Investigation of europium(III) uptake from highly sulphate solution via cloud point extraction by mono-Schiff base combined with Triton X-100

Abstract

ABSTRACT Owing to its unique physico-chemical properties, europium is one of the most precious and sought-after rare earth elements in the field of high technology. The major economic and commercial importance of such an element, combined with the pollution risks associated with its intensive use, require the development of efficient and eco-compatible recovery and recycling processes. This study focuses on the recovery of europium from highly saline sulphate media (0.5 mol/L) using an environmentally friendly two-phase aqueous extraction technique (known as cloud point extraction (CPE)), using 2((phenylimino)methyl)phenol mono-Schiff base (HPIMP) as the extractant and Triton X-100 as the non-ionic surfactant. The influence of key experimental parameters such as pH, extractant concentration, surfactant concentration and separation temperature on the europium extraction process was systematically studied and optimized. Under optimum experimental conditions, a quasi-quantitative extraction with a minimal volume fraction of surfactant-rich phase (φs = 0.025), and concentration factor of (CF = 38) was achieved at pH 9.8, in one stage. The analysis of the extraction data revealed that the CPE of europium(III) takes place by a cation exchange-solvation mechanism. The stoichiometry of the complex extracted into the surfactant-rich phase was ascertained to have a composition of 1:2 [Eu:HPIMP] with the slope analysis method. A higher extraction constant was obtained for CPE compared with conventional solvent extraction, confirming the feasibility and usefulness of CPE for Eu(III) recovery. On the other hand, this new HPIMP/Triton X-100 chelating system showed superior extractability for Eu(III) in the CPE process relative to other systems reported previously.