Institute of Solid State Chemistry of Ural Branch of Russian Academy of Sciences, Ekaterinburg, Russia:

A. G. Shirokova, Senior Researcher
L. A. Pasechnik, Senior Researcher, e-mail: pasechnik@ihim.uran.ru
S. P. Yatsenko, Professor, Head of Laboratory

This article describes the state-of-the-art achievements in synthesis and application of micro-encapsulated systems (MС). There were obtained the MС, containing organic phosphorus compounds – tributyl phosphate (TBP), di-2-(ethylhexyl)phosphoric acid (D2EHPA), and crown ethers – dibenzo-18-crown-6, 18-crown-6, and a mixture of DB18C6 with TBP or D2EHPA. The peculiarities of micro-encapsulated extractants and mechanisms of rare-earth element extraction from 6М sulfuric solutions were examined by IR spectroscopy. It was found that the acid losses a part of hydrated shell and extracts scandium by cation-exchange mechanism after incorporation of D2EHPA into polymer pores. Extraction of scandium from MС-DB18C6 occurs via formation of a guest-host complex, taking place also in MС synthesis, containing a mixture of DB18C6 + TBP or DB18C6 + D2EHPA. In the latter cases, this reduces their extracting activity due to partial blocking of active centers of both extractants, while the antisynergetic effect with formation of a ternary complex is observed during scandium extraction. For encapsulated TBP, no differences were found in hydrate-solvate mechanism of scandium extraction comparing with its liquid state. The synthesized MС had different degree of Y, Sc, La and Ce extraction from individual or mixed solutions (see the panoramic diagram of element extraction). The structure of the synthesized samples was studied via electron microscopy and its dependence on synthesis conditions was established. Addition of polar solvent promotes the formation of the structure of volumetric 70-100 μm «halls» and a relief porous surface. In the presence of non-polar solvent, a folded structure is formed, which is pierced by channels with a fine-pored surface. If no solvents are used, dense materials with smoothed surface are produced. It is shown how the morphological characteristics can be changed for optimization of extracting properties of MС.

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