- Email: [email protected]
Separation of valuable elements from NiMH battery leach liquor via antisolvent precipitation
Separation and Purification Technology 234 (2020) 115812
Contents lists available at ScienceDirect
Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Separation of valuable elements from NiMH battery leach liquor via antisolvent precipitation Kivanc Korkmaz, Mahmood Alemrajabi, Åke C. Rasmuson, Kerstin M. Forsberg
T
⁎
KTH Royal Institute of Technology, Department of Chemical Engineering, Stockholm, Sweden
A R T I C LE I N FO
A B S T R A C T
Keywords: Hydrometallurgy Anti-solvent crystallization NiMH battery recycling Rare earth recovery
Rare earth elements (REE) have been selectively recovered from NiMH battery leach liquors by antisolvent precipitation. The active anode material was leached using sulfuric acid. The REE were then separated from the other elements by precipitation as sulfates after addition of either ethanol or 2-propanol (antisolvent). In a second step, Ni and Co are separated as sulfates by the same technique. The concentration of elements in different acid alcohol mixtures at 25 °C and −10 °C respectively are presented as a function of time after addition of the alcohol, and the optimum conditions for separation of the REE in pure form are presented. Under optimum conditions, 5.6 mol/L (Organic/Aqueous (O/A) volumetric ratio = 0.7) of 2-propanol at 25 °C, 82% of the REE have precipitated 3 h after addition of the antisolvent and the purity is 99.9%.
1. Introduction Nickel metal hydride (NiMH) batteries are used to power hybrid electric vehicles (HEV). The NiMH batteries contain high amounts of valuable elements such as nickel, cobalt and rare earth elements (REE). This makes end-of-life NiMH batteries an excellent candidate for urban mining. From a European perspective, this is not only justified by the high economic values of the metals but also by the high supply risk of the critical elements Co and REE [1–4]. The REE have a high demand due to their key importance in various products in the form of e.g. battery alloys and permanent magnets. It is foreseen that this demand for REE, especially praseodymium, neodymium, and dysprosium, will increase in coming years due to their use as part of strong magnets for various applications [1,3,5,6]. The Panasonic prismatic NiMH module HEV battery used by Toyota Prius has been characterized in different studies [7,8]. These batteries consist of nickel hydroxide in the cathode, with additives of Co, Zn, and Y, and an AB5 type alloy in the anode (A: La, Ce, Nd, Pr, B = Ni, Co, Mn, Al) [6–9]. The valuable elements can be recovered from end-of-life batteries by pyrometallurgical or hydrometallurgical processes [9–14]. Pyrometallurgical processes are simple but the energy demand is high compared to hydrometallurgical processes. Furthermore, the REE ends up in a slag. The REE can be recovered from the slag by further processing which consists of various hydrometallurgical steps [12,15]. By hydrometallurgical processes a full recovery of all the valuable metals as salts with high purity is possible. Recovery of valuable elements (Ni,
⁎
Co, and REE) from NiMH batteries via hydrometallurgical processing starts with an almost complete dissolution of the battery material followed by solvent extraction and/ or precipitation to separate the elements in different fractions of economic value [8,12,16–22]. Precipitation is widely used in hydrometallurgical processes for separation and purification purposes [23–25]. Precipitation from acidic leach liquors can be achieved by different methods such as evaporation of the solvent or by neutralization. Evaporation has a high energy cost and is not a good choice for corrosive solutions. Further, it is difficult to sustain selective precipitation of a specific salt in evaporation and neutralization precipitation processes and the precipitate is often of low quality in terms of size and purity [24,26,27]. One alternative technique is called antisolvent precipitation or organic displacement crystallization. This technique is based on changing the solubility of the solute and creating a supersaturated solution by adding a water-miscible organic solvent, thus forcing the targeted salts to precipitate. The ability to lower the solubility of some inorganic solutes via the addition of an organic solvent has been documented in previous studies [24,26,28]. The ability of a solvent to solubilize an ion can be captured by the dielectric constant (ε) of the solvent. The dielectric constant is a measure of the polarizability of a substance. Water, which has a relatively high dielectric constant, can attract and form layers surrounding both negatively and positively charged ions and thus keep them apart. Alcohols have lower dielectric constants than water, which means that they have a lower ability to keep charged ions apart. Thus, by adding alcohols to water the solubility of the solutes decreases and if the
Corresponding author at: KTH Royal Institute of Technology, Department of Chemical Engineering, Teknikringen 42, SE-100 44 Stockholm. E-mail address: [email protected] (K.M. Forsberg).
https://doi.org/10.1016/j.seppur.2019.115812 Received 7 May 2019; Received in revised form 3 July 2019; Accepted 13 July 2019 Available online 15 July 2019 1383-5866/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al.
saturation point is exceeded precipitation occurs. When the carbon chain of aliphatic compounds is longer the solvent possesses a more hydrophobic character resulting in a lower dielectric constant [28]. In addition, an organic solvent can have an affinity for water molecules thus decreasing the water activity and consequently the solubility of the hydrated solutes [29,30]. Anti-solvent precipitation has many applications in e.g. specialty chemicals production and pharmaceutical production but only a few applications in inorganic processing within hydrometallurgy. An early example is the recovery of nickel sulfate from the de-copperized electrolyte, where the purity of the nickel sulfate product was high enough to be considered for use in the electroplating industry [27]. After the precipitation step, it is possible to separate the antisolvent from the acid by distillation and thereby be able to recirculate both the acid and the antisolvent to the process. In this work, the selective separation of REE from NiMH battery leach liquor by antisolvent precipitation has been systematically investigated. To the best of our knowledge antisolvent precipitation of REE sulfate salts from NiMH battery, leach liquors have not yet been investigated. It is a suitable method to selectively recover the REE as highly soluble sulfate salts in a process where the solvents can be recovered and reused.
Table 2 Concentration of alcohol for different organic to aqueous (O/A) volumetric ratios. Volumetric ratio, O/ A (–)
Concentration1 of ethanol (mol/L)
Concentration1 of 2propanol (mol/L)
0.1 0.3 0.34 0.45 0.5 0.56 0.7 0.9 1.1 1.3 1.5
1.61 4.15 4.53 5.64 6.06 6.54 7.55 8.74 9.72 10.53 11.22
1.21 3.11 – – 4.53 – 5.64 6.54 7.27 7.87 8.39
1
Expressed in moles per total volume of liquid.
addition of the alcohols to the initial aqueous solution and by a change in temperature. Since the volumes of alcohol and aqueous solution are not additive, the total volumes were measured and incorporated into the calculations. In addition, the decrease in the concentration of the elements due to precipitation must be distinguished from the decrease in concentration by dilution resulting from the addition of the antisolvent. Liquid samples were diluted 100 times and stored in HDPE bottles before ICP-OES analysis. Some samples were further diluted to reach appropriate concentrations for ICP-OES measurements of elements present at high concentration (Ni, La). The presence of alcohol can have an influence on both aerosol generation and transport and on the plasma characteristics in ICP-OES analysis [31]. However, the concentration of alcohol was low in all the samples analyzed by ICPOES (< 0.1 mol/L) with negligible matrix effects. Solid samples were collected, washed with ethanol mixed with water and then with pure ethanol and dried at room temperature before further analysis. Scanning electron microscopy (SEM) with an EDS detector and powder-Xray diffraction (XRD) analyses were conducted on solid samples. The complete set of experiments is given in Table 1. The experiments were designed to study the composition of the aqueous phase as a function of time after addition of specific amounts of either ethanol or 2-propanol. The temperature was kept constant at 25 °C or −10 °C. A flowsheet of the process is presented in Fig. 1.
2. Experimental procedure A discharged Panasonic prismatic NiMH module HEV battery was used for the experimental work. The battery modules were manually dismantled and the anode active material, containing the main part of the REE present in the battery together with the valuable elements Ni and Co, was scraped from the supports. The active anode material contains 33% by mass of REE and the REE are present in an AB5 type alloy [7]. Active anode material was leached with 2 mol/L H2SO4 at 25 °C for 4 h under atmospheric pressure and constant stirring, enough to suspend all solid material. After 4 h most of the material was dissolved and a small amount of leach residue was separated from the liquid phase by filtration. Ethanol and 2-propanol were selected as antisolvents. These alcohols are not expected to react with the sulfuric acid under the conditions applied. The respective alcohol was added to the leach liquor via a pipette or with controlled injection rates via a syringe pump. The injection time is short (see Table 1) and time zero is always reported as the time after complete addition of the antisolvent. After each addition (reported as the volumetric ratio of organic (antisolvent) to the aqueous phase (leach liquor), O/A, see Table 2) the solutions were left for a certain amount of time (durations up to 7 days) under constant stirring. Samples were collected at different times using syringes from which the solid material was immediately removed from the liquid phase using syringe filters (0.2 µm). The volumes and masses of all samples and added alcohols were recorded and the data is presented as the concentration of elements in mass or mole per unit volume initial aqueous solution (i.e. not the new solvent mixture). This is important since the density of the solvent mixture will change by the
3. Results and discussion 3.1. Effect of time In Fig. 2a, the concentrations of Ni and La at different O/A ratios after addition of ethanol at 25 °C are presented as a function of time. The concentration of Ni is read from the y-axis to the left while the concentration of La is read from the y-axis to the right. The dosing of ethanol took three minutes and the time when all antisolvent has been
Table 1 Set of experiments. Exp. set
Organic antisolvent
Organic to acid (O/A) volumetric ratios
1 2 3: 3: 4: 4: 5: 5:
Ethanol 2-propanol 2-propanol Ethanol 2-propanol Ethanol 2-propanol Ethanol
0.1 0.1 0.5 0.34 0.5 0.34 0.7 0.1
A B A B A B
0.3 0.3 0.7 0.45 0.7 0.45 0.9 0.3
0.5 0.5 0.9 0.56 0.9 0.56 – 0.7
0.7 0.7 – 0.8 – – – 0.9
0.9 0.9 – 0.9 – – – –
1.1 1.1 – – – – – –
1.3 1.3 – – – – – –
1.5 1.5 – – – – – –
Temp. (°C)
Duration1 (h = hours, d = days)
Antisolvent addition rate2 (mL/min)
25 25 25 25 25 25 −10 −10
7d 7d 10 d 10 d 24 h 3h 3h 3h
3 3 3 3 1 1 3 3
Time the solutions were left stirred at the specific O/A ratio before final sampling. Samples were taken as a function of time in some of the experiments. The final concentrations of added antisolvent were in the range of 1.2–11.2 mol/L. This corresponds to a dosing time from 1 to 9 min depending on the antisolvent type, final molarity, and dosing rate. 1 2
2
Separation and Purification Technology 234 (2020) 115812 35
12
30
10 Ni: O/A=0.37
25
8
20 6 15 4
10 5
2
0
0
La Concentration (g/L)
Ni Concentration (g/L)
K. Korkmaz, et al.
Ni: O/A=0.52 Ni: O/A=0.67 Ni: O/A=0.8 Ni: O/A=0.9 La: O/A=0.37 La: O/A=0.52 La: O/A=0.67 La: O/A=0.8
a
La: O/A=0.9
Time 35
12
30
10
Ni Concentration (g/L)
8
20 6 15 4
10
La Concentration (g/L)
Ni Set 2, O/A=0.5 25
Ni Set 3A, O/A=0.5 Ni Set 4A, O/A=0.5 Ni Set 2, O/A=0.7 Ni Set 3A, O/A=0.7 Ni Set 4A, O/A=0.7 Ni Set 3A, O/A=0.9 Ni Set 4A, O/A=0.9
2
5
La Set 3A, O/A=0.5 La Set 3A, O/A=0.7
0
La Set 3A, O/A=0.9
0
b
Time
Fig. 2. Concentration of Ni and La as a function of time at 25 °C after addition of (a) ethanol (Set 3: Part B) and (b) 2-propanol (set 2, 3 and 4, part A). Abbreviations: m: minutes, h: hours, d: days.
Fig. 1. Flowsheet of the process.
Concentration (g/L)
added are reported as time zero. The concentrations are reported as the mass of element per unit volume initial aqueous phase (acidic leach liquor in the absence of alcohol). This means that the reported concentrations will not change if no precipitation occurs. Some experiments were performed in duplicate and the results indicate that the experiments are reproducible (see Fig. 2b and supplementary data Fig. B). The results show that most of La have precipitated after 10 min at an O/A ratio of 0.56, 0.80 and 0.90 while up to two hours are needed to reach a constant concentration of La in the solution at an O/A ratio of 0.45. For an O/A ratio of 0.34, up to three hours are needed to reach a constant concentration of La. No precipitation of Ni was observed at an O/A ratio of 0.34, 0.45 and 0.56 during the length of the experiments (10 days). At an O/A ratio of 0.8, there is a slight decrease in Ni over time, indicating that a solid phase containing Ni is precipitating. For an O/A ratio of 0.9 (8.74 mol/L of ethanol), there is instantaneous precipitation visible by the naked eye and no further decrease in Ni from 10 min to 24 h. The rapid decrease in the concentration of Ni at higher O/A ratio can be explained by a higher supersaturation giving a higher driving force for nucleation and crystal growth. The concentration of Ni was also measured nine days after antisolvent addition at an O/A ratio of 0.9 and the concentration was still in the same range (22.7 g/L). The same trends can be observed up to 10 days after the addition of 2propanol, see Fig. 2b. However, here the concentration of Ni continues to decrease during 2 days for an O/A ratio of 0.9 (6.54 mol/L of 2propanol), and then the concentration increases. This can be explained by the dissolution of the solid phase containing Ni indicating that the solid phase that initially nucleated is not thermodynamically stable under the final conditions. Fig. 3 shows that the precipitation of Ce, Nd, Pr, and Co occurs within the first 10 min at an O/A ratio of 0.9 while Y, Al, and Mn
Concentration (g/L)
a
b
3.0 2.8 2.5 2.3 2.0 1.8 1.5 1.3 1.0 0.8 0.5 0.3 0.0
Co Mn Al Y Ce Pr Nd 0
10
30
60 120 Time (minutes)
180
360
1440
3.3 3.0 2.8 2.5 2.3 2.0 1.8 1.5 1.3 1.0 0.8 0.5 0.3 0.0
Co Mn Al Y Ce Pr Nd 0
10min 30min
1h
2h
3h 6h Time
1d
2d
4d
7d
10d
Fig. 3. (a) concentration of elements as a function of time at 25 °C in 8.74 mol/ L ethanol (O/A = 0.9) and (b) in 6.54 mol/L ethanol (O/A = 0.56) (set 3: Part B).
3
Separation and Purification Technology 234 (2020) 115812
Concentration (g/L)
K. Korkmaz, et al. 3.0 2.8 2.5 2.3 2.0 1.8 1.5 1.3 1.0 0.8 0.5 0.3 0.0
Concentration (g/L)
b
Co Mn Al Y Ce Pr Nd 0
a
solid phases transformed during this time. However, the mixture of phases detected in the present work (e.g. both Ce2(SO4)3·4H2O and Ce2(SO4)3·9H2O) indicates that equilibrium conditions have not yet been reached seven days after addition of antisolvent. A mixture of different REE sulfate hydrates were also detected seven days after adding ethanol as antisolvent at an O/A ratio of 0.7, see supplementary data Fig. A. In order to study the solid phases containing Ni and Co, which precipitates at higher O/A ratios, an experiment was performed in which the REE containing solid phase was filtered off 24 h after adding 2-propanol (O/A ratio of 0.5). Thereafter an additional amount of 2propanol was added to obtain an O/A ratio of 0.9. The solid phase was then filtered off seven days after addition of the antisolvent. The major solid phases detected in this sample were NiSO4·6H2O and CoSO4·6H2O and a mixed phase CoNi(SO4)2(H2O)12 was also detected (See Fig. 5b). Scanning electron images of precipitates collected seven days after the addition of 2-propanol, at an O/A ratio of 0.9, is presented in Fig. 6. The sample contains a mixture of small and large particles. EDS was used to investigate the composition of the particles (see supplementary data, Table A). It was found that the small sized (micrometer scale) particles contained REE while the larger (mm scale) particles contained either Ni or Co. The results when dosing ethanol and 2-propanol respectively at a rate of either 1 mL/min or 3 mL/min was applied are presented in Fig. 7. The times when all antisolvent had been added are reported as time zero, which corresponds to 7 and 2.3 min for a dosing rate of 1 and 3 mL/min respectively to reach an O/A of 0.7. The results show that there is no drastic difference in applying these two dosing rates.
10min 30min
1h
2h
3h 6h Time
1d
2d
4d
7d
3.3 3.0 2.8 2.5 2.3 2.0 1.8 1.5 1.3 1.0 0.8 0.5 0.3 0.0
10d
Co Mn Al Y Ce Pr Nd 0
10min 30min
1h
2h
3h 6h Time
1d
2d
4d
7d
10d
Fig. 4. Concentration of elements as a function of time in 2-propanol at 25 °C for (a) O/A = 0.9, (b) O/A = 0.7 (set 3: Part A).
remain in solution during the whole duration of the experiment (24 h). For a lower concentration of ethanol (O/A = 0.56) and up to 10 days after antisolvent addition, the same trends are observed for all elements except Co. Under these conditions, Co remains in solution. The concentrations of Ce, Nd, Pr, Y, Co, Mn and Al after the addition of 2-propanol are presented in Fig. 4. For an O/A ratio of 0.9 Ce, Pr, Nd, and Co precipitate within 10 min after addition of the antisolvent while the concentration of Y, Al and Mn remain constant. After three hours the concentration of Co has increased, indicating dissolution of the solid phase containing Co. This is the same experiment as presented in Fig. 2b where the increasing concentration of Ni is observed after about four days. The concentrations of the elements after 10 days are lower in the presence of 2-propanol than ethanol at the same O/A ratios, except for Al and Y that remain in solution under all conditions investigated. The solid phase collected seven days after the addition of 2-propanol, at an O/A ratio of 0.5, (exp. set 2) consisted of a mixture of different solid phases containing REE (see Fig. 5a). The major phases (in amount) found under these conditions were rare earth sulfate hydrates and yttrium oxysulfates; e.g. both Ce2(SO4)3·4H2O and Ce2(SO4)3·9H2O was detected as well as Y2O2SO4 and Y2(SO4)3. It is known that the REE can form a range of different sulfate hydrate salts, including polymorphs [32–34]. In pure water at 25 °C the lighter REE (Ce, La) are most stable as nonahydrates while the heavier REE form octahydrates. Lower hydrates are generally obtained at a higher temperature and when the sulfuric acid concentration increases. In addition, organic solvents can decrease the water activity, giving rise to lower hydrates being the most stable form upon the addition of alcohol [30]. To the best of our knowledge, there is no information in the literature about which REE sulfate hydrate forms that are most stable in different mixtures of sulfuric acid and alcohols. Due to the complexity of the system, it is difficult to determine which is the most stable solid phase for each REE under each condition and the solubility of these phases. Especially since the phases nucleating upon addition of the antisolvent might not be the phases that are the thermodynamically most stable under the applied conditions. In the present work, a mixture of solid REE containing sulfate hydrates was detected in samples collected seven days after antisolvent addition. The solid phase was washed with pure ethanol and dried under ambient conditions (at room temperature) and analyzed by powder XRD the same day; it is possible that the
3.2. Effect of solvent composition and antisolvent polarity The concentration of the different elements at 25 °C, seven days after the addition of different amounts of ethanol and 2-propanol respectively (exp. set 1 and 2) are presented in Figs. 8–10. At an organic to aqueous (O/A) ratio of 0.5 about 49% by mass of the REE has precipitated seven days after addition of antisolvent while Ni, Co, Mn, and Al remain in solution, both when using ethanol and 2propanol as antisolvents, see Figs. 8–10. An organic to the aqueous ratio of 0.5 corresponds to a concentration of 6.1 mol/L of ethanol and 4.5 mol/L of 2-propanol. As can be seen in Figs. 8–10, as the amount of antisolvent added increases the concentration of the REE decreases. Nickel and cobalt precipitate from the leach liquor at an O/A ratio of between 0.7 and 0.9 (7.6–8.7 mol ethanol/L and 5.6–6.5 mol 2-propanol/L). At the highest O/A ratio of 1.5, about 95–99% of the REE, 72.7% of Ni and 71.2% of Co (by mass) have precipitated. No precipitation of Al and Mn could be detected even at an O/A ratio of 1.5 (11.2 mol ethanol/L and 8.4 mol 2-propanol/L). The total concentration of Mn and Al are slightly higher for O/A ratios above 0.7, see Figs. 8 and 9. This can be explained by the large amount of Ni, La, and Co precipitating under these conditions. These elements precipitate as metal sulfate hydrate salts (see Fig. 5) and thereby the solution becomes concentrated in terms of the remaining elements. In Figs. 11 and 12 the molar concentration of the REE in different concentrations of the alcohols are presented. The concentration of the REE (seven days after antisolvent addition) is in the same range or slightly lower in 2-propanol compared to ethanol. It is reasonable that a higher concentration of ethanol than 2-propanol is needed to precipitate the REE since the dielectric constant of ethanol (25) is higher than that of 2-propanol (20) at 25 °C. A trend can be found considering the variation in concentration of the respective REE and their atomic numbers. The lightest lanthanide La (lowest charge density) is present at the highest concentration while the heaviest lanthanide Nd (highest charge density) is present at the lowest concentration. Yttrium is not a lanthanide but is counted as one of the REE due to its similar ionic radius and thus behavior (the REE all have a mainly ionic character of bonding). The ionic radius of hydrated Y+3 (1.02 Å, 8-coordinate) is 4
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al.
Fig. 5. XRD analyses of the precipitate obtained for (a) O/A = 0.5 and (b) O/A = 0.9 with 2-propanol as antisolvent.
smaller than that of Pr+3 (1.16 Å, 9-coordinate) and thus Y+3 has the highest charge density of the investigated REE [35]. Yttrium precipitates after addition of 4.15 mol/L of ethanol and 3.11 mol/L of 2propanol respectively where the concentration of Y in the aqueous phase is lower than the other rare earth elements (see Fig. 11). However, as the concentration of the alcohols increases the detected decrease in the concentration of Y is less than for the lanthanides. This behavior requires further analysis. However, it is important to note that a mixture of solid phases is detected in the precipitate after seven days (see Fig. 5). Thus, equilibrium conditions have not been reached after seven days and the solid phases still slowly transform into more stable phases. In Fig. 13 the concentration of REE as a function of time after addition of ethanol or 2-propanol respectively at a concentration of 4.53 mol/L are presented. All antisolvent was added at a rate of 1 mL/
min (experiment Set 4 Part A and B). As can be seen in Fig. 13 the concentration of Ce, Nd and Pr are slightly lower in 4.53 mol/L of 2propanol than in 4.53 mol/L of ethanol at all points in time after precipitation has occurred. By comparing with the data in Figs. 8 and 9 (seven days after antisolvent addition) by interpolating between the data at an O/A ratio of 0.3 and 0.5 it can be seen that the concentrations of the REE are slightly lower after 180 min than after seven days. This could be explained by that the solid phases initially precipitating are slowly transformed over time into other more stable phases and equilibrium conditions have not been reached after 180 min. The results show that it is possible to separate the elements in 3 groups: (1) REE, (2) Ni and Co and (3) Al and Mn. The optimal condition for selective separation of the REE from the leach solution is an O/A ratio of 0.7, using either 2-propanol or ethanol as antisolvent.
5
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al. 3.5
Concentration (g/L)
3.0 2.5 Co
2.0
Mn Al
1.5
Y 1.0
Ce Pr
0.5
Nd
0.0 Original Liq
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
O/A (ml/ml)
Fig. 8. Concentration of elements versus O/A ratios with ethanol assisted precipitation (set 1). Fig. 6. Scanning electron microscopy images of crystals collected 7 days after the addition of 2-propanol (O/A = 0.9). Analysis by EDS showed that the larger crystals contain Ni or Co while the adhering fine particles contained REE.
3.5 3 Concentration (g/L)
Concentration (g/L)
3
2 La-1ml/min
2.5
Mn
2
Al
1.5
Y Ce
1
Pr
La-3ml/min
0.5
Ce-1ml/min Ce-3ml/min 1
Co
Nd
0
Pr-1ml/min Pr-3ml/min
O/A (ml/ml)
a
Fig. 9. Concentration of elements versus O/A ratios with 2-propanol assisted precipitation (set 2).
0 0
10
30 60 Time (minutes)
180
1440
35 Ni (2-propanol)
30
La (2-propanol) Concentration (g/L)
Concentration (g/L)
3
2 La-1ml/min
25
Ni (ethanol)
20
La (ethanol)
15 10 5
La-3ml/min Ce-1ml/min
0
Ce-3ml/min 1
Pr-1ml/min
O/A (ml/ml)
Pr-3ml/min
Fig. 10. Concentration of Ni and La versus O/A ratios (Set 1 and 2).
b
three hours after antisolvent addition at 25 °C and −10 °C respectively is presented. At 25 °C the solution is undersaturated to saturated with respect to Co both in ethanol and 2-propanol while at −10 °C precipitation of Co has occurred in both systems. Lanthanum and cerium have precipitated from the leach liquor both at 25 °C and −10 °C 180 min after addition of either ethanol or 2-propanol. The decrease in the concentration of La is 7.7% in ethanol and 2.9% in 2-propanol when lowering the temperature from 25 °C to −10 °C. The decrease in the concentration of Ce is also low lowering the temperature from 25 °C to −10 °C. Furthermore, it can be observed that the concentrations of Ni and Co are lower in 2-propanol than in ethanol at the same volumetric dosage at −10 °C. The results are similar for an O/A ratio of 0.9 for ethanol and 2-propanol respectively (see Fig. C in the appendix). It was also found that the precipitation of all elements occurred under a period
0 0
10
30 Time (minutes)
60
180
Fig. 7. Effect of dosing rate on REE concentrations with respect to time (a) 2propanol; O/A = 0.7, (b) ethanol; O/A = 0.56.
3.3. Effect of temperature In Fig. 14 the concentration of Ni at 25 °C and at −10 °C three hours after addition of ethanol and 2-propanol respectively is presented. At 25 °C the solution is undersaturated to saturated with respect to Ni both in ethanol and 2-propanol while at −10 °C precipitation of Ni has occurred in both systems. In Fig. 15 the concentration of La, Ce, and Co 6
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al. 600
Concentration (mmol/L)
500 400 300 200 100 0 Ni/Ethanol
Ni/2-Propanol
Original Liquid
25oC
-10oC
Fig. 14. Concentration of Ni after 180 min in experiments at −10 °C and 25 °C after addition of ethanol and 2-propanol with O/A = 0.7.
Fig. 11. Concentration of Ce, Nd, Pr, and Y versus alcohol concentration.
70
Concentration (mmol/L)
60 50 40 30 20 10 0
Fig. 12. Concentration of La and Ce versus alcohol concentration.
Ce/Ethanol
Co/Ethanol
La/Ethanol Ce/2-Propanol Co/2-Propanol La/2-Propanol
Original Liquid 25.0
25oC
-10oC
Fig. 15. Concentration of Ce, Co and La after 180 min in experiments at −10 °C and 25 °C after addition of ethanol and 2-propanol with O/A = 0.7. Ce, 2Propanol Ce, Ethanol
15.0
10.0
Nd, 2Propanol Nd, Ethanol
5.0
Pr, 2Propanol Pr, Ethanol
Precipitated fraction (%)
Concentration (mmol/L)
20.0
100 80 60 40 20 0
0.0 0
10
30 Time (minutes)
60
180
Fig. 13. Elemental concentrations in 4.53 mol/L ethanol (O/A = 0.34) and 2propanol (O/A = 0.50).
-10oC
25oC
Fig. 16. Fraction of elements precipitated after 180 min for O/A = 0.7.
of fewer than 30 min at both low and high temperature under all conditions studied (see Fig. C in the appendix). Since the concentration of Ni and Co in the leach liquor decrease to a higher extent than the REE do when decreasing the temperature from 25 °C to −10 °C the potential to separate the REE from the Ni and Co decreases. In addition, cooling the solution to −10 °C cost energy. It is thus better to perform the separation at 25 °C. The fractionated percentages of La, Ce, Co and Ni with respect to the reagent used and at −10 °C and 25 °C can be seen in Fig. 16.
containing solid phases are preferably filtered of 0.5–1 h after addition of the antisolvent (Fig. 2). After addition of 7.6 mol/L (O/A = 0.56) of ethanol at 25 °C, 86.5% of the REE (89.1% of the light REE) have precipitated three hours after antisolvent addition. In a batch process seeds of REE sulfate hydrates will be added, which will have a direct impact on the time of operation. The addition of seeds and time of operation needs to be optimized in upscaling of the process. The precipitated mass fraction of REE (purity) is calculated as the mass of precipitated REE divided by the total mass of precipitated metal ions (La, Ce, Nd, Pr, Y, Ni, Co, Mn, and Al). The masses are obtained from a mass balance based on the concentrations in the aqueous phase, measured by ICP-OES, before and after precipitation. The purity of the REE products obtained under different conditions determined by this method is presented in Table 3. The highest purity is obtained three hours after addition of 7.6 mol/L of ethanol (99.99%). Similarly, after
3.4. Industrial perspective Antisolvent precipitation can be applied to selectively separate the REE (La, Ce, Nd, Pr, Y) from the other elements present in NiMH battery leach liquor. If the separation is operated in batch scale at 25 °C the REE 7
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al.
doi.org/10.1016/j.seppur.2019.115812.
Table 3 Precipitation percentages and purities at 25 °C (Set 1, 2, 3A and 3B). Alcohol
Time
O/A (–)
Conc. (mol/L)
Recovery, light REE (%)
Recovery, tot. REE (%)
Purity of REE (%)
Ethanol Ethanol 2-propanol 2-propanol
3h 3h 3h 3h
0.56 0.90 0.70 0.90
7.55 8.74 5.64 6.54
89.12 93.84 84.40 90.79
86.52 91.32 81.88 88.29
99.99 68.40 99.99 56.17
References [1] K. Binnemans, P.T. Jones, T. Müller, L. Yurramendi, Rare earths and the balance problem: how to deal with changing markets? J. Sustain. Metall. 4 (1) (2018) 126–146, https://doi.org/10.1007/s40831-018-0162-8. [2] E. Commission, Critical raw materials for the EU, in: Report of the Ad-hoc Working Group on Defining Critical Raw Materials, 2010. [3] D. Guyonnet, M. Planchon, A. Rollat, V. Escalon, J. Tuduri, N. Charles, S. Vaxelaire, D. Dubois, H. Fargier, Material flow analysis applied to rare earth elements in Europe, J. Clean. Prod. 107 (2015) 215–228, https://doi.org/10.1016/j.jclepro. 2015.04.123. [4] S.W.J.H. Christina Tsiarta, in: E. Commission (Ed.), Final Implementation Report for the Directive 2006/66/EC on Batteries and Accumulators, 10 July 2015. [5] US Department of Energy, Critical Materials Strategy, 2011. [6] A. Rollat, D. Guyonnet, M. Planchon, J. Tuduri, Prospective analysis of the flows of certain rare earths in Europe at the 2020 horizon, Waste Manage. 49 (2016) 427–436, https://doi.org/10.1016/j.wasman.2016.01.011. [7] K. Korkmaz, M. Alemrajabi, Å.C. Rasmuson, K. Forsberg, Sustainable hydrometallurgical recovery of valuable elements from spent nickel-metal hydride HEV batteries, Metals 8 (12) (2018), https://doi.org/10.3390/met8121062. [8] K. Larsson, C. Ekberg, A. Odegaard-Jensen, Dissolution and characterization of HEV NiMH batteries, Waste Manage. 33 (3) (2013) 689–698, https://doi.org/10.1016/j. wasman.2012.06.001. [9] K. Binnemans, P.T. Jones, B. Blanpain, T. Van Gerven, Y. Yang, A. Walton, M. Buchert, Recycling of rare earths: a critical review, J. Cleaner Prod. 51 (2013) 1–22, https://doi.org/10.1016/j.jclepro.2012.12.037. [10] C. Tunsu, M. Petranikova, M. Gergorić, C. Ekberg, T. Retegan, Reclaiming rare earth elements from end-of-life products: a review of the perspectives for urban mining using hydrometallurgical unit operations, Hydrometallurgy 156 (2015) 239–258, https://doi.org/10.1016/j.hydromet.2015.06.007. [11] D.C.R. Espinosa, A.M. Bernardes, J.A.S. Tenório, An overview on the current processes for the recycling of batteries, J. Power Sources 135 (1–2) (2004) 311–319, https://doi.org/10.1016/j.jpowsour.2004.03.083. [12] J. Nan, D. Han, M. Yang, M. Cui, X. Hou, Recovery of metal values from a mixture of spent lithium-ion batteries and nickel-metal hydride batteries, Hydrometallurgy 84 (1–2) (2006) 75–80, https://doi.org/10.1016/j.hydromet.2006.03.059. [13] S. Al-Thyabat, T. Nakamura, E. Shibata, A. Iizuka, Adaptation of minerals processing operations for lithium-ion (LiBs) and nickel metal hydride (NiMH) batteries recycling: critical review, Miner. Eng. 45 (2013) 4–17, https://doi.org/10.1016/j. mineng.2012.12.005. [14] B. Ebin, M. Petranikova, C. Ekberg, Physical separation, mechanical enrichment and recycling-oriented characterization of spent NiMH batteries, J. Mater. Cycles Waste Manage. (2018), https://doi.org/10.1007/s10163-018-0751-4. [15] V. Innocenzi, N.M. Ippolito, I. De Michelis, M. Prisciandaro, F. Medici, F. Vegliò, A review of the processes and lab-scale techniques for the treatment of spent rechargeable NiMH batteries, J. Power Sour. 362 (2017) 202–218, https://doi.org/ 10.1016/j.jpowsour.2017.07.034. [16] P. Zhang, T. Yokoyama, O. Itabashi, Y. Wakui, T.M. Suzuki, K. Inoue, Hydrometallurgical process for recovery of metal values from spent nickel-metal hydride secondary batteries, Hydrometallurgy 50 (1) (1998) 61–75, https://doi. org/10.1016/S0304-386X(98)00046-2. [17] P. Zhang, T. Yokoyama, O. Itabashi, Y. Wakui, T.M. Suzuki, K. Inoue, Recovery of metal values from spent nickel–metal hydride rechargeable batteries, J. Power Sour. 77 (2) (1999) 116–122, https://doi.org/10.1016/S0378-7753(98)00182-7. [18] N. Tzanetakis, K. Scott, Recycling of nickel-metal hydride batteries. I: dissolution and solvent extraction of metals, J. Chem. Technol. Biotechnol. 79 (9) (2004) 919–926, https://doi.org/10.1002/jctb.1081. [19] D.A. Bertuol, A.M. Bernardes, J.A.S. Tenório, Spent NiMH batteries-the role of selective precipitation in the recovery of valuable metals, J. Power Sour. 193 (2) (2009) 914–923, https://doi.org/10.1016/j.jpowsour.2009.05.014. [20] L.E.O.C. Rodrigues, M.B. Mansur, Hydrometallurgical separation of rare earth elements, cobalt and nickel from spent nickel-metal-hydride batteries, J. Power Sour. 195 (11) (2010) 3735–3741, https://doi.org/10.1016/j.jpowsour.2009.12.071. [21] X. Yang, J. Zhang, X. Fang, Rare earth element recycling from waste nickel-metal hydride batteries, J. Hazard. Mater. 279 (2014) 384–388, https://doi.org/10.1016/ j.jhazmat.2014.07.027. [22] L. Pietrelli, B. Bellomo, D. Fontana, M. Montereali, Characterization and leaching of NiCd and NiMH spent batteries for the recovery of metals, Waste Manage. 25 (2) (2005) 221–226, https://doi.org/10.1016/j.wasman.2004.12.013. [23] G.P. Demopoulos, Aqueous precipitation and crystallization for the production of particulate solids with desired properties, Hydrometallurgy 96 (3) (2009) 199–214, https://doi.org/10.1016/j.hydromet.2008.10.004. [24] D.A. Weingaertner, S. Lynn, D.N. Hanson, Extractive crystallization of salts from concentrated aqueous solution, Ind. Eng. Chem. Res. 30 (3) (1991) 490–501, https://doi.org/10.1021/ie00051a009. [25] P.A. Barata, M.L. Serrano, Salting-out precipitation of potassium dihydrogen phosphate (KDP). I. Precipitation mechanism, J. Cryst. Growth 160 (3) (1996) 361–369, https://doi.org/10.1016/0022-0248(95)00740-7. [26] G. Moldoveanu, Crystallisation of Inorganic Compounds with Alcohols, 2005. [27] G.A. Moldoveanu, G.P. Demopoulos, Producing high-grade nickel sulfate with solvent displacement crystallization, JOM 54 (1) (2002) 49–53, https://doi.org/10. 1007/bf02822606. [28] G.A. M, G.P. D, Organic solvent-assisted crystallization of inorganic salts from
addition of 5.6 mol/L (O/A = 0.7) of 2-propanol at 25 °C, 81.9% of the REE (84.4% of the light REE) have precipitated after three hours and the purity is high (99.99%). In a second step, the Ni and Co can be separated as a mixture of sulfate salts by the same technique, see Figs. 8–10. The REE are mainly obtained as REE sulfate hydrates which is advantageous due to the high solubility of these salts in water. The salts can thus easily be dissolved and further processed for individual separation of the REE e.g. by solvent extraction or chromatography in preparative scale [36]. For an industrial process, the choice of antisolvent should rely on aspects such as the economy, availability, and safety as well as the overall process outline including conditions for solvent recovery. Today, the market price of ethanol (1600 $/tonne) is higher than that of 2-propanol (1200 $/tonne) [37,38]. The antisolvent can be recovered from the aqueous phase after precipitation by e.g. distillation and then be reused as a precipitation agent [39–41]. 4. Conclusions It is possible to selectively separate rare earth elements (REE) from sulfuric acid NiMH battery leach liquors by addition of ethanol and 2propanol respectively. The REE precipitates as a mixture of different sulfate phases. The REE can be recovered with negligible co-precipitation of the other elements at an initial concentration of 7.6 mol/L of ethanol and 5.6 mol/L of 2-propanol at 25 °C. The total recovery of REE is 86.5% after addition of 7.6 mol/L of ethanol and 81.9% after addition of 5.6 mol/L of 2-propanol at 25 °C. The concentrations of the different REE 7 days after antisolvent addition correlate with their atomic numbers where the lightest lanthanide La (lowest charge density) is present at the highest concentration while the heaviest lanthanide Nd (highest charge density) is present at the lowest concentration. Yttrium does not follow the trend based on ionic size (or charge density) observed for the lanthanides. The concentration of the elements (7 days after antisolvent addition) is in the same range or slightly lower in 2propanol compared to ethanol. The concentration difference between the REE and the other main elements present in the leach liquor is less at −10 °C compared to 25 °C and thus it is better to perform the separation at 25 °C. The concentration of La decrease by 7.7% in ethanol and by 2.9% in 2-propanol when lowering the temperature from 25 °C to −10 °C while the concentration of Ni decreases by 42.5% in ethanol and by 66.4% in 2-propanol. Acknowledgements The authors would like to acknowledge the Swedish Energy Agency, Sweden for funding the project (project nr 37724-1) and Chalmers University of Technology, Department of Chemistry and Chemical Engineering for supplying the battery modules and Swedish Environmental Research Institute (IVL) for instrumentation and expertise in connection to conducting the nanofiltration experiments. Part of the work was also supported by the Swedish Foundation for Strategic Research, Sweden SSF with the grant number of IRT 11-0026. Appendix A. Supplementary material Supplementary data to this article can be found online at https:// 8
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al.
[29] [30]
[31]
[32]
[33] [34]
[35]
CON-09-10-22. [36] R.M. Ashour, M. Samouhos, E. Polido Legaria, M. Svärd, J. Högblom, K. Forsberg, M. Palmlöf, V.G. Kessler, G.A. Seisenbaeva, Å.C. Rasmuson, DTPA-functionalized silica nano-and microparticles for adsorption and chromatographic separation of rare earth elements, ACS Sustain. Chem. Eng. 6 (5) (2018) 6889–6900, https://doi. org/10.1021/acssuschemeng.8b00725. [37] M. Hirtzer, U.S. Ethanol Prices Drop to 13-year Lows on Bigger Supply, 2018 < https://www.reuters.com/article/usa-ethanol/u-s-ethanol-prices-drop-to13-year-lows-on-bigger-supply-idUSL2N1Y31EP > . [38] I. News, Europe IPA Spot Prices Fall on Propylene December Drop, Sustainability (2018) < https://www.icis.com/explore/resources/news/2018/12/05/10291138/ europe-ipa-spot-prices-fall-on-propylene-december-drop/ > . [39] Y. Yang, K. Boots, D. Zhang, A sustainable ethanol distillation system Food Bioprod. Process. 4 (2012) 92–105. [40] M. Gavahian, A. Farahnaky, S. Sastry, Ohmic-assisted hydrodistillation: a novel method for ethanol distillation 98 (2015). [41] N. Vorayos, T. Kiatsiriroat, N. Vorayos, Performance analysis of solar ethanol distillation, Renew. Energy 31 (15) (2006) 2543–2554, https://doi.org/10.1016/j. renene.2006.01.016.
acidic media, J. Chem. Technol. Biotechnol. 90 (4) (2015) 686–692, https://doi. org/10.1002/jctb.4355. D. Peeters, Hydrogen bonds in small water clusters: a theoretical point of view, J. Mol. Liq. 67 (1995) 49–61, https://doi.org/10.1016/0167-7322(95)00865-9. H. Zhu, C. Yuen, D.J.W. Grant, Influence of water activity in organic solvent + water mixtures on the nature of the crystallizing drug phase. 1. Theophylline, Int. J. Pharm. 135 (1) (1996) 151–160, https://doi.org/10.1016/0378-5173(95)04466-3. G. Grindlay, L. Gras, J. Mora, M.T.C. de Loos-Vollebregt, Carbon-related matrix effects in inductively coupled plasma atomic emission spectrometry, Spectrochim. Acta, Part B 63 (2) (2008) 234–243, https://doi.org/10.1016/j.sab.2007.11.024. T. Mioduski, Identification of saturating solid phases in the system Ce2(SO4), 3–H2O from the solubility data, J. Therm. Anal. Calorim. 55 (3) (1999) 751, https://doi. org/10.1023/a:1010161212184. M.S. Wickleder, Inorganic lanthanide compounds with complex anions, Chem. Rev. 102 (6) (2002) 2011–2088, https://doi.org/10.1021/cr010308o. B.M. Casari, V. Langer, New structure type among octahydrated rare-earth sulfates, β-Ce2(SO4)3·8H2O, and a new Ce2(SO4)3·4H2O polymorph, Z. Anorg. Allg. Chem. 633 (7) (2007) 1074–1081, https://doi.org/10.1002/zaac.200700003. I. Persson, Hydrated metal ions in aqueous solution: how regular are their structures? Pure Appl. Chem. 82 (10) (2010) 1901–1917, https://doi.org/10.1351/PAC-
9
Contents lists available at ScienceDirect
Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Separation of valuable elements from NiMH battery leach liquor via antisolvent precipitation Kivanc Korkmaz, Mahmood Alemrajabi, Åke C. Rasmuson, Kerstin M. Forsberg
T
⁎
KTH Royal Institute of Technology, Department of Chemical Engineering, Stockholm, Sweden
A R T I C LE I N FO
A B S T R A C T
Keywords: Hydrometallurgy Anti-solvent crystallization NiMH battery recycling Rare earth recovery
Rare earth elements (REE) have been selectively recovered from NiMH battery leach liquors by antisolvent precipitation. The active anode material was leached using sulfuric acid. The REE were then separated from the other elements by precipitation as sulfates after addition of either ethanol or 2-propanol (antisolvent). In a second step, Ni and Co are separated as sulfates by the same technique. The concentration of elements in different acid alcohol mixtures at 25 °C and −10 °C respectively are presented as a function of time after addition of the alcohol, and the optimum conditions for separation of the REE in pure form are presented. Under optimum conditions, 5.6 mol/L (Organic/Aqueous (O/A) volumetric ratio = 0.7) of 2-propanol at 25 °C, 82% of the REE have precipitated 3 h after addition of the antisolvent and the purity is 99.9%.
1. Introduction Nickel metal hydride (NiMH) batteries are used to power hybrid electric vehicles (HEV). The NiMH batteries contain high amounts of valuable elements such as nickel, cobalt and rare earth elements (REE). This makes end-of-life NiMH batteries an excellent candidate for urban mining. From a European perspective, this is not only justified by the high economic values of the metals but also by the high supply risk of the critical elements Co and REE [1–4]. The REE have a high demand due to their key importance in various products in the form of e.g. battery alloys and permanent magnets. It is foreseen that this demand for REE, especially praseodymium, neodymium, and dysprosium, will increase in coming years due to their use as part of strong magnets for various applications [1,3,5,6]. The Panasonic prismatic NiMH module HEV battery used by Toyota Prius has been characterized in different studies [7,8]. These batteries consist of nickel hydroxide in the cathode, with additives of Co, Zn, and Y, and an AB5 type alloy in the anode (A: La, Ce, Nd, Pr, B = Ni, Co, Mn, Al) [6–9]. The valuable elements can be recovered from end-of-life batteries by pyrometallurgical or hydrometallurgical processes [9–14]. Pyrometallurgical processes are simple but the energy demand is high compared to hydrometallurgical processes. Furthermore, the REE ends up in a slag. The REE can be recovered from the slag by further processing which consists of various hydrometallurgical steps [12,15]. By hydrometallurgical processes a full recovery of all the valuable metals as salts with high purity is possible. Recovery of valuable elements (Ni,
⁎
Co, and REE) from NiMH batteries via hydrometallurgical processing starts with an almost complete dissolution of the battery material followed by solvent extraction and/ or precipitation to separate the elements in different fractions of economic value [8,12,16–22]. Precipitation is widely used in hydrometallurgical processes for separation and purification purposes [23–25]. Precipitation from acidic leach liquors can be achieved by different methods such as evaporation of the solvent or by neutralization. Evaporation has a high energy cost and is not a good choice for corrosive solutions. Further, it is difficult to sustain selective precipitation of a specific salt in evaporation and neutralization precipitation processes and the precipitate is often of low quality in terms of size and purity [24,26,27]. One alternative technique is called antisolvent precipitation or organic displacement crystallization. This technique is based on changing the solubility of the solute and creating a supersaturated solution by adding a water-miscible organic solvent, thus forcing the targeted salts to precipitate. The ability to lower the solubility of some inorganic solutes via the addition of an organic solvent has been documented in previous studies [24,26,28]. The ability of a solvent to solubilize an ion can be captured by the dielectric constant (ε) of the solvent. The dielectric constant is a measure of the polarizability of a substance. Water, which has a relatively high dielectric constant, can attract and form layers surrounding both negatively and positively charged ions and thus keep them apart. Alcohols have lower dielectric constants than water, which means that they have a lower ability to keep charged ions apart. Thus, by adding alcohols to water the solubility of the solutes decreases and if the
Corresponding author at: KTH Royal Institute of Technology, Department of Chemical Engineering, Teknikringen 42, SE-100 44 Stockholm. E-mail address: [email protected] (K.M. Forsberg).
https://doi.org/10.1016/j.seppur.2019.115812 Received 7 May 2019; Received in revised form 3 July 2019; Accepted 13 July 2019 Available online 15 July 2019 1383-5866/ © 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/BY/4.0/).
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al.
saturation point is exceeded precipitation occurs. When the carbon chain of aliphatic compounds is longer the solvent possesses a more hydrophobic character resulting in a lower dielectric constant [28]. In addition, an organic solvent can have an affinity for water molecules thus decreasing the water activity and consequently the solubility of the hydrated solutes [29,30]. Anti-solvent precipitation has many applications in e.g. specialty chemicals production and pharmaceutical production but only a few applications in inorganic processing within hydrometallurgy. An early example is the recovery of nickel sulfate from the de-copperized electrolyte, where the purity of the nickel sulfate product was high enough to be considered for use in the electroplating industry [27]. After the precipitation step, it is possible to separate the antisolvent from the acid by distillation and thereby be able to recirculate both the acid and the antisolvent to the process. In this work, the selective separation of REE from NiMH battery leach liquor by antisolvent precipitation has been systematically investigated. To the best of our knowledge antisolvent precipitation of REE sulfate salts from NiMH battery, leach liquors have not yet been investigated. It is a suitable method to selectively recover the REE as highly soluble sulfate salts in a process where the solvents can be recovered and reused.
Table 2 Concentration of alcohol for different organic to aqueous (O/A) volumetric ratios. Volumetric ratio, O/ A (–)
Concentration1 of ethanol (mol/L)
Concentration1 of 2propanol (mol/L)
0.1 0.3 0.34 0.45 0.5 0.56 0.7 0.9 1.1 1.3 1.5
1.61 4.15 4.53 5.64 6.06 6.54 7.55 8.74 9.72 10.53 11.22
1.21 3.11 – – 4.53 – 5.64 6.54 7.27 7.87 8.39
1
Expressed in moles per total volume of liquid.
addition of the alcohols to the initial aqueous solution and by a change in temperature. Since the volumes of alcohol and aqueous solution are not additive, the total volumes were measured and incorporated into the calculations. In addition, the decrease in the concentration of the elements due to precipitation must be distinguished from the decrease in concentration by dilution resulting from the addition of the antisolvent. Liquid samples were diluted 100 times and stored in HDPE bottles before ICP-OES analysis. Some samples were further diluted to reach appropriate concentrations for ICP-OES measurements of elements present at high concentration (Ni, La). The presence of alcohol can have an influence on both aerosol generation and transport and on the plasma characteristics in ICP-OES analysis [31]. However, the concentration of alcohol was low in all the samples analyzed by ICPOES (< 0.1 mol/L) with negligible matrix effects. Solid samples were collected, washed with ethanol mixed with water and then with pure ethanol and dried at room temperature before further analysis. Scanning electron microscopy (SEM) with an EDS detector and powder-Xray diffraction (XRD) analyses were conducted on solid samples. The complete set of experiments is given in Table 1. The experiments were designed to study the composition of the aqueous phase as a function of time after addition of specific amounts of either ethanol or 2-propanol. The temperature was kept constant at 25 °C or −10 °C. A flowsheet of the process is presented in Fig. 1.
2. Experimental procedure A discharged Panasonic prismatic NiMH module HEV battery was used for the experimental work. The battery modules were manually dismantled and the anode active material, containing the main part of the REE present in the battery together with the valuable elements Ni and Co, was scraped from the supports. The active anode material contains 33% by mass of REE and the REE are present in an AB5 type alloy [7]. Active anode material was leached with 2 mol/L H2SO4 at 25 °C for 4 h under atmospheric pressure and constant stirring, enough to suspend all solid material. After 4 h most of the material was dissolved and a small amount of leach residue was separated from the liquid phase by filtration. Ethanol and 2-propanol were selected as antisolvents. These alcohols are not expected to react with the sulfuric acid under the conditions applied. The respective alcohol was added to the leach liquor via a pipette or with controlled injection rates via a syringe pump. The injection time is short (see Table 1) and time zero is always reported as the time after complete addition of the antisolvent. After each addition (reported as the volumetric ratio of organic (antisolvent) to the aqueous phase (leach liquor), O/A, see Table 2) the solutions were left for a certain amount of time (durations up to 7 days) under constant stirring. Samples were collected at different times using syringes from which the solid material was immediately removed from the liquid phase using syringe filters (0.2 µm). The volumes and masses of all samples and added alcohols were recorded and the data is presented as the concentration of elements in mass or mole per unit volume initial aqueous solution (i.e. not the new solvent mixture). This is important since the density of the solvent mixture will change by the
3. Results and discussion 3.1. Effect of time In Fig. 2a, the concentrations of Ni and La at different O/A ratios after addition of ethanol at 25 °C are presented as a function of time. The concentration of Ni is read from the y-axis to the left while the concentration of La is read from the y-axis to the right. The dosing of ethanol took three minutes and the time when all antisolvent has been
Table 1 Set of experiments. Exp. set
Organic antisolvent
Organic to acid (O/A) volumetric ratios
1 2 3: 3: 4: 4: 5: 5:
Ethanol 2-propanol 2-propanol Ethanol 2-propanol Ethanol 2-propanol Ethanol
0.1 0.1 0.5 0.34 0.5 0.34 0.7 0.1
A B A B A B
0.3 0.3 0.7 0.45 0.7 0.45 0.9 0.3
0.5 0.5 0.9 0.56 0.9 0.56 – 0.7
0.7 0.7 – 0.8 – – – 0.9
0.9 0.9 – 0.9 – – – –
1.1 1.1 – – – – – –
1.3 1.3 – – – – – –
1.5 1.5 – – – – – –
Temp. (°C)
Duration1 (h = hours, d = days)
Antisolvent addition rate2 (mL/min)
25 25 25 25 25 25 −10 −10
7d 7d 10 d 10 d 24 h 3h 3h 3h
3 3 3 3 1 1 3 3
Time the solutions were left stirred at the specific O/A ratio before final sampling. Samples were taken as a function of time in some of the experiments. The final concentrations of added antisolvent were in the range of 1.2–11.2 mol/L. This corresponds to a dosing time from 1 to 9 min depending on the antisolvent type, final molarity, and dosing rate. 1 2
2
Separation and Purification Technology 234 (2020) 115812 35
12
30
10 Ni: O/A=0.37
25
8
20 6 15 4
10 5
2
0
0
La Concentration (g/L)
Ni Concentration (g/L)
K. Korkmaz, et al.
Ni: O/A=0.52 Ni: O/A=0.67 Ni: O/A=0.8 Ni: O/A=0.9 La: O/A=0.37 La: O/A=0.52 La: O/A=0.67 La: O/A=0.8
a
La: O/A=0.9
Time 35
12
30
10
Ni Concentration (g/L)
8
20 6 15 4
10
La Concentration (g/L)
Ni Set 2, O/A=0.5 25
Ni Set 3A, O/A=0.5 Ni Set 4A, O/A=0.5 Ni Set 2, O/A=0.7 Ni Set 3A, O/A=0.7 Ni Set 4A, O/A=0.7 Ni Set 3A, O/A=0.9 Ni Set 4A, O/A=0.9
2
5
La Set 3A, O/A=0.5 La Set 3A, O/A=0.7
0
La Set 3A, O/A=0.9
0
b
Time
Fig. 2. Concentration of Ni and La as a function of time at 25 °C after addition of (a) ethanol (Set 3: Part B) and (b) 2-propanol (set 2, 3 and 4, part A). Abbreviations: m: minutes, h: hours, d: days.
Fig. 1. Flowsheet of the process.
Concentration (g/L)
added are reported as time zero. The concentrations are reported as the mass of element per unit volume initial aqueous phase (acidic leach liquor in the absence of alcohol). This means that the reported concentrations will not change if no precipitation occurs. Some experiments were performed in duplicate and the results indicate that the experiments are reproducible (see Fig. 2b and supplementary data Fig. B). The results show that most of La have precipitated after 10 min at an O/A ratio of 0.56, 0.80 and 0.90 while up to two hours are needed to reach a constant concentration of La in the solution at an O/A ratio of 0.45. For an O/A ratio of 0.34, up to three hours are needed to reach a constant concentration of La. No precipitation of Ni was observed at an O/A ratio of 0.34, 0.45 and 0.56 during the length of the experiments (10 days). At an O/A ratio of 0.8, there is a slight decrease in Ni over time, indicating that a solid phase containing Ni is precipitating. For an O/A ratio of 0.9 (8.74 mol/L of ethanol), there is instantaneous precipitation visible by the naked eye and no further decrease in Ni from 10 min to 24 h. The rapid decrease in the concentration of Ni at higher O/A ratio can be explained by a higher supersaturation giving a higher driving force for nucleation and crystal growth. The concentration of Ni was also measured nine days after antisolvent addition at an O/A ratio of 0.9 and the concentration was still in the same range (22.7 g/L). The same trends can be observed up to 10 days after the addition of 2propanol, see Fig. 2b. However, here the concentration of Ni continues to decrease during 2 days for an O/A ratio of 0.9 (6.54 mol/L of 2propanol), and then the concentration increases. This can be explained by the dissolution of the solid phase containing Ni indicating that the solid phase that initially nucleated is not thermodynamically stable under the final conditions. Fig. 3 shows that the precipitation of Ce, Nd, Pr, and Co occurs within the first 10 min at an O/A ratio of 0.9 while Y, Al, and Mn
Concentration (g/L)
a
b
3.0 2.8 2.5 2.3 2.0 1.8 1.5 1.3 1.0 0.8 0.5 0.3 0.0
Co Mn Al Y Ce Pr Nd 0
10
30
60 120 Time (minutes)
180
360
1440
3.3 3.0 2.8 2.5 2.3 2.0 1.8 1.5 1.3 1.0 0.8 0.5 0.3 0.0
Co Mn Al Y Ce Pr Nd 0
10min 30min
1h
2h
3h 6h Time
1d
2d
4d
7d
10d
Fig. 3. (a) concentration of elements as a function of time at 25 °C in 8.74 mol/ L ethanol (O/A = 0.9) and (b) in 6.54 mol/L ethanol (O/A = 0.56) (set 3: Part B).
3
Separation and Purification Technology 234 (2020) 115812
Concentration (g/L)
K. Korkmaz, et al. 3.0 2.8 2.5 2.3 2.0 1.8 1.5 1.3 1.0 0.8 0.5 0.3 0.0
Concentration (g/L)
b
Co Mn Al Y Ce Pr Nd 0
a
solid phases transformed during this time. However, the mixture of phases detected in the present work (e.g. both Ce2(SO4)3·4H2O and Ce2(SO4)3·9H2O) indicates that equilibrium conditions have not yet been reached seven days after addition of antisolvent. A mixture of different REE sulfate hydrates were also detected seven days after adding ethanol as antisolvent at an O/A ratio of 0.7, see supplementary data Fig. A. In order to study the solid phases containing Ni and Co, which precipitates at higher O/A ratios, an experiment was performed in which the REE containing solid phase was filtered off 24 h after adding 2-propanol (O/A ratio of 0.5). Thereafter an additional amount of 2propanol was added to obtain an O/A ratio of 0.9. The solid phase was then filtered off seven days after addition of the antisolvent. The major solid phases detected in this sample were NiSO4·6H2O and CoSO4·6H2O and a mixed phase CoNi(SO4)2(H2O)12 was also detected (See Fig. 5b). Scanning electron images of precipitates collected seven days after the addition of 2-propanol, at an O/A ratio of 0.9, is presented in Fig. 6. The sample contains a mixture of small and large particles. EDS was used to investigate the composition of the particles (see supplementary data, Table A). It was found that the small sized (micrometer scale) particles contained REE while the larger (mm scale) particles contained either Ni or Co. The results when dosing ethanol and 2-propanol respectively at a rate of either 1 mL/min or 3 mL/min was applied are presented in Fig. 7. The times when all antisolvent had been added are reported as time zero, which corresponds to 7 and 2.3 min for a dosing rate of 1 and 3 mL/min respectively to reach an O/A of 0.7. The results show that there is no drastic difference in applying these two dosing rates.
10min 30min
1h
2h
3h 6h Time
1d
2d
4d
7d
3.3 3.0 2.8 2.5 2.3 2.0 1.8 1.5 1.3 1.0 0.8 0.5 0.3 0.0
10d
Co Mn Al Y Ce Pr Nd 0
10min 30min
1h
2h
3h 6h Time
1d
2d
4d
7d
10d
Fig. 4. Concentration of elements as a function of time in 2-propanol at 25 °C for (a) O/A = 0.9, (b) O/A = 0.7 (set 3: Part A).
remain in solution during the whole duration of the experiment (24 h). For a lower concentration of ethanol (O/A = 0.56) and up to 10 days after antisolvent addition, the same trends are observed for all elements except Co. Under these conditions, Co remains in solution. The concentrations of Ce, Nd, Pr, Y, Co, Mn and Al after the addition of 2-propanol are presented in Fig. 4. For an O/A ratio of 0.9 Ce, Pr, Nd, and Co precipitate within 10 min after addition of the antisolvent while the concentration of Y, Al and Mn remain constant. After three hours the concentration of Co has increased, indicating dissolution of the solid phase containing Co. This is the same experiment as presented in Fig. 2b where the increasing concentration of Ni is observed after about four days. The concentrations of the elements after 10 days are lower in the presence of 2-propanol than ethanol at the same O/A ratios, except for Al and Y that remain in solution under all conditions investigated. The solid phase collected seven days after the addition of 2-propanol, at an O/A ratio of 0.5, (exp. set 2) consisted of a mixture of different solid phases containing REE (see Fig. 5a). The major phases (in amount) found under these conditions were rare earth sulfate hydrates and yttrium oxysulfates; e.g. both Ce2(SO4)3·4H2O and Ce2(SO4)3·9H2O was detected as well as Y2O2SO4 and Y2(SO4)3. It is known that the REE can form a range of different sulfate hydrate salts, including polymorphs [32–34]. In pure water at 25 °C the lighter REE (Ce, La) are most stable as nonahydrates while the heavier REE form octahydrates. Lower hydrates are generally obtained at a higher temperature and when the sulfuric acid concentration increases. In addition, organic solvents can decrease the water activity, giving rise to lower hydrates being the most stable form upon the addition of alcohol [30]. To the best of our knowledge, there is no information in the literature about which REE sulfate hydrate forms that are most stable in different mixtures of sulfuric acid and alcohols. Due to the complexity of the system, it is difficult to determine which is the most stable solid phase for each REE under each condition and the solubility of these phases. Especially since the phases nucleating upon addition of the antisolvent might not be the phases that are the thermodynamically most stable under the applied conditions. In the present work, a mixture of solid REE containing sulfate hydrates was detected in samples collected seven days after antisolvent addition. The solid phase was washed with pure ethanol and dried under ambient conditions (at room temperature) and analyzed by powder XRD the same day; it is possible that the
3.2. Effect of solvent composition and antisolvent polarity The concentration of the different elements at 25 °C, seven days after the addition of different amounts of ethanol and 2-propanol respectively (exp. set 1 and 2) are presented in Figs. 8–10. At an organic to aqueous (O/A) ratio of 0.5 about 49% by mass of the REE has precipitated seven days after addition of antisolvent while Ni, Co, Mn, and Al remain in solution, both when using ethanol and 2propanol as antisolvents, see Figs. 8–10. An organic to the aqueous ratio of 0.5 corresponds to a concentration of 6.1 mol/L of ethanol and 4.5 mol/L of 2-propanol. As can be seen in Figs. 8–10, as the amount of antisolvent added increases the concentration of the REE decreases. Nickel and cobalt precipitate from the leach liquor at an O/A ratio of between 0.7 and 0.9 (7.6–8.7 mol ethanol/L and 5.6–6.5 mol 2-propanol/L). At the highest O/A ratio of 1.5, about 95–99% of the REE, 72.7% of Ni and 71.2% of Co (by mass) have precipitated. No precipitation of Al and Mn could be detected even at an O/A ratio of 1.5 (11.2 mol ethanol/L and 8.4 mol 2-propanol/L). The total concentration of Mn and Al are slightly higher for O/A ratios above 0.7, see Figs. 8 and 9. This can be explained by the large amount of Ni, La, and Co precipitating under these conditions. These elements precipitate as metal sulfate hydrate salts (see Fig. 5) and thereby the solution becomes concentrated in terms of the remaining elements. In Figs. 11 and 12 the molar concentration of the REE in different concentrations of the alcohols are presented. The concentration of the REE (seven days after antisolvent addition) is in the same range or slightly lower in 2-propanol compared to ethanol. It is reasonable that a higher concentration of ethanol than 2-propanol is needed to precipitate the REE since the dielectric constant of ethanol (25) is higher than that of 2-propanol (20) at 25 °C. A trend can be found considering the variation in concentration of the respective REE and their atomic numbers. The lightest lanthanide La (lowest charge density) is present at the highest concentration while the heaviest lanthanide Nd (highest charge density) is present at the lowest concentration. Yttrium is not a lanthanide but is counted as one of the REE due to its similar ionic radius and thus behavior (the REE all have a mainly ionic character of bonding). The ionic radius of hydrated Y+3 (1.02 Å, 8-coordinate) is 4
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al.
Fig. 5. XRD analyses of the precipitate obtained for (a) O/A = 0.5 and (b) O/A = 0.9 with 2-propanol as antisolvent.
smaller than that of Pr+3 (1.16 Å, 9-coordinate) and thus Y+3 has the highest charge density of the investigated REE [35]. Yttrium precipitates after addition of 4.15 mol/L of ethanol and 3.11 mol/L of 2propanol respectively where the concentration of Y in the aqueous phase is lower than the other rare earth elements (see Fig. 11). However, as the concentration of the alcohols increases the detected decrease in the concentration of Y is less than for the lanthanides. This behavior requires further analysis. However, it is important to note that a mixture of solid phases is detected in the precipitate after seven days (see Fig. 5). Thus, equilibrium conditions have not been reached after seven days and the solid phases still slowly transform into more stable phases. In Fig. 13 the concentration of REE as a function of time after addition of ethanol or 2-propanol respectively at a concentration of 4.53 mol/L are presented. All antisolvent was added at a rate of 1 mL/
min (experiment Set 4 Part A and B). As can be seen in Fig. 13 the concentration of Ce, Nd and Pr are slightly lower in 4.53 mol/L of 2propanol than in 4.53 mol/L of ethanol at all points in time after precipitation has occurred. By comparing with the data in Figs. 8 and 9 (seven days after antisolvent addition) by interpolating between the data at an O/A ratio of 0.3 and 0.5 it can be seen that the concentrations of the REE are slightly lower after 180 min than after seven days. This could be explained by that the solid phases initially precipitating are slowly transformed over time into other more stable phases and equilibrium conditions have not been reached after 180 min. The results show that it is possible to separate the elements in 3 groups: (1) REE, (2) Ni and Co and (3) Al and Mn. The optimal condition for selective separation of the REE from the leach solution is an O/A ratio of 0.7, using either 2-propanol or ethanol as antisolvent.
5
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al. 3.5
Concentration (g/L)
3.0 2.5 Co
2.0
Mn Al
1.5
Y 1.0
Ce Pr
0.5
Nd
0.0 Original Liq
0.1
0.3
0.5
0.7
0.9
1.1
1.3
1.5
O/A (ml/ml)
Fig. 8. Concentration of elements versus O/A ratios with ethanol assisted precipitation (set 1). Fig. 6. Scanning electron microscopy images of crystals collected 7 days after the addition of 2-propanol (O/A = 0.9). Analysis by EDS showed that the larger crystals contain Ni or Co while the adhering fine particles contained REE.
3.5 3 Concentration (g/L)
Concentration (g/L)
3
2 La-1ml/min
2.5
Mn
2
Al
1.5
Y Ce
1
Pr
La-3ml/min
0.5
Ce-1ml/min Ce-3ml/min 1
Co
Nd
0
Pr-1ml/min Pr-3ml/min
O/A (ml/ml)
a
Fig. 9. Concentration of elements versus O/A ratios with 2-propanol assisted precipitation (set 2).
0 0
10
30 60 Time (minutes)
180
1440
35 Ni (2-propanol)
30
La (2-propanol) Concentration (g/L)
Concentration (g/L)
3
2 La-1ml/min
25
Ni (ethanol)
20
La (ethanol)
15 10 5
La-3ml/min Ce-1ml/min
0
Ce-3ml/min 1
Pr-1ml/min
O/A (ml/ml)
Pr-3ml/min
Fig. 10. Concentration of Ni and La versus O/A ratios (Set 1 and 2).
b
three hours after antisolvent addition at 25 °C and −10 °C respectively is presented. At 25 °C the solution is undersaturated to saturated with respect to Co both in ethanol and 2-propanol while at −10 °C precipitation of Co has occurred in both systems. Lanthanum and cerium have precipitated from the leach liquor both at 25 °C and −10 °C 180 min after addition of either ethanol or 2-propanol. The decrease in the concentration of La is 7.7% in ethanol and 2.9% in 2-propanol when lowering the temperature from 25 °C to −10 °C. The decrease in the concentration of Ce is also low lowering the temperature from 25 °C to −10 °C. Furthermore, it can be observed that the concentrations of Ni and Co are lower in 2-propanol than in ethanol at the same volumetric dosage at −10 °C. The results are similar for an O/A ratio of 0.9 for ethanol and 2-propanol respectively (see Fig. C in the appendix). It was also found that the precipitation of all elements occurred under a period
0 0
10
30 Time (minutes)
60
180
Fig. 7. Effect of dosing rate on REE concentrations with respect to time (a) 2propanol; O/A = 0.7, (b) ethanol; O/A = 0.56.
3.3. Effect of temperature In Fig. 14 the concentration of Ni at 25 °C and at −10 °C three hours after addition of ethanol and 2-propanol respectively is presented. At 25 °C the solution is undersaturated to saturated with respect to Ni both in ethanol and 2-propanol while at −10 °C precipitation of Ni has occurred in both systems. In Fig. 15 the concentration of La, Ce, and Co 6
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al. 600
Concentration (mmol/L)
500 400 300 200 100 0 Ni/Ethanol
Ni/2-Propanol
Original Liquid
25oC
-10oC
Fig. 14. Concentration of Ni after 180 min in experiments at −10 °C and 25 °C after addition of ethanol and 2-propanol with O/A = 0.7.
Fig. 11. Concentration of Ce, Nd, Pr, and Y versus alcohol concentration.
70
Concentration (mmol/L)
60 50 40 30 20 10 0
Fig. 12. Concentration of La and Ce versus alcohol concentration.
Ce/Ethanol
Co/Ethanol
La/Ethanol Ce/2-Propanol Co/2-Propanol La/2-Propanol
Original Liquid 25.0
25oC
-10oC
Fig. 15. Concentration of Ce, Co and La after 180 min in experiments at −10 °C and 25 °C after addition of ethanol and 2-propanol with O/A = 0.7. Ce, 2Propanol Ce, Ethanol
15.0
10.0
Nd, 2Propanol Nd, Ethanol
5.0
Pr, 2Propanol Pr, Ethanol
Precipitated fraction (%)
Concentration (mmol/L)
20.0
100 80 60 40 20 0
0.0 0
10
30 Time (minutes)
60
180
Fig. 13. Elemental concentrations in 4.53 mol/L ethanol (O/A = 0.34) and 2propanol (O/A = 0.50).
-10oC
25oC
Fig. 16. Fraction of elements precipitated after 180 min for O/A = 0.7.
of fewer than 30 min at both low and high temperature under all conditions studied (see Fig. C in the appendix). Since the concentration of Ni and Co in the leach liquor decrease to a higher extent than the REE do when decreasing the temperature from 25 °C to −10 °C the potential to separate the REE from the Ni and Co decreases. In addition, cooling the solution to −10 °C cost energy. It is thus better to perform the separation at 25 °C. The fractionated percentages of La, Ce, Co and Ni with respect to the reagent used and at −10 °C and 25 °C can be seen in Fig. 16.
containing solid phases are preferably filtered of 0.5–1 h after addition of the antisolvent (Fig. 2). After addition of 7.6 mol/L (O/A = 0.56) of ethanol at 25 °C, 86.5% of the REE (89.1% of the light REE) have precipitated three hours after antisolvent addition. In a batch process seeds of REE sulfate hydrates will be added, which will have a direct impact on the time of operation. The addition of seeds and time of operation needs to be optimized in upscaling of the process. The precipitated mass fraction of REE (purity) is calculated as the mass of precipitated REE divided by the total mass of precipitated metal ions (La, Ce, Nd, Pr, Y, Ni, Co, Mn, and Al). The masses are obtained from a mass balance based on the concentrations in the aqueous phase, measured by ICP-OES, before and after precipitation. The purity of the REE products obtained under different conditions determined by this method is presented in Table 3. The highest purity is obtained three hours after addition of 7.6 mol/L of ethanol (99.99%). Similarly, after
3.4. Industrial perspective Antisolvent precipitation can be applied to selectively separate the REE (La, Ce, Nd, Pr, Y) from the other elements present in NiMH battery leach liquor. If the separation is operated in batch scale at 25 °C the REE 7
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al.
doi.org/10.1016/j.seppur.2019.115812.
Table 3 Precipitation percentages and purities at 25 °C (Set 1, 2, 3A and 3B). Alcohol
Time
O/A (–)
Conc. (mol/L)
Recovery, light REE (%)
Recovery, tot. REE (%)
Purity of REE (%)
Ethanol Ethanol 2-propanol 2-propanol
3h 3h 3h 3h
0.56 0.90 0.70 0.90
7.55 8.74 5.64 6.54
89.12 93.84 84.40 90.79
86.52 91.32 81.88 88.29
99.99 68.40 99.99 56.17
References [1] K. Binnemans, P.T. Jones, T. Müller, L. Yurramendi, Rare earths and the balance problem: how to deal with changing markets? J. Sustain. Metall. 4 (1) (2018) 126–146, https://doi.org/10.1007/s40831-018-0162-8. [2] E. Commission, Critical raw materials for the EU, in: Report of the Ad-hoc Working Group on Defining Critical Raw Materials, 2010. [3] D. Guyonnet, M. Planchon, A. Rollat, V. Escalon, J. Tuduri, N. Charles, S. Vaxelaire, D. Dubois, H. Fargier, Material flow analysis applied to rare earth elements in Europe, J. Clean. Prod. 107 (2015) 215–228, https://doi.org/10.1016/j.jclepro. 2015.04.123. [4] S.W.J.H. Christina Tsiarta, in: E. Commission (Ed.), Final Implementation Report for the Directive 2006/66/EC on Batteries and Accumulators, 10 July 2015. [5] US Department of Energy, Critical Materials Strategy, 2011. [6] A. Rollat, D. Guyonnet, M. Planchon, J. Tuduri, Prospective analysis of the flows of certain rare earths in Europe at the 2020 horizon, Waste Manage. 49 (2016) 427–436, https://doi.org/10.1016/j.wasman.2016.01.011. [7] K. Korkmaz, M. Alemrajabi, Å.C. Rasmuson, K. Forsberg, Sustainable hydrometallurgical recovery of valuable elements from spent nickel-metal hydride HEV batteries, Metals 8 (12) (2018), https://doi.org/10.3390/met8121062. [8] K. Larsson, C. Ekberg, A. Odegaard-Jensen, Dissolution and characterization of HEV NiMH batteries, Waste Manage. 33 (3) (2013) 689–698, https://doi.org/10.1016/j. wasman.2012.06.001. [9] K. Binnemans, P.T. Jones, B. Blanpain, T. Van Gerven, Y. Yang, A. Walton, M. Buchert, Recycling of rare earths: a critical review, J. Cleaner Prod. 51 (2013) 1–22, https://doi.org/10.1016/j.jclepro.2012.12.037. [10] C. Tunsu, M. Petranikova, M. Gergorić, C. Ekberg, T. Retegan, Reclaiming rare earth elements from end-of-life products: a review of the perspectives for urban mining using hydrometallurgical unit operations, Hydrometallurgy 156 (2015) 239–258, https://doi.org/10.1016/j.hydromet.2015.06.007. [11] D.C.R. Espinosa, A.M. Bernardes, J.A.S. Tenório, An overview on the current processes for the recycling of batteries, J. Power Sources 135 (1–2) (2004) 311–319, https://doi.org/10.1016/j.jpowsour.2004.03.083. [12] J. Nan, D. Han, M. Yang, M. Cui, X. Hou, Recovery of metal values from a mixture of spent lithium-ion batteries and nickel-metal hydride batteries, Hydrometallurgy 84 (1–2) (2006) 75–80, https://doi.org/10.1016/j.hydromet.2006.03.059. [13] S. Al-Thyabat, T. Nakamura, E. Shibata, A. Iizuka, Adaptation of minerals processing operations for lithium-ion (LiBs) and nickel metal hydride (NiMH) batteries recycling: critical review, Miner. Eng. 45 (2013) 4–17, https://doi.org/10.1016/j. mineng.2012.12.005. [14] B. Ebin, M. Petranikova, C. Ekberg, Physical separation, mechanical enrichment and recycling-oriented characterization of spent NiMH batteries, J. Mater. Cycles Waste Manage. (2018), https://doi.org/10.1007/s10163-018-0751-4. [15] V. Innocenzi, N.M. Ippolito, I. De Michelis, M. Prisciandaro, F. Medici, F. Vegliò, A review of the processes and lab-scale techniques for the treatment of spent rechargeable NiMH batteries, J. Power Sour. 362 (2017) 202–218, https://doi.org/ 10.1016/j.jpowsour.2017.07.034. [16] P. Zhang, T. Yokoyama, O. Itabashi, Y. Wakui, T.M. Suzuki, K. Inoue, Hydrometallurgical process for recovery of metal values from spent nickel-metal hydride secondary batteries, Hydrometallurgy 50 (1) (1998) 61–75, https://doi. org/10.1016/S0304-386X(98)00046-2. [17] P. Zhang, T. Yokoyama, O. Itabashi, Y. Wakui, T.M. Suzuki, K. Inoue, Recovery of metal values from spent nickel–metal hydride rechargeable batteries, J. Power Sour. 77 (2) (1999) 116–122, https://doi.org/10.1016/S0378-7753(98)00182-7. [18] N. Tzanetakis, K. Scott, Recycling of nickel-metal hydride batteries. I: dissolution and solvent extraction of metals, J. Chem. Technol. Biotechnol. 79 (9) (2004) 919–926, https://doi.org/10.1002/jctb.1081. [19] D.A. Bertuol, A.M. Bernardes, J.A.S. Tenório, Spent NiMH batteries-the role of selective precipitation in the recovery of valuable metals, J. Power Sour. 193 (2) (2009) 914–923, https://doi.org/10.1016/j.jpowsour.2009.05.014. [20] L.E.O.C. Rodrigues, M.B. Mansur, Hydrometallurgical separation of rare earth elements, cobalt and nickel from spent nickel-metal-hydride batteries, J. Power Sour. 195 (11) (2010) 3735–3741, https://doi.org/10.1016/j.jpowsour.2009.12.071. [21] X. Yang, J. Zhang, X. Fang, Rare earth element recycling from waste nickel-metal hydride batteries, J. Hazard. Mater. 279 (2014) 384–388, https://doi.org/10.1016/ j.jhazmat.2014.07.027. [22] L. Pietrelli, B. Bellomo, D. Fontana, M. Montereali, Characterization and leaching of NiCd and NiMH spent batteries for the recovery of metals, Waste Manage. 25 (2) (2005) 221–226, https://doi.org/10.1016/j.wasman.2004.12.013. [23] G.P. Demopoulos, Aqueous precipitation and crystallization for the production of particulate solids with desired properties, Hydrometallurgy 96 (3) (2009) 199–214, https://doi.org/10.1016/j.hydromet.2008.10.004. [24] D.A. Weingaertner, S. Lynn, D.N. Hanson, Extractive crystallization of salts from concentrated aqueous solution, Ind. Eng. Chem. Res. 30 (3) (1991) 490–501, https://doi.org/10.1021/ie00051a009. [25] P.A. Barata, M.L. Serrano, Salting-out precipitation of potassium dihydrogen phosphate (KDP). I. Precipitation mechanism, J. Cryst. Growth 160 (3) (1996) 361–369, https://doi.org/10.1016/0022-0248(95)00740-7. [26] G. Moldoveanu, Crystallisation of Inorganic Compounds with Alcohols, 2005. [27] G.A. Moldoveanu, G.P. Demopoulos, Producing high-grade nickel sulfate with solvent displacement crystallization, JOM 54 (1) (2002) 49–53, https://doi.org/10. 1007/bf02822606. [28] G.A. M, G.P. D, Organic solvent-assisted crystallization of inorganic salts from
addition of 5.6 mol/L (O/A = 0.7) of 2-propanol at 25 °C, 81.9% of the REE (84.4% of the light REE) have precipitated after three hours and the purity is high (99.99%). In a second step, the Ni and Co can be separated as a mixture of sulfate salts by the same technique, see Figs. 8–10. The REE are mainly obtained as REE sulfate hydrates which is advantageous due to the high solubility of these salts in water. The salts can thus easily be dissolved and further processed for individual separation of the REE e.g. by solvent extraction or chromatography in preparative scale [36]. For an industrial process, the choice of antisolvent should rely on aspects such as the economy, availability, and safety as well as the overall process outline including conditions for solvent recovery. Today, the market price of ethanol (1600 $/tonne) is higher than that of 2-propanol (1200 $/tonne) [37,38]. The antisolvent can be recovered from the aqueous phase after precipitation by e.g. distillation and then be reused as a precipitation agent [39–41]. 4. Conclusions It is possible to selectively separate rare earth elements (REE) from sulfuric acid NiMH battery leach liquors by addition of ethanol and 2propanol respectively. The REE precipitates as a mixture of different sulfate phases. The REE can be recovered with negligible co-precipitation of the other elements at an initial concentration of 7.6 mol/L of ethanol and 5.6 mol/L of 2-propanol at 25 °C. The total recovery of REE is 86.5% after addition of 7.6 mol/L of ethanol and 81.9% after addition of 5.6 mol/L of 2-propanol at 25 °C. The concentrations of the different REE 7 days after antisolvent addition correlate with their atomic numbers where the lightest lanthanide La (lowest charge density) is present at the highest concentration while the heaviest lanthanide Nd (highest charge density) is present at the lowest concentration. Yttrium does not follow the trend based on ionic size (or charge density) observed for the lanthanides. The concentration of the elements (7 days after antisolvent addition) is in the same range or slightly lower in 2propanol compared to ethanol. The concentration difference between the REE and the other main elements present in the leach liquor is less at −10 °C compared to 25 °C and thus it is better to perform the separation at 25 °C. The concentration of La decrease by 7.7% in ethanol and by 2.9% in 2-propanol when lowering the temperature from 25 °C to −10 °C while the concentration of Ni decreases by 42.5% in ethanol and by 66.4% in 2-propanol. Acknowledgements The authors would like to acknowledge the Swedish Energy Agency, Sweden for funding the project (project nr 37724-1) and Chalmers University of Technology, Department of Chemistry and Chemical Engineering for supplying the battery modules and Swedish Environmental Research Institute (IVL) for instrumentation and expertise in connection to conducting the nanofiltration experiments. Part of the work was also supported by the Swedish Foundation for Strategic Research, Sweden SSF with the grant number of IRT 11-0026. Appendix A. Supplementary material Supplementary data to this article can be found online at https:// 8
Separation and Purification Technology 234 (2020) 115812
K. Korkmaz, et al.
[29] [30]
[31]
[32]
[33] [34]
[35]
CON-09-10-22. [36] R.M. Ashour, M. Samouhos, E. Polido Legaria, M. Svärd, J. Högblom, K. Forsberg, M. Palmlöf, V.G. Kessler, G.A. Seisenbaeva, Å.C. Rasmuson, DTPA-functionalized silica nano-and microparticles for adsorption and chromatographic separation of rare earth elements, ACS Sustain. Chem. Eng. 6 (5) (2018) 6889–6900, https://doi. org/10.1021/acssuschemeng.8b00725. [37] M. Hirtzer, U.S. Ethanol Prices Drop to 13-year Lows on Bigger Supply, 2018 < https://www.reuters.com/article/usa-ethanol/u-s-ethanol-prices-drop-to13-year-lows-on-bigger-supply-idUSL2N1Y31EP > . [38] I. News, Europe IPA Spot Prices Fall on Propylene December Drop, Sustainability (2018) < https://www.icis.com/explore/resources/news/2018/12/05/10291138/ europe-ipa-spot-prices-fall-on-propylene-december-drop/ > . [39] Y. Yang, K. Boots, D. Zhang, A sustainable ethanol distillation system Food Bioprod. Process. 4 (2012) 92–105. [40] M. Gavahian, A. Farahnaky, S. Sastry, Ohmic-assisted hydrodistillation: a novel method for ethanol distillation 98 (2015). [41] N. Vorayos, T. Kiatsiriroat, N. Vorayos, Performance analysis of solar ethanol distillation, Renew. Energy 31 (15) (2006) 2543–2554, https://doi.org/10.1016/j. renene.2006.01.016.
acidic media, J. Chem. Technol. Biotechnol. 90 (4) (2015) 686–692, https://doi. org/10.1002/jctb.4355. D. Peeters, Hydrogen bonds in small water clusters: a theoretical point of view, J. Mol. Liq. 67 (1995) 49–61, https://doi.org/10.1016/0167-7322(95)00865-9. H. Zhu, C. Yuen, D.J.W. Grant, Influence of water activity in organic solvent + water mixtures on the nature of the crystallizing drug phase. 1. Theophylline, Int. J. Pharm. 135 (1) (1996) 151–160, https://doi.org/10.1016/0378-5173(95)04466-3. G. Grindlay, L. Gras, J. Mora, M.T.C. de Loos-Vollebregt, Carbon-related matrix effects in inductively coupled plasma atomic emission spectrometry, Spectrochim. Acta, Part B 63 (2) (2008) 234–243, https://doi.org/10.1016/j.sab.2007.11.024. T. Mioduski, Identification of saturating solid phases in the system Ce2(SO4), 3–H2O from the solubility data, J. Therm. Anal. Calorim. 55 (3) (1999) 751, https://doi. org/10.1023/a:1010161212184. M.S. Wickleder, Inorganic lanthanide compounds with complex anions, Chem. Rev. 102 (6) (2002) 2011–2088, https://doi.org/10.1021/cr010308o. B.M. Casari, V. Langer, New structure type among octahydrated rare-earth sulfates, β-Ce2(SO4)3·8H2O, and a new Ce2(SO4)3·4H2O polymorph, Z. Anorg. Allg. Chem. 633 (7) (2007) 1074–1081, https://doi.org/10.1002/zaac.200700003. I. Persson, Hydrated metal ions in aqueous solution: how regular are their structures? Pure Appl. Chem. 82 (10) (2010) 1901–1917, https://doi.org/10.1351/PAC-
9