Nanotechnology for hydrometallurgy

Rare Earth Elements (REE) are a group of 17 chemically similar metals that have gained an increasing importance over the past decades, due to their unique properties that make them crucial for many applications, especially in high-tech products. The term “rare” is rather historical than descriptive, since they are quite abundant in the Earth’s crust. However, their extraction and separation can be challenging. This thesis aims to develop a competitive technology, based on functional nanoadsorbents, for extraction and separation of REE in solution that can be industrially applied. Silica (SiO2) nanoparticles (NPs) with an iron oxide core were selected as the base for the nanoadsorbents. Nanoscale SiO2 exhibits a large surface area that is very advantageous for adsorption purposes. Furthermore, they can be surface functionalized with different organic molecules (ligands). The iron oxide core allows the solid nanoadsorbents to be easily removed magnetically from solution. First, the synthesis of the nanoadsorbents was optimized and three different organosilanes were synthesized, grafted onto SiO2 NPs and tested for REE uptake. One of the three organosilanes showed to be reasonably efficient and was further tested with magnetic NP for selective uptake of REE. Structural studies of molecular model compounds gave molecular insights into the observed selectivity. Next, adsorption conditions were carefully modified to, presumably, double the obtained REE uptake. Unexpectedly, the uptake increased up to 30 times, which suggested that a different uptake mechanism was involved. The mechanism was investigated and revealed the induced seeding of a crystalline phase of REE(OH)3 on the surface. Preliminary tests on REE carbonate from REE ores gave very encouraging results. Finally, a deeper understanding into the selective REE uptake was achieved via structural studies of different ligands and their interaction with different REE, creating the basis for molecular recognition approach. Four ligands specific to different REE were identified and their interaction with REE explained from a molecular point of view. One of these ligands was chosen for upscaling of the technology, by evaluating its potential as packing material for chromatographic separation of REE. The studies provided very attractive results, with good separation of 6 different REE from a solution

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

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

Toward Molecular Recognition of REEs: Comparative Analysis of Hybrid Nanoadsorbents with the Different Complexonate Ligands EDTA, DTPA, and TTHA

Highly efficient tailored SiO₂-based nanoadsorbents were synthesized for the selective extraction of rare-earth elements (REEs). Three different complexonates (EDTA, DTPA, and TTHA) were investigated in terms of uptake capacity and selectivity, showing capacities of up to 300 mg of RE³⁺/g and distinct preferential trends depending on the complexonate. EDTA-functionalized nanoadsorbents showed higher uptake for Dy³⁺, DTPA-functionalized ones for Nd³⁺, and TTHA-functionalized ones for La³⁺. The selectivity was even more pronounced in desorption at pH 3, with separation factors of up to 76 in ternary mixtures. A broad comparative study of single-crystal structures of the complexes between REE and the nongrafted complexonates at different pHs led to a molecular understanding of their individual modes of action. EDTA-derived nanoadsorbents combine concerted action and chelation, whereas the latter is the preferential coordination mechanism for DTPA- and TTHA-derived nanoadsorbents. These different mechanisms result in quite specific REE affinities, which opens great possibilities toward molecular recognition of REEs and for tailoring nanoadsorbents for a particular REE or group of REEs in their production from minerals and in recycling. It also brings new insights into how REEs are adsorbed on nanomaterials applied in a broad variety of fields, including bioimaging and MRI

Hybrid silica nanoparticles for sequestration and luminescence detection of trivalent rare-earth ions (Dy3+ and Nd3+) in solution

New hybrid material-based adsorbents acting also as luminescent probes upon uptake of trivalent rare-earth (RE) ions Nd3+ and Dy3+ have been developed. SiO2 NPs functionalized by three different organic ligands, N-aminopropylen-amidoiminodiacetic acid (L1), pyridine-alpha,beta-dicarboxylic acid bis(propylenamide) (L2), and N-propylen-iminodiacetic acid (L3), have been produced and fully characterized by C-13, H-1, and Si-29 solid-state NMR, FTIR, TGA, XRD, TEM, nitrogen gas adsorption, and also by NTA and DLS in solution. The synthesized hybrid materials are well dispersible and stable in aqueous solutions according to NTA and consist of spheres with diameters less than 100 nm. Their affinities to the lanthanide ions Dy3+ and Nd3+ have been investigated in aqueous solution and characterized by SEM-EDS and complexometric titration, demonstrating that they can be successfully used as adsorbents for sequestration of trivalent RE ions. The adsorbed RE ions can efficiently be desorbed from saturated nanoadsorbents by addition of hydrochloric acid. The produced nanomaterials may also be used as luminescent probes for Dy3+ and Nd3+ ions in solution

Hybrid silica nanoparticles for sequestration and luminescence detection of trivalent Rare Earth ions (Dy3+ and Nd3+) in solution.

International audienceNew hybrid material-based adsorbents acting also as luminescent probes upon uptake of trivalent rare-earth (RE) ions Nd3+ and Dy3+ have been developed. SiO2 NPs functionalized by three different organic ligands, N-aminopropylen-amido-iminodiacetic acid (L1), pyridine-α,β-dicarboxylic acid bis(propylenamide) (L2), and N-propylen-iminodiacetic acid (L3), have been produced and fully characterized by 13C, 1H, and 29Si solid-state NMR, FTIR, TGA, XRD, TEM, nitrogen gas adsorption, and also by NTA and DLS in solution. The synthesized hybrid materials are well dispersible and stable in aqueous solutions according to NTA and consist of spheres with diameters less than 100 nm. Their affinities to the lanthanide ions Dy3+ and Nd3+ have been investigated in aqueous solution and characterized by SEM–EDS and complexometric titration, demonstrating that they can be successfully used as adsorbents for sequestration of trivalent RE ions. The adsorbed RE ions can efficiently be desorbed from saturated nanoadsorbents by addition of hydrochloric acid. The produced nanomaterials may also be used as luminescent probes for Dy3+ and Nd3+ ions in solution

DTPA-Functionalized Silica Nano- and Microparticles for Adsorption and Chromatographic Separation of Rare Earth Elements

Silica nanoparticles and porous microparticles have been successfully functionalized with a monolayer of DTPA-derived ligands. The ligand grafting is chemically robust and does not appreciably influence the morphology or the structure of the material. The produced particles exhibit quick kinetics and high capacity for REE adsorption. The feasibility of using the DTPA-functionalized microparticles for chromatographic separation of rare earth elements has been investigated for different sample concentrations, elution modes, eluent concentrations, eluent flow rates, and column temperatures. Good separation of the La(III), Ce(III), Pr(III), Nd(III), and Dy(III) ions was achieved using HNO3 as eluent using a linear concentration gradient from 0 to 0.15 M over 55 min. The long-term performance of the functionalized column has been verified, with very little deterioration recorded over more than 50 experiments. The results of this study demonstrate the potential for using DTPA-functionalized silica particles in a chromatographic process for separating these valuable elements from waste sources, as an environmentally preferable alternative to standard solvent-intensive processes.QC 20180509</p