- Email: [email protected]
Metal recovery from waste printed circuit boards by flotation technology with non-ionic renewable collector
Journal of Cleaner Production 255 (2020) 120289
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Metal recovery from waste printed circuit boards by flotation technology with non-ionic renewable collector Xiang-nan Zhu a, *, Tao Cui b, Biao Li c, Chun-chen Nie a, Hao Zhang a, Xian-jun Lyu a, You-jun Tao d, Jun Qiu a, Lin Li a, Guang-wen Zhang d a
College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao, Shandong, 266590, China College of Junshan, Zaozhuang Vocational College, Zaozhuang, Shandong, 277800, China Mining and Minerals Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA d School of Chemical Engineering and Technology, China University of Mining & Technology, Xuzhou, Jiangsu, 221116, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 August 2019 Received in revised form 22 January 2020 Accepted 26 January 2020 Available online 28 January 2020
Using waste oil as renewable collector, flotation method was proposed to recover metal from waste printed circuit boards (WPCBs). The flotation mechanism was revealed by functional group composition, which was analyzed by infrared spectrometer (FT-IR) and X-ray photoelectron spectroscopy (XPS). Elemental analysis shows that Cu and Fe in WPCBs are mainly concentrated in 1e0.5 mm and 0.5 mm respectively with ideal dissociation, which is verified by SEM þ EDS analysis. Waste oil from kitchen waste was purified and used as flotation collector to realize the separation of metal particles and nonmetal particles. The effect of collector dosage on the flotation behavior of 1e0.5 mm and 0.5 mm was analyzed respectively. Flotation results show that metal content in concentrate increases with the increase of collector dosage, which is accompanied by recovery decrease. For 1e0.5 mm, concentrate with 47.77% Cu and 91.15% recovery was obtained with 8 kg/t collector. For 0.5 mm, Fe and Cu content achieved 40.01% and 8.03% respectively, with recovery of 71.99% and 91.61% when the collector dosage was 1 kg/t. The functional group composition was determined by FT-IR and the carbon-based functional group content was tested by XPS, which illustrates the adsorption of the collector on the particle surface. The physical methods proposed in this study contribute to the cleanliness of the metal recovery process and realize the resource utilization of two kinds of waste. © 2020 Elsevier Ltd. All rights reserved.
Handling Editor: Baoshan Huang Keywords: WPCBs Waste oil Metal recovery Dissociation Flotation Renewable collector
1. Introduction Advances in technology have driven the development of human civilization (Ahmet et al., 2018; Menderes et al., 2019). With the advancement of electronic technology and the improvement of residents’ purchasing power, the life cycle of electronic equipment is gradually shortening (Anshu and Subrata, 2017). The resource utilization of electronic waste has gained the interest of researchers in previous studies (Huang et al., 2009; Li et al., 2007; Wang et al., 2017). Green strategies of waste disposal have attracted much attention (Sellitto, 2018). Recycling of waste products (Savaskan et al., 2004), closed supply chain (Liu et al., 2017) and green supply (Qu et al., 2019) have been concerned. Worldwide, billions of cell phones computers, televisions and other electronic products
* Corresponding author. E-mail address: [email protected] (X.-n. Zhu). https://doi.org/10.1016/j.jclepro.2020.120289 0959-6526/© 2020 Elsevier Ltd. All rights reserved.
are produced every year. Due to the lack of mature recycling technology, abandoned mobile phones are usually difficult to dispose, which become metal mines in city (Zhang et al., 2018a). Waste printed circuit boards (WPCBs) are core components of mobile phones and are enriched with a variety of metal elements. The recovery of the metal in WPCBs can effectively reduce the demand for traditional ore, and can also reduce the environmental pollution risk of e-waste (Zhang et al., 2016, 2017). Due to the significant difference of mechanical properties between different components, the application of composite force field can effectively liberate various components (Wang and Xu, 2015). The commonly used crushing equipment is hammer crusher, impact crusher and shear crusher (Georgi-Maschler et al., 2012; Granata et al., 2012; Abdelbasir et al., 2018). The separation process of dissociated particles of WPCBs can be realized by utilizing physical properties differences between particles, which have proven to be efficient. Gravity separation (Zhu et al., 2020a), magnetic separation (Veit et al., 2005), electrostatic
2
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
separation (Wu et al., 2008), chemical leaching (Gurung et al., 2013) are widely reported. In addition, it is also feasible to separate different components by utilizing the hydrophobic differences between fine particles, usually 0.5 mm (Zhu et al., 2019a; Yu et al., 2020). As for flotation, more attention is paid to flotation process flow and flotation reagents (Zhu et al., 2019b; You et al., 2019), such as gemini surfactant (Huang et al., 2019a, 2019b) and renewable collector (Zhu et al., 2020b). Pyrolysis-Ultrasonic-Assisted flotation was studied to separate the graphite and lithium cobaltate in spent lithium ion batteries, n-Dodecane was used as collector and the methyl isobutyl carbinol was used as frother (Zhang et al., 2018b). Effect of additives on the flotation performance of waste plastics show that calcium carbonate can enhance the hydrophilicity of the plastic surface and reduce its floatability (Wang et al., 2014). Flotation technology was utilized to recover indium tin oxide from electronic waste, dodecylamine and 2-octanol were used as collector and frother respectively (Wang et al., 2018). As for flotation of WPCBs, a few studies have been carried out. Reverse flotation was investigated to separate the non-metallic form metals, and methyl isobutyl carbinol can strengthen the contact angle of particles (Florescampos et al., 2017). Reverse flotation technology was used to recover metals from broken WPCBs with kerosene as collector, and terpenic oil as frother, metal grade can reach 16.86% with 94.69% recovery (He and Duan, 2017). The collector used in the flotation process is mainly the traditional non-regenerative collector. Fortunately, waste oils from kitchen waste can also be used as collectors for flotation of various minerals (Yi et al., 2015; Zhu et al., 2019c). In previous studies, the feasibility of recovering metals from WPCBs by flotation was verified. However, many scientific issues require further research, such as the floatability of 1e0.5 mm particles, the adsorption mechanism of collector and particles, and the more environmentally friendly collector. Therefore, this study was conducted on the above three issues. In order to realize the cleanliness flotation of WPCBs and reduce the dependence on traditional non-regenerative collectors, a kind of renewable collector obtained from kitchen waste was prepared and the adaptability of waste oil to flotation process of WPCBs was studied. The effect of collector dosage on flotation behavior was verified by flotation tests. In addition, functional group composition of samples was detected by FT-IT and XPS to reveal the flotation mechanism. 2. Materials and methods 2.1. Materials Printed circuit boards (PCBs) are broken to dissociate different components through impact crusher and shear crusher. Meanwhile, waste oil from kitchen waste was collected and purified by precipitation, decolorization and dehydration treatment. Purified product was used as collector in subsequent reverse flotation. The design of the experiment is shown in Fig. 1. As shown in Fig. 1, two types of waste, namely waste oil and WPCBs, can be reused through the flotation technology. Metal and non-metal components in WPCBs powders can be effectively separated based on significant differences in floatability, and renewable collectors prepared from waste oils can significantly enhance the floatability difference under intense stirring. Air is pumped into the slurry to form bubbles, and hydrophobic particles adhere to the bubbles and float to form tailings. Metal particles cannot be floated and become concentrates. 2.2. Analysis of element distribution and dissociation characteristics In order to analyze the elemental distribution of different size
fractions, the broken products were divided into narrow size fractions by screening tests. The aperture sizes of the sieve were 2, 1, 0.5, 0.25, 0.125, 0.074 and 0.045 mm. The element composition of each size fractions was analyzed by X-ray fluorescence spectrometry (XRF, Axios, Panalytical, Netherlands). Thus, the elements distribution can be obtained. The dissociation degree is the prerequisite for the subsequent efficient sorting. Therefore, the dissociation characteristics of the valuable components at different size fractions were analyzed by the combined application of scanning electron microscopy and spectrometers (SEM þ EDS, APREO, FEI, USA). The detection process was carried out at room temperature in high vacuum mode, and WPCBs powder to be detected was sprayed with gold to improve conductivity. 2.3. FT-IR measurement In order to analyze the functional groups composition of the broken products of WPCBs, FT-IR spectrums of 1e0.5 mm and 0.5 mm were detected. Samples to be detected were crushed to 200 meshes and dried at 90 C for 24 h. The samples were pressed with potassium bromide (analytically pure) at 10 MPa with 1 min. Infrared spectrometer Nicolet 380 (Thermo, America) was used in this test and the spectrum was obtained between 400 cm1 and 4000 cm1 with resolution of 2 cm1. Thus, the adsorption phenomenon between the flotation reagents and the particle surface was analyzed. 2.4. XPS analysis The interface property is the decisive factor of the interaction between collector and WPCBs particles. Composition of carbonbased functional groups in WPCBs powders was analyzed by Xray photoelectron spectroscopy (XPS, ESCALAB 250Xi, Thermo, USA). Binding energy was corrected by setting the C1 s peak. The content of hydrophobic and hydrophilic groups was quantitatively analyzed. 2.5. Flotation performance with renewable collector as collector In order to recover the metal from the nonmetal, flotation technology was used. The 1e0.5 mm and 0.5 mm of the dissociated products were respectively subjected to flotation. Lab-used single XFDIV (0.5 L) flotation machine was conducted for the flotation experiments with 30 g feed in each test. The impeller speed was adjusted to 1920 r/min for 2 min to ensure the uniform dispersion of particles. The flow of air was controlled at 0.15 m3/h. The collector for preset dosage was added and stirred for 2 min. Subsequently, 2-octanol that used as frother was added and mixed for 1 min. Aeration process was carried out, and the scraper was started. The process continues until no more particles were being recovered. The mass and element composition of the concentrate and tailing were measured. 3. Results and discussion 3.1. Elements distribution in different size fraction Images and elemental compositions of screening products, 2e1, 1e0.5, 0.5e0.25, 0.25e0.125, 0.125e0.074, 0.074e0.045, 0.045 mm, are shown in Fig. 2 and Fig. 3 respectively. As shown in Fig. 2, the seven size fractions show different colors, which indicated that the composition of each size is different. Various components (metal, non-metal, etc.) in WPCBs have significant differences in mechanical properties, so selective crushing
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
3
Fig. 1. Design scheme for resource utilization of waste oil and WPCBs.
2-1 mm
1-0.5 mm
0.5-0.25 mm
0.25-0.125 mm
content of finer particle is less than 2%. However, Fe is mainly concentrated in 0.5 mm with 20% content, and the content of 2e1 mm and 1e0.5 mm is relatively low, only about 2%. Nonmetallic components containing Si and Ca are the main impurities. Considering the difference in elemental enrichment in different size fractions, flotation performance of 1e0.5 mm and 0.5 mm are studied respectively. 3.2. Dissociation characteristics of different size particles
0.125-0.074 mm
0.074-0.045 mm
-0.045 mm
Fig. 2. Visual image of broken product.
The morphology and elemental section distribution of 1e0.5 mm and 0.5 mm are shown in Fig. 4. Fig. 4 (a) shows that slender particles are observed in the range of 1e0.5 mm, and thin circular particles have also been discovered. EDS results shows that these elongated particles are dissociated impurity particles enriched with Si and Al, which is usually used as glass fiber for WPCBs substrates. This also shows that the Al in elemental analysis exists in the form of glass fiber. The SEM and EDS analysis results presents in Fig. 4 (b) show that the fine strip particles that are observed in the 0.5 mm are also glass fibre, which is verified by the distribution of Si elements. In addition, dissociated Cu and Fe particles were also discovered. The particle morphology and element distribution in Fig. 4 show that most of the particles with different components exist as independent particles. It can be inferred that particles can be broken to 1 mm to achieve ideal dissociation. 3.3. Functional groups characteristic analysis
Fig. 3. Element composition of broken product (Oxide content).
phenomenon occurs in the crushing process, which is the reason for the component differences in different size fractions. The results of Fig. 3 show that the metals in WPCBs are mainly Cu and Fe. Significant differences exist in the elemental composition of different size fractions. As for Cu, 1e0.5 mm has the highest content with 32%, followed by 2e1 mm and 0.5e0.25 mm. The Cu
Infrared spectrum analysis results of 1e0.5 mm and 0.5 mm are shown in Fig. 5. The results presented in Fig. 5 show that the absorption peaks of functional groups in 1e0.5 mm and 0.5 mm samples are similar. Peaks exhibited between 1058 cm1 and 1242 cm1 are CeO. eCH3 is characterized by the peaks of 1457 cm1 and 2931 cm1. Peaks at 1506 cm1, 1634 cm1 representing C]C (Han et al., 2018). eCH3 is the main hydrophobic group, which can promote the attachment of particles to bubbles to enhance the flotation process. Edible oil is a lipid substance, which contains a long carbon chain, mainly CeH, CeC bonds, and also contains CeO and C]O bonds. Therefore, the hydrophobic groups in collectors prepared from waste oils can physically adsorb with the hydrophobic groups in WPCBs powder to enhance the hydrophobicity. In WPCBs powders, organic matter is usually used as an adhesive to solidify glass fibers. Therefore, collectors can selectively enhance the
(a) 1-0.5 mm
(b) -0.5 mm Fig. 4. Particle morphology and element distribution of broken product.
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
Fig. 5. FT-IR spectrums of 1e0.5 mm and 0.5 mm size fraction.
5
(a) 1-0.5 mm
hydrophobicity of impurity particles, which is an important factor to realize the flotation separation process. In order to further analyze the content of hydrophobic groups in carbon-based functional groups in WPCBs, narrow sweep of carbon elements was carried out, and peak fitting was used to determine the content of functional groups. The results are shown in Fig. 6. Carbon-based functional groups are caused by organic matter, including adhesives and curing agents, which can significantly change the hydrophobicity of particles. As shown in Fig. 6, the area of functional groups of CeC/CeH is significantly greater than that of other peaks. Through peak fitting calculation, the hydrophobic group content of 1e0.5 mm reaches 66.19%, and that of 0.5 mm reaches 64.90%, which leads to strong hydrophobicity. 3.4. Flotation behavior of WPCBs powder The macroscopic flotation behavior of 1e0.5 mm and 0.5 mm is shown in Fig. 7. As shown in Fig. 7 (a), for 1e0.5 mm, in the absence of collector and frother, the bubbles are uneven and unstable, and few particles are floating out. Flotation bubbles become small and uniform under the action of frother, but only a few particles are floating out. Further, plenty of particles are flotated under the action of collectors and frother, which indicates that the flotation effect has been significantly strengthened. For 0.5 mm, the macroscopic flotation behavior shown in Fig. 7 (b) is different from the results that presented in Fig. 7 (a). That is, flotation performance of 0.5 mm particle in the absence of flotation agents is more significant than that of 1e0.5 mm. A certain amount of floats are observed, which indicates that the natural floatability of 0.5 mm is better than that of 1e0.5 mm. Further, it can also be observed that the flotation process of 0.5 mm particles becomes stable and strengthened under the action of collectors and frother. It can be deduced that the collector can significantly improve the floatability of the non-metallic particles to enhance the flotation efficiency. The effect of collector dosage on concentrate grade and recovery rate is shown in Fig. 8. As shown in Fig. 8, when the collector dosage increases from 2 kg/t to 10 kg/t, the Cu content increases gradually from 36.85% to 47.77%. Meanwhile, Si content gradually decreases from 27.17% to
(b) -0.5 mm Fig. 6. C1s XPS spectra of 1e0.5 mm and 0.5 mm.
20.91%. Fe content is basically stable with content of 2.8%. In addition, the recovery of each element decreases gradually with the increase of the collector dosage, and the recovery of Si decreases most significantly, from 90.80% to 48.53%. The Fe recovery decreases from 90.80% to 74.67%. The Cu recovery reduces from 99.24% to 91.15%. The effect of collector dosage on concentrate grade and recovery rate of 0.5 mm is shown in Fig. 9. The result shown in Fig. 9 is consistent with Fig. 8. That is, Si content in concentrate decreases with the increase of collector dosage, while Cu content increases with the increase of collector dosage. Moreover, the recovery of each element decreases with the increase of collector dosage, which is mainly caused by the reduction of concentrate yield. When the dosage of collector increases from 1 kg/t to 8 kg/t, the Fe content in the concentrate increases from 40.01% to 48.02%, and the recovery decreases from 71.99% to 27.82%; the Cu content increases from 8.03% to 13.57% corresponding with a recovery decreases from 91.61% to 51.57%. Si decreases from 9.86% to 6.09%, and the recovery reduces from 14.01% to 2.8%.
6
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
(a) 1-0.5 mm
(b) -0.5 mm Fig. 7. Flotation behavior of 1e0.5 mm and 0.5 mm with different flotation reagent.
Fig. 8. Influence of collector dosage on flotation performance of 1e0.5 mm.
4. Conclusion Recovery technology of metals in WPCBs is necessary to make WPCBs a resource rather than an environmental threat. This study proposes a physical sorting technology, namely flotation approach, for metal recovery. Further, the renewable collector prepared from waste oil makes the flotation process more environmentally friendly.
Fig. 9. Influence of collector dosage on flotation performance of 0.5 mm.
Elemental distribution shows effective dissociation can be achieved when the WPCBs are broken to 1 mm. Cu is mainly concentrated in 1e0.5 mm and Fe is mainly concentrated in 0.5 mm. The effect of regenerated collector dosage on flotation performance of 1e0.5 mm and 0.5 mm was analyzed. The metal content in concentrate increases with the increase of collector dosage, which is accompanied by a decrease in recovery. For 1e0.5 mm, the Cu, Si, and Fe contents in concentrate can be
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
obtained at 47.77%, 20.91% and 3.24% with recovery of 91.15%, 48.53% and 74.67% respectively when 10 kg/t collector is used. For 0.5 mm, the concentrate with 40.01% Fe, 8.03% Cu and 9.86% Si is achieved, corresponding with 71.99%, 91.61% and 14.04% recovery when the collector dosage is 1 kg/t. The flotation mechanism was revealed by FT-IR and XPS detection. The results of functional group analysis showes that the main hydrophobic group on the particle surface is CeC/CeH, and the hydrophilic group is CeO and C]O. The hydrophobic group could enhance the adsorption of the collector to improve the hydrophobicity of the non-metallic particles. Further, quantitative analysis of hydrophobic group show that the content of hydrophobic groups in 1e0.5 mm and 0.5 mm reaches 66.19% and 64.90% respectively. 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. CRediT authorship contribution statement Xiang-nan Zhu: Writing - original draft, Writing - review & editing. Tao Cui: Writing - original draft, Writing - review & editing. Biao Li: Writing - original draft, Writing - review & editing. Chunchen Nie: Project administration, Writing - review & editing. Hao Zhang: Project administration, Writing - review & editing. Xianjun Lyu: Project administration, Writing - review & editing. Youjun Tao: Project administration, Writing - review & editing. Jun Qiu: Project administration, Writing - review & editing. Lin Li: Project administration, Writing - review & editing. Guang-wen Zhang: Project administration, Writing - review & editing. Acknowledgement This work was supported by Natural Science Foundation of Shandong Province (ZR2019BEE055), and supported by Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (2017RCJJ035). References Abdelbasir, S.M., Ssm, H., Kamel, A.H., El-Nasr, R.S., 2018. Status of electronic waste recycling techniques: a review. Environ. Sci. Pollut. Res. 25 (4), 1e15. _ Ahmet, Ipekçi, Menderes, Kam, Hamit, Saruhan, 2018. Investigation of 3D printing occupancy rates effect on mechanical properties and surface roughness of PETG material products. J. New Res. Sci(JNRS). 7 (2), 1e8. Anshu, Priya, Subrata, Hait, 2017. Comparative assessment of metallurgical recovery of metals from electronic waste with special emphasis on bioleaching. Environ. Sci. Pollut. Res. 24, 6989e7008. nchez, E.J., 2017. Study of the physiFlorescampos, R., Estradaruiz, R.H., Velardesa cochemical effects on the separation of the non-metallic fraction from printed circuit boards by inverse flotation. Waste Manag. 69, 400e406. Georgi-Maschler, T., Friedrich, B., Weyhe, R., Heegn, H., Rutz, M., 2012. Development of a recycling process for li-ion batteries. J. Power Sources 207 (6), 173e182. Granata, G., Pagnanelli, F., Moscardini, E., Takacova, Z., Havlik, T., Toro, L., 2012. Simultaneous recycling of nickel metal hydride, lithium ion and primary lithium batteries: accomplishment of European guidelines by optimizing mechanical pre-treatment and solvent extraction operations. J. Power Sources 212, 205e211. Gurung, M., Adhikari, B.B., Kawakita, H., Ohto, K., Inoue, K., Alam, S., 2013. Recovery of gold and silver from spent mobile phones by means of acidothiourea leaching followed by adsorption using biosorbent prepared from persimmon tannin. Hydrometallurgy 133, 84e93. Han, J., Chenlong, D., Guofeng, L., Long, H., Xuesen, C., Dan, W., 2018. The influence of waste printed circuit boards characteristics and nonmetal surface energy regulation on flotation. Waste Manag. 80, 81e88. He, J., Duan, C., 2017. Recovery of metallic concentrations from waste printed circuit
7
boards via reverse floatation. Waste Manag. 60, 618e628. Huang, K., Guo, Jie, Xu, Z., 2009. Recycling of waste printed circuit boards: a review of current technologies and treatment status in China. J. Hazard Mater. 164, 399e408. Huang, Z., Cheng, C., Liu, Z., Feng, B., Hu, Y., Luo, W., He, G., Yu, X., Fu, W., 2019a. Highly efficient potassium fertilizer production by using a gemini surfactant. Green Chem. 21, 1406e1411. Huang, Z., Cheng, C., Liu, Z., Zeng, H., Feng, B., Zhong, H., Luo, W., Hu, Y., Guo, Z., He, G., Fu, W., 2019b. Utilization of a new Gemini surfactant as the collector for the reverse froth flotation of phosphate ore in sustainable production of phosphate fertilizer. J. Clean. Prod. 221, 108e112. Li, J., Lu, H., Guo, J., Xu, Z., Zhou, Y., 2007. Recycle technology for recovering resources and products from waste printed circuit boards. Environ. Sci. Technol. 41, 1995e2000. Liu, L., Wang, Z., Xu, L., Hong, X., Govindan, K., 2017. Collection effort and reverse channel choices in a closed-loop supply chain. J. Clean. Prod. 144, 492e500. _ Menderes, Kam, Hamit, Saruhan, Ahmet, Ipekçi, 2019. Investigation the effect of 3d printer system vibrations on surface roughness of the printed products. Düzce Üni. Bilim Teknol. Der. 7, 147e157. Qu, S., Zhou, Y., Zhang, Y., Wahab, M.I.M., Zhang, G., Ye, Y., 2019. Optimal strategy for a green supply chain considering shipping policy and default risk. Comput. Ind. Eng. 131, 172e186. Savaskan, R.C., Bhattacharya, S., Van Wassenhove, L.N., 2004. Closed-Loop supply chain models with product remanufacturing. Manag. Sci. 50 (2), 239e252. Sellitto, M.A., 2018. Assessment of the effectiveness of green practices in the management of two supply chains. Bus. Process Manag. J. 24 (1), 23e48. rio, J.A.S., Bernardes, A.M., Rodrigues, J.S., 2005. UtiliVeit, H.M., Diehl, T.R., Teno zation of magnetic and electrostatic separation in the recycling of printed circuit boards scrap. Waste Manag. 25 (1), 67e74. Wang, C., Wang, H., Fu, J., Gu, G., 2014. Effects of additives on pvc plastics surface and the natural flotability. Colloid. Surface. 441 (3), 544e548. Wang, J., Xu, Z., 2015. Disposing and recycling waste printed circuit boards: disconnecting, resource recovery, and pollution control. Environ. Sci. Technol. 49, 721e733. Wang, H., Zhang, S., Li, B., Pan, De’an, Wu, Y., Zuo, T., 2017. Recovery of waste printed circuit boards through pyrometallurgical processing: a review. Resour. Conserv. Recycl. 126, 209e218. Wang, S., He, Y., Yang, J., Feng, Y., 2018. Enrichment of indium tin oxide from colour filter glass in waste liquid crystal display panels through flotation. J. Clean. Prod. 189, 464e471. Wu, J., Li, J., Xu, Z., 2008. Electrostatic separation for multi-size granule of crushed printed circuit board waste using two-roll separator. J. Hazard Mater. 159 (2), 230e234. Yi, Q., Li, W., Zhang, X., Feng, J., Zhang, J., Wu, J., 2015. Tech-economic evaluation of waste cooking oil to bio-flotation agent technology in the coal flotation industry. J. Clean. Prod. 95, 131e141. You, X., He, M., Zhu, X., Wei, H., Cao, X., Wang, P., Li, L., 2019. Influence of surfactant for improving dewatering of brown coal: a comparative experimental and MD simulation study. Separ. Purif. Technol. 210, 473e478. Yu, Y., Li, A., Xu, Z., Zhou, A., Li, Z., Zhang, N., Liu, Q., 2020. New insights into the slime coating caused by montmorillonite in the flotation of coal. J. Clean. Prod. 242, 118540 https://doi.org/10.1016/j.jclepro.2019.118540. Zhang, G., Wang, H., Tao, Z., Xing, Y., Xie, W., He, Y., 2016. Removing inorganics from nonmetal fraction of waste printed circuit boards by triboelectric separation. Waste Manag. 49, 230e237. Zhang, G., He, Y., Wang, H., Zhang, T., Yang, X., Wang, S., 2017. Application of triboelectric separation to improve the usability of nonmetallic fractions of waste printed circuit boards: removing inorganics. J. Clean. Prod. 142, 1911e1917. Zhang, G., He, Y., Feng, Y., Zhang, T., Wang, H., 2018a. Recovery of residual metals from fine nonmetallic fractions of waste printed circuit boards using a vibrated gas-solid fluidized bed. Separ. Purif. Technol. 207, 321e328. Zhang, G., He, Y., Feng, Y., Wang, H., Zhu, X., 2018b. Pyrolysis-ultrasonic-Assisted flotation technology for recovering graphite and LiCoO2 from spent lithium-ion batteries. ACS Sustain. Chem. Eng. 6, 10896e10904. Zhu, X., Nie, C., Zhang, H., Lyu, X., Tao, Y., Qiu, J., Li, L., Zhang, G., 2019a. Recovery of high-grade copper from waste printed circuit boards by mechanical-grinding assisted flotation. J. Clean. Prod. 232, 1251e1256. Zhu, X., Nie, C., Zhang, H., Lyu, X., Qiu, J., Li, L., 2019b. Recovery of metals in waste printed circuit boards by flotation technology with soap collector prepared by waste oil through saponification. Waste Manag. 89, 21e26. Zhu, X., Lyu, X., Wang, Q., Qiu, J., Wang, S., Liu, X., Li, L., 2019c. Clean utilization of waste oil: soap collectors prepared by alkaline hydrolysis for fluorite flotation. J. Clean. Prod. 240, 118179 https://doi.org/10.1016/j.jclepro.2019.118179. Zhu, X., Nie, C., Wang, S., Xie, Y., Zhang, H., Lyu, X., Qiu, J., Li, L., 2020a. Cleaner approach to the recycling of metals in waste printed circuit boards by magnetic and gravity separation. J. Clean. Prod. 248, 119235 https://doi.org/10.1016/ j.jclepro.2019.119235. Zhu, X., Wang, D., Ni, Y., Wang, J., Nie, C., Yang, C., Lyu, X., Qiu, J., Li, L., 2020b. Cleaner approach to fine coal flotation by renewable collectors prepared by waste oil transesterification. J. Clean. Prod. 252, 119822 https://doi.org/10.1016/ j.jclepro.2019.119822.
Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Metal recovery from waste printed circuit boards by flotation technology with non-ionic renewable collector Xiang-nan Zhu a, *, Tao Cui b, Biao Li c, Chun-chen Nie a, Hao Zhang a, Xian-jun Lyu a, You-jun Tao d, Jun Qiu a, Lin Li a, Guang-wen Zhang d a
College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao, Shandong, 266590, China College of Junshan, Zaozhuang Vocational College, Zaozhuang, Shandong, 277800, China Mining and Minerals Engineering Department, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24060, USA d School of Chemical Engineering and Technology, China University of Mining & Technology, Xuzhou, Jiangsu, 221116, China b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 20 August 2019 Received in revised form 22 January 2020 Accepted 26 January 2020 Available online 28 January 2020
Using waste oil as renewable collector, flotation method was proposed to recover metal from waste printed circuit boards (WPCBs). The flotation mechanism was revealed by functional group composition, which was analyzed by infrared spectrometer (FT-IR) and X-ray photoelectron spectroscopy (XPS). Elemental analysis shows that Cu and Fe in WPCBs are mainly concentrated in 1e0.5 mm and 0.5 mm respectively with ideal dissociation, which is verified by SEM þ EDS analysis. Waste oil from kitchen waste was purified and used as flotation collector to realize the separation of metal particles and nonmetal particles. The effect of collector dosage on the flotation behavior of 1e0.5 mm and 0.5 mm was analyzed respectively. Flotation results show that metal content in concentrate increases with the increase of collector dosage, which is accompanied by recovery decrease. For 1e0.5 mm, concentrate with 47.77% Cu and 91.15% recovery was obtained with 8 kg/t collector. For 0.5 mm, Fe and Cu content achieved 40.01% and 8.03% respectively, with recovery of 71.99% and 91.61% when the collector dosage was 1 kg/t. The functional group composition was determined by FT-IR and the carbon-based functional group content was tested by XPS, which illustrates the adsorption of the collector on the particle surface. The physical methods proposed in this study contribute to the cleanliness of the metal recovery process and realize the resource utilization of two kinds of waste. © 2020 Elsevier Ltd. All rights reserved.
Handling Editor: Baoshan Huang Keywords: WPCBs Waste oil Metal recovery Dissociation Flotation Renewable collector
1. Introduction Advances in technology have driven the development of human civilization (Ahmet et al., 2018; Menderes et al., 2019). With the advancement of electronic technology and the improvement of residents’ purchasing power, the life cycle of electronic equipment is gradually shortening (Anshu and Subrata, 2017). The resource utilization of electronic waste has gained the interest of researchers in previous studies (Huang et al., 2009; Li et al., 2007; Wang et al., 2017). Green strategies of waste disposal have attracted much attention (Sellitto, 2018). Recycling of waste products (Savaskan et al., 2004), closed supply chain (Liu et al., 2017) and green supply (Qu et al., 2019) have been concerned. Worldwide, billions of cell phones computers, televisions and other electronic products
* Corresponding author. E-mail address: [email protected] (X.-n. Zhu). https://doi.org/10.1016/j.jclepro.2020.120289 0959-6526/© 2020 Elsevier Ltd. All rights reserved.
are produced every year. Due to the lack of mature recycling technology, abandoned mobile phones are usually difficult to dispose, which become metal mines in city (Zhang et al., 2018a). Waste printed circuit boards (WPCBs) are core components of mobile phones and are enriched with a variety of metal elements. The recovery of the metal in WPCBs can effectively reduce the demand for traditional ore, and can also reduce the environmental pollution risk of e-waste (Zhang et al., 2016, 2017). Due to the significant difference of mechanical properties between different components, the application of composite force field can effectively liberate various components (Wang and Xu, 2015). The commonly used crushing equipment is hammer crusher, impact crusher and shear crusher (Georgi-Maschler et al., 2012; Granata et al., 2012; Abdelbasir et al., 2018). The separation process of dissociated particles of WPCBs can be realized by utilizing physical properties differences between particles, which have proven to be efficient. Gravity separation (Zhu et al., 2020a), magnetic separation (Veit et al., 2005), electrostatic
2
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
separation (Wu et al., 2008), chemical leaching (Gurung et al., 2013) are widely reported. In addition, it is also feasible to separate different components by utilizing the hydrophobic differences between fine particles, usually 0.5 mm (Zhu et al., 2019a; Yu et al., 2020). As for flotation, more attention is paid to flotation process flow and flotation reagents (Zhu et al., 2019b; You et al., 2019), such as gemini surfactant (Huang et al., 2019a, 2019b) and renewable collector (Zhu et al., 2020b). Pyrolysis-Ultrasonic-Assisted flotation was studied to separate the graphite and lithium cobaltate in spent lithium ion batteries, n-Dodecane was used as collector and the methyl isobutyl carbinol was used as frother (Zhang et al., 2018b). Effect of additives on the flotation performance of waste plastics show that calcium carbonate can enhance the hydrophilicity of the plastic surface and reduce its floatability (Wang et al., 2014). Flotation technology was utilized to recover indium tin oxide from electronic waste, dodecylamine and 2-octanol were used as collector and frother respectively (Wang et al., 2018). As for flotation of WPCBs, a few studies have been carried out. Reverse flotation was investigated to separate the non-metallic form metals, and methyl isobutyl carbinol can strengthen the contact angle of particles (Florescampos et al., 2017). Reverse flotation technology was used to recover metals from broken WPCBs with kerosene as collector, and terpenic oil as frother, metal grade can reach 16.86% with 94.69% recovery (He and Duan, 2017). The collector used in the flotation process is mainly the traditional non-regenerative collector. Fortunately, waste oils from kitchen waste can also be used as collectors for flotation of various minerals (Yi et al., 2015; Zhu et al., 2019c). In previous studies, the feasibility of recovering metals from WPCBs by flotation was verified. However, many scientific issues require further research, such as the floatability of 1e0.5 mm particles, the adsorption mechanism of collector and particles, and the more environmentally friendly collector. Therefore, this study was conducted on the above three issues. In order to realize the cleanliness flotation of WPCBs and reduce the dependence on traditional non-regenerative collectors, a kind of renewable collector obtained from kitchen waste was prepared and the adaptability of waste oil to flotation process of WPCBs was studied. The effect of collector dosage on flotation behavior was verified by flotation tests. In addition, functional group composition of samples was detected by FT-IT and XPS to reveal the flotation mechanism. 2. Materials and methods 2.1. Materials Printed circuit boards (PCBs) are broken to dissociate different components through impact crusher and shear crusher. Meanwhile, waste oil from kitchen waste was collected and purified by precipitation, decolorization and dehydration treatment. Purified product was used as collector in subsequent reverse flotation. The design of the experiment is shown in Fig. 1. As shown in Fig. 1, two types of waste, namely waste oil and WPCBs, can be reused through the flotation technology. Metal and non-metal components in WPCBs powders can be effectively separated based on significant differences in floatability, and renewable collectors prepared from waste oils can significantly enhance the floatability difference under intense stirring. Air is pumped into the slurry to form bubbles, and hydrophobic particles adhere to the bubbles and float to form tailings. Metal particles cannot be floated and become concentrates. 2.2. Analysis of element distribution and dissociation characteristics In order to analyze the elemental distribution of different size
fractions, the broken products were divided into narrow size fractions by screening tests. The aperture sizes of the sieve were 2, 1, 0.5, 0.25, 0.125, 0.074 and 0.045 mm. The element composition of each size fractions was analyzed by X-ray fluorescence spectrometry (XRF, Axios, Panalytical, Netherlands). Thus, the elements distribution can be obtained. The dissociation degree is the prerequisite for the subsequent efficient sorting. Therefore, the dissociation characteristics of the valuable components at different size fractions were analyzed by the combined application of scanning electron microscopy and spectrometers (SEM þ EDS, APREO, FEI, USA). The detection process was carried out at room temperature in high vacuum mode, and WPCBs powder to be detected was sprayed with gold to improve conductivity. 2.3. FT-IR measurement In order to analyze the functional groups composition of the broken products of WPCBs, FT-IR spectrums of 1e0.5 mm and 0.5 mm were detected. Samples to be detected were crushed to 200 meshes and dried at 90 C for 24 h. The samples were pressed with potassium bromide (analytically pure) at 10 MPa with 1 min. Infrared spectrometer Nicolet 380 (Thermo, America) was used in this test and the spectrum was obtained between 400 cm1 and 4000 cm1 with resolution of 2 cm1. Thus, the adsorption phenomenon between the flotation reagents and the particle surface was analyzed. 2.4. XPS analysis The interface property is the decisive factor of the interaction between collector and WPCBs particles. Composition of carbonbased functional groups in WPCBs powders was analyzed by Xray photoelectron spectroscopy (XPS, ESCALAB 250Xi, Thermo, USA). Binding energy was corrected by setting the C1 s peak. The content of hydrophobic and hydrophilic groups was quantitatively analyzed. 2.5. Flotation performance with renewable collector as collector In order to recover the metal from the nonmetal, flotation technology was used. The 1e0.5 mm and 0.5 mm of the dissociated products were respectively subjected to flotation. Lab-used single XFDIV (0.5 L) flotation machine was conducted for the flotation experiments with 30 g feed in each test. The impeller speed was adjusted to 1920 r/min for 2 min to ensure the uniform dispersion of particles. The flow of air was controlled at 0.15 m3/h. The collector for preset dosage was added and stirred for 2 min. Subsequently, 2-octanol that used as frother was added and mixed for 1 min. Aeration process was carried out, and the scraper was started. The process continues until no more particles were being recovered. The mass and element composition of the concentrate and tailing were measured. 3. Results and discussion 3.1. Elements distribution in different size fraction Images and elemental compositions of screening products, 2e1, 1e0.5, 0.5e0.25, 0.25e0.125, 0.125e0.074, 0.074e0.045, 0.045 mm, are shown in Fig. 2 and Fig. 3 respectively. As shown in Fig. 2, the seven size fractions show different colors, which indicated that the composition of each size is different. Various components (metal, non-metal, etc.) in WPCBs have significant differences in mechanical properties, so selective crushing
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
3
Fig. 1. Design scheme for resource utilization of waste oil and WPCBs.
2-1 mm
1-0.5 mm
0.5-0.25 mm
0.25-0.125 mm
content of finer particle is less than 2%. However, Fe is mainly concentrated in 0.5 mm with 20% content, and the content of 2e1 mm and 1e0.5 mm is relatively low, only about 2%. Nonmetallic components containing Si and Ca are the main impurities. Considering the difference in elemental enrichment in different size fractions, flotation performance of 1e0.5 mm and 0.5 mm are studied respectively. 3.2. Dissociation characteristics of different size particles
0.125-0.074 mm
0.074-0.045 mm
-0.045 mm
Fig. 2. Visual image of broken product.
The morphology and elemental section distribution of 1e0.5 mm and 0.5 mm are shown in Fig. 4. Fig. 4 (a) shows that slender particles are observed in the range of 1e0.5 mm, and thin circular particles have also been discovered. EDS results shows that these elongated particles are dissociated impurity particles enriched with Si and Al, which is usually used as glass fiber for WPCBs substrates. This also shows that the Al in elemental analysis exists in the form of glass fiber. The SEM and EDS analysis results presents in Fig. 4 (b) show that the fine strip particles that are observed in the 0.5 mm are also glass fibre, which is verified by the distribution of Si elements. In addition, dissociated Cu and Fe particles were also discovered. The particle morphology and element distribution in Fig. 4 show that most of the particles with different components exist as independent particles. It can be inferred that particles can be broken to 1 mm to achieve ideal dissociation. 3.3. Functional groups characteristic analysis
Fig. 3. Element composition of broken product (Oxide content).
phenomenon occurs in the crushing process, which is the reason for the component differences in different size fractions. The results of Fig. 3 show that the metals in WPCBs are mainly Cu and Fe. Significant differences exist in the elemental composition of different size fractions. As for Cu, 1e0.5 mm has the highest content with 32%, followed by 2e1 mm and 0.5e0.25 mm. The Cu
Infrared spectrum analysis results of 1e0.5 mm and 0.5 mm are shown in Fig. 5. The results presented in Fig. 5 show that the absorption peaks of functional groups in 1e0.5 mm and 0.5 mm samples are similar. Peaks exhibited between 1058 cm1 and 1242 cm1 are CeO. eCH3 is characterized by the peaks of 1457 cm1 and 2931 cm1. Peaks at 1506 cm1, 1634 cm1 representing C]C (Han et al., 2018). eCH3 is the main hydrophobic group, which can promote the attachment of particles to bubbles to enhance the flotation process. Edible oil is a lipid substance, which contains a long carbon chain, mainly CeH, CeC bonds, and also contains CeO and C]O bonds. Therefore, the hydrophobic groups in collectors prepared from waste oils can physically adsorb with the hydrophobic groups in WPCBs powder to enhance the hydrophobicity. In WPCBs powders, organic matter is usually used as an adhesive to solidify glass fibers. Therefore, collectors can selectively enhance the
(a) 1-0.5 mm
(b) -0.5 mm Fig. 4. Particle morphology and element distribution of broken product.
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
Fig. 5. FT-IR spectrums of 1e0.5 mm and 0.5 mm size fraction.
5
(a) 1-0.5 mm
hydrophobicity of impurity particles, which is an important factor to realize the flotation separation process. In order to further analyze the content of hydrophobic groups in carbon-based functional groups in WPCBs, narrow sweep of carbon elements was carried out, and peak fitting was used to determine the content of functional groups. The results are shown in Fig. 6. Carbon-based functional groups are caused by organic matter, including adhesives and curing agents, which can significantly change the hydrophobicity of particles. As shown in Fig. 6, the area of functional groups of CeC/CeH is significantly greater than that of other peaks. Through peak fitting calculation, the hydrophobic group content of 1e0.5 mm reaches 66.19%, and that of 0.5 mm reaches 64.90%, which leads to strong hydrophobicity. 3.4. Flotation behavior of WPCBs powder The macroscopic flotation behavior of 1e0.5 mm and 0.5 mm is shown in Fig. 7. As shown in Fig. 7 (a), for 1e0.5 mm, in the absence of collector and frother, the bubbles are uneven and unstable, and few particles are floating out. Flotation bubbles become small and uniform under the action of frother, but only a few particles are floating out. Further, plenty of particles are flotated under the action of collectors and frother, which indicates that the flotation effect has been significantly strengthened. For 0.5 mm, the macroscopic flotation behavior shown in Fig. 7 (b) is different from the results that presented in Fig. 7 (a). That is, flotation performance of 0.5 mm particle in the absence of flotation agents is more significant than that of 1e0.5 mm. A certain amount of floats are observed, which indicates that the natural floatability of 0.5 mm is better than that of 1e0.5 mm. Further, it can also be observed that the flotation process of 0.5 mm particles becomes stable and strengthened under the action of collectors and frother. It can be deduced that the collector can significantly improve the floatability of the non-metallic particles to enhance the flotation efficiency. The effect of collector dosage on concentrate grade and recovery rate is shown in Fig. 8. As shown in Fig. 8, when the collector dosage increases from 2 kg/t to 10 kg/t, the Cu content increases gradually from 36.85% to 47.77%. Meanwhile, Si content gradually decreases from 27.17% to
(b) -0.5 mm Fig. 6. C1s XPS spectra of 1e0.5 mm and 0.5 mm.
20.91%. Fe content is basically stable with content of 2.8%. In addition, the recovery of each element decreases gradually with the increase of the collector dosage, and the recovery of Si decreases most significantly, from 90.80% to 48.53%. The Fe recovery decreases from 90.80% to 74.67%. The Cu recovery reduces from 99.24% to 91.15%. The effect of collector dosage on concentrate grade and recovery rate of 0.5 mm is shown in Fig. 9. The result shown in Fig. 9 is consistent with Fig. 8. That is, Si content in concentrate decreases with the increase of collector dosage, while Cu content increases with the increase of collector dosage. Moreover, the recovery of each element decreases with the increase of collector dosage, which is mainly caused by the reduction of concentrate yield. When the dosage of collector increases from 1 kg/t to 8 kg/t, the Fe content in the concentrate increases from 40.01% to 48.02%, and the recovery decreases from 71.99% to 27.82%; the Cu content increases from 8.03% to 13.57% corresponding with a recovery decreases from 91.61% to 51.57%. Si decreases from 9.86% to 6.09%, and the recovery reduces from 14.01% to 2.8%.
6
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
(a) 1-0.5 mm
(b) -0.5 mm Fig. 7. Flotation behavior of 1e0.5 mm and 0.5 mm with different flotation reagent.
Fig. 8. Influence of collector dosage on flotation performance of 1e0.5 mm.
4. Conclusion Recovery technology of metals in WPCBs is necessary to make WPCBs a resource rather than an environmental threat. This study proposes a physical sorting technology, namely flotation approach, for metal recovery. Further, the renewable collector prepared from waste oil makes the flotation process more environmentally friendly.
Fig. 9. Influence of collector dosage on flotation performance of 0.5 mm.
Elemental distribution shows effective dissociation can be achieved when the WPCBs are broken to 1 mm. Cu is mainly concentrated in 1e0.5 mm and Fe is mainly concentrated in 0.5 mm. The effect of regenerated collector dosage on flotation performance of 1e0.5 mm and 0.5 mm was analyzed. The metal content in concentrate increases with the increase of collector dosage, which is accompanied by a decrease in recovery. For 1e0.5 mm, the Cu, Si, and Fe contents in concentrate can be
X.-n. Zhu et al. / Journal of Cleaner Production 255 (2020) 120289
obtained at 47.77%, 20.91% and 3.24% with recovery of 91.15%, 48.53% and 74.67% respectively when 10 kg/t collector is used. For 0.5 mm, the concentrate with 40.01% Fe, 8.03% Cu and 9.86% Si is achieved, corresponding with 71.99%, 91.61% and 14.04% recovery when the collector dosage is 1 kg/t. The flotation mechanism was revealed by FT-IR and XPS detection. The results of functional group analysis showes that the main hydrophobic group on the particle surface is CeC/CeH, and the hydrophilic group is CeO and C]O. The hydrophobic group could enhance the adsorption of the collector to improve the hydrophobicity of the non-metallic particles. Further, quantitative analysis of hydrophobic group show that the content of hydrophobic groups in 1e0.5 mm and 0.5 mm reaches 66.19% and 64.90% respectively. 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. CRediT authorship contribution statement Xiang-nan Zhu: Writing - original draft, Writing - review & editing. Tao Cui: Writing - original draft, Writing - review & editing. Biao Li: Writing - original draft, Writing - review & editing. Chunchen Nie: Project administration, Writing - review & editing. Hao Zhang: Project administration, Writing - review & editing. Xianjun Lyu: Project administration, Writing - review & editing. Youjun Tao: Project administration, Writing - review & editing. Jun Qiu: Project administration, Writing - review & editing. Lin Li: Project administration, Writing - review & editing. Guang-wen Zhang: Project administration, Writing - review & editing. Acknowledgement This work was supported by Natural Science Foundation of Shandong Province (ZR2019BEE055), and supported by Scientific Research Foundation of Shandong University of Science and Technology for Recruited Talents (2017RCJJ035). References Abdelbasir, S.M., Ssm, H., Kamel, A.H., El-Nasr, R.S., 2018. Status of electronic waste recycling techniques: a review. Environ. Sci. Pollut. Res. 25 (4), 1e15. _ Ahmet, Ipekçi, Menderes, Kam, Hamit, Saruhan, 2018. Investigation of 3D printing occupancy rates effect on mechanical properties and surface roughness of PETG material products. J. New Res. Sci(JNRS). 7 (2), 1e8. Anshu, Priya, Subrata, Hait, 2017. Comparative assessment of metallurgical recovery of metals from electronic waste with special emphasis on bioleaching. Environ. Sci. Pollut. Res. 24, 6989e7008. nchez, E.J., 2017. Study of the physiFlorescampos, R., Estradaruiz, R.H., Velardesa cochemical effects on the separation of the non-metallic fraction from printed circuit boards by inverse flotation. Waste Manag. 69, 400e406. Georgi-Maschler, T., Friedrich, B., Weyhe, R., Heegn, H., Rutz, M., 2012. Development of a recycling process for li-ion batteries. J. Power Sources 207 (6), 173e182. Granata, G., Pagnanelli, F., Moscardini, E., Takacova, Z., Havlik, T., Toro, L., 2012. Simultaneous recycling of nickel metal hydride, lithium ion and primary lithium batteries: accomplishment of European guidelines by optimizing mechanical pre-treatment and solvent extraction operations. J. Power Sources 212, 205e211. Gurung, M., Adhikari, B.B., Kawakita, H., Ohto, K., Inoue, K., Alam, S., 2013. Recovery of gold and silver from spent mobile phones by means of acidothiourea leaching followed by adsorption using biosorbent prepared from persimmon tannin. Hydrometallurgy 133, 84e93. Han, J., Chenlong, D., Guofeng, L., Long, H., Xuesen, C., Dan, W., 2018. The influence of waste printed circuit boards characteristics and nonmetal surface energy regulation on flotation. Waste Manag. 80, 81e88. He, J., Duan, C., 2017. Recovery of metallic concentrations from waste printed circuit
7
boards via reverse floatation. Waste Manag. 60, 618e628. Huang, K., Guo, Jie, Xu, Z., 2009. Recycling of waste printed circuit boards: a review of current technologies and treatment status in China. J. Hazard Mater. 164, 399e408. Huang, Z., Cheng, C., Liu, Z., Feng, B., Hu, Y., Luo, W., He, G., Yu, X., Fu, W., 2019a. Highly efficient potassium fertilizer production by using a gemini surfactant. Green Chem. 21, 1406e1411. Huang, Z., Cheng, C., Liu, Z., Zeng, H., Feng, B., Zhong, H., Luo, W., Hu, Y., Guo, Z., He, G., Fu, W., 2019b. Utilization of a new Gemini surfactant as the collector for the reverse froth flotation of phosphate ore in sustainable production of phosphate fertilizer. J. Clean. Prod. 221, 108e112. Li, J., Lu, H., Guo, J., Xu, Z., Zhou, Y., 2007. Recycle technology for recovering resources and products from waste printed circuit boards. Environ. Sci. Technol. 41, 1995e2000. Liu, L., Wang, Z., Xu, L., Hong, X., Govindan, K., 2017. Collection effort and reverse channel choices in a closed-loop supply chain. J. Clean. Prod. 144, 492e500. _ Menderes, Kam, Hamit, Saruhan, Ahmet, Ipekçi, 2019. Investigation the effect of 3d printer system vibrations on surface roughness of the printed products. Düzce Üni. Bilim Teknol. Der. 7, 147e157. Qu, S., Zhou, Y., Zhang, Y., Wahab, M.I.M., Zhang, G., Ye, Y., 2019. Optimal strategy for a green supply chain considering shipping policy and default risk. Comput. Ind. Eng. 131, 172e186. Savaskan, R.C., Bhattacharya, S., Van Wassenhove, L.N., 2004. Closed-Loop supply chain models with product remanufacturing. Manag. Sci. 50 (2), 239e252. Sellitto, M.A., 2018. Assessment of the effectiveness of green practices in the management of two supply chains. Bus. Process Manag. J. 24 (1), 23e48. rio, J.A.S., Bernardes, A.M., Rodrigues, J.S., 2005. UtiliVeit, H.M., Diehl, T.R., Teno zation of magnetic and electrostatic separation in the recycling of printed circuit boards scrap. Waste Manag. 25 (1), 67e74. Wang, C., Wang, H., Fu, J., Gu, G., 2014. Effects of additives on pvc plastics surface and the natural flotability. Colloid. Surface. 441 (3), 544e548. Wang, J., Xu, Z., 2015. Disposing and recycling waste printed circuit boards: disconnecting, resource recovery, and pollution control. Environ. Sci. Technol. 49, 721e733. Wang, H., Zhang, S., Li, B., Pan, De’an, Wu, Y., Zuo, T., 2017. Recovery of waste printed circuit boards through pyrometallurgical processing: a review. Resour. Conserv. Recycl. 126, 209e218. Wang, S., He, Y., Yang, J., Feng, Y., 2018. Enrichment of indium tin oxide from colour filter glass in waste liquid crystal display panels through flotation. J. Clean. Prod. 189, 464e471. Wu, J., Li, J., Xu, Z., 2008. Electrostatic separation for multi-size granule of crushed printed circuit board waste using two-roll separator. J. Hazard Mater. 159 (2), 230e234. Yi, Q., Li, W., Zhang, X., Feng, J., Zhang, J., Wu, J., 2015. Tech-economic evaluation of waste cooking oil to bio-flotation agent technology in the coal flotation industry. J. Clean. Prod. 95, 131e141. You, X., He, M., Zhu, X., Wei, H., Cao, X., Wang, P., Li, L., 2019. Influence of surfactant for improving dewatering of brown coal: a comparative experimental and MD simulation study. Separ. Purif. Technol. 210, 473e478. Yu, Y., Li, A., Xu, Z., Zhou, A., Li, Z., Zhang, N., Liu, Q., 2020. New insights into the slime coating caused by montmorillonite in the flotation of coal. J. Clean. Prod. 242, 118540 https://doi.org/10.1016/j.jclepro.2019.118540. Zhang, G., Wang, H., Tao, Z., Xing, Y., Xie, W., He, Y., 2016. Removing inorganics from nonmetal fraction of waste printed circuit boards by triboelectric separation. Waste Manag. 49, 230e237. Zhang, G., He, Y., Wang, H., Zhang, T., Yang, X., Wang, S., 2017. Application of triboelectric separation to improve the usability of nonmetallic fractions of waste printed circuit boards: removing inorganics. J. Clean. Prod. 142, 1911e1917. Zhang, G., He, Y., Feng, Y., Zhang, T., Wang, H., 2018a. Recovery of residual metals from fine nonmetallic fractions of waste printed circuit boards using a vibrated gas-solid fluidized bed. Separ. Purif. Technol. 207, 321e328. Zhang, G., He, Y., Feng, Y., Wang, H., Zhu, X., 2018b. Pyrolysis-ultrasonic-Assisted flotation technology for recovering graphite and LiCoO2 from spent lithium-ion batteries. ACS Sustain. Chem. Eng. 6, 10896e10904. Zhu, X., Nie, C., Zhang, H., Lyu, X., Tao, Y., Qiu, J., Li, L., Zhang, G., 2019a. Recovery of high-grade copper from waste printed circuit boards by mechanical-grinding assisted flotation. J. Clean. Prod. 232, 1251e1256. Zhu, X., Nie, C., Zhang, H., Lyu, X., Qiu, J., Li, L., 2019b. Recovery of metals in waste printed circuit boards by flotation technology with soap collector prepared by waste oil through saponification. Waste Manag. 89, 21e26. Zhu, X., Lyu, X., Wang, Q., Qiu, J., Wang, S., Liu, X., Li, L., 2019c. Clean utilization of waste oil: soap collectors prepared by alkaline hydrolysis for fluorite flotation. J. Clean. Prod. 240, 118179 https://doi.org/10.1016/j.jclepro.2019.118179. Zhu, X., Nie, C., Wang, S., Xie, Y., Zhang, H., Lyu, X., Qiu, J., Li, L., 2020a. Cleaner approach to the recycling of metals in waste printed circuit boards by magnetic and gravity separation. J. Clean. Prod. 248, 119235 https://doi.org/10.1016/ j.jclepro.2019.119235. Zhu, X., Wang, D., Ni, Y., Wang, J., Nie, C., Yang, C., Lyu, X., Qiu, J., Li, L., 2020b. Cleaner approach to fine coal flotation by renewable collectors prepared by waste oil transesterification. J. Clean. Prod. 252, 119822 https://doi.org/10.1016/ j.jclepro.2019.119822.