Recovery of neodymium, dysprosium, and iron from spent mobile phone camera module magnets through a hydrometallurgical method
Graphical abstract
Introduction
Neodymium (Nd) and dysprosium (Dy) are important ingredients of mobile phone camera modules because of their unique physicochemical properties. Spent mobile phone camera modules are important secondary sources of Nd and Dy. The recovery of rare earth elements, such as Nd and Dy, from secondary sources has been gaining significant interest because of their growing demand, in contrast to limited natural oral production and low recycling rates (Padhan and Sarangi, 2017). In Korea, as the smartphone market booms, large amounts of spent mobile phones have manifested because of their short market life cycle and frequent model changes. The majority of spent mobile phones collected are exported or conflagrated and dumped, while only 2.5% of them are processed for recovery (Ari, 2016). The target metals to be recovered are Au, Ag, Pd, Cu, Co, and Li, depending on the salvaged parts of the spent mobile phone (Ari, 2016). The development of a cost-effective process for the recovery of Nd and Dy from spent mobile phone camera modules is important, considering the related economic and environmental aspects.
Hydrometallurgical methods have been used for the recovery of Nd and/or Dy from various secondary resources, such as scraps, alloys by leaching (Yoon et al., 2016, Binnemans et al., 2013, Yoon et al., 2014, Lee et al., 2013), and solvent extraction (Yoon et al., 2016, Panda et al., 2012, Sun et al., 2018, Padhan et al., 2017, Gergoric et al., 2017) In our previous study, some studies on the extraction of Nd and Dy from various aqueous solutions were summarized (Sun et al., 2018). Considering that the solvent extraction method exhibits advantages of high selectivity and efficiency, it has been deemed as an important method for valuable metal recovery from secondary sources (Parhi et al., 2016, Banda et al., 2012, Radhika et al., 2010).
In this study, the recovery of Nd, Dy, and iron (Fe) from spent mobile phone camera modules was investigated using a hydrometallurgical method. Nd, Dy, and Fe, with other minor metal ions, were first leached using an HNO3 solution. The optimum leaching condition was obtained by varying the parameters, such as the concentration of lixivant, reaction temperature, and pulp density. Thereafter, using the obtained leachate solution, Nd/Dy was extracted using trioctylphosphine oxide (TOPO), which was utilized at a selected condition in the presence of a large amount of Fe. Nd/Dy was stripped from the loaded TOPO using a hydrochloric acid (HCI) solution. After the removal of Nd/Dy, Fe was recovered via extraction with TOPO, followed by stripping with oxalic acid. The advantage of this method is that it avoids the loss of Nd/Dy, which may occur in the commonly used precipitation method for the removal of Fe. McCabe-Thiele diagrams were constructed for both the extraction and stripping of Nd/Dy and Fe. Simulated counter-current extraction and stripping experiments were also conducted to validate the results.
Section snippets
Materials
Spent mobile phone camera modules were obtained from a refining factory in Korea. They were roasted at 300–800 °C, at 5 °C/min, for 3 h, and cooled (21–25 °C) in a furnace. The results showed that when the roasting temperature was not lower than 600 °C, the flammable components were burned, and the iron cases of the modules were separated with the magnets. The magnets were washed with distilled water and dried at 100 °C for 24 h. Thereafter, the magnets were crushed and homogenized via mixing,
Leaching of metals
To find an optimum leaching condition to dissolve Nd and Dy from the spent mobile phone camera module, the effects of several variables, such as the nature and concentration of lixiviant, reaction temperature, and pulp density, were investigated.
Conclusions
The separation and recovery of Nd, Dy, and Fe from spent mobile phone camera modules were achieved via leaching with HNO3, followed by solvent extraction with TOPO. The extraction behaviors of Nd, Dy, and Fe were dependent on the concentrations of TOPO and HNO3 in the feed solution. Based on the foregoing, Nd and Dy were completely extracted from the leachate solution, which contained Fe and other minor metal ions, in two stages using 0.5 mol/L of TOPO at the unit A/O ratio. A small amount of
CRediT authorship contribution statement
Pan-Pan Sun: Conceptualization, Data curation, Validation, Methodology, Software, Writing - original draft. Hyeon Seo: Investigation, Formal analysis, Methodology, Software. Sung-Yong Cho: Resources, Supervision, Writing - review & editing.
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.
Acknowledgment
This work was supported by the Basic Science Research Program (No. 2020R1I1A3A04037308) through the National Research Foundation of Korea (NRF), funded by the Ministry of Education. And Project (P0015130) funded by Korea Institute for Advancement of Technology. The authors are grateful for the financial support. The authors also express their sincere gratitude to the Korea Basic Science Institute (KBSI), Gwangju branch for providing the ICP-OES data. The authors would like to thank Editage (//www.editage.co.kr
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