Magnetic nanohydrometallurgy: Principles and concepts applied to metal ion separation and recovery

Abstract

Magnetic nanohydrometallurgy (MNHM) can be seen as a nanotechnological version of hydrometallurgy employing complexing molecules attached to superparamagnetic nanoparticles instead of conventional chemical agents and extracting solvents. In essence, the functionalized nanoparticles preserve chemical mobility and provide a high surface concentration of complexing groups for interacting with metal ions. After the capture, because of their strong magnetism, the particles can be easily removed with a magnet, allowing a rapid and clean separation of the sequestered metal ions. In MNHM, similarly to hydrometallurgy, the metal ions are discriminated by and released from the complexing nanoparticles according to their relative stability constants, affording a round operational scheme. MNHM, however, exhibits greater advantages due to its simplicity and greener performance than hydrometallurgy since it does not use solvent extraction or ionic exchange procedures. In addition, on the laboratory scale, the whole process can be completely automated. However, although both MNHM and hydrometallurgy apply complexing agents to capture metal ions, the fundamental aspects of the coordination chemistry of complexing nanoparticles are still missing in the literature. Since they are essential to understanding the kinetics and equilibrium reactions involved, this paper is dedicated to their appreciation, providing an updated overview of the MNHM process and its possible application in the recovery of strategic elements, such as Cu, Co, Ag, Hg, Au, and the lanthanide ions.