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<p>Deep-sea rare earth elements and yttrium (REY)-rich mud has emerged as a promising alternative resource to meet the growing global demand for REY, yet the processes controlling REY enrichment in these deposits remain debated. In particular, the relative roles of apatite versus Fe–Mn (oxyhydr)oxides as REY sinks at the sediment–seawater interface are still poorly constrained by experimental data. In this study, batch experiments were conducted to evaluate REY sorption onto hydroxyapatite (Hap) and goethite (Goe). The two minerals exhibit sharply contrasting behaviors and mechanisms. Goe shows classical pH-dependent, reversible sorption, with preferential uptake of heavy REY under mildly acidic conditions, consistent with surface complexation. In contrast, Hap displays non-classical isotherms, pH-independent uptake, and minimal desorption over 10 days, suggesting a strong and potentially irreversible mechanism, most plausibly via structural incorporation. This interpretation is supported by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy coupled with energy-dispersive spectroscopy (TEM/EDS). Moreover, Hap reduces dissolved REY to concentrations approaching seawater level, whereas Goe does not. These results provide experimental constraints on REY enrichment mechanisms in deep-sea settings and suggest that while Fe (oxyhydr)oxides may contribute to initial scavenging, direct capture by Hap may dominate long-term REY retention. Our findings further highlight phosphate-rich zones as priority targets for future REY exploration.</p> Graphical abstract <p></p>

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Contrasting sorption behaviors of rare earth elements and yttrium on apatite and goethite: Implications for REY enrichment in deep-sea mud

  • 期刊论文

  • 发表日期：

    2026年6月3日

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  • Chao Ren,
  • Yufan Yuan,
  • Yi Huang,
  • Wenxian Gou

摘要

Deep-sea rare earth elements and yttrium (REY)-rich mud has emerged as a promising alternative resource to meet the growing global demand for REY, yet the processes controlling REY enrichment in these deposits remain debated. In particular, the relative roles of apatite versus Fe–Mn (oxyhydr)oxides as REY sinks at the sediment–seawater interface are still poorly constrained by experimental data. In this study, batch experiments were conducted to evaluate REY sorption onto hydroxyapatite (Hap) and goethite (Goe). The two minerals exhibit sharply contrasting behaviors and mechanisms. Goe shows classical pH-dependent, reversible sorption, with preferential uptake of heavy REY under mildly acidic conditions, consistent with surface complexation. In contrast, Hap displays non-classical isotherms, pH-independent uptake, and minimal desorption over 10 days, suggesting a strong and potentially irreversible mechanism, most plausibly via structural incorporation. This interpretation is supported by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy coupled with energy-dispersive spectroscopy (TEM/EDS). Moreover, Hap reduces dissolved REY to concentrations approaching seawater level, whereas Goe does not. These results provide experimental constraints on REY enrichment mechanisms in deep-sea settings and suggest that while Fe (oxyhydr)oxides may contribute to initial scavenging, direct capture by Hap may dominate long-term REY retention. Our findings further highlight phosphate-rich zones as priority targets for future REY exploration.

Graphical abstract