Recovery of neodymium, dysprosium, and iron from spent mobile phone camera module magnets through a hydrometallurgical method

Highlights

• Nd, Dy, and Fe from spent mobile phone camera modules were dissolved using HNO₃ solution.

• Nd, Dy, and a small amount of Fe were selectively extracted from the leachate with 0.5 mol/L of TOPO.

• Selective stripping of Nd and Dy from loaded TOPO was achieved using 3 mol/L of HCl.

• Fe was extracted from the leachate after the removal of Nd and Dy with 1 mol/L of TOPO.

• TOPO was regenerated by stripping the loaded Fe with 1 mol/L of oxalic acid.

Abstract

Neodymium (Nd), dysprosium (Dy), and iron (Fe) were recovered from spent mobile phone camera modules via leaching and a solvent extraction procedure. Nd, Dy, and Fe, together with other minor metal ions in the pretreated spent mobile phone camera modules, were dissolved using an HNO₃ solution. The leaching parameters, such as concentration of lixivant, reaction temperature, pulp density, which possibly affect the dissolution efficiency of metal ions, were investigated. From the obtained leachate containing Nd, Dy, Fe, Ni, Co, and B, Nd and Dy, with a small amount of Fe, were extracted using 0.5 mol/L of trioctylphosphine oxide (TOPO). Selective stripping of Nd and Dy from the loaded TOPO was achieved using 3 mol/L hydrochloric acid. After removing Nd and Dy from the leachate, Fe was extracted using 1 mol/L of TOPO followed by stripping with oxalic acid. McCabe-Thiele diagrams for the extraction and stripping of Nd/Dy and Fe were constructed. The results were validated via counter-current simulation experiments using a real leachate solution. Finally, an integrated process for recovery of Nd, Dy, and Fe from the nitric acid leachate of spent mobile phone camera modules was proposed.

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.