Extraction of metals from natural waters: A neutron characterization of the nanostructured manganese-oxide-based adsorbents

A methodology has been developed for extraction of metals, i.e., lithium, gold and inorganic arsenic, from natural waters using nanostructured manganese-oxide-based adsorbents. The methods are extremely efficient, highly selective, recyclable, and environmentally benign. A key process to functionalize the Li-, Au- and As-adsorption relies on the protonation of nanoparticles of Mn-spinel, Mn₂O₃- and Bi-doped Mn₂O₃ adsorbents, respectively, so that proper exchange or redox reactions with the targeted metal ions or complexes become possible in spite of the very dilute contents in aqueous solutions. We have applied small-to-wide angle neutron diffraction and inelastic scattering to determine the fractal-like morphology of the nanocomposites, the mixed crystal phases therein and the atomic dynamics. In the case of the pure and hydrogenated Mn-spinel, the neutron data were compared with first-principles calculations of the phonon density of states and the local vibrations modes of adsorbed hydrogen atoms.