Di Deng et al, 2022 - Recuperação seletiva de cobre por eletrodeposição utilizando EDTA e Ácido Cítrico

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Separation and Purification Technology 301 (2022) 121917
Available online 29 August 2022
1383-5866/© 2022 Elsevier B.V. All rights reserved.
Selective recovery of copper from electroplating sludge by integrated EDTA 
mixed with citric acid leaching and electrodeposition 
Di Deng , Chunjian Deng *, Tingting Liu , Dingqian Xue , Jie Gong , Rong Tan , Xue Mi , 
Baichuan Gong , Zhongbing Wang , Chunli Liu , Guisheng Zeng * 
Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, Nanchang Hangkong University, Nanchang 330063, China 
National-Local Joint Engineering Research Center of Heavy Metals Pollutants Control and Resource Utilization, Nanchang Hangkong University, Nanchang 330063, 
China 
A R T I C L E I N F O 
Keywords: 
Electroplating sludge 
Electrodeposition 
Metal chelate leaching 
Copper recovery 
A B S T R A C T 
Electroplating sludge (ES) is hazardous to human health or the environment when improperly treated, while it is 
a valuable resource due to its content of precious metals. In this study, copper was selectively leached out and 
electrodeposited from ES containing copper, iron and other metals. Copper was extracted from ES by a mixture 
solution of EDTA and citric acid. The leaching efficiency of copper was 85 % in 5 h under the conditions of 70 
mM EDTA, 120:1 liquid–solid ratio and 10 mM citric acid. An amidoxime-functionalized porous carbon (Ami-PC) 
electrode material was utilized for the electrodeposition of a simulated leaching solution containing copper (750 
ppm) and iron (250 ppm). The optimized electrodeposition conditions were voltage (6, 0) V, duty ratio 80 %, 
initial pH 3.23, and 4 h. Finally, leaching and electrodeposition were carried out synchronously, with the copper 
recovery efficiency reaching 82.21 %. The results show that electrodeposition while leaching has the advantage 
of less time cost. EDTA had the same leaching ability after three cycles. This study provides a new technical route 
for the efficient recovery of valuable metals from industrial waste residue. 
1. Introduction 
With the development of the economy and industrialization over 
decades, the electroplating industry has made great progress. Electro-
plating sludge (ES) is generated during the treatment of electroplating 
wastewater[1,2]. As a hazardous waste, ESs are landfilled or solidified to 
stabilize toxic and harmful substances[3,4]. Currently, ES is regarded as 
a resource for the reclamation of some valuable heavy metals[5]. 
Compared with other metal recovery methods from ES, hydromet-
allurgical processes have been considered promising because they show 
effectiveness in the extraction of metals[6,7]. As the first step of hy-
drometallurgy, metal dissolution involves chemical leaching and bio-
leaching[8,9]. Popular chemical leaching includes acid and alkaline 
leaching. Yi et al. [10] used sulfuric acid leaching for the treatment of 
copper-containing electroplating sludge. Under the optimal conditions 
of 1 M sulfuric acid and a 15:1 liquid–solid ratio, the copper leaching 
efficiency reached 90 %. Moreover, the copper in electroplating sludge 
was recovered by ammonia leaching and hydrogen reduction under high 
pressure, and the copper leaching efficiency was over 77.42 % by using a 
6.5 M ammonia concentration[11]. Although both acid and alkaline 
leaching can extract metals from electroplating sludge with good per-
formance, there are disadvantages, such as a lack of selective leaching, 
secondary pollution and the corrosion of equipment. Bioleaching[12,13] 
can overcome the above disadvantages, but it possesses the shortcom-
ings of slow dynamic speed and difficulty in subsequent recovery. Thus, 
it is urgent to develop an efficient and environmentally friendly method 
for recovering valuable metals from electroplating sludge. 
EDTA is the most promising and effective chelating agent because of 
its strong complexing ability and relative low cost compared to other 
chelating agents, such as aminotriacetic acid[14,15]. Most of the com-
plexes formed by EDTA with metal ions are charged and soluble in 
water, which provides the conditions for the electrochemical recovery of 
target metals[16]. Citric acid (CA) can not only chelate heavy metals but 
also reduce the acidity and alkalinity of the leaching agent and promote 
the leaching of insoluble heavy metals in ES[17,18]. 
Electrodeposition has been widely regarded as an environmentally 
friendly and economical method for the recovery of valuable metals 
from aqueous solutions[19]. Recently, the emergence of different novel 
* Corresponding authors. 
E-mail addresses: cjdeng@nchu.edu.cn (C. Deng), zengguisheng@hotmail.com (G. Zeng). 
Contents lists available at ScienceDirect 
Separation and Purification Technology 
journal homepage: www.elsevier.com/locate/seppur 
https://doi.org/10.1016/j.seppur.2022.121917 
Received 30 June 2022; Received in revised form 28 July 2022; Accepted 8 August 2022 
mailto:cjdeng@nchu.edu.cn
mailto:zengguisheng@hotmail.com
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Separation and Purification Technology 301 (2022) 121917
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materials has also showed their competitiveness in environmental pro-
tection.These promising novel materials exhibit several excellent prop-
erties, for example large surface area, great mechanical strength, and 
high chemical inertness[20–22]. Amidoxime-functionalized porous 
carbon (Ami-PC) electrodes with a high surface area and strong 
chelating sites can fully bind heavy metal cations to achieve an ideal 
removal effect [23–25]. Direct current is often used in industrial elec-
troplating and electrolytic production. However, DC voltage can cause 
great energy loss and concentration polarization during electrochemical 
processes [26]. Asymmetric alternating current can not only improve 
the current efficiency of electrodeposition by reducing the possibility of 
the hydrogen evolution reaction but also eliminate concentration po-
larization by regulating the concentration of metal ions at the electrode- 
solution interface [27,28]. 
In this work, the applicability of copper selective recovery by inte-
grating EDTA leaching with electrodeposition was demonstrated. In the 
presence of the mixture of EDTA and CA, the copper was selectively 
leached out with the existence of iron and other metals in the 
Table 1 
Chemical composition of the electroplating sludge. 
Element Cu Fe Ni Ca Na Mg S P K 
Contents % 11.12 17.14 3.21 4.478 0.540 0.474 0.274 1.557 1.024 
Fig. 1. XPS analysis of the main metal elements in the electroplating sludge. 
Fig. 2. (a) Schematic diagram of an electrodeposition reactor. (b) Leaching electrodeposition mechanism diagram. (c) An asymmetrical AC schematic with a duty 
cycle of 80% (Note: duty cycle refers to the percentage of the circuit’s cycle time that the circuit is switched on.). 
D. Deng et al. 
Separation and Purification Technology 301 (2022) 121917
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electroplating sludge. Copper was electrodeposited on the Ami-PC 
electrode under an asymmetric alternating voltage. EDTA solution was 
recycled for repeated use. 
2. Materials and methods 
2.1. Materials 
The copper electroplating sludge used in this experiment came from 
an electroplating plant in Nanchang, China. The electroplating sludge 
was first dried at 105 ◦C to achieve constant weight and crushed into 
small particles of less than 1.43 mm. The electrode carbon felt was 
purchased from Beijing Jinglong Special Carbon andGraphite Factory. 
The characteristics of the electroplating sludge are shown in Table 1. 
The morphology of the metal in the electroplating sludge was further 
analysed by XPS. As shown in Fig. 1, iron in electroplating sludge mainly 
exists in the form of FeO[29] and Fe2O3[30], while copper mainly exists 
in the form of Cu(OH)2 and CuO[31]. 
All experiments were performed using deionized water at room 
temperature and pressure (unless otherwise specified). The chemicals 
used were all analytical reagents (AR) purchased from Tianjin Damao 
Chemical Reagent Factory (Tianjin, China). 
2.2. Ami-PC electrode fabrication 
The carbon felt was cut into 25 × 20 mm sheets. For the removal of 
reductive substances and organic matter on their surfaces, the sheets 
were subsequently cleaned with 2 % nitric acid solution and 98 % 
ethanol by ultrasonication. Then, the sheets were rinsed with deionized 
water and dried to constant weight. 
Carbon black (1.5 mg), polyacrylonitrile (PAN, average MW 15000, 
2 mg), and N,N-dimethylformamide (DMF, 40 mL) were mixed and 
stirred overnight to form a uniform slurry. The carbon felt sheets were 
dip-coated with the slurry and dried at 90 ◦C for 1 h to remove the 
organic solvent. The coated carbon felt sheets were put into a 25 mL 
water bath. Na2CO3 (1.5 g) and NH2OH⋅HCl (2 g) were added to the 
water for the amidoximation reaction. The water bath was kept at 70 ◦C 
for 90 min. Then, the carbon felt sheets were washed with deionized 
water and dried in a vacuum furnace (80 ◦C). 
2.3. Copper leaching 
In each leaching experiment, a certain amount of electroplating 
sludge was put into the electrolytic reactor. EDTA solution or a mixed 
solution of EDTA and CA was circulated by a peristaltic pump to leach 
the electroplating sludge. After a certain time, the leach solution was 
collected, and the leached residue was fully washed. The contents of 
copper and iron in the leach solution were determined. The effects of the 
initial concentration of EDTA, ratio of liquid to solid, ratio of EDTA to 
CA and time on the copper leaching efficiency were studied. Each of the 
above experiments was repeated 3 times under the same conditions, and 
the average value was taken. 
2.4. Copper recovery 
The experiments were carried out in a copper recovery device, as 
shown in Fig. 2. The device was composed of two electrodes (Ami-PC 
and PC electrodes), which were placed in a cell and connected to a 
power supply. The asymmetrical alternating current was generated by 
GIGOL DG1000Z[27]. Metal salt solution was circulated through the 
electrode plates by a peristaltic pump. 
The types of solutions include the mixture solution of EDTA +
CuSO4⋅ 5H2O, the mixture solution of EDTA + CA + CuSO4⋅5H2O and 
the leaching solution of electroplating sludge with EDTA or/and CA. 
Fig. 3. Characterization of the Ami-PC. (a) The electrical impedances of CF and Ami-PC. (b) Fourier transform infrared spectroscopy (FTIR) spectrum of materials 
coated with PAN before and after the amidoximation reaction. (c) XPS spectra (N 1 s) of Ami-PC. (d) CF contact angle. (e) Permeability test of a water droplet. 
D. Deng et al. 
Separation and Purification Technology 301 (2022) 121917
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2.5. Characterization and analytical methods 
The concentrations of metal ions were measured by inductively 
coupled plasma–mass spectrometry (MWD-500, ICP–MS, ASX-560, 
Thermo Scientific). XPS was used to analyse the morphology of the 
metal. Fourier transform infrared (FTTR) spectroscopy and XPS were 
used to measure the functional groups loaded on the electrode materials. 
The impedance and hydrophilicity of the electrode materials were 
measured by an electrochemical workstation and contact angle metre 
(SDC-100), respectively. XRD (Rigaka Intelligent Laboratory, D8Advan- 
A25) was used to analyse the main phases on the electrode after 
electrodeposition. 
The metal leaching efficiency in the electroplating sludge are 
expressed in (W%) as. 
w =
(
1 −
CiMi
C0M0
)
× 100% 
where w is the leaching efficiency of heavy metal elements (%), C0 is 
the initial content of heavy metal elements in the electroplating sludge, 
M0 is the initial mass of the original electroplating sludge, Ci is the 
elemental content of heavy metals after leaching of the residue, and Mi is 
the leaching residue mass. 
The electrodeposition efficiency CE (%) of copper in the electrolyte is 
expressed as. 
CE =
(
1 −
CiVi
C0V0
)
× 100% 
where CE is the recovery efficiency of copper metal (%), Ci is the 
amount of copper metal in the electrodeposition solution, Vi is the 
volume of electrodeposited liquid, C0 is the initial content of copper 
metal in the electrodeposition solution, and V0 is the initial volume of 
the electrodeposition solution. 
3. Results and discussion 
3.1. Characterization of the Ami-PC electrode 
The modification of carbon felt mainly improved the hydrophilicity 
of electrode materials and prevented the formation of polymer coatings 
to decrease the conductivity of electrode materials[32,33]. 
The conductivity of Ami-PC was measured with an electrochemical 
workstation (Fig. 3 a). Compared with carbon felt, the conductivity of 
Ami-PC was slightly reduced due to the nonconductive polymer shell. 
FTIR measurements were carried out to investigate the functional 
groups on the surface of the Ami-PC electrodes and PAN (Fig. 3 b). There 
is an obvious stretching vibration peak at 2243 cm− 1 in PAN, which is 
the characteristic peak of the nitrile Group C–––N[34,35]. This peak had 
obviously disappeared after the amidoxime reaction. A broad band at 
1648 cm− 1 was allotted to the stretching vibration of C––N. The 
stretching vibration peak of N–O appeared at approximately 935 cm-1, 
and the band at approximately 1385 cm− 1 was attributed to the C–N 
stretching vibration[36]. Fig. 3 c shows the spectra of N1 s, C1 s and O1 s 
at the Ami-PC electrode. The binding energies of 399.3 eV and 397.9 eV 
represent–C–NOH and–C–NH2 groups, respectively[23,37]. It has been 
Fig. 4. The relationship between EDTA concentrations, liquid–solid ratio, amount of EDTA mixed with citric acid, and time on the leaching efficiency of copper and 
iron. (a) Effects of different EDTA concentrations on the leaching efficiency of copper and iron in electroplating sludge. (b) Effects of different liquid–solid ratios on 
the leaching efficiency of copper and iron in electroplating sludge. (c) Effects of EDTA mixed with different concentrations of CA on the leaching efficiency of copper 
and iron in electroplating sludge. (d) Effect of time on the leaching efficiency of metallic copper and iron in electroplating sludge. 
D. Deng et al. 
Separation and Purification Technology 301 (2022) 121917
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proven that the electrode can graft the target functional group onto the 
carbon felt by the amidoxime reaction. 
Amidoxime groups can change the hydrophilicity of carbon felt to a 
great extent. The contact angle of carbon felt (CF) was observed to be 
110.45◦(Fig. 3 d), while that of Ami-PC cannot be obtained because the 
water droplet just penetrates the Ami-PC. The great improvement in 
hydrophilicity is because amino groups and oxime groups can form 
hydrogen bonds with H2O molecules[23]. When CF comes into contact 
with water, the hydrophobic surface will form an air gap around the 
fibre, and the water droplets cannot moisten carbon felt (Fig. 3 e). 
Fig. 5. Plot of voltage, duty cycle, pH and electrolyte flow rate against copper recovery.(a) The effect of voltage on the recovery ofcopper in the electrolyte. (b) The 
effect of duty cycle on the recovery of copper in the electrolyte. (c) The effect of initial pH value on the recovery of copper in the electrolyte. (d) The effect of flow rate 
on the recovery of copper in the electrolyte. (e) Selective recovery of copper from the electrolyte. (f) Morphology of complexes of copper and EDTA at different 
pH values. 
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Separation and Purification Technology 301 (2022) 121917
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3.2. Copper leaching 
Selective leaching of copper is achieved in this section by mixing a 
small amount of AC with EDTA. The copper content in the sludge is 11.1 
%, and the iron content is 17.1 % according to the quantitative analysis. 
To improve the purity of recovered copper, it is very important to reduce 
the portion of iron during leaching. The weak acidity of EDTA is insuf-
ficient to convert iron oxides into iron ions, but it can react directly with 
copper hydroxide. The complexes formed by EDTA with copper ions are 
charged and soluble in water, which provides a theoretical basis for the 
electrochemical recovery of copper. The addition of a small amount of 
CA increases the concentration of H+, which is helpful to the leaching 
efficiency of copper. The direct reaction of EDTA with copper hydroxide 
in electroplating sludge provides an idea for the selective leaching of 
more copper from electroplating sludge. The chemical Formulas (1), (2) 
and (3) contain the stability constants of Cu(II), Fe(III), Fe(II) and EDTA. 
Cu2+(aq) + H2EDTA(aq) = CuH2EDTA(aq), logKS = 18.7(1) 
Fe3+(aq) + H2EDTA(aq) = FeH2EDTA(aq) + H+(aq), logKS = 24.22(2) 
Fe2+（aq）+H2EDTA（aq）=FeH2EDTA(aq）,logKS = 14.82(3) 
3.2.1. Effect of initial EDTA concentration on the leaching efficiency 
The effect of the initial concentration of EDTA on the copper(iron) 
leaching efficiency was investigated. The result is shown in Fig. 4 a. 
When the initial concentration of EDTA was 10 mM, the leaching effi-
ciency of copper from the electroplating sludge within 5 h was 21.24 %. 
When the initial concentration of EDTA was 70 mM, the leaching effi-
ciency was 75.6 %. When the concentration continued to rise, the 
leaching efficiency of copper remained constant, but the leaching effi-
ciency of iron increased. This is because EDTA reacts with copper hy-
droxide in the electroplating sludge. When the concentration of EDTA 
continues to increase, the excess EDTA leaches other metals, such as 
ions, instead of copper from the electroplating sludge, and the leaching 
efficiency of metallic iron is increased. The results showed that the 
initial concentration of EDTA was conducive to the leaching of copper 
and that 70 mM was rather suitable. 
3.2.2. Effect of the liquid–solid ratio on the leaching efficiency 
The effect of the liquid–solid ratio on the copper(iron) leaching ef-
ficiency was studied. The liquid–solid ratio was defined as the ratio of 
EDTA volume and electroplating sludge mass. The initial concentration 
of EDTA solution was set at 70 mM at room temperature. As shown in 
Fig. 5 b, the leaching efficiency of iron increased with increasing liq-
uid–solid ratio, while the leaching efficiency of copper reached a 
maximum at 120 mL/g. This may be attributed to the excessive EDTA 
involved in the leaching of iron. When the concentration of EDTA was 
70 mM and the volume of extractant was increased at room temperature, 
the leaching efficiency reached 53.16 %, 64.16 %, 67.64 %, 75.63 %, 
and 73.17 %, respectively. As shown in Fig. 4 b, when the liquid–solid 
ratio reaches 120 mL/g, the leaching efficiency of copper is higher, but 
the leaching efficiency of iron increases from 17.95 % to 19.53 % with 
increasing liquid–solid ratio. The reason is that the excess EDTA is 
involved in the reaction of iron, which leads to an increase in the 
leaching of iron. 
3.2.3. Effect of EDTA mixed with citric acid concentration on leaching 
efficiency 
The effect of citric acid concentration on the copper(iron) leaching 
efficiency was studied. The initial concentration of EDTA solution was 
set at 70 mM at room temperature. As shown in Fig. 4 c, the leaching 
efficiency of iron increased with increasing CA concentration, while the 
leaching efficiency of copper reached 85.37 % with 10 mM citric acid. 
The adequate addition of citric acid can drive the soluble copper 
compound to a complete reaction with the leaching agent. However, the 
reaction of iron(III) oxide and ferric oxide with EDTA occurred as the 
concentration of citric acid increased. When citric acid was added to 25 
mM, the leaching efficiency of copper did not change obviously, but the 
leaching efficiency of iron increased from 17.95 % to 35.31 %. There-
fore, adding 10 mM citric acid is the best experimental condition, which 
can not only increase the leaching effect of copper but also reduce the 
leaching effect of iron. 
3.2.4. Effect of time on the copper/iron leaching efficiency 
The leaching experiments were carried out with a liquid-to-solid 
ratio of 120 mL/g at room temperature. The leaching agent was 70 
mM fresh EDTA mixed with 10 mM citric acid. As shown in Fig. 4 d, the 
leaching efficiency of copper and iron showed an increasing trend with 
the extension of time. The leaching efficiency of copper was 34.60 % at 
1 h, while at 5 h, the leaching efficiency reached 85.21 %. After that, the 
copper leaching efficiency did not increase significantly. 
3.3. Electrodeposition experiment with simulated solution 
The electrodeposition method was evaluated for the selective sepa-
ration of copper from iron for their potential difference. Experiments 
were carried out with a mixed solution of Cu-EDTA (750 ppm) and Fe- 
EDTA (250 ppm) as the simulated electrolyte. The effects of power 
voltages, power duty cycle, solution pH, and flow rate on the recovery of 
copper were studied. 
Increasing the voltage of electrodeposition can effectively recover 
the copper from the leaching solution, and the increase in voltage may 
also increase the current density of electrodeposition. As shown in Fig. 5 
a, the recovery efficiency of copper is only 33.2 % when the voltage is (4, 
0) V, while it is over 98 % when the voltage is increased to (6, 0) V. In the 
process of electrodeposition, the electrode reaction generally goes 
through three stages: the electrode reaction control stage, diffusion 
control stage and side reaction stage. At the beginning of the reaction, 
with increasing voltage, the movement rate of heavy metal ions and the 
deposition efficiency increase. 
As shown in Fig. 5 b, the recovery efficiency of copper is only 30.53 
% (voltage: (6, 0) V duty cycle: 40 %). When the duty cycle was 
increased to 70 %-80 %, the efficiency of copper recovery went to 91 
%-98 %. The experimental results showed that an 80 % duty cycle would 
be good for copper recovery. The concentration of metal ions at the 
electrode-solution interface is regulated by the on and off of the current, 
thereby eliminating the polarization of the concentration difference. 
When the circuit is switched on, the ion concentration at the interface 
decreases rapidly, and concentration polarization occurs. When the 
circuit is switched off, the ion concentration at the interface will rise 
again, thus eliminating concentration polarization. The proper duty 
cycle can not only reduce the energy consumption but also reduce the 
hydrogen evolution reaction of the anode during electrodeposition. 
Copper recovery under a (6, 0) V voltage and 80 % duty ratio was 
tested with different pH values of the simulated electrolyte solution. The 
pH value could also affect the electrode side reaction and the initial 
speciation of target heavy metals. A higher H+ concentration leadsto 
faster ion transfer than the electrochemical reaction; thus, concentration 
polarization would occur, and the hydrogen evolution overpotential 
would decrease. At the same time, the activation polarization also leads 
to a decrease in the hydrogen evolution overpotential. A lower hydrogen 
evolution overpotential will benefit the hydrogen evolution reaction. 
The target metal ion reduction would be restrained, which reduces the 
recovery efficiency of the related metal. When the electrolyte is neutral, 
the concentration of OH– increases near the cathode due to the evolution 
of hydrogen, which makes the metal ions hydrolyse or even precipitate 
near the cathode. As shown in Fig. 5 c, the recovery efficiency of copper 
reaches a maximum at Solution initial pH = 3.23. When the Solution 
initial pH continues to increase, the recovery efficiency of copper de-
creases obviously. When Solution initial pH = 7.48, copper recovery 
D. Deng et al. 
Separation and Purification Technology 301 (2022) 121917
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continues to decrease to 70.41 %. The target metal complex morphology 
in the electrolyte was analysed by Visual MINTEQ software, and the 
result is shown in Fig. 5 f. Copper exists in the form of CuH2EDTA (aq) 
when the pH lies 2 ~ 3. The concentration of Cu2+ is higher in the same 
pH range, which makes it easier to electrodeposit copper. With 
increasing pH, the copper in the solution gradually changes from the 
form of CuH2EDTA (aq) to CuHEDTA-and CuEDTA2-. With the formation 
of the copper complex, copper electrodeposition requires more time or 
higher potential. 
The effect of the electrolyte flow rate on the recovery efficiency of 
copper was studied, as shown in Fig. 5 d. The recovery efficiency in all of 
the experiments reached 97 %. The higher the flow rate is, the stronger 
the stirring action in the solution. As a result, the thickness of the 
diffusion layer would be decreased. The electrolytic process controlled 
by diffusion is improved, and the efficiency of electrodeposition is 
increased. 
Under the above conditions ((6,0) V, 80 %, pH = 3.23, 20 mL/min, 4 
h), the experiment of copper electrodeposition in electrolyte was carried 
out. As shown in Fig. 5 e, the concentration of iron ions in the simulated 
electrolyte solution decreased slightly during the electrodeposition. The 
reason can be attributed to the sensible potential difference between 
copper and iron. Iron deposition cannot be reached under the above 
conditions. Thus, the selective recovery of copper was realized. 
3.4. Electrodeposition experiments of metallic copper in electroplated 
sludge 
The selective electrodeposition recovery of copper from electro-
plating sludge was conducted by two different methods: As shown in 
Fig. 6 a, electrodeposition while leaching (Method 1) and electrodepo-
sition after leaching (Method 2). In Method 1, copper deposition and ES 
leaching were performed simultaneously. The copper recovery effi-
ciency was 82.21 % under the conditions (duty cycle 80 %, potential 
(6,0) V, flow rate 20 mL/min) within 5 h. In Method 2, the electrode-
position of copper was performed after 4 h of leaching. After 4 h of 
deposition, 83.25 % copper in the electroplating sludge was recovered 
with Method 2 under the same conditions. The copper recovery effi-
ciency of Method 1 was almost the same with Method 2 within less time. 
In addition, the phase structures of the deposited electrode sheet 
were studied by XRD. As shown in Fig. 6 b, the diffraction peak of copper 
is the main crystalline, while there is no obvious peak for other metal 
species. As shown in Fig. 6 c, the XPS spectrum of Cu 2p copper has a 
major peak at 932.6 eV[27] and another peak in CuO, Cu2þ at 941.7 eV 
[31]. Despite the high iron content and the presence of other impurities 
in the sludge, more than 82 % of copper was selectively recovered by 
leaching with EDTA mixed with CA and electrodeposition. Fig. 6 
d shows the main form of copper complex ions in the solution. During 
electrodeposition, these ions migrate, diffuse and electrodeposit in the 
solution under the action of an electric field force. This also provides us 
with an idea of the electrochemical recovery of copper. 
Fig. 6. (a) Recovery of copper from real electroplating sludge. (b) XRD patterns of copper products deposited on the working electrode under optimal conditions. (c) 
XPS analysis of the main metal elements in the copper products. (d) Species distribution of 750 ppm copper ions and 250 ppm iron ions in 70 mM EDTA solution. In a 
wide pH range, approximately 100 % of heavy metal cations exist in the form of anionic complexes (MEDTA2-). 
D. Deng et al. 
Separation and Purification Technology 301 (2022) 121917
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3.5. Repeated use of leaching agent 
The feasibility of the repeated use of EDTA was verified by the 
following steps. First, iron ions and other impurity metal ions in the 
remaining solution in Experiment 3.4 were precipitated by adjusting the 
pH to 13 with NaOH. After that, the pH of the leaching solution after 
precipitation and filtration was adjusted to 3.54. Then, the obtained 
solution was mixed with CA as a leaching agent to leach new ESs for the 
selective recovery of copper. The previous steps were repeated three 
times, and the leaching efficiency was measured. As shown in Fig. 7, the 
leaching agent is recycled 3 times, and the results show that the leaching 
efficiency of copper can reach more than 80 % after 3 cycles of recycling. 
4. Conclusion 
In this study, Ami-PC electrodes were prepared to selectively recover 
copper from ES in an environmentally friendly way. The hydrophilicity 
of the carbon felt was greatly changed by the loading of amidoxime 
functional groups. Copper was selectively leached out from the ES by the 
mixed EDTA solution with CA. Under normal temperature, the leaching 
efficiency of copper was 85 % in 5 h under the conditions of 70 mM 
EDTA, 120:1 liquid–solid ratio and 10 mM citric acid. 
A porous carbon (Ami-PC) electrode was prepared by the amidoxime 
reaction of carbon felt. The hydrophilicity of the electrode material was 
greatly changed by the formation of amidoxime functional groups. 
Amidoxime groups also enable most cations to contact the electrode 
surface directly, chelate with amidoxime groups, and electrodeposit to 
metal in situ electrocrystallization. The copper deposit efficiency is over 
98 % based on the simulated leaching solution under the following 
conditions: duty cycle of 80 %, potential (6,0) V, and a flow rate of 20 
mL/min. The feasibility of electrodeposition while leaching was studied, 
and 82.21 % copper in the ES was recovered in the zero-valent form. The 
leaching ability of EDTA was almost the same after three repeated uses. 
CRediT authorship contribution statement 
Di Deng: Investigation, Formal analysis, Data curation, Writing – 
original draft. Chunjian Deng: Conceptualization, Funding acquisition, 
Project administration. Tingting Liu: Methodology, Software. Ding-
qian Xue: Writing – original draft. Jie Gong: Investigation. Rong Tan: 
Data curation. Xue Mi: Investigation, Methodology, Data curation. 
Baichuan Gong: Supervision, Validation. Zhongbing Wang: Review, 
Editing. Chunli Liu: Formal analysis, Data curation. Guisheng Zeng: 
Conceptualization, Funding acquisition, Project administration. 
Declaration of Competing Interest 
The authors declare that they have no known competing financial 
interests or personal relationships that could have appeared to influence 
the work reported in this paper.Data availability 
Data will be made available on request. 
Acknowledgments 
The Key Research and Development Program of Jiangxi Province 
(grant No. CK202002472). 
References 
[1] J.Z. Zhou, Y.Y. Wu, C. Liu, A. Orpe, Q. Liu, Z.P. Xu, G.R. Qian, S.Z. Qiao, Effective 
self-purification of polynary metal electroplating wastewaters through formation of 
layered double hydroxides, J. Environ. Sci. Technol. 44 (23) (2010) 8884–8890. 
[2] C. Li, F. Xie, Y. Ma, T. Cai, H. Li, Z. Huang, G. Yuan, Multiple heavy metals 
extraction and recovery from hazardous electroplating sludge waste via 
ultrasonically enhanced two-stage acid leaching[J], J. Hazard. Mater. 178 (1-3) 
(2010) 823–833. 
[3] L. Mao, R. Tang, Y. Wang, Y. Guo, P. Su, W. Zhang, Stabilization of electroplating 
sludge with iron sludge by thermal treatment via incorporating heavy metals into 
spinel phase[J], J. Cleaner Prod. 187 (2018) 616–624. 
[4] P. Wu, L. Zhang, Y. Liu, X. Xie, J. Zhou, H. Jia, P. Wei, Enhancing Cu-Zn-Cr-Ni Co- 
extraction from electroplating sludge in acid leaching process by optimizing Fe3+
addition and redox potential[J], Environ. Eng. Sci. 36 (9) (2019) 1244–1257. 
[5] P.T. Huyen, T.D. Dang, M.T. Tung, N.T.T. Huyen, T.A. Green, S. Roy, 
Electrochemical copper recovery from galvanic sludge[J], Hydrometallur-gy 164 
(2016) 295–303. 
[6] V. Gunarathne, A.U. Rajapaksha, M. Vithanage, N. Adassooriya, A. Cooray, 
S. Liyanage, B. Athapattu, N. Rajakaruna, A.D. Igalavithana, D. Hou, D.S. Alessi, Y. 
S. Ok, Heavy metal dissolution mechanisms from electrical industrial sludge[J], 
Sci. Total Environ. 696 (2019) 133922. 
[7] U. Thawornchaisit, K. Juthaisong, K. Parsongjeen, P. Phoengchan, Optimizing acid 
leaching of copper from the wastewater treatment sludge of a printed circuit board 
industry using factorial experimental design[J], J. Mater. Cycles Waste Manage. 21 
(6) (2019) 1291–1299. 
[8] A.H. Kaksonen, S. Särkijärvi, J.A. Puhakka, E. Peuraniemi, S. Junnikkala, O. 
H. Tuovinen, Solid phase changes in chemically and biologically leached copper 
smelter slag[J], Miner. Eng. 106 (2017) 97–101. 
[9] J. Wang, R.-y. Zhou, J.-X. Yu, H.-S. Wang, Q.-Y. Guo, K.-q. Liu, H.-D. Chen, R.- 
A. Chi, Sequential recovery of Cu (II), Cr (III), and Zn (II) from electroplating 
sludge leaching solution by an on-line biosorption method with dosage controlling 
[J], J. Cleaner Prod. 337 (2022) 130427. 
[10] L. S. Yi, L. H. Zhao, Y. H. Xu, et al. Study on leaching and solvent extraction 
recovery of copper from electroplating sludge[J]. Mining and Metallurgy 
Engineering, 2019, 39 (4): 115-118, 122, https://doi.org/10.39 69/j.issn.0253- 
6099.2019.04.027. 
[11] J.H. Cheng, X. Chen, et al., Recovery of Copper and Nickel from Electroplating 
Sludge by Ammonia Leaching and Hydrogen Reduction under High Pressure[J], 
Environ. Sci. Technol. S1):135–137,140 (2010), https://doi.org/10.3969/j. 
issn.1003-6504.2010.6E.037. 
[12] J. Sun, W. Zhou, L. Zhang, H. Cheng, Y. Wang, R. Tang, H. Zhou, Bioleaching of 
copper-containing electroplating sludge[J], J. Environ. Manage. 285 (2021), 
https://doi.org/10.1016/j.jenvman.2021.112133. 
[13] Y. Yang, X. Liu, J. Wang, Q. Huang, Y. Xin, B. Xin, Screening bioleaching systems 
and operational conditions for optimal Ni recovery from dry electroplating sludge 
and exploration of the leaching mechanisms involved[J], Geomicrobiol J. 33 (3-4) 
(2016) 179–184. 
[14] S. Sharma, A. Gautam, S.A. Gautam, Greener Approach to Extract Copper from 
Fertilizer Industry Spent Catalyst[J], Arabian Journal for Science and Engineering 
45 (9) (2020) 7529–7538, https://doi.org/10.1007/s13369-020-04652-x. 
[15] T. Palden, L. Machiels, B. Onghena, M. Regadío, K. Binnemans, Selective leaching 
of lead from lead smelter residues using EDTA[J], RSC Adv. 10 (69) (2020) 
42147–42156. 
[16] J. Xu, C. Liu, P.-C. Hsu, J. Zhao, T. Wu, J. Tang, K. Liu, Y.i. Cui, Remediation of 
heavy metal contaminatedsoil by asymmetrical alternating current 
electrochemistry[J], Nat. Commun. 10 (1) (2019), https://doi.org/10.1038/ 
s41467-019-10472-x. 
[17] S. Cheng, Q. Lin, Y. Wang, H. Luo, Z. Huang, H. Fu, H. Chen, R. Xiao, The removal 
of Cu, Ni, and Zn in industrial soil by washing with EDTA-organic acids[J], Arabian 
J. Chem. 13 (4) (2020) 5160–5170. 
[18] X. Ke, F.J. Zhang, Y. Zhou, H.J. Zhang, G.L. Guo, Y.u. Tian, Removal of Cd, Pb, Zn, 
Cu in smelter soil by citric acid leaching[J], Chemosphere 255 (2020) 126690. 
[19] R. Martins, P.H. Britto-Costa, L.A.M. Ruotolo, Removal of toxic metals from 
aqueous effluents by electrodeposition in a spouted bed electrochemical reactor, 
Environ. Technol. 33 (10) (2012) 1123–1131. 
Fig. 7. Leaching efficiency of copper from electroplating sludge by recovered 
leaching agent. 
D. Deng et al. 
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0005
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0005
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0005
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0010
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0010
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0010
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0010
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0015
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0015
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0015
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0020
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0020
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0020
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0025
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0025
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0025
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0030
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0030
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0030
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0030
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0035
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0035
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0035
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0035
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0040
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0040
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0040
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0045
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0045
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0045
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0045
https://doi.org/10.3969/j.issn.1003-6504.2010.6E.037
https://doi.org/10.3969/j.issn.1003-6504.2010.6E.037
https://doi.org/10.1016/j.jenvman.2021.112133
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0065
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0065
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0065
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0065
https://doi.org/10.1007/s13369-020-04652-x
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0075
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0075
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0075
https://doi.org/10.1038/s41467-019-10472-x
https://doi.org/10.1038/s41467-019-10472-x
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0085
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0085
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0085
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0090
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0090
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0095
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0095
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0095
Separation and Purification Technology 301 (2022) 121917
9
[20] Y. Zhang, H. Liu, F. Gao, X. Tan, Y. Cai, B. Hu, Q. Huang, M. Fang, X. Wang, 
Application of MOFs and COFs for photocatalysis in CO2 reduction, H2 generation,and environmental treatment[J], EnergyChem 4 (4) (2022) 100078. 
[21] X. Liu, G. Verma, Z. Chen, et al. Metal-organic framework nanocrystals derived 
hollow porous materials: synthetic strategies and emerging applications[J]. The 
Innovation, 2022: 100281.https://doi.org/10.1016/j.xinn.2022.100281. 
[22] S. Yu, H. Tang, D.i. Zhang, S. Wang, M. Qiu, G. Song, D. Fu, B. Hu, X. Wang, 
MXenes as emerging nanomaterials in water purification and environmental 
remediation[J], Sci. Total Environ. 811 (2022) 152280. 
[23] T. Wu, C. Liu, B. Kong, J. Sun, Y. Gong, K. Liu, J. Xie, A. Pei, Y.i. Cui, Amidoxime- 
functionalized macroporous carbon self-refreshed electrode materials for rapid and 
high-capacity removal of heavy metal from water[J], ACS Cent. Sci. 5 (4) (2019) 
719–726. 
[24] X. Liu, Y. Xie, M. Hao, Z. Chen, H. Yang, G.I.N. Waterhouse, S. Ma, X. Wang, Highly 
Efficient Electrocatalytic Uranium Extraction from Seawater over an Amidoxime- 
Functionalized In–N–C Catalyst[J]. Advanced, Science 9 (23) (2022) 2201735. 
[25] H. Yang, X. Liu, M. Hao, Y. Xie, X. Wang, H.e. Tian, G.I.N. Waterhouse, P.E. Kruger, 
S.G. Telfer, S. Ma, Functionalized iron–nitrogen–carbon electrocatalyst provides a 
reversible electron transfer platform for efficient uranium extraction from seawater 
[J], Adv. Mater. 33 (51) (2021) 2106621. 
[26] C. Liu, P.-C. Hsu, J. Xie, J. Zhao, T. Wu, H. Wang, W. Liu, J. Zhang, S. Chu, Y.i. Cui, 
A half-wave rectified alternating current electrochemical method for uranium 
extraction from seawater, Nat Energy 2 (4) (2017). 
[27] C. Liu, T. Wu, P.-C. Hsu, J. Xie, J. Zhao, K. Liu, J. Sun, J. Xu, J. Tang, Z. Ye, D. Lin, 
Y.i. Cui, Direct/alternating current electrochemicalmethod for removing and 
recovering heavy metal from water using graphene oxide electrode[J].ACS, NANO 
13 (6) (2019) 6431–6437. 
[28] C. M. AMARESH, K. T. AWALENDRA, V. SRINIVAS.Effect of deposition parameters 
on microstructure of electrodeposited nickel thin films[J].Journalof Materials 
Science,2009,44:3520-3527, https://doi.org/10.1007/s10853-009-3475-y. 
[29] D.D. Hawn, B.M. DeKoven, Deconvolution as a correction for photoelectron 
inelastic energy losses in the core level XPS spectra of iron oxides[J], Surf. 
Interface Anal. 10 (2–3) (1987) 63–74, https://doi.org/10.1002/sia.740100203. 
[30] Y.W. Jang, J.H. Hong, J.G.J. Mkim, et al., Effects of copper on the corrosion 
properties of low-alloy steel in an acid-chloride environment[J], Met. Mater. Int. 
15 (4) (2009) 623–629, https://doi.org/10.1007/s12540-009-0623-5. 
[31] S. Anantharaj, H. Sugime, S. Noda, Ultrafast growth of a Cu (OH) 2–CuO 
nanoneedle array on Cu foil for methanol oxidation electrocatalysis[J], ACS Appl. 
Mater. Interfaces 12 (24) (2020) 27327–27338, https://doi.org/10.1021/ 
acsami.0c08979. 
[32] T.X.H. Le, C. Charmette, M. Bechelany, M. Cretin, Facile preparation of porous 
carbon cathode to eliminate paracetamol in aqueous medium using electro-Fenton 
system[J], Electrochim. Acta 188 (2016) 378–384. 
[33] T. Liu, X. Li, H. Nie, C. Xu, H. Zhang, Investigation on the effect of catalyst on the 
electrochemical performance of carbon felt and graphite felt for vanadium flow 
batteries[J], J. Power Sources 286 (2015) 73–81. 
[34] K. Saeed, S. Haider, T.-J. Oh, S.-Y. Park, Preparation of amidoxime-modified 
polyacrylonitrile (PAN-oxime) nanofibers and their applications to metal ions 
adsorption[J], J. Membr. Sci. 322 (2) (2008) 400–405. 
[35] H.-B. Pan, L.-J. Kuo, C.M. Wai, N. Miyamoto, R. Joshi, J.R. Wood, J.E. Strivens, C. 
J. Janke, Y. Oyola, S. Das, R.T. Mayes, G.A. Gill, Elution of uranium and transition 
metals from amidoxime-based polymer adsorbents for sequestering uranium from 
seawater[J], Ind. Eng. Chem. Res. 55 (15) (2016) 4313–4320. 
[36] Y. Xue, M. Cao, J. Gao, Y. Gui, J. Chen, P. Liu, F. Ma, Y. Yan, M. Qiu, 
Electroadsorption of uranium on amidoxime modified graphite felt[J], Sep. Purif. 
Technol. 255 (2021), https://doi.org/10.1016/j.seppur.2020.117753. 
[37] F. Liu, W. Huang, S. Wang, B. Hu, Investigation of adsorption properties and 
mechanism of uranium (VI) and europium (III) on magnetic amidoxime- 
functionalized MCM-41[J], Appl. Surf. Sci. 594 (2022) 153376. 
D. Deng et al. 
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0100
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0100
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0100
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0110
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0110
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0110
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0115
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0115
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0115
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0115
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0120
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0120
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0120
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0125
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0125
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0125
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0125
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0130
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0130
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0130
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0135
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0135
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0135
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0135
https://doi.org/10.1002/sia.740100203
https://doi.org/10.1007/s12540-009-0623-5
https://doi.org/10.1021/acsami.0c08979
https://doi.org/10.1021/acsami.0c08979
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0160
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0160
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0160
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0165
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0165
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0165
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0170
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0170
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0170
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0175
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0175
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0175
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0175
https://doi.org/10.1016/j.seppur.2020.117753
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0185
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0185
http://refhub.elsevier.com/S1383-5866(22)01472-1/h0185
	Selective recovery of copper from electroplating sludge by integrated EDTA mixed with citric acid leaching and electrodepos ...
	1 Introduction
	2 Materials and methods
	2.1 Materials
	2.2 Ami-PC electrode fabrication
	2.3 Copper leaching
	2.4 Copper recovery
	2.5 Characterization and analytical methods
	3 Results and discussion
	3.1 Characterization of the Ami-PC electrode
	3.2 Copper leaching
	3.2.1 Effect of initial EDTA concentration on the leaching efficiency
	3.2.2 Effect of the liquid–solid ratio on the leaching efficiency
	3.2.3 Effect of EDTA mixed with citric acid concentration on leaching efficiency
	3.2.4 Effect of time on the copper/iron leaching efficiency
	3.3 Electrodeposition experiment with simulated solution
	3.4 Electrodeposition experiments of metallic copper in electroplated sludge
	3.5 Repeated use of leaching agent
	4 Conclusion
	CRediT authorship contribution statement
	Declaration of Competing Interest
	Data availability
	Acknowledgments
	References