Chapter 6
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Nanostructured Organosilica Hybrids as Highly Efficient and Regenerable Sorbents for Rare Earth Extraction Justyna Florek,* Dominic Larivière, and Freddy Kleitz Department of Chemistry, Université Laval 1045, av. de la Médecine, Quebec City, G1V 0A6, Quebec, Canada *E-mail:
[email protected].
Due to the rapidly growing energy demand and increasing production of high technology devices, the development of new sequestration materials for rare earth elements (REEs) has become critical. Nowadays, lanthanides (Ln) play a major role as supplies for the transition to cleaner energy and production of economically important modern devices, like wind turbines (Pr, Nd, Sm, Dy), batteries (La), fluorescent and luminescent phosphor lamps (La, Gd, Tb, Eu, Yb), car catalysts (Ce) or hybrid vehicles (Dy, La, Nd). However, for all these applications, only a high purity fraction of a single rare earth element can be used. Frequently, the presence of other REEs as contaminants in a pure single-element REE fraction alters the efficiency of electronic/optic devices. Although, several methods have been used for REEs extraction, such as liquid-liquid extraction (LLE) or liquid-solid extraction (supported liquid-liquid extraction, SLE, solid-phase extraction, SPE), the selective separation and purification of REEs still remain challenging. Mostly, the difficulties arise from the fact that these metals have very similar chemical properties. Among various extracting agents used for lanthanide separation, the diglycolamide (DGA)-based materials have attracted great attention as some of the most effective agents. In this contribution, we review our advances concerning the development of mesoporous hybrid sorbents for REEs. In particular, series of DGA-modified mesoporous silica (KIT-6)
© 2016 American Chemical Society Cheng et al.; Nanotechnology: Delivering on the Promise Volume 2 ACS Symposium Series; American Chemical Society: Washington, DC, 2016.
sorbents were synthesized and tested for the REEs separation. Moreover, it has been proposed that by tunning the ligand bite angle and/or its environment it becomes possible to tune the extraction selectivity.
Downloaded by CORNELL UNIV on September 6, 2016 | http://pubs.acs.org Publication Date (Web): August 29, 2016 | doi: 10.1021/bk-2016-1224.ch006
Introduction Nowadays, the natural REEs resources are very limited and most of the common extraction/separation processes industrially used are not adequate for sustainable development, and current green chemistry trends (1). Industrially, the extraction and purification of REEs are commonly based on multiple liquid-liquid extractions (LLE) or chromatographic-based resins separation techniques, such as supported liquid-liquid extraction (SLE) or solid-phase extraction (SPE). However, the extraction chromatographic-based (EXC) resins, a branch of the SLE family, are plagued with several issues, such as lack of reusability, degradation of stationary phase, elution of organic phase or high risk of sample cross-contamination. On the other hand, the main drawback associated to ion-exchange type resins (IEC) is related to the lack of selectivity (2). Consequently, new materials with well-developed structure, high extraction capacity, selectivity and stability, are rapidly needed. In this context, we believe that well-designed selective chelating ligands, properly attached to mesoporous silica supports, should provide a better and greener alternative to the commercial resins. In our recent studies, we showed that phosphorous-modified mesoporous materials (e.g., KIT 6 P, SBA 15 P sorbents) can be considered as potential sorbents for the efficient extraction and separation of actinides (3, 4). As previously reported, these sorbents show very fast adsorption (with equilibrium reached within 1 min) and high uranium uptake, being around 10000 mL g-1 (3). Moreover, these materials exhibit good stability in the extraction condition tested (pH=4, HNO3, 30 min extraction time), which allowed us to recycle these sorbents several times with no loss of extraction performance. Among different supports tested for actinide extraction, the functionalized KIT-6 material showed the highest extraction capacity, and therefore this material was used in our supplementary studies. KIT 6 mesoporous silica can be regarded as a three-dimensional (cubic) analog of SBA-15 silica material with well-ordered large cylindrical pores, high surface area and large pore volume (5). Similar to its SBA-15 counterpart, the pores of KIT-6 material can easily be tuned by varying the synthesis conditions, such as aging time and/or temperature (6). Based on these studies, we developed a new family of sorbents for selective separation of REE elements. In that case, we used large-pore KIT-6 material modified with DGA-functionalities (i.e., diglycolamide-based ligands) and obtained sorbents with enhanced selectivity towards heavier REEs, in comparison to the commercially available products (7, 8). Moreover, the investigation of the sequestration capability of these mesoporous sorbents revealed that adsorption equilibrium was achieved much faster than with commercial EXC resins (
