Competitive extraction and stripping behaviors of rare earth elements from industrial wet-process phosphoric acid using di-(2-ethyl-hexyl) phosphoric acid solvent: Optimization and thermodynamic studies

Abstract

Rare earth elements (REEs) have gained a great amount of attention in the last decades, as they become indispensable and ubiquitous owing to their versatile applications in modern world and high technologies. The main aim of this work is to study the extraction behavior of REEs from the wet process phosphoric acid (WPPA) using Di-(2-ethylhexyl) phosphoric acid (D2EHPA) with a focus on yttrium (Y) and scandium (Sc) as the major REEs. The extraction and stripping operating conditions of REEs from WPPA were optimized, including the extractant concentration, the O:A ratio (organic phase / aqueous phase), the contact time, the residence time and stirring speed. Single-stage extraction results revealed an extraction efficiency of 58 and 56 % for ΣREEs and Sc, respectively.Besides, it was demonstrated that D2EHPA shows a high affinity towards yttrium (Y) with high extraction of 91 % under the optimized conditions of 2 M of D2EHPA, O:A = 1, 600 rpm during 20 min. The McCabe–Thiele diagrams were established to specify the required theoretical number of extraction stages of ΣREEs. It was revealed that four stages are required for ΣREEs extraction, two stages for Sc and a single extraction stage for Y at an O:A ratio of 1. The best extraction efficiencies were obtained for a total percentage of 97, 87 and 90 % for ΣREEs, Sc and Y, respectively. The stripping was successfully achieved using H2SO4 solution with efficiencies of 73 and 90 % for ΣREEs and Y, respectively. Finally, an integrated process for the recovery of REEs from WPPA was proposed.