Improvement of magnetic solvent extraction using functionalized silica-coated Fe3O4 nanoparticles

Abstract

The application of hydrophobic magnetic nanoparticles functionalized with long carbon chain molecules, such as oleic acid, in the solvent extraction process results in a faster phase disengagement and does not affect the extraction and stripping percentages of cobalt with Cyanex 272, as has been reported in previous studies. However, the chemical stability of this organic phase is limited by its applicability only in contact with aqueous solutions of pH ≥ 2.0. Aiming to overcome such an operational constraint, this study proposed the use of nanoparticles coated with silica and functionalized with a long carbon-chain silane (OTS) in the solvent extraction process. Due to the silica-layer coating of the magnetic core of magnetite and maghemite, such nanoparticles became stable when in contact with aqueous solutions of high acidity of up to 2 mol/L. The proposed nanoparticles were characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy, and magnetic analysis. Their effect on the solvent extraction of cobalt with Cyanex 272 was investigated using magnetic fluids with different concentrations (0, 10, 20, and 30 g/L of magnetic nanoparticles). It was also observed that, under the conditions studied in this work, the presence of these magnetic nanoparticles did not interfere in the efficiency of metal extraction and stripping. Moreover, the time for the phase disengagement can be reduced by a factor of 25 when compared to the process without magnetic nanoparticles.