• No results found

Leaching of Copper from Cuprous Oxide in Aerated Sulfuric Acid

N/A
N/A
Protected

Academic year: 2020

Share "Leaching of Copper from Cuprous Oxide in Aerated Sulfuric Acid"

Copied!
5
0
0

Loading.... (view fulltext now)

Full text

(1)

Leaching of Copper from Cuprous Oxide in Aerated Sulfuric Acid

Ilhwan Park

1

, Kyoungkeun Yoo

1,*

, Richard Diaz Alorro

2

, Min-seuk Kim

3

and Soo-kyung Kim

3 1Department of Energy & Resources Engineering, Korea Maritime and Ocean University, Busan 49112, South Korea

2Department of Mining Engineering and Metallurgical Engineering, Western Australian School of Mines (WASM), Curtin University, Kalgoorlie, WA 6430, Australia

3Mineral Resources Division, Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon 34132, South Korea The leaching behavior of copper from Cu2O in H2SO4 solution was investigated to establish the leaching process for cathode powders produced by the recycling of waste printed circuit boards. When air was not introduced in sulfuric acid solution, the dissolution of copper from Cu2O was inhibited by the formation of elemental copper (Cu0). The dissociated cuprous ions (Cu+) transformed into elemental copper (Cu0) or cupric ions (Cu2+) owing to the instability of Cu+ in H2SO4. Cu+ can be reduced to elemental copper (Cu0) by accepting an electron generated from the oxidation of another Cu+ to Cu2+, which is known as a disproportionation reaction. The introduction of air enhanced the leaching efficiency of copper due to the role of oxygen in the air as oxidant by accepting the electron generated from the oxidation of Cu+ to Cu2+. In the leaching test using Cu2O reagent, the leaching efficiencies of copper increased with increasing air flow rate, temperature and agi-tation speed, but decreased with increasing pulp density. Copper leaching efficiency increased to up to 99% within 60 min in the aerated sulfu-ric acid solution at 30 C, 400 rpm, and pulp density of 2%. [doi:10.2320/matertrans.M2017147]

(Received May 8, 2017; Accepted July 18, 2017; Published August 25, 2017)

Keywords: cuprous oxide, disproportionation reaction, sulfuric acid medium, aeration

1.  Introduction

The rapid growth in the rate of global electronic waste (e-waste) generation is a growing concern. E-wastes, such as spent printed circuit boards (PCBs), may contain more valu-able metals than their typical ores1–3). As shown in Table 14), even though PCBs contain rather small amounts of precious metals, recovery of precious metals with a high recovery ra-tio is important because they account for 93% of the total economic value of PCBs4). Conventional studies and pro-cesses have adopted the approach of extensive comminution followed by leaching for the recovery of precious metals from waste PCBs3,5). However, loss of precious metals has been reported in the process, especially during grinding4).

A recycling process comprising of smelting and subse-quent electrorefining, as depicted in Fig. 1, was established by the Korea Institute of Geoscience and Mineral Resources (KIGAM)6). In this process, precious metals are concen-trated as anode slimes after smelting and electrorefining, which alleviated the loss of these metals. Other metals such as copper, nickel, and iron are recovered as cathode powder. The copper was found to be cuprous oxide (Cu2O) and ele-mental copper (Cu0) in the preliminary study.

Only a few studies examined the leaching of cuprite (Cu2O)7–10). In these studies, leaching tests were carried out using various solutions, such as sulfuric acid with ferric sul-fate7), sulfuric acid with perchloric acid8,9), and sulfuric acid with sulfur dioxide10). The leaching efficiency of copper was reported to be about 50% in the case of leaching in sulfuric acid solution without other oxidants7–9). Although Sullivan and Oldright7) and Majima et al.9) observed that the intro-duction of oxygen or air enhanced the leaching efficiency of copper by employing single experimental set without further discussion, they did not investigate the effects of gas type or gas flow rate as their work focused on the effects of ferric

[image:1.595.305.551.371.498.2]

* Corresponding author, E-mail: kyoo@kmou.ac.kr Fig. 1Flow sheet of recycling process developed by KIGAM. Table 1 Distribution of mass versus value share.

Mass% Fe Al Cu Plastics Ag/ppm Au/ppm Pd/ppm

TV board 28 10 10 28 280 20 10

PC board 7 5 20 23 1000 250 110

Cellphone 5 1 13 56 1380 350 210

DVD player 62 2 5 24 115 15 4

Value Share Fe Al Cu Sum PM Ag Au Pd

TV board 4% 11% 42% 43% 8% 27% 8%

PC board 0% 1% 14% 85% 5% 65% 15%

Cellphone 0% 0% 7% 93% 5% 67% 21%

DVD player 13% 4% 36% 47% 5% 37% 5%

[image:1.595.345.504.479.771.2]
(2)

sulfate and perchloric acid as oxidants. Temperature and agi-tation speed can also be considered as indirect parameters because increasing the temperature decreases dissolved oxy-gen concentration, and increasing the agitation speed in-creases the air inflow into solution by the formation of swirl-ing motions.

It is expected that the economic efficiency will be im-proved if the leaching efficiency of copper is enhanced by introducing air without adding any oxidizing agent, such as HClO4 and Fe3+ used in the conventional studies7–9). Therefore, in the present study, leaching tests using cuprous oxide were conducted in sulfuric acid solution and the ef-fects of leaching parameters, such as air flow rate, gas type, temperature, agitation speed, sulfuric acid concentration, and pulp density, on the leaching efficiency of copper were discussed with the aim of improving the dissolution of cop-per from the cathode powder obtained from the recycling process shown in Fig. 1.

2. Experiments

2.1  Materials

The cathode powder sample used in the experiments was acquired from KIGAM. The sample was sieved using a 75 µm screen. Figure 2(a) shows the SEM image (with JSM-6490, JEOL Ltd.) of the cathode powder, where agglomer-ated submicron particles were observed. The X-ray diffrac-tion (XRD) pattern (see Fig. 3) of the cathode powder sample revealed that copper existed in the form of cuprous oxide and elemental copper (Cu0). The sample was digested with HNO3 and HF to measure the metal content. Acid di-gestion was performed by Yucheon Tech Co. (Daejeon, Korea). The chemical composition of the sample is pre-sented in Table 2. It contained 89.4% copper, 2.32% iron, 0.9% tin, 0.77% nickel, and 0.51% zinc; other metals were not detected. Cuprous oxide and sulfuric acid used in the ex-periments were of reagent grade. As shown in Fig. 2(b), the reagent-grade cuprous oxide consists of 1–3 µm particles.

2.2  Leaching and analysis procedures

Experiments on the dissolution of the cathode powder sample and Cu2O reagent in H2SO4 solution were conducted in a 500-mL three-necked Pyrex reactor set in a heating mantle. The reactor was fitted with an agitator and reflux condenser. The reflux condenser was inserted in one port to

prevent solution losses at high temperatures. In a typical run, 200 mL of acid solution (1–5 M H2SO4) was poured into the reactor and permitted to attain thermal equilibrium (30– 90 C). Predetermined amount of the cathode powder sample or Cu2O reagent was added to the reactor, and the agitator was set to operate at speeds of 200–1000 rpm. Nitrogen gas, air, or oxygen gas was introduced into the reactor at a flow rate of 0–1000 cc/min. During the experiment, 3 mL of the sample solution was withdrawn periodically at a desired time interval by means of a syringe. The sample solution was filtered using a 0.45-µm membrane filter, and then, the filtrate was diluted with 5% HNO3 for copper, iron, nickel, lead, and zinc analyses or 15% HCl solution for tin analysis.

The sample solutions were analyzed by atomic absorption spectrometry (AA7000, Shimadzu Co., Ltd., Japan) and in-ductively coupled plasma-atomic emission spectrometry (ICP-AES, Optima 8300DV, PerkinElmer Co., Ltd., USA). The leaching residue was also characterized by XRD (D/ Max-2500PC, Rigaku Co., Japan).

3.  Results and Discussions

As shown in Fig. 3, copper was present in the form of Cu2O and elemental copper (Cu0) in the cathode powder

Fig. 3 XRD pattern of cathode powder sample used in this study.

Table 2 Chemical composition of cathode powder sample.

Element Cu Fe Sn Ni Zn

Mass% 89.4 2.32 0.9 0.77 0.51

[image:2.595.322.530.386.519.2] [image:2.595.112.489.633.772.2]
(3)

sample. Therefore, the copper leaching tests were performed in sulfuric acid with a Cu2O reagent to investigate the opti-mum conditions for the dissolution of the cathode powder sample, aiming to improve the economic efficiency of the recycling process shown in Fig. 1.

The effects of temperature on the leaching efficiency of copper were investigated under the following conditions: 1 M H2SO4, 400 rpm, pulp density of 2%, and without the introduction of air. As shown in Fig. 4, the leaching efficien-cies first increased rapidly and then gradually afterwards. Generally, an increase in temperature can enhance metal dis-solution in an exothermic reaction; however, in the current study, results showed the opposite. The leaching efficiency for copper at 120 min was found to be 82.3% at 30 C but it decreased to 69.4% at 90 C. The leaching residues were ex-amined by XRD and were compared to the reagent-grade Cu2O, to find what caused the opposite effect of temperature on leaching. The XRD patterns are shown in Fig. 5. As can be seen in this figure, peaks of Cu metal are present in all leaching residues. This observation has been reported in pre-vious studies9,10), and it can be represented by the reaction as expressed in eq. (1):

Cu2O+2H+=Cu2++Cu+H2O (1)

Generally, cuprous ions (Cu+) are unstable in sulfuric acid11). If there is no any other oxidant in the system, when

one of two Cu+ oxidizes to cupric ions (Cu2+) by losing an electron, the other Cu+ must reduce to elemental copper (Cu0) by gaining the electron; this balances out the reaction. This kind of reaction is known as a disproportionation reac-tion. During agitation, a swirl is formed which introduces oxygen from air into the leach solution and acts as an oxi-dant. In this case, Cu metal is not formed and all copper can be dissolved as Cu2+ as follows:

Cu2O+4H++12O2=2Cu2++2H2O (2)

However, the increase in temperature reduced the concen-tration of dissolved oxygen, and higher leaching efficiency was obtained at the lower temperature as shown in Fig. 4.

As shown in Fig. 6, when air was introduced into the reac-tor at a flow rate of 1000 cc/min, the copper leaching effi-ciencies increased up to 99% within 30 min with an increase in temperature at the beginning of the leaching test. This re-sult indicates that the introduction of air could enhance the dissolution of Cu2O in sulfuric acid.

The effects of agitation speed on the leaching efficiency of copper were investigated alongside the leaching test to examine the effects of liquid film boundary diffusion sur-rounding the solid particles on the leaching efficiency of the Cu2O reagent in 1 M H2SO4 solution at 30 C with a pulp density of 5% and air flow rate of 1000 cc/min. The results

Fig. 4 Effect of temperature on leaching efficiency of copper in 1 M H2SO4 solution at 400 rpm with pulp density of 2% and without the in-troduction of air.

Fig. 5 XRD pattern of precipitates recovered from leaching test performed under conditions of 1 M H2SO4 solution, 400 rpm, pulp density of 2%, and without the introduction of air.

Fig. 6 Effect of temperature on leaching efficiency of copper in 1 M H2SO4 solution at 400 rpm with pulp density of 2% and air flow rate of 1000 cc/min.

[image:3.595.319.533.410.549.2] [image:3.595.61.278.414.549.2] [image:3.595.319.536.614.751.2] [image:3.595.64.274.615.752.2]
(4)

of this leaching test are shown in Fig. 7. The leaching effi-ciencies increased rapidly within 10 min and then gradually with time. The leaching efficiencies also increased when the agitation speed was increased to 800 rpm. A higher agitation speed could possibly improve the distribution of dissolved oxygen. However, no improvement was observed when the agitation speed was increased from 800 rpm to 1000 rpm.

Figure 8 shows the effects of the air flow rate on the leaching efficiency of copper in 1 M H2SO4 at 30 C and 800 rpm with a pulp density of 2%. The leaching efficiency increased with increasing air flow rate. However, the im-provement in the leaching efficiency was not significant af-ter 60 min when the air flow rate was increased further from 100 cc/min to 1000 cc/min. At these air flow rates, leaching efficiencies higher than 99% were observed within 60 min.

[image:4.595.319.533.412.549.2]

Figure 9 shows the effects of gas type on the leaching effi-ciency. The introduction of oxygen gas significantly en-hanced the leaching efficiency compared to the introduction of air; the leaching efficiency of copper increased to almost 100% within 15 min with oxygen flow rate of 50 cc/min, whereas it took 120 min to dissolve all copper sample with air flow rate of 50 cc/min when temperature and pulp den-sity were fixed at 30 C and 2%, respectively. Furthermore, the introduction of nitrogen gas suppressed the dissolution of copper. These results are in good agreement with the re-actions in eqs. (1) and (2).

Figure 10 shows the effects of sulfuric acid concentration

on the leaching efficiency in sulfuric acid solution at 30 C and 1000 rpm with a pulp density of 5% and air flow rate of 1000 cc/min. The difference in leaching efficiencies was negligible at sulfuric acid concentrations of 1–4 M after 30 minutes; however, at the concentration of 5 M, the leaching efficiency decreased to 53% at 120 min. The leaching resi-due was collected and investigated by XRD, and it was de-termined to be copper sulfate hydrate (CuSO4·5H2O), as shown in Fig. 11.

Since pulp density is an essential factor to consider for system upgrades, the leaching behavior of copper was inves-tigated in 1 M H2SO4 solution at 30 C and 400 rpm with an air flow rate of 1000 cc/min. Figure 12 shows that the leach-ing efficiencies decreased with an increase in pulp density from 1% to 10%. A leaching efficiency over 99% was ob-tained at the pulp density of 5% at 60 min, while an effi-ciency of 68.3% was obtained at the pulp density of 10% at 120 min, in which case the pH was measured to be 3.5. Equation (2) indicates that hydrogen ions are consumed during the dissolution of copper in the case where oxygen is introduced in sulfuric acid solution. The increase in pH de-creased the leaching efficiency of copper with higher pulp density.

To affirm the results of leaching tests using Cu2O reagent, a leaching test using the cathode powder obtained from the recycling process shown in Fig. 1 containing copper, nickel,

Fig. 8 Effect of air flow rate on leaching efficiency of copper in 1 M H2SO4 solution at 30 C and 800 rpm with pulp density of 2%.

[image:4.595.61.279.422.557.2]

Fig. 9 Effect of gas type on leaching efficiency of copper in 1 M H2SO4 solution at 30 C and 400 rpm with pulp density of 2% and gas flow rate of 50 cc/min.

[image:4.595.318.535.612.751.2]

Fig. 10 Effect of sulfuric acid concentration on leaching efficiency of cop-per in H2SO4 solution at 30 C and 1000 rpm with pulp density of 5% and air flow rate of 1000 cc/min.

[image:4.595.61.278.615.752.2]
(5)
[image:5.595.244.542.413.753.2]

iron, zinc, tin (Table 1). The leaching conditions for the test were 1 M H2SO4 solution, 50 C, 1000 rpm, pulp density of 5% and air flow rate of 1000 cc/min. As shown in Fig. 13, the leaching efficiencies of copper, nickel, iron, and zinc in-creased to values over 99% within 10 min. This leaching rate was found to be very fast compared to that of the leach-ing of reagent-grade Cu2O and can be attributed to the much smaller particle size of the cathode powder as shown in Fig. 2. Furthermore, iron dissolved from the cathode pow-der, could be changed into ferric ions by aeration, and the ferric ion has been known as a strong oxidant12,13) enhancing the leaching rate of copper.

The leaching efficiency of Sn first increased and then de-creased to almost 0%. Sn has been reported to have lower solubility in sulfuric acid compared to hydrochloric acid13), and generally, Sn4+ ions precipitate to SnO

214–16). The leach-ing efficiencies of copper, nickel, iron, and zinc were rela-tively low owing to the formation of elemental copper (Cu0) in the sulfuric acid leaching test without the introduction of oxygen (or air) (data not shown); however, the introduction of air resulted to sufficiently enhanced leaching efficiencies. Therefore, dissolution of copper from cuprous oxide was achieved successfully by sulfuric acid leaching with the in-troduction of air.

4.  Conclusion

The dissolution of Cu2O in sulfuric acid has been reported to be suppressed by a disproportionation reaction, wherein half of the cuprous ions are reduced to elemental copper (Cu0). In this study, effects of oxygen introduction on the leaching behavior of copper were evaluated via examination of the effects of leaching factors such as the air flow rate, sulfuric acid concentration, temperature, agitation speed, and pulp density on the leaching efficiency.

The leaching efficiencies of copper increased with in-creasing air flow rate, temperature, and agitation speed but decreased with increasing pulp density. Sulfuric acid con-centrations of 1–4 M did not affect the leaching efficiency after 30 minutes, but at a concentration of 5 M, the effi-ciency decreased owing to the formation of cupric sulfate precipitate. Since oxygen in the air acts as an oxidant for cu-prous ions, the introduction of oxygen or air could enhance the dissolution of Cu2O in sulfuric acid solution.

Acknowledgments

This research was supported by the Basic Research Project of the Korea Institute of Geoscience and Mineral Resources (KIGAM) funded by the Ministry of Trade, Industry & Energy (MOTIE) of Korea.

REFERENCES

1) T.D. Chi, J.-C. Lee, B.D. Pandey, K. Yoo and J. Jeong: Miner. Eng. 24 (2011) 1219–1222.

2) T.D. Chi, J.-C. Lee, B.D. Pandey, J. Jeong and K. Yoo, T.H. Huynh: J. Chem. Eng. J. 44 (2011) 692–700.

3) J.-M. Yoo, J. Jeong, K. Yoo, J.-C. Lee and W. Kim: Waste Manag. 29 (2009) 1132–1137.

4) C. Hagelüken: Proc. 2006 IEEE International Symposium on Electronics & the Environment. (IEEE Computer Society, Technical Committee on Electronics and the Environment, 2006) pp. 218–223. 5) T.H. Nguyen and M.S. Lee: Geosystem Eng. 19 (2016) 247–259. 6) B.-S. Kim, J.-C. Lee, J. Jeong, D.-H. Yang, D. Shin and K.-I. Lee:

Mater. Trans. 54 (2013) 1045–1048.

7) T. D. Sullivan, G. L. Oldright: The dissolution of cuprite in sulfuric acid and in ferric sulphate solution. U.S. Bur. Mines Rep. Invest. R.I.2967, 1929.

8) M.E. Wadsworth and D.R. Wadia: Trans. Metall. AIME 203 (1955) 755–759.

9) H. Majima, Y. Awakura, K. Enami, H. Ueshima and T. Hirato: Metall. Trans., B, Process Metall. 20B (1989) 573–580.

10) A.A. Youzbashi and S.G. Dixit: Metall. Trans., B, Process Metall. 24B (1993) 563–570.

11) K. Yoo, S.-K. Kim, J.-C. Lee, M. Ito, M. Tsunekawa and N. Hiroyoshi: Miner. Eng. 23 (2010) 471–477.

12) S.-H. Lee, O. Kwon, K. Yoo and R.D. Alorro: Metals (Basel) 5 (2015) 1812–1820.

13) S.-H. Lee, K. Yoo, M.K. Jha and J.-C. Lee: Hydrom. 157 (2015) 184–187.

14) S. Jeon, I. Park, K. Yoo and H. Ryu: Geosystem Eng. 18 (2015) 213–218.

15) K. Yoo, J.-C. Lee, K.-S. Lee, B.-S. Kim, M.-S. Kim, S.-K. Kim and B.D. Pandey: Mater. Trans. 53 (2012) 2175–2180.

16) K. Yoo, K. Lee, M.K. Jha, J.-C. Lee and K. Cho: J. Nanosci. Nanotechnol. 16 (2016) 11238–11241.

[image:5.595.62.276.416.558.2]

Fig. 13 Leaching behaviors of copper, nickel, iron, tin, and zinc in 1 M H2SO4 leaching test at 50 C and 1000 rpm with pulp density of 5% and air flow rate of 1000 cc/min.

[image:5.595.61.280.614.752.2]

Figure

Fig. 1 Flow sheet of recycling process developed by KIGAM.
Fig. 3 XRD pattern of cathode powder sample used in this study.
Fig. 6 Effect of temperature on leaching effciency of copper in 1 M H2SO4 solution at 400 rpm with pulp density of 2% and air fow rate of 1000 cc/min.
Fig. 10 Effect of sulfuric acid concentration on leaching effciency of cop-per in H2SO4 solution at 30°C and 1000 rpm with pulp density of 5% and air fow rate of 1000 cc/min.
+2

References

Related documents

compartment and a two-compartment model to the plasma concentrations of tramadol, to develop a basic population PK model for tramadol.. The estimated population para- meters

Female mice lacking GalNAc-4-ST1 demonstrated elevated estrogen levels and exhibited precocious sexual maturation and increased fecundity.. Female mice remained in estrus for

To further characterize the microglia phenotype ob- served in the TgCRND8 plaque niche, we compared the gene signatures identified here to those of the microglial

Keywords: Finite element method; Finite element analysis; Finite models; Modified mini implants; Dual ball head implant; Stress and displacement of

Step 5: Produce new solutions for each onlooker bees, evaluate them, and apply the greedy selection process.. Step 6: Stop the exploitation process of the sources

three phase voltage source inverter has connected in grid. The current control pulse width modulation technique is used. The main task of the control scheme in a CC-PWM converter is

Brain: no external signs of trauma to the head; bilateral subdural hematomas with sub- arachnoid hemorrhages, as well, over both cerebral hemispheres; extensive bleedings at the

1000 eggs were collected from 775 hens of the ninth generation of Khorasan-Razavi Province native fowl breeding center at the age of 28 to 29 weeks and transferred