Proceedings of the 10th World Congress on Mechanical, Chemical, and Material Engineering (MCM'24)
Barcelona, Spain - August 22-24, 2024
Paper No. MMME 120
DOI: 10.11159/mmme24.120

Development of Innovative and Sustainable Methodologies Applied
To the Recovery of Copper in Integrated Circuit Boards
Lídia Cunha1,2*, Joana Monteiro1,2, Andreia Azevedo1, Aurora Futuro1,2, José Soeiro1,2, Rui Sousa1,2Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
CERENA—Polo FEUP—Centre for Natural Resources and the Environment, Faculty of Engineering, University of Porto,4200-465 Porto, Portugal*Corresponding authors: Lídia Cunha, E-mail: up20140672@fe.up.pt
12Abstract
The high demand for electronic devices is increasing drastically, raising concerns about the generation of spent printed circuit boards,
which contain a significant amount of semi-precious and precious metals. The so-called digital and energy transition creates additional
stress in the raw materials supply chain, requiring innovative approaches to extract critical raw materials from waste.
The present research focuses on studying the physical and hydrometallurgy process to extract copper from integrated circuit boards. Sofar, it was possible to perform the physical process in order to obtain a sample manly composed of metals to proceed with thehydrometallurgical process. The results from the hydrometallurgical process demonstrate that selective leaching is achievable.
Preliminary studies indicate that it is possible to extract more than 70% of Cu.
Keywords: printed circuit boards, copper extraction, electronic waste, green leaching

1. Introduction

In 2024, the estimated global electronic waste (e-waste) is 63.3 million metric tons, and it is expected to reach 74.7
million by 2030 [1]. By 2050, the demand for several metals will increase - 35% copper (Cu), 45% silicon (Si), 100% nickel(Ni), and 3.5% lithium (Li), among others. To comply with the global net carbon emissions goals, it will be necessary tobuild more than 50 Li mines, 60 Ni mines, and 17 Cu mines [2]. Therefore, the increasing demand for electronic devices
containing precious metals and other valuable materials has raised concerns about the supply chain, the sustainability ofmining practices, and the safe dismantling and disposal of e-waste [3].
Recycling printed circuit boards (PCBs) allows for the recovery of semi-precious and precious metals, reducing the needfor extracting and processing primary resources. This conserves natural resources and reduces the environmental impact ofmining and processing raw materials. As visualized in Table 1, PCBs are present in all electronic devices, representing 30.3%
of mobile phones, 11.6% of televisions and 13.7% of laptops [4,5]. Additionally, Cu and iron (Fe) are the most representative
metals in e-waste, along with aluminium (Al), Ni and lead (Pb).
Table 1 Average weight, percentage of PCBs, semi-precious metal content in e-waste and precious metal content of PCBs.

Mobilephone
Television
LaptopSemi-precious metal content in ewaste (%)

Precious metal content of
PCB (mg/ kg)

Cu

Fe

Al

NiPb

Au

Ag

Pd

Average weight(kg/unit)

Percentage ofPCBs (%)

0.125

30.3

135

1

0.1

0.3

1500

3800

300

16.8
2.46

11.6
13.7

1022

28
37

10
0.3

0.3
0.3-2

1.0
3.7

250
240

500
570

150

Reference[4,6][4,5,7,8]

Regarding their values as waste, semi-precious and precious metals are potential resource to develop novel productswith a high impact on society [9].

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This work highlights the potential for Cu extraction. In Figure 1, illustrates the PCBs processing and thehydrometallurgy process that have been studied to extract the required metal.

Figure 1 E-waste processing and metallurgical process.

The focus of the present research was divided in two phases. In the first phase, PCBs pre-treatment was performed,involving physical methods that rely on mechanical techniques. Disassembly and mechanical processes are required toliberate and separate the metallic parts from PCBs to deliver a metallic-enriched product to the subsequenthydrometallurgy processes [9]. Following dismantling, the next stage involved size reduction, where crushers andgrinders equipment were used. Then, a shaking table was utilized to separate materials with different densities due totheir different relative movements against gravitational forces. In the second phase, the hydrometallurgy process wasexecuted, where the selective leaching using appropriate lixiviants for Cu extraction was studied.

2. Materials and Procedure
2.1 Materials

The PCBs samples (52 0500 mg/kg of Cu, 85 000 mg/kg of Fe, 12 350 mg/kg of Ni, 62 047 mg/kg of Zn) wereobtained from ARG company. Hydrogen peroxide 30% brought from VWR Chemicals (batch 22A254127). Sulfuric
acid 95-98% (batch 0002307670) purchased from PanReac AppliChem (ITW Reagents). Nitric acid 70% pure, in water
purchased from Thermo Scientific.

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2.2 Equipment

Samples separator (PT 100), griding mill and sieves from Retsch company. Shredder acquired from Erdwich company.
Overhead stirrer from Hei-TORQUE 100. Chemical analysis of Cu, Fe, Zn and Ni were performed by atomic absorption in
an Analityk Jena ZEEnit70 equipment. X-ray fluorescence (XFR) from Oxford instruments.

2.3 Procedure
2.3.1 Samples preparation

In Figure 2, the schematic process for obtaining the required samples to perform the leaching experiments is presented.
First, the PCBs samples were transformed into small pieces using a guillotine. After using the shedder, a total of 10 kg ofsample was obtained. Then, out of the 10 kg, 8 kg were subjected to a griding mill to liberate the plastic matrix and achievea significant size reduction. The samples with sizes between 2.36/0.106 mm were separated using a shaking table (based ondensity). This allowed for the separation of concentrates from the middle and tailings samples. The concentrated samples,
which are mainly composed of metal fractions, were then subjected to XFR analysis.

Figure 2 Schematic representation of the samples preparation.

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2.3.2 PCBs Leaching using sulphuric acid (H2SO4) and hydrogen peroxide (H2O2)

Four experiments were conducted using H2SO4 at different concentrations - 1, 2, 3 and 4M – as visualized in Table
with a Solid/Liquid (S/L) ratio of 1/10. Initially, H2SO4 was added to approximately 25g of PCBs residue, followed byaddition of 15 V% H2O2 (30%) in relation to the H2SO4 concentration.
Table 2 PCBs leaching using H2SO4 and H2O2.

Experiment
1234Ratio (S/L)

Stirring speed(rpm)

Reactiontime (h)1/10300

4H2SO4(M)1234

H2O2(M)
4.4

3. Results and Discussion
3.1 Samples preparation

The XFR analysis was performed to define the chemical assay of feed material and the following size fractions: (+)2.36mm, between 2.36 and 0.106 mm (2.36/0.106mm), and less than (-)0.106mm. In the fractions with a size +2.36 mm, asignificant presence of plastics materials was observed (Figure 3).

Figure 3 Fraction with a size +2.36 mm.
The fraction 2.36/0.106 mm was submitted a gravity concentration method using a Wilfley shaking table (Figure 4), toseparate particles of different specific gravity, in order to obtain a final sample containing only heavy particles - metals
without any plastic material – light particles. This method allows for the separation of three types of samples: concentrates(high density), the middles (intermediate density) and the tailings (lowdensity). As expected, the middles and tailings samples contained a lower
metal content because they are primarily composed of plastic materials. The
concentrates contain a significant amount of Cu (43%) because it is mainly
used as electric current conductor [10]. This is followed by Fe (9%), Sn(4.1%), Zn (3.8%), Pb (2.9%), Ni (0.8%) and Ag (0.081%) as illustrated inTable 3. Consequently, this specific fraction was selected for use in thesubsequent experiments.
Figure 4 Shaking table.

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Table 3 XFR analysis of the concentrates.

Wilfley Shaking Table
Concentrates

CuFe

Zn

Pb

4393.8

2.9

Ni%
0.8

AsSnAg

Au

0.42

4.1

0.081

n.a3.1.2 PCBs Leaching using sulphuric acid (H2SO4) and hydrogen peroxide (H2O2)
Initially, a sample characterization was performed using aqua regia in order to determine the approximate content of Cu
in the samples.
Following, the main target of these experiments was to study the ideal concentrations for the selective extraction ofmetals. Therefore, the purpose of the 1st step was to extract Fe by varying the H2SO4 concentration. The 2nd step consisted ofextracting Cu by applying the previous procedure in order to determine the concentration that allows the highest Cu extraction
rate. In addition, the differences in Cu leaching efficiency were studied by varying the concentration of H2SO4 from 1 to 4M
for 4 hours of leaching time. In Figure 5, is represented the schematic procedure, applied for Fe and Cu extraction.
Additionally, for the performed experiments it was possible to observe that a green solution was obtained from the 1st stepand blue leaching solution from the 2nd step, which suggests that Fe was obtained in 1st step and Cu in 2nd step.

Figure 5 Schematic leaching procedure.

As depicted in Table 4, for experiment 1 it was possible to extract 51% of Fe for the 1st step. As expected, a higher
content of Cu and Zn was extracted in the 2nd step, 40% and 33%. These are low extraction efficiencies when compared withthe total quantity in the feed.
For the experiment 2 a significant amount of Fe was extracted after the 1st step, 76%. Although, for the 2nd step, a low
content of the remaining Cu, Zn and Ni was achieved, 48%, 54% and 23%.
In experiment 3, 70% of Fe was extracted after the 1st step, thus, with a significant reduction in other metals such as Cu,Zn and Ni, with extraction rates of 44%, 69% and 41%. The 2nd step allowed the extraction of 72% of the remaining Cu anda lower content of Zn and Ni, 37% and 18%.
In the last experiment, only 28% of Cu was extracted in the 1st step, with higher contents of Fe, Zn and Ni, 87%, 59%
and 44%. In the 2nd step, 25% of Ni was extracted, despite the extraction of 60% of Zn, only 40% of the remaining Cu wasextracted. Therefore, these results indicate that the concentration at 4M of H2SO4 does not allow for a higher extraction ofCu compared to the other concentrations of H2SO4, especially when compared with experiment 3, where was obtained thehighest Fe and Cu extraction.

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Table 4 AAS analysis of the leaching solution from the 1st and 2nd step for the experiment 1, 2, 3 and 4.

Experiment

Extraction, %MetalCuFeNiZn

1st
2nd

2
40

51
314
11833

1st876

25

18

2

nd

48

14

2354

1st44

70

41

69

2

nd72

61837

1st28

87

44

59

240

20

2560

Step

1234ndThe results metal content of the residues produced during the leaching tests is portrayed in Table 5.The experiment thatevidenced better extraction rate was experiment 3. For the 1st step, there is a significant Cu amount in the PCBs residue, it
only changed from 43% to 32%. In addition, it occurred a higher modification for Fe (9% to 2.9%), Zn (3.8% and 0.70%)
and Ni (0.8% to 0.33%). The 2nd step, the obtained values using XRF are in accordance with AAS, as it detected only 2.7%of Cu in the residue.
Table 5 XRF analysis of the PCBs (feed) sample and the final residue from the 1st and 2nd step.

SampleCuFeZnPbNiSnAgAu%PCBs4393.8

2.90.84.10.081-Residue from 1st Step

32

2.9

0.70

3.90.33

1.7

0.16

0.10*

Residue from 2nd Step

2.720.12

2.5

0.24

0.79

0.15

-*value detected only in one measure

4. Conclusion

The applied physical process made it possible to obtain an enriched-metal product composed by semi-precious andprecious metals.
PCBs residue is composed of a highly heterogenous material, requiring two steps in order to obtain a final pregnant
solution enriched in one type of metal. The performed leaching indicates that selective leaching can be feasible to extract
different metals from PCBs. Until the moment, using a concentration of 3M of H2SO4 and 4.4M of H2O2, with a S/L rationof 1/10 and a stirring speed of 300 rpm for 4h of leaching time, it was possible to extract 70% of Fe after the 1st and 72% of
the remaining Cu from the 2nd step. Although, more studies need to be performed in order to increase the Cu recuperation
after the 2nd step. Towards this end, as future work, it will be studied the influence of H2SO4 and H2O2 concentrations, alongwith various parameters such as S/L ratio, stirring speed and leaching time. Additionally, triplicates for the optimized
operating conditions need to be performed.

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This is a promising process for the industry, because it is efficient, easy to operate and control, and allows a selective
extraction of Cu. Therefore, it is vital to foster sustainable and innovative ways to recycle PCBs to mitigate its impact on theenvironment and people’s health, respecting the principles of a linear economy and overcoming the limitations of traditional
supply chains. Additionally, it is critical to develop different pathways for the extraction of metals, encouraging thedevelopment of new methodologies to take profit from the existing metals. Additionally, H2SO4 is considered less harmful
to the environment than other reagents such as cyanide. Also, it does not present the same acute health risks to workers andis less prone to accidental spills or exposure incidents.

Acknowledgements

ERA-MIN3/0003/2021 and DOI 10.54499/ERA‐MIN3/0003/2021 (https://doi.org/10.54499/ERAMIN3/0003/2021)
with the designation "Development of innovative and sustainable approaches applied to the recovery of gold and criticalelements from ores and spent printed circuit boards", funded by the Foundation for Science and Technology, I.P. throughnational funds under the ERA-MIN3 network and the ERA-NET Cofund in raw materials. Acknowledgements to CERENA,Base Funding - UIDB/04028/2020 and Programmatic Funding - UIDP/04028/2020 of the Research Center for Natural
Resources and Environment – CERENA - funded by national funds through the FCT/MCTES (PIDDAC).

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