Properties of new three-component hydrophobic eutectic solvents based on BTMPPA

Today, a pressing scientific task is the development of new solvents for extraction processes. One of the promising classes of solvents are hydrophobic eutectic solvents (HES), the main advantages of which are the ease of their production, low fire hazard and the ability to vary their properties by correctly selecting components. HES is often prepared on the basis of two components – an extracting compound (e.g. TOPO, BTMPPA) and a so-called solvent (e.g. menthol, thymol). However, to improve the physicochemical and extraction properties of eutectic solvents, modifier components can be introduced. Studying the possibility of varying the properties of HES by changing their composition is a pressing issue today.

The aim of the present work is to study of properties of new hydrophobic eutectic solvents based on di(2,4,4-trimethylpentyl)phosphinic acid (BTMPPA), trioctylphosphine oxide (TOPO), metyltrioctylammonium chloride (MTOAC) and phenol.

The HESs were prepared from the main extractant (BTMPPA), modifier (TOPO/ MTOAC) and «solvent” (phenol) in a molar ratio of 1:1:2. Based on the ¹H, ³¹P NMR and IR spectroscopy data, a hydrogen bond formation in the proposed HESs was established. The physical properties of the proposed extractants were studied, namely, the dependence of density, viscosity and refractive index on temperature. The HES stability during interaction with water and mineral acid solutions was also studied. The viscosity of HES BTMPPA/TOPO/phenol reaches 64 mPa·s at 25°C, which shows its potential applicability in technological processes. The proposed solvents were tested as extractants for Nd(III) and Dy(III) from nitrate solutions.

Thus, the promising use of HESs BTMPPA/(MTOAC or TOPO)/phenol in the extraction of rare earth elements from nitrate solution was shown. The obtained data can be used in the development of new effective hydrometallurgical processes of rare earth elements extraction from leaching solution of spent magnetic materials.