Selective separation of various heavy metals from synthesized phosphoric acid solutions

Abstract

Separating the impurities (such as metallic ions) from phosphoric acid solutions has been a major challenge in phosphoric acid purification as current technologies (such as solvent extraction) are costly. Therefore, emulsion liquid membranes (ELMs) were employed in this study as an alternative technology for the purification of phosphoric acid solutions due to their outstanding selectivity, high extraction efficiency, and relatively low energy consumption compared to other separation methods. Three carrier agents (Cyanex 301, Cyanex 302, and Alamine 336) were evaluated for their suitability in extracting various metallic ions, for the development and optimization of a Type II ELM system in a Taylor-vortex column. At moderate pH (>2), ELMs with Alamine 336 were most efficient (metal removal efficiency of almost 100%); however, their removal efficiency significantly decreased for the simulated phosphoric acid solution. Only ELMs with Cyanex 301 showed the potential to separate some of the tested metals, such as cadmium, lead, and zinc from the synthesized phosphoric acid. The observed failure of the ELM process for the extraction of multiple metals might have resulted from either the lack of proper bonding between the carrier agents and metals or the instability of emulsion membranes under extreme pH conditions.