**7. Conclusions**

Magnetic nanohydrometallurgy employing iron oxide nanoparticles functionalized with ethylenediaminepropylsilane and the diethylenediaminepentaacetic acid agents can effectively capture lanthanide ions from aqueous solution, allowing their magnetic extraction at pH 6 and release below pH 2, respectively. Preferential binding of heavy lanthanides has been observed and is dictated by their affinity constants reflecting the lanthanide contraction series. For a binary mixture, a high separation efficiency (>99%) can be achieved after two or three successive complexation and release stages. As the number of components increases, more repetitive extraction cycles become necessary. Therefore, MNHM allows the separation of lanthanide elements using engineered nanoparticles, by performing under green and sustainable conditions, i.e., at room temperature, in aqueous solution, and mild pHs, dispensing the use of classical physical separation processes and organic solvents. It can be easily automated, allowing the use of small reactors. The technology can enable urban mining applications, for instance in the neodymium and dysprosium extraction from the magne<sup>t</sup> components of the electronic wastes.

**Author Contributions:** Methodology, investigation and writing, F.M.d.M.; conceptualization, investigation and methodology, S.N.A.; conceptualization, supervision and writing, H.E.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP 2018/21489-1) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 405301/2013-8).

**Acknowledgments:** The authors are in debit to Alceu Totti Silveira for his help in X-ray fluorescence measurements and Ulisses Condomitti for this important contributions to the development of the MNHM technology.

**Conflicts of Interest:** The authors declare no conflict of interest.
