Electrochemical recovery of cobalt using nanoparticles film of copper hexacyanoferrates from aqueous solution

Journal of Hazardous Materials 384 (2020) 121252

Contents lists available at ScienceDirect

Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat

Electrochemical recovery of cobalt using nanoparticles film of copper hexacyanoferrates from aqueous solution

T

Xinxin Longa, Rongzhi Chena, , Jihua Tana, , Yifeng Lub, Jixiang Wanga, Tijun Huangb, Qin Leia ⁎

a b

⁎

College of Resources and Environment, University of Chinese Academy of Sciences, Yuquan Road 19A, Beijing, 100049, China School of Life Sciences, Yunnan University, East Outer Ring Road, Kunming, 650500, China

GRAPHICAL ABSTRACT

ARTICLE INFO

ABSTRACT

Editor: Xiaohong Guan

Nanoparticles film of copper metal hexacyanoferrates (CuHCF) was fabricated to electrochemically separate Co2+ in aqueous solutions under various conditions such as applied potential, solution pHs, initial concentrations, contact time and coexisting ions. Results showed that the removal efficiency conducted in reduction potential was obviously higher than that in oxidation potential. The optimal pH for Co2+ adsorption occurred at 8.0. Coexisting ions studies revealed that Co2+ could be removed from aqueous solutions containing Li+, Cu2+ and Al3+. Considering that cobalt and lithium are the main metallic elements in LiCoO2, the effect of different ionic strengths (IS) of LiNO3 (0.5, 1, 2, 5, 10) on adsorption was further investigated. Results showed that IS of LiNO3 had little impact on the removal efficiency of Co2+, which indicated the potential of selective recovery of cobalt from LiCoO2 in spent lithium-ion batteries. X-ray energy-dispersion spectroscopy (EDS) confirmed that the Co2+ could be adsorbed effectively onto CuHCF film. The adsorption was well described by Langmuir isotherm and the maximum sorption capacity is 218.82 mg/g. The kinetic rate of Co2+ adsorption was rapid initially and attained equilibrium within 60 min, and the data well fitted the Redlich-Peterson and the Elovich model, implying a chemisorption dominated process.

Keywords: Electrochemical adsorption Cobalt ion Metal hexacyanoferrates Isotherm and kinetic

1. Introduction Lithium-ion batteries (LIBs) have been widely used as electrochemical power sources (Wang et al., 2016a; Li et al., 2016; Park et al., 2017). LiCoO2 is commonly used as the cathode material for LIBs, due to its high energy density, operating voltage and good electrochemical ⁎

performance (Wang et al., 2016a; Dutta et al., 2018). 25% of cobalt produced across the world is used in the LIBs industry (Golmohammadzadeh et al., 2018), and the consumption demand is still increasing continually, resulting in a significant increase of the cobalt price in recent years. Cobalt is toxic and could cause cancer owing to its strong permeability (Wang et al., 2016b). Without proper

Corresponding author. E-mail addresses: [email protected] (R. Chen), [email protected] (J. Tan).

https://doi.org/10.1016/j.jhazmat.2019.121252 Received 3 July 2019; Received in revised form 13 September 2019; Accepted 16 September 2019 Available online 18 September 2019 0304-3894/ © 2019 Elsevier B.V. All rights reserved.

Journal of Hazardous Materials 384 (2020) 121252

X. Long, et al.

disposal, spent LiCoO2 cathode will not only cause a loss of valuable resources, but also rise the environmental poisoning. Therefore, it is getting more attractive and urgent to recover cobalt from the spent LIB at the viewpoint of full resources utilization and environment protection. Techniques mostly used to recover cobalt from LiCoO2 can be categorized as pyrometallurgical and hydrometallurgical methods (Golmohammadzadeh et al., 2017; Chen et al., 2019; Sattar et al., 2019; Aboelazm et al., 2018). Pyrometallurgical process was usually used for industrial scale, characterized by negative impacts mainly owing to elevated energy consumption and large pollutant emissions (Pagnanelli et al., 2016). On the contrary, hydrometallurgical processes such as electrochemical and biometallurgical, are eco-friendly solutions for both environmental emission reduction and energy conservation. However, these processes often include the steps such as acid leaching, physical separation, solvent extraction, or precipitation to recover cobalt and lithium only (Meshram et al., 2016), accompanied by toxic gases release, hard solid-liquid separation, secondary pollution, high energy consumption, and so on. (Dutta et al. (2018)) recovered metals from spent LIBs by close loop separation process, in which, additional H2O2 and various precipitants were required for the separation recovery. Myoung et al. (Myounga et al., 2002) obtained Co3O4 by electrochemical–hydrothermal method, thermal treatment was necessary at the last step. Compared to the approaches above, electrochemical adsorption method has many advantages, such as high performance, easy operation, low cost, easy separation and environment-friendly. Each metal ion has its own electrode potential in aqueous solution, it is possible to selectively recover valuable ions from solutions containing various metal ions under potential control (Liu et al., 2018). After electrodes dissolving occurs, Co2+ could be adsorbed separately from the resultant solution onto adsorbent by applying a reduction potential. Notably, additional extractants are not required in this process, and the applied potential is less negative than that required by electrodeposition. The selection of adsorbent is crucial for the combination, since the electrochemical adsorption is a combination of electrochemical and adsorption processes. Copper hexacyanoferrate (CuHCF), a chemically stable and low toxicity prussian blue analogue (PBA), has shown a high adsorption capacity due to its cubic framework and its tunable, open channels (Chen and Chan, 2003; Roque-Malherbe et al., 2015; Li et al., 2018). It has been usually used as a modified electrode for electrochemical separation of cesium from wastewater due to reversible redox reactions (such as FeIII/FeII) accompanied with reversible intercalation and deintercalation of hydrated alkali cations (Tao et al., 2019). In our previous studies, we introduced a simple coprecipitationspin coating method to prepare CuHCF modified electrode, which exhibited higher electrochemical adsorption capacity than other PBAs (Long et al., 2019). It seems very desirable to take a deeper insight on the electrochemical adsorption process of Co2+. Hereby, in this paper, CuHCF films were synthesized to selectively adsorb Co2+ from solution by electrochemical method. The effects of applied potential, solution pHs, initial concentrations, contact time and coexisting ions on the adsorption efficiency were explored to further optimize the adsorption system. The adsorption isotherm and kinetics were also investigated to discuss the possible mechanisms.

2.2. Preparation of modified electrodes

2. Material and methods

K 4 [Fe II (CN )6]

As described in our previous studies (Wang et al., 2018), CuHCF nanoparticles inks was prepared by wet chemical coprecipitation. One group of parallel samples was dried in an oven at 60 ℃ to obtain powder samples for subsequent characterizations, and the remaining samples were surface modified by K4[Fe(CN)6]·3H2O as hydrophilic moieties to gain the soluble 5% nanoparticles inks. ITO plates were washed by acetone to remove organic matter, and followed by O2 Plasma treatment for 10 min (Plasma Etch, PE25, USA) to remove other impurities. CuHCF films modified electrodes were prepared by printing nanoparticles inks on ITO plates using a KW-4A spin-coater instrument, dried in an oven at 120 °C for 2 h. 2.3. Characterizations of CuHCF Surface morphologies of CuHCF films were observed by fieldemission scanning electron microscope (FE-SEM, Hitachi S-4800, Japan) and atomic force microscopy (AFM, Shimadzu SPM-9700, Japan). Crystalline structures were characterized by X-ray powder diffractometry (XRD, Rigaku SmartLab, Japan) and fourier transform infrared spectroscopy (FTIR, Bruker Vertex 70, Germany). 2.4. Electrochemical adsorption experiments Batch adsorption were carried out in a 50 mL beaker containing 40 mL solutions stirred at 500 rpm by a magnetic stirrer (DL Instruments Ltd., MS-H280-Pro, China). The electrochemical experiments were conducted in a three-electrode system, in which a saturated calomel electrode (vs. SCE, Hg/Hg2Cl2/KCl)) was used as reference electrode. A Pt wire of 0.03 cm in diameter and 70 cm in length was rotary bended like a spring to amplify its surface area, and then used as the counter electrode. The bended spring structure of counter electrode is designed to maximize its surface area and prevent polarization effects. The ITO plate loaded with nanoparticles film as working electrode (2.5 cm × 1.5 cm). The counter and the working electrode were placed parallelly at a distance of 0.8 cm, in which the SCE was close to them. All electrochemical tests and analysis were performed using a Chen Hua electrochemical workstation (CHI660e, China). The mass of CuHCF film was measured by electrochemical quartz crystal microbalance (EQCM, PAR model 263A, USA). The frequency changes (Δf) of the quartz crystal are correlated with the mass changes (Δm) according to the Sauerbrey’s equation (eq. 1) (Kim et al., 2017):

m=

f× A×

×µ (1)

2f 0 2

where f0 is the resonant frequency of the crystal (9.0 MHz), A is the surface area of the Au electrode (0.196 cm2), ρ is the density of the crystal (2.648 g/cm3), and μ is the shear modulus of the crystal (2.947 × 1011 g/cm/s2). The mass per unit film area on quartz crystal is 20 μg/ cm2. In our case, area of the prepared CuHCF films are 3.75 cm2, thus the film mass is approximately 75 μg. CuHCF films were firstly pretreated at the applied potentials +1.3 V (vs. SCE) for 30 min in 1 mg/L KNO3 solution to discharge the residual K+ during the synthesis (Chen et al., 2013). The relevant reaction is shown as follows:

4K+ + [Fe III (CN )6 ]3 + e

(2)

Afterwards, the films were transferred to 1 mg/L Co2+ solution to adsorb Co2+ by applying reduction potential. Contrast tests were conducted at the same time without applying potentials. The adsorption of Co2+ onto the CuHCF film was investigated as a function of applied potential, pH, coexisting ions, initial concentration and contact time. Considering the influence of applied potential, the adsorption experiments were carried out at contact time of 30 min and initial concentration of 1 mg/l, at the different applied potential values

2.1. Materials and reagents All reagents, such as Cu(NO3)2·xH2O, Co(NO3)2·6H2O, LiNO3, K3[Fe (CN)6], K3[Fe(CN)6]·3H2O, KNO3, HNO3, NH3·H2O, used in the operations were of analytical grade or better without further purification. Indium tin oxide (ITO) as support substances. Ultrapure water (18 MΩ cm) was used throughout all the experiments. 2

Journal of Hazardous Materials 384 (2020) 121252

X. Long, et al.

in the range of -0.4 V to +0.4 V. Co2+ adsorbed on CuHCF film before and after electrochemical experiments were examined by X-ray energydispersion spectroscopy (EDS, Bruker XFlash 6130, Germany). To obtain the optimum pH, the initial pH values of Co2+ solutions were adjusted from 2.0 to 10.0 using HNO3 and NH3·H2O, and measured by a digital pH meter (AS ONE AS-211, Japan). Valence analysis of cobalt ions was performed with X-ray photoelectron spectroscopy (XPS, Thermo EscaLab 250Xi, USA). Following a similar procedure, the effect of coexisting ions was investigated in a series of 1 mg/L Co2+ initial solutions containing various types of metal ions, such as, Li+, Cu2+, Ni2+, and Al3+. In addition, since cobalt and lithium are the main metal elements coexisted in LiCoO2 electrode of spent LIB, we further examined the effect of ionic strengths (IS) of LiNO3, by varying its concentration (0.5, 1.0, 2.0, 5.0, and 10.0 mg/L) in 1 mg/L Co2+ initial solutions. To examine effect of contact time, the experiments were performed in 1 mg/L initial Co2+ solutions, and the samples were taken at appropriate time intervals: 5, 10, 20, 30, 60, 90, and 120 min. The total volume loss is less than 3%. Ions concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS, Thermo Fisher Scientific iCAP Q, USA). The results of electrochemical adsorption were given as adsorption amount on unit mass of CuHCF (Q, mg/g), which was calculated according to the equation as fellow (3):

Q=

(C0

Ct ) × V m

KDR is activity coefficient of Dubinin–Radushkevich isotherm, ε is Polanyi potential. βRP of Redlich-Peterson model is the exponent which lies between 0 and 1, the significance of β is as given as: β = 1 (Langmuir adsorption isotherm model is a preferable adsorption isotherm model); β = 0 (Freundlich adsorption isotherm model is a preferable adsorption isotherm model) (Anbalagan et al., 2016). The other symbols are constants of the formulas to which they belong. The data obtained from different sample intervals above were used to fit the adsorption kinetic models, such as pseudo-first order (Eq. 11), pseudo-second order (Eq. 12), intraparticle diffusion (Eq. 13) and Elovich model (Eq. 14).

ln(Qe

1

Qt =

(5)

lnCe n

(6)

R×T R×T lnaT + lnCe bT bT

(7)

lnQe = lnKF +

Qe =

lnQe = lnQm

KDR ×

= R × T × ln(1 + Qe =

KRP × Ce 1 + RP × Ce RP

2

1 ) Ce

ln( × ) +

1

ln t

(14)

2.6. Desorption experiments After adsorption process, the CuHCF films were washed using ultrapure water, and transferred to the pristine electrolyte without Co2+ for film regeneration. Desorption experiments were carried out in a 50 mL beaker, by applying an oxidation potential +1.3 V (vs. SCE) on CuHCF films for 30 min. The adsorption/desorption cycle were repeated for 3 times. The Co2+ concentrations were measured by ICP-MS.

The equilibrium adsorption data at various initial concentrations were analyzed using the following isotherm models, Langmuir (Eq. 4), Freundlich (Eq. 6), Temkin (Eq. 7), Dubinin–Radushkevich (Eq. 8) (Kong et al., 2018) and Redlich-Peterson (Eq. 10) (Aazza et al., 2018) model.

1 1 + KL C0

(13)

where, Qe (mg/g) and Qt (mg/g) were the adsorption amounts of Co2+ at the adsorption equilibrium and time t, respectively. k1 and k2 were the rate constants. Kp is the intraparticle diffusion rate constant and C is the intercept. α is the initial uptake rate (mg/g min) and β is the degree of activation energy and surface coverage (g/mg).

2.5. Theoretical background

RL =

1

(11) (12)

Qt = K p × t 2 + C

(3)

(4)

k1 × t

t 1 t = + Qt Qe k2 × Qe2

Where C0 (mg/L) and Ct (mg/L) stand for the Co2+ concentration at initial stages and time t stages respectively, V is the solution volume and m is the weight of CuHCF nanoparticles film. All the data values shown in Figures have deducted the adsorption parts in traditional adsorption system.

Ce 1 C = + e Qe Qm × KL Qm

Qt ) = ln Qe

3. Results and discussion 3.1. Morphology and structure Surface morphology of nanoparticles film was shown in Fig. 1a and 1b. The formation of porous structure might facilitate the mass transfer and diffusion rate of ions within films (Lv et al., 2017). Both of them could prove the existence of the nanoparticles, and the nanoparticles size of CuHCF ranged from 20 to 50 nm. Structure of CuHCF powders characterized by XRD was shown in Fig. 1c, in which, CuHCF exhibit four predominant 2θ peaks in the range of 17 ˜ 40° corresponding to the (2 0 0), (2 2 0), (4 0 0) and (4 2 0) diffraction planes of face-centeredcubic (FCC) lattice structure (Chang et al., 2018a; Liao et al., 2016; Zhu et al., 2018). Fig. 1d illustrated the FTIR spectra of CuHCF powders. The vibrational band near 2099 cm−1 related to the stretching vibration absorption band of the —C≡N group (Zong et al., 2017; Manakasettharn et al., 2018). The two peaks at around 596 cm−1 and 491 cm−1 were attributed respectively to the formation of Fe—C and Fe—C≡N (Zong et al., 2017; Kalaiyarasan et al., 2017; Agnihotry et al., 2006).

(8) (9) (10)

3.2. Effect of applied potential

Here, Ce (mg/L), Qe (mg/g) and Qm (mg/g) are the equilibrium concentration, adsorption capacity and theoretical maximum adsorption capacity, respectively. The meanings of Ce, Qe and Qm mentioned below are all the same. KL, is the adsorption isotherm constant. The dimensionless constant RL (Eq. 5) of the Langmuir model indicates whether the adsorption is irreversible (RL = 0), favorable (0 < RL < 1), linear (RL = 1), or unfavorable (RL > 1) (Lv et al., 2017). C0 (mg/L) is the initial concentration. R is the gas constant, 8.314 (J/mol K), T (K) is the temperature, bT (kJ/mol) is the adsorption heat of Temkin isotherm.

As presented in Fig. 2a, the removal efficiency conducted in reduction potential (-0.4 V, -0.2 V) was obviously higher than that in oxidation potential (+0.2 V, +0.4 V). In the electrolyte solution contained 0.001 mol/L Co2+, no complete reduction peak occurred in the CV (Fig. 2b) when the reduction potential was set as +0.2 V and +0.4 V. On the other hand, the CVs of CuHCF film at the reduction potential of -0.2 V and -0.4 V have one distinct reduction peak. In our 3

Journal of Hazardous Materials 384 (2020) 121252

X. Long, et al.

Fig. 1. (a) FE-SEM and (b) AFM image of CuHCF nanoparticles film; (c) XRD pattern and (d) FITR spectrum of CuHCF powders.

study, the Co2+ concentration was set as 1 mg/L, which is much lower than Co2+ concentration in CV experiments. The lower ion concentration, the lower ion diffusion coefficient and hence the worse solution conductivity. Thus, the reduction peak will shift from +0.35 V to a more negative potential. This result is coincident with the effect of applied potential on the removal efficiency. The applied potential was less negative than the electrodeposition potential of cobalt (Garcia

et al., 2011, 2008), thus, hexacyanoferrate (III) ions were transformed to hexacyanoferrate (II) ions under the condition of reduction, and Co2+ with positive charges were loaded on CuHCF films. The adsorption reaction can be described as follows:

Cu3 [Fe III (CN )6 ]2 + 2e + Co2 +

CoCu3 [Fe II (CN )6]2

(15)

The spectra of Fe 2p3/2 are presented in Fig. 2c. Only the signature Fig. 2. (a) Effect of applied potential on the removal efficiency (Co2 + concentration: 1 mg/ L, electrode area: 1.5 cm × 2.5 cm, 30 min); (b) Cyclic voltammograms of CuHCF film in Co2+ solution (Co2+ concentration: 0.001 mol/L; electrode area: 1.5 cm × 1.25 cm, scan rate: 0.005 V/s); (c) XPS spectra of Fe 2p for CuHCF films before (CuHCF) and after adsorption (CuHCF-Co2+); (d) EDS spectra of CuHCF films before and after adsorption.

4

Journal of Hazardous Materials 384 (2020) 121252

X. Long, et al.

Fig. 3. (a) Effect of pH on the removal efficiency (Co2+ concentration: 1 mg/L, electrode area: 1.5 cm × 2.5 cm, time: 30 min, applied potential: -0.2 V); (b) XPS detail scans of the Co 2p areas.

of FeIII appeared around 710 eV before adsorption. While Fe exists in both FeII (710.14 eV) and FeIII (708.35 eV) states after adsorption. These demonstrated the electrochemical transformation of [FeIII(CN)6]3+/ [FeII(CN)6]4+. EDS results of CuHCF films before and after adsorption in Fig. 2d confirmed that the Co2+ ions were adsorbed effectively onto CuHCF film.

controlled trial (Fig. S3) could be used to verify the formation of precipitation at high pH. The other one reason is the dissolution of CuHCF films observed under alkaline experimental conditions, which is consistent with the phenomena observed during the experiment.

3.3. Effect of pH

As illustrated by Fig. 4a, the presence of Li+, Cu2+, Al3+ barely affected the electrochemical adsorption of Co2+. The removal efficiency was dramatically decreased by the introduction of Ni2+, which might due to the close CVs (shown in Fig. 4b) of CuHCF film in mixture solutions containing Ni2+ and Co2+ ions. Cations layer containing both Co2+ and Ni2+ was formed around the surface of CuHCF film by electrostatic adsorption effect (shown in Fig. 4c) as negative potential was applied. The hydrated radii of Ni2+ and Co2+ are 4.04 Å and 4.23 Å (Nightingale, 1959), respectively. The smaller hydrated radius might make it easier for Ni2+ ions to enter the lattice, and then hinder the adsorption of Co2+ ions by occupying adsorption sites and blocking lattice channels. Compared with the coexisting cations free experiment (shown in Fig. 4d), the insignificant change in removal efficiency indicated that CuHCF films can effectively adsorb Co2+ even with the increase of Li+ concentration, which implied the possibility of cobalt recovery from LiCoO2 of spent LIBs.

3.4. Effect of coexisting ions

Fig. 3a revealed that pH played a crucial role on cobalt sorption on CuHCF films. Adsorption efficiency of Co2+gradually increased with rising initial pH from 2.0 to 8.0, which is in coinciding with the result described in (Yuan et al. (2018)). However, a decrease of Co2+ removal efficiency occurred with the increase of initial pH from 9.0 to 10.0. The optimal pH for cobalt uptake appeared to be pH 8.0, with an adsorption capacity of 175.78 mg/g. The adsorption was insignificant at pH ≤ 4.0, this is because the adsorbent surface was slightly positively charged and the electrostatic repulsion effect prevented to the adsorption of positively charged Co2+ (Son et al., 2018). On the other hand, the lower adsorption capacity under acidic condition could be explained by the competition between beta-delayed protons (Yuan et al. (2018)). The higher adsorption efficiency at higher pH levels might be due to the formation of Co(NH3)63+. The hydrated radius of Co(NH3)63+ is 3.96 Å, smaller than that of Co2+ (4.23 Å) (Nightingale, 1959), which made it easier for Co(NH3)63+ to enter the crystal lattice. The possible reactions can be shown as follows:

6NH3·H2 O + 4[Co (NH3 )6

Co2 +

]2 +

[Co (NH3 )6

+ O2 + 2H2 O

]2 +

(16)

+ 6H2 O

4[Co (NH3 )6

3.5. Effect of initial concentrations and adsorption isotherm

]3 +

+ 4OH

The effect of initial concentrations on adsorption capacity of CuHCF films for Co2+ was shown in Fig. 5a. It was found that the plot displayed a two-stage process, a fast increase at low concentrations followed by a plateau extending to the equilibrium at a higher level of initial concentration. At low concentrations, the sorption sites of CuHCF films are available with high attraction towards Co2+ until the Co2+ concentration becomes too low to overcome diffusion hindrance of the remaining adsorption sites (El-Bahy et al., 2018). As the increase in initial concentration, the driving force from concentration gradient between the solution and the interface of adsorbent increased (Zhu et al., 2017; Hayati et al., 2018), leading to the rapid increase of equilibrium adsorption capacity. With the initial concentration increasing subsequently, the adsorption sites reached saturation gradually, thus the removal efficiency insignificantly changed (Igberase et al., 2017). In the Table 1, the adsorption isotherms data of Co2+ onto CuHCF nanoparticles film followed the properties of Redlich-Peterson model well with relatively high R2 value (R2 > 0.99), the value of βRP was very close to 1, which means that it approaches Langmuir isotherm model. Langmuir model was adopted to describe reversible chemical adsorption of monolayer adsorbate molecule on homogeneous sites of the adsorbent (Chen et al., 2014). In our study, the Co2+ ions are inserted

(17)

3+

The formation of Co(NH3)6 plays a key role in the removal process. Thus, we considered this electrochemical adsorption involves ion exchange, but could not be simply defined as electrochemically switched ion exchange (ESIX) (Tao et al., 2019). Proof test was conducted by adjusting pH to neutral using HCl. The typical UV absorption peak of [Co(NH3)6]Cl3 was detected at 475 nm by UV–vis spectrophotometer (Agilent Technologies Carry 60, USA), which indicated the formation of Co(NH3)63+ complex ions. A [Co(NH3)6]Cl3 standard curve is generated to quantify [Co(NH3)6]Cl in the samples (shown in Fig. S1). The Co 2p spectrum (Fig. 3b) were fitted with three simulated peaks. The Co 2p3/2 signal at 783.01 eV corresponds to Co (II); the one at 786.75 eV has a spin-orbit splitting ΔE of 14.56 eV, less than 15 eV, corresponding to Co(III) (Ivanova et al., 2007); and the curve-fitting peak from binding energy of 790.2 eV is a strong satellite shake-up structure for high-spin Co (II) species (Barrioni et al., 2018). The dramatic drop of the adsorption efficiency can be attributed to the following two reasons. One is that the Co(II) is mainly in the form of cobalt hydroxide precipitation when pH ≥ 9.0, according to the Pourbaix diagram for Cobalt-H2O system (Garcia et al., 2008). Green precipitation (shown in Fig. S2) and 5

Journal of Hazardous Materials 384 (2020) 121252

X. Long, et al.

Fig. 4. (a) Effect of coexisting ions on the removal efficiency; (b) Cyclic voltammograms of CuHCF film in Co2+ and Ni2+ ion solutions (ion concentration: 0.5 mol/L; electrode area: 1.5 cm × 1.25 cm); (c) Schematic of effect of Ni2+ ions on the adsorption process of Co2+ ions (ion concentration: 1 mg/L); (d) concentration of Li+ on the removal efficiency (Co2+ concentration: 1 mg/L, electrode area: 1.5 cm × 2.5 cm, time: 30 min). Fig. 5. (a) The effect of initial concen trations on the adsorption capacity, the insets are equilibrium adsorption data fitted by Langmuir, Freundlich, Temkin, Dubinin–Radushkevich and Redlich-Peterson models; (b) Pseudo-first order, pseudo-second order, intraparticle diffusion and Elovich kinetic models for electrochemical adsorption of Co2+ on CuHCF films.

6

Journal of Hazardous Materials 384 (2020) 121252

X. Long, et al.

Table 1 The parameters and correlation coefficients of isotherm models and kinetic models. Isotherm models

Parameters

Kinetic models

Constants

Langmuir

Qm (mg/g) KL R2 n

218.82

Pseudo-firstorder

KF R2 aT bT R2 Qm (mg/g) KDR R2 KRP αRP βRP R2

159.8130 0.9847 290.4323 86.4515 0.9799 205.14

Qe (mg/g) k1 R2 Qe (mg/g) k2 R2 Kp C R2 α

0.0011 0.9806 9.9210 21.9841 0.8879 37.2300

β R2

0.0449 0.9977

　

　

Freundlich

Temkin Dubinin–Radushkevich

Redlich-Peterson

　

4.0803 0.9860 6.2387

3.84E-08 0.9641 1609.8296 8.5965 0.9167 0.9936

Pseudosecond-order Intraparticle diffusion Elovich

　

108.69 0.0756 0.9418 116.02

Fig. 6. Cycles of Co2+ adsorption/desorption using CuHCF film in an electrochemical system (Co2+ concentration: 1 mg/L, electrode area: 1.5 cm × 2.5 cm, time: 30 min).

3.7. Desorption and regeneration As the result shown in Fig. 6, the adsorption amount of Co2+ ions onto CuHCF film remained stable after 3 cycles. Results also indicated that most of the sorption ability can be successfully regenerated by switching the potential. However, around 60% of the adsorbed Co2+ were detected in the elutions. This might be due to the loss of cobalt ions during the washing process.

in lattice of CuHCF film by applying reduction potential, and the adsorption/desorption cycles could be achieved accompanied by the transformation of [FeIII(CN)6]3+/ [FeII(CN)6]4+. These imply that the adsorption process can be well described by Langmuir model. The theoretical monolayer sorption capacity of Co2+ on CuHCF films was 218.82 mg/g. The values of RL were between 0 and 1, indicating the favorable adsorption of Co2+ onto CuHCF nanoparticles film. Furthermore, the RL values decreased with the increasing initial Co2+ concentration, suggesting that the process of adsorption was more favorable with higher initial Co2+ concentration (Deng et al., 2018).

4. Conclusions This study showed that Co2+ could be removed efficiently from aqueous solutions by CuHCF nanoparticles film, the maximum removal efficiency occurred at initial pH of 8. The existence and ionic strength of Li+ hardly affect the adsorption of Co2+, implying the potential of cobalt recovery from spent LiCoO2 cathodes using electrochemical method. The adsorption behavior followed the Redlich-Peterson isotherm model, and adsorption kinetics of Co2+ onto CuHCF nanoparticles film can be explained by the Elovich model. The results implied that chemical adsorption played a dominant role in cobalt recovery using nanoparticles film of CuHCF. Most of the sorption ability can be successfully regenerated by switching the applied potential.

3.6. Effect of contact time and adsorption kinetics The adsorption data in different time intervals occurred in two phases as well: a first rapid-raising step followed by a slower stage to accomplish the equilibrium (illustrated in Fig. 5b). The first rapid period was due to the availability of superficial adsorption sites (Aazza et al., 2018), and then adsorption rate decreased as the number of binding sites restricted. Two reasons for the adsorption equilibrium should be considered, one of them relates to the decrease in the number of the receptor sites (Abukhadra et al., 2018), the other is the decline of Co2+ concentration in solution under the continuous adsorption of Co2+. The kinetic models, linking the sorption rate with the concentration of reactants and constant parameters, will give directions to the sorption mechanism (Chen et al., 2017). Elovich model was confirmed as the best fit one to the experimental data with R2 > 0.99. The Elovich model has been used in chemical adsorption processes with a fast rate involving energetical heterogeneous adsorbing surfaces (Abukhadra et al., 2018; Chang et al., 2018b; Natarajan and Bajaj, 2016), which was proved to describe the solid-liquid interaction effectively (Kong et al., 2018). Compared with pseudo-first-order model, pseudo-second-order model can better describe the removal process due to a higher correlation coefficient and a closer Qe to experimental data, indicating the adsorption mechanism might involve chemisorption (Deng et al., 2018). The curve fitted linearly with the intraparticle diffusion model (Fig. S4) did not pass through the origin, suggesting that intraparticle diffusion did not play a crucial role in adsorption process (Su et al., 2018). All the results above indicated that the chemisorption of Co2+ on the binding site of CuHCF films was the main rate-limiting step of adsorption (Chang et al., 2018a; Zhang et al., 2018).

Declaration of Competing Interest None. Acknowledgements Authors acknowledge the research staffs in University of Chinese Academy of Sciences to provide technical assistance on FE-SEM, XRD, FTIR, EDS and XPS test and analysis. This work was supported by Beijing Natural Science Foundation (No. 2184128), National Natural Science Foundation of China (contract No. 21806166), and Guangdong Foundation for Program of Science and Technology Research (Grant No.2017B030314057). Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jhazmat.2019.121252. 7

Journal of Hazardous Materials 384 (2020) 121252

X. Long, et al.

References

Kong, J., Gu, R., Yuan, J., Liu, W., Wu, J., Fei, Z., Yue, Q., 2018. Adsorption behavior of Ni (II) onto activated carbons from hide waste and high-pressure steaming hide waste. Ecotoxicol. Environ. Saf. 156, 294–300. Li, J., Wang, G., Xu, Z., 2016. Environmentally-friendly oxygen-free roasting/wet magnetic separation technology for in situ recycling cobalt, lithium carbonate and graphite from spent LiCoO2/graphite lithium batteries. J. Hazard. Mater. 302, 97–104. Li, J., Li, H., Li, J., Wu, G., Shao, Y., Li, Y., Zhang, Q., Wang, H., 2018. A single-walled carbon nanotubes/poly(3,4-ethylenedioxythiophene)-poly (styrenesulfonate)/copper hexacyanoferrate hybrid film for high-volumetric performance flexible supercapacitors. J. Power Sources 386, 96–105. Liao, J.Y., Hu, Q., Zou, B.K., Xiang, J.X., Chen, C.H., 2016. The role of potassium ions in iron hexacyanoferrate as a cathode material for hybrid ion batteries. Electrochim. Acta 220, 114–121. Liu, W., Sun, B., Zhang, D., Chen, L., Yang, T., 2018. Effect of pH on the selective separation of metals from acidic wastewater by controlling potential. Sep. Purif. Technol. 205, 223–230. Long, X., Chen, R., Yang, S., Wang, J., Huang, T., Lei, Q., Tan, J., 2019. Preparation, characterization and application in cobalt ion adsorption using nanoparticle films of hybrid copper–nickel hexacyanoferrate. RSC Adv. 9, 7485–7494. Lv, L., Chen, N., Feng, C., Zhang, J., Li, M., 2017. Heavy metal ions removal from aqueous solution by xanthate-modified cross-linked magnetic chitosan/poly(vinyl alcohol) particles. RSC Adv. 7, 27992–28000. Manakasettharn, S., Takahashi, A., Kawamoto, T., Noda, K., Sugiyama, Y., Nakamura, T., 2018. Highly sensitive and exceptionally wide dynamic range detection of Ammonia gas by indium hexacyanoferrate nanoparticles using FTIR spectroscopy. Anal. Chem. 90, 4856–4862. Meshram, P., Abhilash, Pandey, B.D., Mankhand, T.R., Deveci, H., 2016. Acid baking of spent lithium ion batteries for selective recovery of major metals: a two-step process. J. Ind. Eng. Chem. 43, 117–126. Myounga, J., Junga, Y., Leeb, J., Tak, Y., 2002. Cobalt oxide preparation from waste LiCoO2 by electrochemical-hydrothermal method. J. Power Sources 112, 639–642. Natarajan, S., Bajaj, H.C., 2016. Recovered materials from spent lithium-ion batteries (LIBs) as adsorbents for dye removal: equilibrium, kinetics and mechanism. J. Environ. Chem. Eng. 4, 4631–4643. Nightingale, E.R., 1959. Phenomenological theory of ion solvation. Effective radii of hydrated ions. J. Phys. Chem. 63, 1381–1387. Pagnanelli, F., Moscardini, E., Altimari, P., Atia, T.A., Toro, L., 2016. Cobalt products from real waste fractions of end of life lithium ion batteries. Waste Manag. 51, 214–221. Park, Y.M., Lim, H., Moon, J.H., Lee, H.N., Son, S.H., Kim, H., Kim, H.J., 2017. High-yield one-pot recovery and characterization of nanostructured cobalt oxalate from spent lithium-ion batteries and successive Re-Synthesis of LiCoO2. Metals 7, 11. Roque-Malherbe, R., Carballo, E., Polanco, R., Lugo, F., Lozano, C., 2015. Structure and adsorption properties of a porous cooper hexacyanoferrate polymorph. J. Phys. Chem. Solids 86, 65–73. Sattar, R., Ilyas, S., Bhatti, H.N., Ghaffar, A., 2019. Resource recovery of critically-rare metals by hydrometallurgical recycling of spent lithium ion batteries. Sep. Purif. Technol. 209, 725–733. Son, E.B., Poo, K.M., Mohamed, H.O., Choi, Y.J., Cho, W.C., Chae, K.J., 2018. A novel approach to developing a reusable marine macro-algae adsorbent with chitosan and ferric oxide for simultaneous efficient heavy metal removal and easy magnetic separation. Bioresour. Technol. 259, 381–387. Su, J., He, S., Zhao, Z., Liu, X., Li, H., 2018. Efficient preparation of cetyltrimethylammonium bromide-graphene oxide composite and its adsorption of Congo red from aqueous solutions. Colloids Surf. A-Physicochem. Eng. Asp. 554, 227–236. Tao, Q., Zhang, X., Prabaharan, K., Dai, Y., 2019. Separation of cesium from wastewater with copper hexacyanoferrate film in an electrochemical system driven by microbial fuel cells. Bioresour. Technol. 278, 456–459. Wang, J., Chen, R., Long, X., Li, Z., 2018. Synthesis of hybrid-metal hexacyanoferrates nanoparticle films and investigation of its hybrid vigor. J. Electroanal. Chem. 810, 191–198. Wang, M., Zhang, C., Zhang, F., 2016a. An environmental benign process for cobalt and lithium recovery from spent lithium-ion batteries by mechanochemical approach. Waste Manag. 51, 239–244. Wang, F., Sun, R., Xu, J., Che, Z., Kang, M., 2016b. Recovery of cobalt from spent lithium ion batteries using sulphuric acid leaching followed by solid-liquid separation and solvent extraction. RSC Adv. 6, 85303–85311. Yuan, G., Zhao, C., Tu, H., Li, M., Liu, J., Liao, J., Yang, Y., Yang, J., Liu, N., 2018. Removal of Co(II) from aqueous solution with Zr-based magnetic metal-organic framework composite. Inorganica Chim. Acta 483, 488–495. Zhang, B., Chen, N., Feng, C., Zhang, Z., 2018. Adsorption for phosphate by crosslinked/ non-crosslinked-chitosan-Fe(III) complex sorbents: characteristic and mechanism. Chem. Eng. J. 353, 361–372. Zhu, X., Xu, W., Tan, G., Wang, Y., 2018. Concentration flow cells for efficient salinity gradient energy recovery with nanostructured open framework hexacyanoferrate electrodes. Chemistryselect 3, 5571–5580. Zhu, Y., Wang, W., Zhang, H., Ye, X., Wub, Z., Wang, A., 2017. Fast and high-capacity adsorption of Rb+ and Cs+ onto recyclable magnetic porous spheres. Chem. Eng. J. 327, 982–991. Zong, Y., Zhang, Y., Lin, X., Ye, D., Luo, X., Wang, J., 2017. Preparation of a novel microsphere adsorbent of prussian blue capsulated in carboxymethyl cellulose sodium for Cs(I) removal from contaminated water. J. Radioanal. Nucl. Chem. 311, 1577–1591.

Aazza, M., Ahlafi, H., Moussout, H., Maghat, H., 2018. Adsorption of metha-nitrophenol onto alumina and HDTMA modified alumina: kinetic, isotherm and mechanism investigations. J. Mol. Liq. 268, 587–597. Aboelazm, E.A.A., Ali, G.A.M., Algarni, H., Yin, H., Zhong, Y.L., Chong, K.F., 2018. Magnetic electrodeposition of the hierarchical cobalt oxide nanostructure from spent lithium-ion batteries: its application as a supercapacitor electrode. J. Phys. Chem. C 122, 12200–12206. Abukhadra, M.R., Dardir, F.M., Shaban, M., Ahmed, E.A., Soliman, M.F., 2018. Superior removal of Co2+, Cu2+ and Zn2+ contaminants from water utilizing spongy Ni/Fe carbonate-fluorapatite; preparation, application and mechanism. Ecotoxicol. Environ. Saf. 157, 358–368. Agnihotry, S.A., Singh, P., Joshi, A.G., Singh, D.P., Sood, K.N., Shivaprasad, S.M., 2006. Electrodeposited Prussian blue films: annealing effect. Electrochim. Acta 51, 4291–4301. Anbalagan, S., Ponnusamy, S.K., Selvam, S.R.P., Sankaranarayan, A., Dutta, A., 2016. Influence of ultrasonication on preparation of novel material for heavy metal removal from wastewater. Korean J. Chem. Eng. 33, 2716–2731. Barrioni, B.R., Norris, E., Jones, J.R., Pereira, M., 2018. The influence of cobalt incorporation and cobalt precursor selection on the structure and bioactivity of sol-gelderived bioactive glass. J. Solgel Sci. Technol. 88, 309–321. Chang, S., Chang, L., Han, W., Li, Z., Dai, Y., Zhang, H., 2018a. In situ green production of Prussian blue/natural porous framework nanocomposites for radioactive Cs+ removal. J. Radioanal. Nucl. Chem. 316, 209–219. Chang, P.-H., Jiang, W.-T., Li, Z., 2018b. Mechanism of tyramine adsorption on Camontmorillonite. Sci. Total Environ. 642, 198–207. Chen, S., Chan, C., 2003. Preparation, characterization, and electrocatalytic properties of copper hexacyanoferrate film and bilayer film modified electrodes. J. Electroanal. Chem. 543, 161–173. Chen, X., Kang, D., Cao, L., Li, J., Zhou, T., Ma, H., 2019. Separation and recovery of valuable metals from spent lithium ion batteries: simultaneous recovery of Li and Co in a single step. Sep. Purif. Technol. 210, 690–697. Chen, R., Tanaka, H., Kawamoto, T., Asai, M., Fukushima, C., Na, H., Kurihara, M., Watanabe, M., Arisaka, M., 2013. Selective removal of cesium ions from wastewater using copper hexacyanoferrate nanofilms in an electrochemical system. Electrochim. Acta 87, 119–125. Chen, R., Ishizaki, M., Asai, M., Fukushima, C., Kurihara, M., Arisaka, M., Nankawa, T., Watanabe, M., Tanaka, H., 2014. Column study on electrochemical separation of cesium ions from wastewater using copper hexacyanoferrate film. J. Radioanal. Nucl. Chem. 303, 1491–1495. Chen, R., Tanaka, H., Kawamoto, T., Wang, J., Zhang, Y., 2017. Battery-type column for cesium ions separation using electroactive film of copper hexacyanoferrate nanoparticles. Sep. Purif. Technol. 173, 44–48. Deng, J.Q., Li, X.D., Liu, Y.G., Zeng, G.M., Liang, J., Song, B., Wei, X., 2018. Alginatemodified biochar derived from Ca(II)-impregnated biomass: excellent anti-interference ability for Pb(II) removal. Ecotoxicol. Environ. Saf. 165, 211–218. Dutta, D., Kumari, A., Panda, R., Jha, S., Gupta, D., Goel, S., Jha, M.K., 2018. Close loop separation process for the recovery of Co, Cu, Mn, Fe and Li from spent lithium-ion batteries. Sep. Purif. Technol. 200, 327–334. El-Bahy, S.M., Fadel, D.A., El-Bahy, Z.M., Metwally, A.M., 2018. Rapid and highly efficient cesium removal by newly synthesized carbomer encapsulated potassium copper hexacyanoferrate composite. J. Environ. Chem. Eng. 6, 1875–1885. Garcia, E.M., Taroco, H.A., Matencio, T., Domingues, R.Z., dos Santos, J.A.F., de Freitas, M.B.J.G., 2011. Electrochemical recycling of cobalt from spent cathodes of lithiumion batteries: its application as coating on SOFC interconnects. J. Appl. Electrochem. 41, 1373–1379. Garcia, E.M., Santos, J.S., Pereira, E.C., Freitas, M.B.J.G., 2008. Electrodeposition of cobalt from spent Li-ion battery cathodes by the electrochemistry quartz crystal microbalance technique. J. Power Sources 185, 549–553. Golmohammadzadeh, R., Faraji, F., Rashchi, F., 2018. Recovery of lithium and cobalt from spent lithium ion batteries (LIBs) using organic acids as leaching reagents: a review. Resour. Conserv. Recycl. 136, 418–435. Golmohammadzadeh, R., Rashchi, F., Vahidi, E., 2017. Recovery of lithium and cobalt from spent lithium-ion batteries using organic acids: process optimization and kinetic aspects. Waste Manag. 64, 244–254. Hayati, B., Maleki, A., Najafi, F., Gharibi, F., McKay, G., Gupta, V.K., Puttaiah, S.H., Marzban, N., 2018. Heavy metal adsorption using PAMAM/CNT nanocomposite from aqueous solution in batch and continuous fixed bed systems. Chem. Eng. J. 346, 258–270. Igberase, E., Osifo, P., Ofomaja, A., 2017. The Adsorption of Pb, Zn, Cu, Ni, and Cd by Modified Ligand in a Single Component Aqueous Solution: Equilibrium, Kinetic, Thermodynamic, and Desorption Studies. Int. J. Anal. Chem. Ivanova, T., Naumkin, A., Sidorov, A., Eremenko, I., Kiskin, M., 2007. X-ray photoelectron spectra and electron structure of polynuclear cobalt complexes. J. Electron. Spectros. Relat. Phenomena 156, 200–203. Kalaiyarasan, G., Aswathi, K., Joseph, J., 2017. Formation of nanoporous NiS films from electrochemically modified GC surface with Nickel Hexacyanoferrate film and its performance for the hydrogen evolution reaction. Int. J. Hydrogen Energy 42, 22866–22876. Kim, J., Urchaga, P., Baranton, S., Coutanceau, C., Jerkiewicz, G., 2017. Interfacial structure of atomically flat polycrystalline Pt electrodes and modified Sauerbrey equation. J. Chem. Soc. Faraday Trans. 19, 21955–21963.

8