Hybrid nanoadsorbents for extraction and separation of rare earth elements in solution

Abstract: Rare Earth Elements (REE) are a group of 17 metals (those known as lanthanides plus Ytrium and Scandium), which are increasingly important for many emerging modern applications. This work is focused on the development of high performance new magnetic silica based nanoadsorbents which are surface functionalized for efficient uptake and separation of REE in solution. In the first step, three different organic reactants (organosilane derivates) were synthesized and grafted onto the surface of custom synthesized silica (SiO₂) nanoparticles (NPs). The effective grafting was checked by ¹³C and ²⁹Si CP-MAS solid state NMR spectroscopy and FTIR spectroscopy. These hybrid nanomaterials were used as models for adsorption of REE in solution and their uptake capacity towards REE (La³⁺, Dy³⁺ and Nd³⁺) was checked via complexometric titrations with model solutions. The materials were also characterized by SEM-EDS and TEM microscopy. In the second part of the work, one of the organic reactants previously synthesized, which displayed the best properties, was used to functionalize the surface of custom-produced core-shell magnetic silica based nanoadsorbents, consisting of a core of g-Fe₂O₃ nanoparticles covered by a protective thin layer of SiO₂. Magnetic nanoadsorbents exhibit many attractive opportunities for industrial purposes due to their easy removal and possibility of reusing the material. These magnetic silica based nanoadsorbents were also characterized by SEM-EDS and TEM microscopy, FTIR spectroscopy and TGA analysis. The uptake efficiency was checked via complexometric titration and selectivity with binary mixtures of REE was also studied, showing a very noteworthy selectivity towards heavier REE These results were confirmed by X-ray single crystal structure studies of the model compounds. Lastly, a preliminary overview on the potential application of these hybrid nanoadsorbent in real industrial leachate solutions was provided. This last part of the work is still being carried out and optimized, being one of the most important and challenging future prospects for this PhD project.