A green yttrium extraction system containing naphthenic acid, trioctyl/decylamine and isopropanol

Abstract

Yttrium extraction usually produces waste water and suffers from difficulty in phase separation when using saponified naphthenic acid as the extractant. Herein, a non-saponified mixed extraction system containing naphthenic acid, trioctyl/decylamine and modifier was developed for yttrium extraction. Unlike the traditional saponified naphthenic acid system using long chain alcohol as the modifier, short chain alcohol of isopropanol was introduced into the extraction system for the first time. When using 20 vol% naphthenic acid, 40 vol% trioctyl/decylamine, 10 vol% sec-octyl alcohol and 25 vol% isopropanol diluted in 5 vol% n-hexane as extractant, a high yttrium extraction efficiency of above 60% could be obtained within a short phase separation time of ∼5 min. The yttrium separation from other rare earth elements could be achieved through two steps of LaCePrNdY/GdSmEuTbDyHoErTmLuYb grouping extraction followed by LaCePrNd/Y separation. Trioctyl/decylamine, sec-octyl alcohol and isopropanol showed the synergistic extraction effect with naphthenic acid, among which isopropanol was the strongest, followed by trioctyl/decylamine and sec-octyl alcohol. Trioctyl/decylamine could extract H+ produced from naphthenic acid, and isopropanol and/or sec-octyl alcohol could bond with naphthenic acid via hydrogen-bond interaction to prevent the formation of naphthenic acid dimers, leading to more coordination sites exposed for yttrium extraction. Furthermore, isopropanol and/or sec-octyl alcohol participated in the coordination in the extracted organic compound. The combination of the above three action had great contribution to the high extraction efficiency and the rapid phase separation. There was no waste water produced during extraction. Therefore, the proposed mixed system is a green and efficient system for yttrium extraction.