Regular Article

Solvent extraction: fundamental equilibrium studies of neodymium and DEHPA

¹ Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institute Freiberg for Resource Technology, Chemnitzer Strasse 40, 09599 Freiberg, Germany
² Engineering Office, MetuRec, An den Eschenbacher Teichen 16, 38678 Clausthal-Zellerfeld, Germany

^* e-mail: c.scharf@hzdr.de

Received: 30 October 2016
Received in final form: 5 January 2017
Accepted: 1 March 2017

Abstract

This article presents equilibrium studies into the NdCl₃–HCl (or NaOH)–H₂O–DEHPA (di-(2-ethylhexyl) phosphoric acid)–kerosene system. The system plays a role in solvent extraction of rare earth elements from aqueous chloride solutions. Thereby neodymium is transferred into the organic phase consisting of DEHPA solved in kerosene. Measurements were taken at DEHPA concentrations between 1 and 40 vol.% and at concentrations of neodymium which prevent a gelatinous organic phase. Results are presented in tables. Three charts of process variables were evaluated which, under the assumption of ideal behaviour, should lead to slopes of 3 in double logarithmic scale in all three cases. Since the actual slopes of measured variables were 2.4, 2.5 and 3.8, ideal behaviour is only a first approximation, and non-ideal aspects need to be further studied. The plot of percentage extraction versus pH shows that neodymium is completely extracted at pH values above 1.