators, cameras, recorders, remote controls, has increased enormously.
These
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batteries, at the end of their lifecycle are discarded generating a huge amount of waste which leads to environmental and economical issues. Tons of battery waste are generated every year all over the globe and require appropriate management. In view of environmental hazard, proper
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disposal of e-waste is very important which may involve landfill deposition, stabilization by incineration and recycling processes (Agrawal et al., 2012). Large volumes of waste generated,
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make landfill deposition expensive due to limited storage capacity of dumpsites. Incineration of waste batteries releases toxins such as mercury, cadmium and dioxins to the atmosphere and is therefore restricted by environmental legislation (Provazi et al., 2011). Recycling of spentbatteries is the best way to solve environmental and economical issues benefiting the future
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generations. 26660 tons of Zn batteries and 6632 tons of Ni-Cd batteries were recycled in 2012 by members of European Battery Recycling Association (EBRA. 2012). A number of pyrometallurgical and hydrometallurgical methods have been reported to recover metal values
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from different types of spent batteries such as Zn-C (Belardi et al., 2012, 2014; Sayilgan et al., 2009), Ni-Cd (Agrawal et al., 2012; Huang et al., 2010), lithium ion (Barik et al., 2017; Chen et
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al., 2015; Jha et al., 2013) and Ni-metal hydride (Larsson and Binnemans, 2014; Li et al., 2009; Meshram et al., 2017). Pyrometallurgical methods include traditional high temperature processes of roasting, smelting and refining. These methods are high energy consuming, less versatile, suitable for high grade ores/materials and emit waste gases which may be toxic many times and thus require dust collecting/ gas cleaning systems (Gupta and Mukherjee, 1990a; Sayilgan et al., 2009). The solid waste generated as molten slag and matte is difficult to handle.
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Hydrometallurgical methods, on the other hand, are based on chemical reactions involving aqueous and organic solutions in the temperature range of 25 to 250oC. Separation of chemically similar metals is easily achieved and the methods are suitable for the processing of complex
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ores/materials and for the production of various by products. Hydrometallurgical methods are comparatively efficient, low cost, metal selective and cause no air pollution (Sayilgan et al., 2009).
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Several hydrometallurgical routes employing different extractants have been explored by various research groups for the recovery of zinc and cadmium from waste batteries. Acidic
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organophosphorous extractants such as DEHPA, di-(2-ethylhexyl) phosphoric acid (Agarwal et al., 2012; Falco et al., 2014), Cyanex 272, bis(2,4,4-trimethylpentyl) phosphinic acid (Baba et al.,
2009;
Falco
et
al.,
2014;
Salgado
et
al.,
2003),
Cyanex
301,
bis(2,4,4-
trimethylpentyl)dithiophosphinic acid (Reddy et al., 2006) and Cyanex 302, bis(2,4,4-
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trimethylpentyl)monothiophosphinic acid (Biswas et al., 2016) have been attempted to recover zinc and cadmium from Zn-C, Zn-MnO2 alkaline and Ni-Cd batteries. These extractants have been used solo or with a modifier (Agarwal et al., 2012). A few solvating organophosphorous
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extractants such as Cyanex 923, a mixture of trialkylphosphine oxides (Deep et al., 2011, 2016; Reddy and Priya, 2006; Reddy et al., 2005) and TBP, Tributyl phosphate (Fernandes et al., 2012)
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have also been explored for the recovery of zinc and cadmium from spent batteries. Recently, imidazolium, ammonium and phosphonium based ionic liquids have been investigated for the extraction of various metal ions. These ionic liquids are better than conventional extractants as they do not release H+ ions into the raffinate and therefore neutralization of released acid is not required (Kumari et al., 2016). Loss of imidazolium cation to the aqueous phase during extraction is a major drawback, making the imidazole-based ionic liquids
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unsuitable for an environment-friendly process. Ammonium based ionic liquids have limitations of hydrophobicity and low thermal stability. These drawbacks are overcome in phosphonium ionic liquids which are gaining attention of separation chemists.
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Phosphonium ionic liquids have emerged as potential extractants due to their unique properties such as non-volatility, nonflammablity, low vapour pressure, high thermal and chemical stability, good extraction power for metal ions and good recycling capacity (Makanyire et al., 2016;
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Regel-Rosocka, 2009; Rout and Binnemans, 2014). Among these Cyphos IL 104 (trihexyl(tetradecyl)-phosphonium bis(2,4,4-trimethylpentyl) phosphinate) was found to be an
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efficient extractant for zinc and cadmium (Mahandra et al., 2017).
In the present work, Cyphos IL 104 has been explored for the first time for the recovery of zinc and cadmium from spent Zn-C and Ni-Cd batteries via solvent extraction route. The study focuses on the recovery of pure zinc and cadmium in solution form as well as zinc and cadmium
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oxides from the loaded organic phases. McCabe Thiele diagrams and counter current simulation studies were carried out for the extraction and stripping of zinc and cadmium from spent batteries leach liquors. Nanosized ZnO and CdO particles were characterized by X-ray
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diffraction spectroscopy (XRD), Field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX). The recovered pure zinc and cadmium oxide
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nanoparticles may find applications in gas sensors, optical waveguides, photodiodes, photonic crystals, transparent conductive films/electrodes, light-emitting devices and solar cells etc. 2. EXPERIMENTAL
2.1 Reagents and chemicals All the reagents and chemicals used were of analytical grade. Cyphos IL 104 was received from Cytec Inc., Netherlands and used as such without any further purification. Toluene was used as a
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diluent to get Cyphos IL 104 solution of desired concentration. Eveready AA type Zn-C and Envie AA type Ni-Cd spent batteries were procured from local market. 2.2 Equipments
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A flask shaker with wrist action (Perfit) was used for equilibrating aqueous and organic phases. Atomic Absorption Spectrometer (AAS) (AAnalyst 800, Perkin Elmer, Germany) was used to determine the metal contents in the aqueous phases. Synthesized metal oxides were characterized
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through powder X-ray diffraction (XRD) using Bruker AXS D8 diffractometer employing CuKα radiation (λ= 1.5418 Å). Surface morphology and particle size were studied with a field
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emission scanning electron microscope (FESEM-Carl Zeiss ULTRA plus55) operating at 15kV. The particle size was measured using Image J software. Elemental compositions of the nanoparticles were determined using EDX (Energy-dispersive X-ray spectrometer) equipment attached to the FE-SEM microscope.
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2.3 Dismantling, digestion and leaching of spent batteries 2.3.1 Zinc-carbon spent batteries
Spent batteries were dismantled and the black powder was separated and dried in an oven at
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800C for 24 hours. Dried powder was then sieved through 75 µm sieve to obtain a fine black
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powder. For digestion, 1.0 g black powder was heated with 20 mL aqua-regia up to boiling for 30 minutes, cooled and filtered (Deep et al., 2011). Filtrate and washings were collected and then appropriately diluted with ultrapure water. Metal contents of digested sample were analyzed using AAS (Table 1).
Leaching was performed by heating 2.5 g of the black powder with 25 mL of 5.0 mol/L HCl for 1 hour at 700C (Deep et al., 2011). The contents were cooled, filtered and diluted to 100 mL maintaining the acidity at 0.5 mol/L HCl and named as [ZC]. Concentrations of different metal 6
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ions in leach liquor [ZC] were checked by AAS (Table 1). For extraction studies, the leach liquor [ZC] was diluted two times maintaining acidity at 0.5 mol/L HCl and designated as [ZC1].
Zinc
Concentration in digested liquor (g/ L) 2.420± 0.050
Manganese 5.066 ± 0.010
Concentration in electrode powder (g/kg)
Concentration in leached liquor (g/ L)
96.8 ± 2.4
2.400±0.030
202.7 ± 0.2
4.870±0.040
Amount leached from electrode powder (g/kg) 96.0 ± 2.6
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Metals analysed
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Table 1. Concentrations of metals in digest and leach liquor [ZC] of spent Zn-C batteries
99.2
194.8 ± 1.6
96.1
0.106 ± 0.008
50.3
(5.275± 0.050) × 10-3
0.211± 0.013
Nickel
(0.110 ± 0.003)× 10-3
0.0025±0.0003
ND
-
-
Cadmium
(0.062±0.001)×10-3
0.0044±0.0012
ND
-
-
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Iron
Note- ND = Not Detected
(2.655±0.020)×10-3
Leaching efficiency (%)
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2.3.2 Nickel-Cadmium batteries
Spent Ni-Cd batteries were dismantled manually and cell components were collected separately.
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In order to extract the active electrode material, polymeric separators around the electrodes were removed. The active anode material was scrapped from the steel mesh, dried at 800C for 24 hours
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and sieved through 75 µm sieve to obtain a fine grey colored powder. Digestion of the active anode material was done following the method used for Zn-C spent batteries and the metal contents of digested sample were checked by AAS (Table 2). Leaching of the active anode material was done as follows: 1.0 g of the sample was added to 15 mL of 5 mol/L HCl and heated to boil for 1 hour at 700C, cooled, filtered and residue was washed with ultrapure water (Deep et al., 2011). The filtrate and washings were collected and diluted to prepare 100 mL of
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leach liquor maintaining acidity at 0.1 mol/L HCl and designated as [NC]. Concentrations of different metal ions in leach liquor of active anode material were assayed by AAS (Table2).
batteries
Concentration in digested liquor (g/L)
Concentration in Concentration of electrode metal in leached powder (g/kg) liquor (g/L)
Cadmium
4.348±0.008
434.8 ± 1.0
4.280±0.020
Nickel
(89.94±0.04)×10-3
8.99 ± 0.004
Iron
(148.4±0.2)×10-3
14.84 ± 0.02
Cobalt
(3.969±0.020)×10-3
0.397 ± 0.0002
Leaching Efficiency (%) 98.4
(89.60±0.46)×10-3
8.96 ± 0.05
99.6
(148.2±0.4)×10-3
14.82 ± 0.4
99.9
(3.765±0.080)×10-3
0.377 ± 0.008
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2.4 Partition studies
Amount leached from electrode powder (g/kg)
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Metals analysed
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Table 2. Concentrations of metals in digest and leach liquor [NC] processed from Ni-Cd spent
An aliquot of leach liquor and the extractant solution (Cyphos IL 104 in toluene) at different phase ratios (depending upon experimental conditions) were equilibrated for 6 minutes
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(Mahandra et al., 2017) at room temperature (25±3oC). After phase separation, the concentrations of metal ions in aqueous phase were checked by AAS and the percentage of metal
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transferred to the organic phase was calculated by mass balance calculations. The coefficient of variance for extraction and stripping data is ±5%. 2.5 Construction of McCabe-Thiele diagrams McCabe Thiele diagrams are required to design a solvent extraction circuit and to predict its performance. In order to construct a McCabe Thiele diagram, an extraction isotherm is generated (Gupta and Mukherjee, 1990b; Ritcey and Ashbrook, 1984). Leach liquor containing 1.240 g/L 8
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zinc in 0.5 mol/L HCl [ZC1] was equilibrated with 0.05 mol/L Cyphos IL 104 at A/O ratios varying from 1/5 to 5/1 keeping the total volume of phases constant. Similarly, leach liquor containing 4.280 g/L cadmium in 0.1 mol/L HCl [NC] was equilibrated with 0.2 mol/L Cyphos
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IL 104 at A/O ratios varying from 1/5 to 5/1. To construct Mc-Cabe Thiele diagrams, plots were drawn between metal concentrations in the organic phase and in raffinate at different A/O ratios. Operating lines for phase ratios A/O = 1/1 and A/O = 3/2 were drawn considering the metal
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content in raffinate and loaded organic phase at the said phase ratios. The slope of the operating line defines aqueous to organic phase ratio. A vertical line on x-axis was drawn from the aqueous
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feed concentration which intersects the operating line at a particular point. From this point, a horizontal line is drawn to intersect the extraction isotherm. From intersection point a perpendicular is drawn on the operating line and from this point again a horizontal line is drawn on the extraction isotherm and so on till it reaches to zero. Now the number of triangles
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generated along with the operating line indicates the number of stages for counter current extraction for quantitative extraction of the metal ion from aqueous feed. Phase ratio is selected on the basis of number of stages and loading factor of the extractant. McCabe Thiele diagrams
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for stripping were also constructed in the same way except that now organic/aqueous phase ratio
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(O/A) was considered and the axes of isotherm plots were reversed. 2.6 Synthesis of zinc and cadmium oxides Equal volumes of 0.2 mol/L Cyphos IL 104 and leach liquor [ZC]/[NC] were equilibrated for 6 minutes at room temperature. Both the phases were allowed to separate and the loaded organic phase was again contacted with fresh leach liquor. The process was repeated four times to obtain zinc/cadmium enriched organic phase. Zinc/cadmium enriched organic phase was then scrubbed with 1.0 mol/L HCl to remove coextracted metal impurities if any. 9
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To the scrubbed zinc enriched organic phase, equal volume of 0.2 mol/L oxalic acid solution was added drop wise and the resulting mixture was stirred for two hours at room temperature. White precipitates thus obtained, were centrifuged at 2500 rpm and the spent organic phase was
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decanted and collected. The precipitates obtained were washed with methanol and dried in an oven at 600C for two hours. The resulting product was grinded in an agate mortar for 30 min at room temperature and zinc oxide was obtained by its thermal decomposition at 4000C for 3 hours
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(Rajesh et al., 2012).
For cadmium oxide, equal volume of 1.0 mol/L NaOH solution was added drop wise to the
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scrubbed cadmium enriched organic phase on a magnetic stirrer at 1200 rpm stirring speed. White precipitates thus obtained at the interface of both the phases were centrifuged at 2500 rpm and washed with ethanol. The precipitates thus obtained were dried in an oven at 800C for one hour. Dried precipitates were calcinated at 4000C for three and half hours to give cadmium oxide
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(Reddy et al., 2010).
The spent organic phases remaining after centrifugation of the precipitates were washed with water and reused for the extraction of zinc and cadmium from fresh leach liquor [ZC] and [NC],
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respectively. In both the cases, quantitative extraction of the respective metal ion was achieved without any significant decrease in extraction efficiency. This indicates that the extractant can be
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reused in further cycles. A rough estimate of the process cost (provided in supplementary information) suggests that proposed methods for the recovery of zinc and cadmium as ZnO and CdO nanoparticles from spent batteries are economical.
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3. RESULTS AND DISCUSSION 3.1 Effect of Cyphos IL 104 concentration
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An aliquot of leach liquor was equilibrated with equal volume of organic phase containing varying concentrations of Cyphos IL 104 (0.008-0.1 mol/L for [ZC1] and 0.04-0.22 mol/L for [NC]) at a fixed and predetermined acidity (Mahandra et al., 2017). In case of Zn-C battery,
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extraction of zinc was quantitative from 0.05 mol/L extractant onwards and manganese showed negligible extraction in the entire investigated range of extractant concentration (Figure 1a). In
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case of Ni-Cd battery, quantitative extraction of cadmium was achieved at 0.2 mol/L Cyphos IL104 where around 17% iron was coextracted (Figure 1b). Extraction of Co and Ni was negligible in the investigated range of Cyphos IL 104 concentration. In all further studies, extraction of iron was minimized by adding 20-fold molar excess of ascorbic acid to the leach
100 90 80
50
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%E
60
40 30 20
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10 0.02
0.04
0.06
100 90
Fe Co Ni Cd
80
Mn Zn
70
0 0.00
(b)
70 60
%E
(a)
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liquor prior to extraction (Mahandra et al., 2017).
50 40 30 20 10 0
0.08
0.10
0.04
[Cyphos IL 104],mol/L
0.08
0.12
0.16
0.20
0.24
[Cyphos IL 104], mol/L
Figure 1
Based on the results, all further studies with Zn-C battery leach liquor [ZC1] were carried out using 0.05 mol/L Cyphos IL 104 and with Ni-Cd battery leach liquor [NC] using 0.2 mol/L Cyphos IL 104. 11
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3.2 McCabe−Thiele Diagrams 3.2.1 McCabe-Thiele diagrams and countercurrent extraction simulations
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Extraction isotherms and McCabe-Thiele diagrams for zinc [ZC1] and cadmium [NC] are presented in Figure 2(a) and 2(b), respectively. It is clear from the plots that in case of zinc at A/O = 1/1 two theoretical extraction stages are required for quantitative extraction of zinc and
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phase ratio of 3/2 is not acceptable because the feed concentration exceeds the loading factor of the organic phase (Figure 2a). Therefore, A/O = 1/1 with two extraction stages was selected for
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zinc extraction. However, in case of cadmium, phase ratio of 3/2 with two stages was selected as A/O = 1/1 leads to single stage extraction i.e. inefficient use of extractant (Figure 2b).
A/O= 3/2
1.2
A/O= 3/3
No. of stages =2
1.0 0.8 0.6 A/O=2/4
/2 =3 O / A =1/1 A/O
0.4 0.2 A/O=1/5 0.2
0.4
0.6
0.8
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0.0 0.0
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[Zn]org, g/L
1.4
1.0
A/O = 4/2
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A/O = 5/1
A/O = 3/2
No. of stages = 2
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1.6
(b)
Cd in Feed Solution = 4.280 g/L
A/O= 5/1
A/O= 4/2
5 4 A/O = 3/3 No. of stages = 1
,
1.8
[Cd]org g/L
2.0
Zn in Feed Solution = 1.240 g/L
(a)
3 2 A/O = 2/4
/2 =3 O / A
1 = 1/ A/O
1 A/O = 1/5 0
1.2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
,
[Cd]aq g/L
[Zn]aq, g/L
Figure 2
Based on the data obtained from McCabe−Thiele diagrams two stage counter current extraction simulations (CCES) were performed at A/O = 1/1 for zinc [ZC1] and A/O = 3/2 for cadmium [NC]. CCES test carried out for [ZC1] resulted in a raffinate containing 0.06×10-3 g/L of zinc corresponding to >99.9% extraction of zinc (Table 3). Co-extraction of Mn(II) was negligible. 12
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Table 3. Results of the two stage countercurrent extraction simulation for recovery of zinc Metal concentration (g/L) Zn
Mn
1.240
2.442
~1.240
-
0.06×10-3
2.442
Feed[ZC1] Loaded Organic phase
1/1
Zn
Mn
>99.9
-
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Raffinate
Extraction efficiency(%)
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A/O phase ratio
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Stream
Results of CCES for [NC] showed 0.5×10-3 g/L cadmium in the raffinate which corresponds to >99.9% extraction of cadmium. Major portions of nickel, cobalt and iron remained in the raffinate and their co-extraction with cadmium was less than 1.0%. The results are shown in
Metal concentration (g/L)
Loaded Organic phase Raffinate
3/2
Extraction efficiency (%)
Cd
Ni
Fe
Co
4.280
89.6×10-3
0.1482
3.765×10-3
6.419
0.15×10-3
-
0.047×10-3
0.5×10-3
89.5×10-3
0.1482
3.734×10-3
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Feed[NC]
A/O Phase ratio
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Table 4. Results of the two stage counter-current extraction simulation for recovery of cadmium
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Cd
Ni
Fe
Co
>99.9
0.1
-
0.82
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Table 4. As mentioned in section 3.1, excess of ascorbic acid was added to the leach liquor [NC] before extraction to suppress the extraction of iron.
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3.2.2 McCabe-Thiele diagrams and countercurrent stripping simulations McCabe Thiele diagrams were constructed to investigate the number of theoretical stages required for quantitative stripping of zinc and cadmium from the respective loaded organic
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phase. EDTA and HNO3 were used for the stripping of zinc and cadmium, respectively (Mahandra et al., 2017). The loaded organic phase, obtained in two stage counter current
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extraction of zinc, was equilibrated for 5 minutes with different concentrations of EDTA (0.010.5 mol/L) at O/A = 1/1 (Figure 3a) and 0.1 mol/L EDTA was selected for further studies.
(a)
(b) 5
100
O/A=5/1
90
60 50
30 0.0
0.1
EP
40
0.2
0.3
0.4
3
O/A=4/2
2
No. of stages =3 O/A=3/3
1
No. of stages =2 O/A=1/1 O/A= 2/4 /A=3/2 O O/A=5/1
0 0.0
0.5
[EDTA], mol/L
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Zn in LO = 1.240 g/L
70
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% Stripping
80
[Zn]aq, g/L
4
0.2
0.4
0.6
0.8
1.0
1.2
[Zn]org, g/L
Figure 3
For stripping isotherm, the loaded organic phase was equilibrated with 0.1 mol/L EDTA at O/A varying from 1/5 to 5/1, maintaining the total volume constant. McCabe-Thiele diagram was drawn which shows that two stages are required at O/A = 1/1 for complete stripping of zinc and three stages at O/A = 3/2. Therefore, O/A = 1/1 with two stages was selected for the stripping of
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zinc (Figure 3b). To confirm the stripping isotherm prediction data, a two-stage counter current stripping simulation (CCSS) was carried out at O/A = 1/1. A solution containing 1.237 g/L zinc corresponding to 99.8% stripping efficiency was obtained.
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For cadmium, the loaded organic phase obtained in two stage counter current extraction was equilibrated for 5 minutes with different concentrations of HNO3 (0.5-2.0 mol/L) at O/A = 1/1 and 1.0 mol/L HNO3 was selected for further studies (Figure 4a). McCabe Thiele diagram
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constructed (Figure 4b) for the stripping of cadmium showed that three stages are required for quantitative stripping of cadmium at O/A = 1/1 and four stages at O/A = 3/2. Therefore, O/A =
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1/1 with three stages was selected for further studies and three stage CCSS test was performed at O/A = 1/1 using 1.0 mol/L HNO3.
(b) 12
100 90
50
40 30
1.0
1.5
AC C
0.5
Cd in LO = 6.419 g/L
60
[Cd]aq, g/L
70
No. of stages = 4
O/A = 4/2
8
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% Stripping
80
0.0
O/A = 5/1
10
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(a)
6
No. of stages = 3
O/A = 3/3
4 O/A = 2/4
2 =3/ O/A=1 O/A
2 O/A = 1/5
0
2.0
0
[HNO3], mol/L
1
2
3
4
5
6
[Cd]org, g/L
Figure 4
The strip solutions and spent organic phases were collected and combined. Combined strip solution contains 6.412 g/L Cd corresponding to a stripping efficiency of 99.9%. The spent organic phases obtained after stripping of zinc and cadmium respectively can be reused for the extraction of zinc/cadmium after washing with water (Mahandra et al., 2017). 15
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Complete process for the recovery of zinc and cadmium from spent batteries leach liquor is
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described in flowsheet in Figure 5.
Spent battery leach liquors
[ZC1]
[NC]
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addition of ascorbic acid
Extraction with 0.20 mol/L Cyphos IL 104 A/O = 3/2, 2 stages
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Extraction with 0.05 mol/L Cyphos IL 104 A/O = 1/1, 2 stages
Loaded Organic phase (Zn)
Raffinate (Mn)
Stripping with 1.0 mol/L HNO3 O/A = 1/1, 3 stages
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Stripping with 0.1 mol/L EDTA O/A = 1/1, 2 stages
Loaded Organic phase (Cd)
Spent organic phase Strip solution Spent organic phase (Cyphos IL 104) (Zn) (Cyphos IL 104)
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Washing with water
Ready to reuse
Washing with water
Ready to reuse
Figure 5
16
Strip solution (Cd)
Raffinate (Fe, Co, Ni)
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3.3 Characterization of zinc and cadmium oxides 3.3.1 XRD analysis Figure 6 shows XRD patterns of the zinc and cadmium oxide particles obtained from calcination
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of precursors at 4000C. XRD pattern of synthesized ZnO (Figure 6a) is indexed to the hexagonal zincite crystalline phase with lattice parameters a = b = 3.2855Å, c = 5.2616Å (JCPDS card number: 36-1451). XRD of synthesized CdO (Figure 6b) corresponds to cubic monteponite
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crystalline phase with lattice parameters a = b = c= 4.7059Å (JCPDS card number: 05-0640). Zinc oxide and cadmium oxide reference peaks are shown as bar graphs in Figure 6a and 6b,
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respectively. The observed diffraction peaks are in good agreement with ZnO and CdO reference peaks. XRD patterns indicate pure phases of zinc oxide and cadmium oxide. The (101) and (111) planes have the strongest line for ZnO and CdO, respectively. The broadening at the bottom of
10
30
40
50
(111)
60
40
(222)
(400)
(311)
50
20 10
0
20
(200)
70
30
(202)
(103)
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80
(104)
30
(112)
(102)
40
(110)
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(100) (002)
60
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Intensity (a.u)
70
90
(220)
80
100
(b)
Intensity (a.u.)
90
(200) (201) (004)
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diffraction peaks denotes smaller crystalline size of ZnO and CdO particles.
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80
20
2Theta (degree)
30
40
50
60
2Theta (degree)
Figure 6
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70
80
90
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The crystallite sizes were calculated using Scherrer’s equation (Khayati et al., 2014) i.e. D = (0.9λ)/(βcosθ), where λ is X- ray wavelength, β is line broadening measured at half-height
and 18.37 nm for zinc oxide and cadmium oxide, respectively.
3.3.2 FE-SEM and EDX analysis
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(FWHM) of the most intense peak of XRD and θ is Bragg angle. The crystallite sizes were 18.24
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Morphology of synthesized ZnO and CdO was studied using FE-SEM and is shown in Figure 7 at two different magnifications. Morphology of synthesized metal oxides is found to be globular
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in shape and nano in size. It is clear from FE-SEM images that CdO particles have strong tendency to form nanoparticle agglomerates resulting in large size particles. The particle size was measured using Image J software (Gaur et al., 2014) in each case. More than 100 particles were randomly selected and their diameter was measured for analyzing the particle size distribution. The size of particles varies in between 20-100 nm and 10-120 nm for ZnO and CdO,
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respectively. Particle size distribution curves have been plotted to analyze the distribution of the particles for both the metal oxides (Figure 8). Gaussian fit confirms the narrow size distribution
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of particles. The mean particle size for ZnO and CdO is 43±13 nm and 55±14 nm, respectively.
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(a)
(d)
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Figure 7
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(a) 35
(b) 35 30
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Distribution (%)
20 15 10 5
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20
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Distribution (%)
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20
Diameter of the nanoparticles (nm)
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Diameter of the nanoparticles (nm)
Figure 8
EDX spectra of ZnO and CdO (Figure 9) indicate that ZnO and CdO structures are composed of only Zn/Cd and O with almost 1:1 atomic percentage. This confirms the synthesis of pure ZnO
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and CdO with proper stoichiometric ratio of Zn/Cd and O (Table 5).
Figure 9
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(b)
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Table 5. Results of elemental analysis of (a) zinc oxide and (b) cadmium oxide Element
Weight%
Atomic%
Weight%
Atomic%
OK
14.06
53.48
Cd L
85.94
Totals
100.00
(b) 20.00
50.53
Zn L
80.00
49.47
Totals
100.00
46.52
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OK
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(a)
Element
4. Comparative Study
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Table 6 summarizes the performance of various extractants reported for the recovery of zinc and cadmium from spent batteries. All the extractants cited in Table 6 show quantitative recovery of said metals from waste battery leach liquor, but the extractant to metal ratio used for quantitative recovery of Zn/Cd is generally higher than required in the present study. The equilibration time
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used in present study is either comparable or less than the reported ones. One of the methods (Agarwal et al., 2012) requires a modifier, isodecanol, along with the extractant, saponified D2EHPA, for the quantitative recovery of cadmium from Ni-Cd battery waste. Salgado et al.
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quantitatively extracted zinc from spent battery leach liquor using Cyanex 272 but the recovery of zinc from the loaded organic phase was not investigated. Deep et al. (2011) obtained ZnO by
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combustion of the loaded organic phase which is of environmental concern. Only a few studies (Biswas et al., 2016; Deep et al., 2011) and the present study report recovery of metals from battery waste as a useful product which paves way for the conversion of e-waste into beneficial product.
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Table 6. Comparison of various extraction systems for the recovery of Zn and Cd from spent batteries
Organic phase
[Extractant]/# [Metal]
Equilibration time (min.)
Strippant
Extraction conditions
Recovered Product
References
Conc., mol/L 3.04 (Pure)
Diluent -
2.2 g/L Zn
~8.99
10
1M H2SO4
A/O = 10/1, one stage (BE)
ZnO
0.1M HCl
A/O = 1/1, one stage (BE)
-
Baba et al., 2009
-
At 50oC, A/O = 1/1, two stages (CE)
-
Salgado et al., 2003
15
1M H2SO4
A/O = 1/1, two stages (CCE)
-
Falco et al., 2014
5
2M HNO3
A/O = 1/1, three stages (CCE)
ZnO
Deep et al., 2011
5
0.77M H2SO4
A/O = 3/2, four stages (CCE)
-
Agarwal et al., 2012
10.71
-
Water pH=6.1
A/O = 1/1, two stages (CCE)
-
Reddy et al., 2006
10.71
5
Water pH=6.1
A/O = 1/1, two stages (CCE)
-
Reddy et al., 2005
25.31
5
0.5M H2SO4
A/O = 1/1, two stages (CCE)
-
Fernandes et al., 2012
2.4 g/L Cd
2.86
5
6M HCl
A/O = 1/1, two stages (CCE)
-
Reddy et al., 2006
1.24 g/L Zn
2.63
6
0.1M EDTA
ZnO
Present study
4.28 g/L Cd
5.26
6
1M HNO3
A/O = 1/1, two stages (CCE) A/O = 3/2, two stages (CCE)
CdO
Present study
Cyanex 302
2.
Cyanex 272
0.032
Kerosene
0.604 g/L Zn
3.46
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3.
Cyanex 272
0.63
Escaid 110
18.96 g/L Zn
2.17
15
4.
Cyanex 272
0.3
Kerosene
6.50 g/L Zn
3.02
5.
Cyanex 923
0.1
Hexane
2.9 g/L Zn
2.26
6.
60%Saponified D2EHPA
0.6
Kerosene+ 5% isodecanol
7.312 g/L Cd
9.23
7.
Cyanex 923
0.6
Kerosene
6.27 g/L Cd
8.
Cyanex 923
0.6
Kerosene
6.27 g/L Cd
9.
TBP
3.62 (Pure)
-
16.1 g/L Cd
10.
Cyanex 301
0.06
Kerosene
11.
Cyphos IL 104
0.05
Toluene
0.2
Toluene
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Extractant
Metal ion in feed
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S. No
Note: BE = batch extraction, CE = cross current extraction, CCE = counter current extraction, # both parameters are in mol/L
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Biswas et al., 2016
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4. CONCLUSION The results of present study show that Cyphos IL 104 is a promising extractant for the recovery of metal values from spent Zn-C and Ni-Cd batteries. Quantitative recovery (>99.9%) of metal
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ions has been achieved in two or three counter current extraction and stripping stages using simple stripping agents. Moreover, zinc and cadmium have been recovered as useful nanosized oxides which have many applications in electronics besides being used as a photo catalyst for
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degradation of pollutants. Recyclability of the used Cyphos IL 104 for the recovery of Zn and Cd from battery waste in successive cycles suggests economic viability of the proposed method for
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commercial use. The metal values recovered from spent batteries in solution form are pure and will help to meet the demand of high grade metals in various industries. The study proposes a simple, convenient and efficient method for the recycling of spent batteries and assumes significance in view of waste management.
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ACKNOWLEDGEMENTS
The authors are thankful to Cytec Inc., Netherlands for providing Cyphos IL 104 as gift sample. Ministry of Human Resources and Development (MHRD) and Council of Scientific & Industrial
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Research (CSIR), New Delhi, India are gratefully acknowledged for providing financial support.
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REFERENCES Agrawal, A., Pathak, P., Mishra, D., Sahu, K.K., 2012. Solvent mediated interactions for the selective recovery of cadmium from Ni–Cd battery waste. J. Mol. Liq. 173, 77–84.
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Baba, A.A., Adekola, A.F., Bale R.B., 2009. Development of a combined pyro- and hydrometallurgical route to treat spent zinc–carbon batteries. J. Hazard. Mater. 171, 838-844.
Barik, S.P., Prabaharan, G., Kumar, L., 2017. Leaching and separation of Co and Mn from
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electrode materials of spent lithium-ion batteries using hydrochloric acid: Laboratory and pilot scale study. J. Clean Prod. 147, 37-43.
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Belardi, G., Lavecchia, R., Medici, F., Piga, L., 2012. Thermal treatment for recovery of manganese and zinc from zinc–carbon and alkaline spent batteries. Waste Manage. 32, 1945– 1951.
Belardi, G., Medici, F., Piga, L., 2014. Influence of gaseous atmosphere during a thermal process
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for recovery of manganese and zinc from spent batteries. J. Power Sources 248, 1290-1298. Biswas, R.K., Habib, M.A., Karmakar, A.K., Tanzin, S., 2016. Recovery of manganese and zinc from waste Zn-C cell powder: mutual separation of Mn(II) and Zn(II) from leach liquor by
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solvent extraction technique. Waste Manage. 51, 149-156. Chen, X., Chen, Y., Zhou, T., Liu, D., Hu, H., Fan S., 2015. Hydrometallurgical recovery of
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metal values from sulfuric acid leaching liquor of spent lithium-ion batteries. Waste Manage. 38, 349-356.
Deep, A., Kumar, K., Kumar, P., Kumar, P., Sharma, A.L., Gupta, B., Bharadwaj, L.M., 2011. Recovery of pure ZnO nanoparticles from spent Zn-MnO2 alkaline batteries. Environ. Sci. Technol. 45, 10551-10556. Deep, A., Sharma, A.L., Mohanta, G.C., Kumar, P., Kim, K.A., 2016. Facile chemical route
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for recovery of high quality zinc oxide nanoparticles from spent alkaline batteries. Waste Manage. 51, 190-195. EBRA, 2012. Noticeable growth of the quantity of batteries recycled by EBRA members.
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http://www.ebra-recycling.org.
Falco, L., Quina, M.J., Gando-Ferreira L.M., Thomas H., Curutchet G., 2014. Solvent extraction studies for separation of Zn(II) and Mn(II) from spent batteries leach solutions. Sep. Sci.
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Technol. 49, 398-409.
Fernandes, A., Afonso, J.C., Dutra, A.J.B., 2012. Hydrometallurgical route to recover nickel,
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cobalt and cadmium from spent Ni-Cd batteries. J. Power Sources 220, 286-291. Gaur U.K., Kumar A., Varma G. D., 2014. The synthesis of self-assembled polycrystalline 1-D CuO nanostructures in aqueous medium and a study of their multifunctional features. Cryst. Eng. Comm. 16, 3005-3014.
press, Florida.
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Gupta C.K., Mukherjee T.K., 1990a. Hydrometallurgy in extraction processes, Volume I, CRC
Gupta C.K., Mukherjee T.K., 1990b. Hydrometallurgy in extraction processes, Volume II, CRC
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press, Florida.
Huang, K., Li, J., Xu, Z., 2010. Characterization and recycling of cadmium from waste nickel–
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cadmium batteries. Waste Manage. 30, 2292-2298. Jha, M.K., Kumari, A., Jha, A.K., Kumar, V., Hait, J., Pandey, B.D., 2013. Recovery of lithium and cobalt from waste lithium ion batteries of mobile phone. Waste Manage. 33, 1890-1897. Kumari A., Sinha M.K., Sahu S.K., Pandey B.D., 2016. Solvent extraction and separation of trivalent lanthanides using Cyphos IL 104, a novel phosphonium ionic liquid as extractant. Solvent Extr. Ion Exch. 34, 469-484.
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Khayati, G.R., Dalvand, H., Darezereshki, E., Irannejad, A., 2014. A facile method to synthesis of CdO nanoparticles from spent Ni–Cd batteries. Mater. Lett. 115, 272-274.
metal hydride battery recycling. Green Chem. 16, 4595-4603.
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Larsson, K., Binnemans, K., 2014. Selective extraction of metals using ionic liquids for nickel
Li, L., Xu, S., Ju, Z., Wu, F., 2009. Recovery of Ni, Co and rare earths from spent Ni–metal hydride batteries and preparation of spherical Ni(OH)2. Hydrometallurgy 100, 41–46.
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Mahandra, H., Singh, R., Gupta, B., 2017. Liquid-liquid extraction studies on Zn(II) and Cd(II) using phosphonium ionic liquid (Cyphos IL 104) and recovery of zinc from
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zinc plating mud. Sep. Purif. Technol. 177, 281-292.
Makanyire, T., Sanchez-Segado, S., Jha, A., 2016. Separation and recovery of critical metal ions using ionic liquids. Adv. Manuf. 4, 33-46.
Meshram, P., Somani, H., Pandey, B.D., Mankhand, T.R., Deveci H., Abhilash, 2017. Two stage
Prod. 157, 322-332.
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leaching process for selective metal extraction from spent nickel metal hydride batteries. J. Clean
Provazi, K., Campos, B.A., Espinosa, D.C.R., Tenório, J.A.S., 2011. Metal separation from
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mixed types of batteries using selective precipitation and liquid–liquid extraction techniques. Waste Manage. 31, 59-64.
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Rajesh, D., Lakshmi, B.V., Sunandana, C.S., 2012. Two-step synthesis and characterization of ZnO nanoparticles. Physica B 407, 4537-4539. Reddy B.R., Priya D.N., 2006. Chloride leaching and solvent extraction of cadmium, cobalt and nickel from spent nickel–cadmium, batteries using Cyanex 923 and 272. J. Power Sources161, 1428-1434.
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Reddy B.R., Priya D.N., Park K.H., 2006. Separation and recovery of cadmium(II), cobalt(II) and nickel(II) from sulphate leach liquors of spent Ni–Cd batteries using phosphorus based extractants. Sep. Purif. Technol. 50, 161-166.
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Reddy B.R., Priya D.N., Rao S.V., Radhika P., 2005. Solvent extraction and separation of Cd(II), Ni(II) and Co(II) from chloride leach liquors of spent Ni–Cd batteries using commercial organophosphorus extractants. Hydrometallurgy 50, 161-166.
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Reddy, S., Swamy, B.E.K., Chandra, U., Sherigara, B.S., Jayadevappa, H., 2010. Synthesis of CdO nanoparticles and their modified carbon paste electrode for determination of dopamine and
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ascorbic acid by using cyclic voltammetry technique. Int. J. Electrochem. Sci. 5, 10-17. Regel-Rosocka, M., 2009. Extractive removal of zinc(II) from chloride liquors with phosphonium ionic liquids/toluene mixtures as novel extractants. Sep. Purif. Technol. 66, 19-24. Ritcey G.M., Ashbrook A.W., 1984. Solvent extraction: principles and applications to process
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metallurgy, Part I, Elsevier, Netherlands.
Rout, A., Binnemans, K., 2014. Liquid–liquid extraction of europium(III) and other trivalent rare-earth ions using a non-fluorinated functionalized ionic liquid. Dalton Trans. 43, 1862-1872.
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Salgado, A.L., Veloso, A.M.O., Pereira, D.D., Gontijo, G.S., Salum, A., Mansur, M.B., 2003. Recovery of zinc and manganese from spent alkaline batteries by liquid–liquid extraction with
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Cyanex 272. J. Power Sources 115, 367-373. Sayilgan, E., Kukrer, T., Civelekoglu, G., Ferella, F., Akcil, A., Veglio, F., Kitis, M., 2009. A review of technologies for the recovery of metals from spent alkaline and zinc–carbon batteries. Hydrometallurgy 97, 158-166.
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Figure Captions Figure 1. Effect of Cyphos IL 104 concentration on the extraction of metals from leach liquors (a) Zn-C leach liquor [ZC1]; [Cyphos IL 104] = 8×10-3 to 0.1 mol/L (b) Ni-Cd leach liquor [NC]; [Cyphos IL 104] = 4×10-2 to 0.22 mol/L
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Figure 2. McCabe−Thiele diagrams for (a) [ZC1] leach liquor. (b) [NC] leach liquor at A/O = 1/5 to 5/1. (a) Organic phase = 0.05 mol/L Cyphos IL 104; aqueous phase = 1.240 g/L Zn, 2.442 g/L Mn in 0.5 mol/L HCl. (b) Organic phase = 0.2 mol/L Cyphos IL 104, aqueous phase = 4.280 g/L Cd, 89.60×10-3 g/L Ni, 148.2×10-3 g/L Fe, 3.765×10-3 g/L Co in 0.1 mol/L HCl
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Figure 3. (a) Effect of EDTA concentrations on the stripping of Zn. Loaded organic phase [LO] = 1.240 g/L Zn; aqueous phase = 0.01-0.5 mol/L EDTA, O/A = 1/1. (b) McCabe−Thiele diagram for Zn stripping at O/A = 1/5 to 5/1. Loaded organic phase [LO] = 1.240 g/L Zn; aqueous phase = 0.1 mol/L EDTA Figure 4. (a) Effect of HNO3 concentrations on the stripping of Cd. Loaded organic phase [LO] = 6.419 g/L Cd; aqueous phase = 0.5-2.0 mol/L HNO3, O/A = 1/1. (b) McCabe−Thiele diagram for Cd stripping at O/A = 1/5 to 5/1. Loaded organic phase [LO] = 6.419 g/L Cd; aqueous phase = 1.0 mol/L HNO3
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Figure 5. Flowsheet for the recovery of zinc and cadmium from chloride leach liquor of spent batteries Figure 6. XRD patterns of (a) Zinc oxide; (b) Cadmium oxide
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Figure 7. FE-SEM images of Zinc oxide (a) and (b); Cadmium oxide (c) and (d) Figure 8. Particle size distribution of (a) Zinc oxide; (b) Cadmium oxide
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Figure 9. EDX images of (a) Zinc oxide; (b) Cadmium oxide
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Highlights Using Cyphos IL 104 quantitative recovery of Zn/Cd from spent batteries achieved More than 98% leaching efficiency observed for Zn/Cd using HCl as strippant
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Pure ZnO and CdO nanoparticles obtained from loaded organic phase
Spent organic phase is recyclable with negligible loss in extractability
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Reusability reduces waste production and cost of the process
S0959-6526(17)32429-0
DOI:
10.1016/j.jclepro.2017.10.129
Reference:
JCLP 10921
To appear in:
Journal of Cleaner Production
Received Date: 17 May 2017 Revised Date:
11 October 2017
Accepted Date: 11 October 2017
Please cite this article as: Mahandra H, Singh R, Gupta B, Recycling of Zn-C and Ni-Cd spent batteries using Cyphos IL 104 via hydrometallurgical route, Journal of Cleaner Production (2017), doi: 10.1016/ j.jclepro.2017.10.129. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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GRAPHICAL ABSTRACT
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Recycling of Zn-C and Ni-Cd spent batteries using Cyphos IL 104 via hydrometallurgical route
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Harshit Mahandra, Rashmi Singh and Bina Gupta* Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee -247667,
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Uttrakhand, India
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*Author for correspondence Prof. Bina Gupta Department of Chemistry Indian Institute of Technology Roorkee Roorkee- 247667 (U.K.), India [email protected] Phone: +91-1332-285326 (off.) Fax: +91-1332-273560
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ABSTRACT The study suggests hydrometallurgical routes for the recovery of zinc and cadmium from spent battery leachates using a novel extractant Cyphos IL 104 diluted in toluene and synthesis of zinc
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and cadmium oxides from the loaded organic phases. Leaching is carried out using 5 mol/L HCl and the composition of the leach liquors obtained from Zn-C and Ni-Cd spent batteries in g/L is Zn- 2.400, Mn - 4.870, Fe - 2.655×10-3, and Cd- 4.280, Ni- 89.60×10-3, Fe- 148.2×10-3, Co-
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3.765×10-3, respectively. McCabe Thiele diagrams are drawn to determine the number of theoretical stages required for the quantitative extraction and stripping of zinc and cadmium and
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the data has been confirmed by counter current simulation studies. McCabe Thiele diagrams indicate two extraction stages for both zinc and cadmium at A/O = 1/1 and A/O = 3/2, respectively. EDTA (0.1 mol/L) and HNO3 (1.0 mol/L) are used as strippant for zinc and cadmium, respectively. Quantitative stripping of zinc and cadmium requires two and three
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counter current stripping stages, respectively at O/A = 1/1. Results of counter current extraction and stripping show quantitative recovery (> 99%) of zinc and cadmium with high purity. Zinc and cadmium oxides have been synthesized from the loaded organic phase using precipitation
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followed by thermal decomposition of precursors at 400oC. Synthesized materials were characterized by XRD, FE-SEM and EDX techniques. Zinc and cadmium oxide particles
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correspond to hexagonal zincite and cubic monteponite structures, respectively. The average particle size of zinc and cadmium oxides is 43±13 nm and 55±14 nm, respectively. The morphology of zinc and cadmium oxide particles is considered to be globular with particle agglomeration. The proposed methods are selective for zinc and cadmium. Results of present study have been compared with the reported data. Keywords: Cyphos IL 104, McCabe-Thiele Diagrams, Ni-Cd batteries, Zn-C batteries
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1. INTRODUCTION Consumption of batteries in different electronic devices such as laptops, cell phones, watches, toys, calculators, cameras, recorders, remote controls, has increased enormously.
These
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batteries, at the end of their lifecycle are discarded generating a huge amount of waste which leads to environmental and economical issues. Tons of battery waste are generated every year all over the globe and require appropriate management. In view of environmental hazard, proper
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disposal of e-waste is very important which may involve landfill deposition, stabilization by incineration and recycling processes (Agrawal et al., 2012). Large volumes of waste generated,
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make landfill deposition expensive due to limited storage capacity of dumpsites. Incineration of waste batteries releases toxins such as mercury, cadmium and dioxins to the atmosphere and is therefore restricted by environmental legislation (Provazi et al., 2011). Recycling of spentbatteries is the best way to solve environmental and economical issues benefiting the future
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generations. 26660 tons of Zn batteries and 6632 tons of Ni-Cd batteries were recycled in 2012 by members of European Battery Recycling Association (EBRA. 2012). A number of pyrometallurgical and hydrometallurgical methods have been reported to recover metal values
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from different types of spent batteries such as Zn-C (Belardi et al., 2012, 2014; Sayilgan et al., 2009), Ni-Cd (Agrawal et al., 2012; Huang et al., 2010), lithium ion (Barik et al., 2017; Chen et
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al., 2015; Jha et al., 2013) and Ni-metal hydride (Larsson and Binnemans, 2014; Li et al., 2009; Meshram et al., 2017). Pyrometallurgical methods include traditional high temperature processes of roasting, smelting and refining. These methods are high energy consuming, less versatile, suitable for high grade ores/materials and emit waste gases which may be toxic many times and thus require dust collecting/ gas cleaning systems (Gupta and Mukherjee, 1990a; Sayilgan et al., 2009). The solid waste generated as molten slag and matte is difficult to handle.
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Hydrometallurgical methods, on the other hand, are based on chemical reactions involving aqueous and organic solutions in the temperature range of 25 to 250oC. Separation of chemically similar metals is easily achieved and the methods are suitable for the processing of complex
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ores/materials and for the production of various by products. Hydrometallurgical methods are comparatively efficient, low cost, metal selective and cause no air pollution (Sayilgan et al., 2009).
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Several hydrometallurgical routes employing different extractants have been explored by various research groups for the recovery of zinc and cadmium from waste batteries. Acidic
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organophosphorous extractants such as DEHPA, di-(2-ethylhexyl) phosphoric acid (Agarwal et al., 2012; Falco et al., 2014), Cyanex 272, bis(2,4,4-trimethylpentyl) phosphinic acid (Baba et al.,
2009;
Falco
et
al.,
2014;
Salgado
et
al.,
2003),
Cyanex
301,
bis(2,4,4-
trimethylpentyl)dithiophosphinic acid (Reddy et al., 2006) and Cyanex 302, bis(2,4,4-
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trimethylpentyl)monothiophosphinic acid (Biswas et al., 2016) have been attempted to recover zinc and cadmium from Zn-C, Zn-MnO2 alkaline and Ni-Cd batteries. These extractants have been used solo or with a modifier (Agarwal et al., 2012). A few solvating organophosphorous
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extractants such as Cyanex 923, a mixture of trialkylphosphine oxides (Deep et al., 2011, 2016; Reddy and Priya, 2006; Reddy et al., 2005) and TBP, Tributyl phosphate (Fernandes et al., 2012)
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have also been explored for the recovery of zinc and cadmium from spent batteries. Recently, imidazolium, ammonium and phosphonium based ionic liquids have been investigated for the extraction of various metal ions. These ionic liquids are better than conventional extractants as they do not release H+ ions into the raffinate and therefore neutralization of released acid is not required (Kumari et al., 2016). Loss of imidazolium cation to the aqueous phase during extraction is a major drawback, making the imidazole-based ionic liquids
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unsuitable for an environment-friendly process. Ammonium based ionic liquids have limitations of hydrophobicity and low thermal stability. These drawbacks are overcome in phosphonium ionic liquids which are gaining attention of separation chemists.
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Phosphonium ionic liquids have emerged as potential extractants due to their unique properties such as non-volatility, nonflammablity, low vapour pressure, high thermal and chemical stability, good extraction power for metal ions and good recycling capacity (Makanyire et al., 2016;
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Regel-Rosocka, 2009; Rout and Binnemans, 2014). Among these Cyphos IL 104 (trihexyl(tetradecyl)-phosphonium bis(2,4,4-trimethylpentyl) phosphinate) was found to be an
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efficient extractant for zinc and cadmium (Mahandra et al., 2017).
In the present work, Cyphos IL 104 has been explored for the first time for the recovery of zinc and cadmium from spent Zn-C and Ni-Cd batteries via solvent extraction route. The study focuses on the recovery of pure zinc and cadmium in solution form as well as zinc and cadmium
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oxides from the loaded organic phases. McCabe Thiele diagrams and counter current simulation studies were carried out for the extraction and stripping of zinc and cadmium from spent batteries leach liquors. Nanosized ZnO and CdO particles were characterized by X-ray
EP
diffraction spectroscopy (XRD), Field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDX). The recovered pure zinc and cadmium oxide
AC C
nanoparticles may find applications in gas sensors, optical waveguides, photodiodes, photonic crystals, transparent conductive films/electrodes, light-emitting devices and solar cells etc. 2. EXPERIMENTAL
2.1 Reagents and chemicals All the reagents and chemicals used were of analytical grade. Cyphos IL 104 was received from Cytec Inc., Netherlands and used as such without any further purification. Toluene was used as a
5
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diluent to get Cyphos IL 104 solution of desired concentration. Eveready AA type Zn-C and Envie AA type Ni-Cd spent batteries were procured from local market. 2.2 Equipments
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A flask shaker with wrist action (Perfit) was used for equilibrating aqueous and organic phases. Atomic Absorption Spectrometer (AAS) (AAnalyst 800, Perkin Elmer, Germany) was used to determine the metal contents in the aqueous phases. Synthesized metal oxides were characterized
SC
through powder X-ray diffraction (XRD) using Bruker AXS D8 diffractometer employing CuKα radiation (λ= 1.5418 Å). Surface morphology and particle size were studied with a field
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emission scanning electron microscope (FESEM-Carl Zeiss ULTRA plus55) operating at 15kV. The particle size was measured using Image J software. Elemental compositions of the nanoparticles were determined using EDX (Energy-dispersive X-ray spectrometer) equipment attached to the FE-SEM microscope.
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2.3 Dismantling, digestion and leaching of spent batteries 2.3.1 Zinc-carbon spent batteries
Spent batteries were dismantled and the black powder was separated and dried in an oven at
EP
800C for 24 hours. Dried powder was then sieved through 75 µm sieve to obtain a fine black
AC C
powder. For digestion, 1.0 g black powder was heated with 20 mL aqua-regia up to boiling for 30 minutes, cooled and filtered (Deep et al., 2011). Filtrate and washings were collected and then appropriately diluted with ultrapure water. Metal contents of digested sample were analyzed using AAS (Table 1).
Leaching was performed by heating 2.5 g of the black powder with 25 mL of 5.0 mol/L HCl for 1 hour at 700C (Deep et al., 2011). The contents were cooled, filtered and diluted to 100 mL maintaining the acidity at 0.5 mol/L HCl and named as [ZC]. Concentrations of different metal 6
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ions in leach liquor [ZC] were checked by AAS (Table 1). For extraction studies, the leach liquor [ZC] was diluted two times maintaining acidity at 0.5 mol/L HCl and designated as [ZC1].
Zinc
Concentration in digested liquor (g/ L) 2.420± 0.050
Manganese 5.066 ± 0.010
Concentration in electrode powder (g/kg)
Concentration in leached liquor (g/ L)
96.8 ± 2.4
2.400±0.030
202.7 ± 0.2
4.870±0.040
Amount leached from electrode powder (g/kg) 96.0 ± 2.6
SC
Metals analysed
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Table 1. Concentrations of metals in digest and leach liquor [ZC] of spent Zn-C batteries
99.2
194.8 ± 1.6
96.1
0.106 ± 0.008
50.3
(5.275± 0.050) × 10-3
0.211± 0.013
Nickel
(0.110 ± 0.003)× 10-3
0.0025±0.0003
ND
-
-
Cadmium
(0.062±0.001)×10-3
0.0044±0.0012
ND
-
-
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Iron
Note- ND = Not Detected
(2.655±0.020)×10-3
Leaching efficiency (%)
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2.3.2 Nickel-Cadmium batteries
Spent Ni-Cd batteries were dismantled manually and cell components were collected separately.
EP
In order to extract the active electrode material, polymeric separators around the electrodes were removed. The active anode material was scrapped from the steel mesh, dried at 800C for 24 hours
AC C
and sieved through 75 µm sieve to obtain a fine grey colored powder. Digestion of the active anode material was done following the method used for Zn-C spent batteries and the metal contents of digested sample were checked by AAS (Table 2). Leaching of the active anode material was done as follows: 1.0 g of the sample was added to 15 mL of 5 mol/L HCl and heated to boil for 1 hour at 700C, cooled, filtered and residue was washed with ultrapure water (Deep et al., 2011). The filtrate and washings were collected and diluted to prepare 100 mL of
7
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leach liquor maintaining acidity at 0.1 mol/L HCl and designated as [NC]. Concentrations of different metal ions in leach liquor of active anode material were assayed by AAS (Table2).
batteries
Concentration in digested liquor (g/L)
Concentration in Concentration of electrode metal in leached powder (g/kg) liquor (g/L)
Cadmium
4.348±0.008
434.8 ± 1.0
4.280±0.020
Nickel
(89.94±0.04)×10-3
8.99 ± 0.004
Iron
(148.4±0.2)×10-3
14.84 ± 0.02
Cobalt
(3.969±0.020)×10-3
0.397 ± 0.0002
Leaching Efficiency (%) 98.4
(89.60±0.46)×10-3
8.96 ± 0.05
99.6
(148.2±0.4)×10-3
14.82 ± 0.4
99.9
(3.765±0.080)×10-3
0.377 ± 0.008
94.9
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428.0 ± 2.0
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2.4 Partition studies
Amount leached from electrode powder (g/kg)
SC
Metals analysed
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Table 2. Concentrations of metals in digest and leach liquor [NC] processed from Ni-Cd spent
An aliquot of leach liquor and the extractant solution (Cyphos IL 104 in toluene) at different phase ratios (depending upon experimental conditions) were equilibrated for 6 minutes
EP
(Mahandra et al., 2017) at room temperature (25±3oC). After phase separation, the concentrations of metal ions in aqueous phase were checked by AAS and the percentage of metal
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transferred to the organic phase was calculated by mass balance calculations. The coefficient of variance for extraction and stripping data is ±5%. 2.5 Construction of McCabe-Thiele diagrams McCabe Thiele diagrams are required to design a solvent extraction circuit and to predict its performance. In order to construct a McCabe Thiele diagram, an extraction isotherm is generated (Gupta and Mukherjee, 1990b; Ritcey and Ashbrook, 1984). Leach liquor containing 1.240 g/L 8
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zinc in 0.5 mol/L HCl [ZC1] was equilibrated with 0.05 mol/L Cyphos IL 104 at A/O ratios varying from 1/5 to 5/1 keeping the total volume of phases constant. Similarly, leach liquor containing 4.280 g/L cadmium in 0.1 mol/L HCl [NC] was equilibrated with 0.2 mol/L Cyphos
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IL 104 at A/O ratios varying from 1/5 to 5/1. To construct Mc-Cabe Thiele diagrams, plots were drawn between metal concentrations in the organic phase and in raffinate at different A/O ratios. Operating lines for phase ratios A/O = 1/1 and A/O = 3/2 were drawn considering the metal
SC
content in raffinate and loaded organic phase at the said phase ratios. The slope of the operating line defines aqueous to organic phase ratio. A vertical line on x-axis was drawn from the aqueous
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feed concentration which intersects the operating line at a particular point. From this point, a horizontal line is drawn to intersect the extraction isotherm. From intersection point a perpendicular is drawn on the operating line and from this point again a horizontal line is drawn on the extraction isotherm and so on till it reaches to zero. Now the number of triangles
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generated along with the operating line indicates the number of stages for counter current extraction for quantitative extraction of the metal ion from aqueous feed. Phase ratio is selected on the basis of number of stages and loading factor of the extractant. McCabe Thiele diagrams
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for stripping were also constructed in the same way except that now organic/aqueous phase ratio
AC C
(O/A) was considered and the axes of isotherm plots were reversed. 2.6 Synthesis of zinc and cadmium oxides Equal volumes of 0.2 mol/L Cyphos IL 104 and leach liquor [ZC]/[NC] were equilibrated for 6 minutes at room temperature. Both the phases were allowed to separate and the loaded organic phase was again contacted with fresh leach liquor. The process was repeated four times to obtain zinc/cadmium enriched organic phase. Zinc/cadmium enriched organic phase was then scrubbed with 1.0 mol/L HCl to remove coextracted metal impurities if any. 9
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To the scrubbed zinc enriched organic phase, equal volume of 0.2 mol/L oxalic acid solution was added drop wise and the resulting mixture was stirred for two hours at room temperature. White precipitates thus obtained, were centrifuged at 2500 rpm and the spent organic phase was
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decanted and collected. The precipitates obtained were washed with methanol and dried in an oven at 600C for two hours. The resulting product was grinded in an agate mortar for 30 min at room temperature and zinc oxide was obtained by its thermal decomposition at 4000C for 3 hours
SC
(Rajesh et al., 2012).
For cadmium oxide, equal volume of 1.0 mol/L NaOH solution was added drop wise to the
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scrubbed cadmium enriched organic phase on a magnetic stirrer at 1200 rpm stirring speed. White precipitates thus obtained at the interface of both the phases were centrifuged at 2500 rpm and washed with ethanol. The precipitates thus obtained were dried in an oven at 800C for one hour. Dried precipitates were calcinated at 4000C for three and half hours to give cadmium oxide
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(Reddy et al., 2010).
The spent organic phases remaining after centrifugation of the precipitates were washed with water and reused for the extraction of zinc and cadmium from fresh leach liquor [ZC] and [NC],
EP
respectively. In both the cases, quantitative extraction of the respective metal ion was achieved without any significant decrease in extraction efficiency. This indicates that the extractant can be
AC C
reused in further cycles. A rough estimate of the process cost (provided in supplementary information) suggests that proposed methods for the recovery of zinc and cadmium as ZnO and CdO nanoparticles from spent batteries are economical.
10
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3. RESULTS AND DISCUSSION 3.1 Effect of Cyphos IL 104 concentration
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An aliquot of leach liquor was equilibrated with equal volume of organic phase containing varying concentrations of Cyphos IL 104 (0.008-0.1 mol/L for [ZC1] and 0.04-0.22 mol/L for [NC]) at a fixed and predetermined acidity (Mahandra et al., 2017). In case of Zn-C battery,
SC
extraction of zinc was quantitative from 0.05 mol/L extractant onwards and manganese showed negligible extraction in the entire investigated range of extractant concentration (Figure 1a). In
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case of Ni-Cd battery, quantitative extraction of cadmium was achieved at 0.2 mol/L Cyphos IL104 where around 17% iron was coextracted (Figure 1b). Extraction of Co and Ni was negligible in the investigated range of Cyphos IL 104 concentration. In all further studies, extraction of iron was minimized by adding 20-fold molar excess of ascorbic acid to the leach
100 90 80
50
EP
%E
60
40 30 20
AC C
10 0.02
0.04
0.06
100 90
Fe Co Ni Cd
80
Mn Zn
70
0 0.00
(b)
70 60
%E
(a)
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liquor prior to extraction (Mahandra et al., 2017).
50 40 30 20 10 0
0.08
0.10
0.04
[Cyphos IL 104],mol/L
0.08
0.12
0.16
0.20
0.24
[Cyphos IL 104], mol/L
Figure 1
Based on the results, all further studies with Zn-C battery leach liquor [ZC1] were carried out using 0.05 mol/L Cyphos IL 104 and with Ni-Cd battery leach liquor [NC] using 0.2 mol/L Cyphos IL 104. 11
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3.2 McCabe−Thiele Diagrams 3.2.1 McCabe-Thiele diagrams and countercurrent extraction simulations
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Extraction isotherms and McCabe-Thiele diagrams for zinc [ZC1] and cadmium [NC] are presented in Figure 2(a) and 2(b), respectively. It is clear from the plots that in case of zinc at A/O = 1/1 two theoretical extraction stages are required for quantitative extraction of zinc and
SC
phase ratio of 3/2 is not acceptable because the feed concentration exceeds the loading factor of the organic phase (Figure 2a). Therefore, A/O = 1/1 with two extraction stages was selected for
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zinc extraction. However, in case of cadmium, phase ratio of 3/2 with two stages was selected as A/O = 1/1 leads to single stage extraction i.e. inefficient use of extractant (Figure 2b).
A/O= 3/2
1.2
A/O= 3/3
No. of stages =2
1.0 0.8 0.6 A/O=2/4
/2 =3 O / A =1/1 A/O
0.4 0.2 A/O=1/5 0.2
0.4
0.6
0.8
AC C
0.0 0.0
EP
[Zn]org, g/L
1.4
1.0
A/O = 4/2
7
A/O = 5/1
A/O = 3/2
No. of stages = 2
6
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1.6
(b)
Cd in Feed Solution = 4.280 g/L
A/O= 5/1
A/O= 4/2
5 4 A/O = 3/3 No. of stages = 1
,
1.8
[Cd]org g/L
2.0
Zn in Feed Solution = 1.240 g/L
(a)
3 2 A/O = 2/4
/2 =3 O / A
1 = 1/ A/O
1 A/O = 1/5 0
1.2
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
,
[Cd]aq g/L
[Zn]aq, g/L
Figure 2
Based on the data obtained from McCabe−Thiele diagrams two stage counter current extraction simulations (CCES) were performed at A/O = 1/1 for zinc [ZC1] and A/O = 3/2 for cadmium [NC]. CCES test carried out for [ZC1] resulted in a raffinate containing 0.06×10-3 g/L of zinc corresponding to >99.9% extraction of zinc (Table 3). Co-extraction of Mn(II) was negligible. 12
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Table 3. Results of the two stage countercurrent extraction simulation for recovery of zinc Metal concentration (g/L) Zn
Mn
1.240
2.442
~1.240
-
0.06×10-3
2.442
Feed[ZC1] Loaded Organic phase
1/1
Zn
Mn
>99.9
-
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Raffinate
Extraction efficiency(%)
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A/O phase ratio
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Stream
Results of CCES for [NC] showed 0.5×10-3 g/L cadmium in the raffinate which corresponds to >99.9% extraction of cadmium. Major portions of nickel, cobalt and iron remained in the raffinate and their co-extraction with cadmium was less than 1.0%. The results are shown in
Metal concentration (g/L)
Loaded Organic phase Raffinate
3/2
Extraction efficiency (%)
Cd
Ni
Fe
Co
4.280
89.6×10-3
0.1482
3.765×10-3
6.419
0.15×10-3
-
0.047×10-3
0.5×10-3
89.5×10-3
0.1482
3.734×10-3
AC C
Feed[NC]
A/O Phase ratio
EP
Stream
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Table 4. Results of the two stage counter-current extraction simulation for recovery of cadmium
13
Cd
Ni
Fe
Co
>99.9
0.1
-
0.82
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Table 4. As mentioned in section 3.1, excess of ascorbic acid was added to the leach liquor [NC] before extraction to suppress the extraction of iron.
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3.2.2 McCabe-Thiele diagrams and countercurrent stripping simulations McCabe Thiele diagrams were constructed to investigate the number of theoretical stages required for quantitative stripping of zinc and cadmium from the respective loaded organic
SC
phase. EDTA and HNO3 were used for the stripping of zinc and cadmium, respectively (Mahandra et al., 2017). The loaded organic phase, obtained in two stage counter current
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extraction of zinc, was equilibrated for 5 minutes with different concentrations of EDTA (0.010.5 mol/L) at O/A = 1/1 (Figure 3a) and 0.1 mol/L EDTA was selected for further studies.
(a)
(b) 5
100
O/A=5/1
90
60 50
30 0.0
0.1
EP
40
0.2
0.3
0.4
3
O/A=4/2
2
No. of stages =3 O/A=3/3
1
No. of stages =2 O/A=1/1 O/A= 2/4 /A=3/2 O O/A=5/1
0 0.0
0.5
[EDTA], mol/L
AC C
Zn in LO = 1.240 g/L
70
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% Stripping
80
[Zn]aq, g/L
4
0.2
0.4
0.6
0.8
1.0
1.2
[Zn]org, g/L
Figure 3
For stripping isotherm, the loaded organic phase was equilibrated with 0.1 mol/L EDTA at O/A varying from 1/5 to 5/1, maintaining the total volume constant. McCabe-Thiele diagram was drawn which shows that two stages are required at O/A = 1/1 for complete stripping of zinc and three stages at O/A = 3/2. Therefore, O/A = 1/1 with two stages was selected for the stripping of
14
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zinc (Figure 3b). To confirm the stripping isotherm prediction data, a two-stage counter current stripping simulation (CCSS) was carried out at O/A = 1/1. A solution containing 1.237 g/L zinc corresponding to 99.8% stripping efficiency was obtained.
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For cadmium, the loaded organic phase obtained in two stage counter current extraction was equilibrated for 5 minutes with different concentrations of HNO3 (0.5-2.0 mol/L) at O/A = 1/1 and 1.0 mol/L HNO3 was selected for further studies (Figure 4a). McCabe Thiele diagram
SC
constructed (Figure 4b) for the stripping of cadmium showed that three stages are required for quantitative stripping of cadmium at O/A = 1/1 and four stages at O/A = 3/2. Therefore, O/A =
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1/1 with three stages was selected for further studies and three stage CCSS test was performed at O/A = 1/1 using 1.0 mol/L HNO3.
(b) 12
100 90
50
40 30
1.0
1.5
AC C
0.5
Cd in LO = 6.419 g/L
60
[Cd]aq, g/L
70
No. of stages = 4
O/A = 4/2
8
EP
% Stripping
80
0.0
O/A = 5/1
10
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(a)
6
No. of stages = 3
O/A = 3/3
4 O/A = 2/4
2 =3/ O/A=1 O/A
2 O/A = 1/5
0
2.0
0
[HNO3], mol/L
1
2
3
4
5
6
[Cd]org, g/L
Figure 4
The strip solutions and spent organic phases were collected and combined. Combined strip solution contains 6.412 g/L Cd corresponding to a stripping efficiency of 99.9%. The spent organic phases obtained after stripping of zinc and cadmium respectively can be reused for the extraction of zinc/cadmium after washing with water (Mahandra et al., 2017). 15
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Complete process for the recovery of zinc and cadmium from spent batteries leach liquor is
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described in flowsheet in Figure 5.
Spent battery leach liquors
[ZC1]
[NC]
SC
addition of ascorbic acid
Extraction with 0.20 mol/L Cyphos IL 104 A/O = 3/2, 2 stages
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Extraction with 0.05 mol/L Cyphos IL 104 A/O = 1/1, 2 stages
Loaded Organic phase (Zn)
Raffinate (Mn)
Stripping with 1.0 mol/L HNO3 O/A = 1/1, 3 stages
EP
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Stripping with 0.1 mol/L EDTA O/A = 1/1, 2 stages
Loaded Organic phase (Cd)
Spent organic phase Strip solution Spent organic phase (Cyphos IL 104) (Zn) (Cyphos IL 104)
AC C
Washing with water
Ready to reuse
Washing with water
Ready to reuse
Figure 5
16
Strip solution (Cd)
Raffinate (Fe, Co, Ni)
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3.3 Characterization of zinc and cadmium oxides 3.3.1 XRD analysis Figure 6 shows XRD patterns of the zinc and cadmium oxide particles obtained from calcination
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of precursors at 4000C. XRD pattern of synthesized ZnO (Figure 6a) is indexed to the hexagonal zincite crystalline phase with lattice parameters a = b = 3.2855Å, c = 5.2616Å (JCPDS card number: 36-1451). XRD of synthesized CdO (Figure 6b) corresponds to cubic monteponite
SC
crystalline phase with lattice parameters a = b = c= 4.7059Å (JCPDS card number: 05-0640). Zinc oxide and cadmium oxide reference peaks are shown as bar graphs in Figure 6a and 6b,
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respectively. The observed diffraction peaks are in good agreement with ZnO and CdO reference peaks. XRD patterns indicate pure phases of zinc oxide and cadmium oxide. The (101) and (111) planes have the strongest line for ZnO and CdO, respectively. The broadening at the bottom of
10
30
40
50
(111)
60
40
(222)
(400)
(311)
50
20 10
0
20
(200)
70
30
(202)
(103)
20
80
(104)
30
(112)
(102)
40
(110)
50
EP
(100) (002)
60
AC C
Intensity (a.u)
70
90
(220)
80
100
(b)
Intensity (a.u.)
90
(200) (201) (004)
100
(a)
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(101)
diffraction peaks denotes smaller crystalline size of ZnO and CdO particles.
0 60
70
80
20
2Theta (degree)
30
40
50
60
2Theta (degree)
Figure 6
17
70
80
90
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The crystallite sizes were calculated using Scherrer’s equation (Khayati et al., 2014) i.e. D = (0.9λ)/(βcosθ), where λ is X- ray wavelength, β is line broadening measured at half-height
and 18.37 nm for zinc oxide and cadmium oxide, respectively.
3.3.2 FE-SEM and EDX analysis
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(FWHM) of the most intense peak of XRD and θ is Bragg angle. The crystallite sizes were 18.24
SC
Morphology of synthesized ZnO and CdO was studied using FE-SEM and is shown in Figure 7 at two different magnifications. Morphology of synthesized metal oxides is found to be globular
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in shape and nano in size. It is clear from FE-SEM images that CdO particles have strong tendency to form nanoparticle agglomerates resulting in large size particles. The particle size was measured using Image J software (Gaur et al., 2014) in each case. More than 100 particles were randomly selected and their diameter was measured for analyzing the particle size distribution. The size of particles varies in between 20-100 nm and 10-120 nm for ZnO and CdO,
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respectively. Particle size distribution curves have been plotted to analyze the distribution of the particles for both the metal oxides (Figure 8). Gaussian fit confirms the narrow size distribution
AC C
EP
of particles. The mean particle size for ZnO and CdO is 43±13 nm and 55±14 nm, respectively.
18
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(b)
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(a)
(d)
AC C
EP
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(c)
Figure 7
19
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(a) 35
(b) 35 30
20 15 10 5
25
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25
Distribution (%)
20 15 10 5
0
0
20
40
60
80
100
SC
Distribution (%)
30
20
Diameter of the nanoparticles (nm)
40
60
80
100
120
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Diameter of the nanoparticles (nm)
Figure 8
EDX spectra of ZnO and CdO (Figure 9) indicate that ZnO and CdO structures are composed of only Zn/Cd and O with almost 1:1 atomic percentage. This confirms the synthesis of pure ZnO
EP AC C
(a)
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and CdO with proper stoichiometric ratio of Zn/Cd and O (Table 5).
Figure 9
20
(b)
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Table 5. Results of elemental analysis of (a) zinc oxide and (b) cadmium oxide Element
Weight%
Atomic%
Weight%
Atomic%
OK
14.06
53.48
Cd L
85.94
Totals
100.00
(b) 20.00
50.53
Zn L
80.00
49.47
Totals
100.00
46.52
SC
OK
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(a)
Element
4. Comparative Study
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Table 6 summarizes the performance of various extractants reported for the recovery of zinc and cadmium from spent batteries. All the extractants cited in Table 6 show quantitative recovery of said metals from waste battery leach liquor, but the extractant to metal ratio used for quantitative recovery of Zn/Cd is generally higher than required in the present study. The equilibration time
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used in present study is either comparable or less than the reported ones. One of the methods (Agarwal et al., 2012) requires a modifier, isodecanol, along with the extractant, saponified D2EHPA, for the quantitative recovery of cadmium from Ni-Cd battery waste. Salgado et al.
EP
quantitatively extracted zinc from spent battery leach liquor using Cyanex 272 but the recovery of zinc from the loaded organic phase was not investigated. Deep et al. (2011) obtained ZnO by
AC C
combustion of the loaded organic phase which is of environmental concern. Only a few studies (Biswas et al., 2016; Deep et al., 2011) and the present study report recovery of metals from battery waste as a useful product which paves way for the conversion of e-waste into beneficial product.
21
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Table 6. Comparison of various extraction systems for the recovery of Zn and Cd from spent batteries
Organic phase
[Extractant]/# [Metal]
Equilibration time (min.)
Strippant
Extraction conditions
Recovered Product
References
Conc., mol/L 3.04 (Pure)
Diluent -
2.2 g/L Zn
~8.99
10
1M H2SO4
A/O = 10/1, one stage (BE)
ZnO
0.1M HCl
A/O = 1/1, one stage (BE)
-
Baba et al., 2009
-
At 50oC, A/O = 1/1, two stages (CE)
-
Salgado et al., 2003
15
1M H2SO4
A/O = 1/1, two stages (CCE)
-
Falco et al., 2014
5
2M HNO3
A/O = 1/1, three stages (CCE)
ZnO
Deep et al., 2011
5
0.77M H2SO4
A/O = 3/2, four stages (CCE)
-
Agarwal et al., 2012
10.71
-
Water pH=6.1
A/O = 1/1, two stages (CCE)
-
Reddy et al., 2006
10.71
5
Water pH=6.1
A/O = 1/1, two stages (CCE)
-
Reddy et al., 2005
25.31
5
0.5M H2SO4
A/O = 1/1, two stages (CCE)
-
Fernandes et al., 2012
2.4 g/L Cd
2.86
5
6M HCl
A/O = 1/1, two stages (CCE)
-
Reddy et al., 2006
1.24 g/L Zn
2.63
6
0.1M EDTA
ZnO
Present study
4.28 g/L Cd
5.26
6
1M HNO3
A/O = 1/1, two stages (CCE) A/O = 3/2, two stages (CCE)
CdO
Present study
Cyanex 302
2.
Cyanex 272
0.032
Kerosene
0.604 g/L Zn
3.46
25
3.
Cyanex 272
0.63
Escaid 110
18.96 g/L Zn
2.17
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4.
Cyanex 272
0.3
Kerosene
6.50 g/L Zn
3.02
5.
Cyanex 923
0.1
Hexane
2.9 g/L Zn
2.26
6.
60%Saponified D2EHPA
0.6
Kerosene+ 5% isodecanol
7.312 g/L Cd
9.23
7.
Cyanex 923
0.6
Kerosene
6.27 g/L Cd
8.
Cyanex 923
0.6
Kerosene
6.27 g/L Cd
9.
TBP
3.62 (Pure)
-
16.1 g/L Cd
10.
Cyanex 301
0.06
Kerosene
11.
Cyphos IL 104
0.05
Toluene
0.2
Toluene
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Extractant
Metal ion in feed
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S. No
Note: BE = batch extraction, CE = cross current extraction, CCE = counter current extraction, # both parameters are in mol/L
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4. CONCLUSION The results of present study show that Cyphos IL 104 is a promising extractant for the recovery of metal values from spent Zn-C and Ni-Cd batteries. Quantitative recovery (>99.9%) of metal
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ions has been achieved in two or three counter current extraction and stripping stages using simple stripping agents. Moreover, zinc and cadmium have been recovered as useful nanosized oxides which have many applications in electronics besides being used as a photo catalyst for
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degradation of pollutants. Recyclability of the used Cyphos IL 104 for the recovery of Zn and Cd from battery waste in successive cycles suggests economic viability of the proposed method for
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commercial use. The metal values recovered from spent batteries in solution form are pure and will help to meet the demand of high grade metals in various industries. The study proposes a simple, convenient and efficient method for the recycling of spent batteries and assumes significance in view of waste management.
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ACKNOWLEDGEMENTS
The authors are thankful to Cytec Inc., Netherlands for providing Cyphos IL 104 as gift sample. Ministry of Human Resources and Development (MHRD) and Council of Scientific & Industrial
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Research (CSIR), New Delhi, India are gratefully acknowledged for providing financial support.
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Figure Captions Figure 1. Effect of Cyphos IL 104 concentration on the extraction of metals from leach liquors (a) Zn-C leach liquor [ZC1]; [Cyphos IL 104] = 8×10-3 to 0.1 mol/L (b) Ni-Cd leach liquor [NC]; [Cyphos IL 104] = 4×10-2 to 0.22 mol/L
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Figure 2. McCabe−Thiele diagrams for (a) [ZC1] leach liquor. (b) [NC] leach liquor at A/O = 1/5 to 5/1. (a) Organic phase = 0.05 mol/L Cyphos IL 104; aqueous phase = 1.240 g/L Zn, 2.442 g/L Mn in 0.5 mol/L HCl. (b) Organic phase = 0.2 mol/L Cyphos IL 104, aqueous phase = 4.280 g/L Cd, 89.60×10-3 g/L Ni, 148.2×10-3 g/L Fe, 3.765×10-3 g/L Co in 0.1 mol/L HCl
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Figure 3. (a) Effect of EDTA concentrations on the stripping of Zn. Loaded organic phase [LO] = 1.240 g/L Zn; aqueous phase = 0.01-0.5 mol/L EDTA, O/A = 1/1. (b) McCabe−Thiele diagram for Zn stripping at O/A = 1/5 to 5/1. Loaded organic phase [LO] = 1.240 g/L Zn; aqueous phase = 0.1 mol/L EDTA Figure 4. (a) Effect of HNO3 concentrations on the stripping of Cd. Loaded organic phase [LO] = 6.419 g/L Cd; aqueous phase = 0.5-2.0 mol/L HNO3, O/A = 1/1. (b) McCabe−Thiele diagram for Cd stripping at O/A = 1/5 to 5/1. Loaded organic phase [LO] = 6.419 g/L Cd; aqueous phase = 1.0 mol/L HNO3
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Figure 5. Flowsheet for the recovery of zinc and cadmium from chloride leach liquor of spent batteries Figure 6. XRD patterns of (a) Zinc oxide; (b) Cadmium oxide
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Figure 7. FE-SEM images of Zinc oxide (a) and (b); Cadmium oxide (c) and (d) Figure 8. Particle size distribution of (a) Zinc oxide; (b) Cadmium oxide
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Figure 9. EDX images of (a) Zinc oxide; (b) Cadmium oxide
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Highlights Using Cyphos IL 104 quantitative recovery of Zn/Cd from spent batteries achieved More than 98% leaching efficiency observed for Zn/Cd using HCl as strippant
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Pure ZnO and CdO nanoparticles obtained from loaded organic phase
Spent organic phase is recyclable with negligible loss in extractability
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Reusability reduces waste production and cost of the process