Regular Article

Diluent effects on the stability range of w/o micellar systems and microemulsions made with anionic extractants

¹ ICSM, University of Montpellier, CEA, CNRS, ENSCM, Marcoule, France
² Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany

^* e-mail: thomas.zemb@icsm.fr

Received: 18 November 2021
Received in final form: 20 June 2022
Accepted: 14 September 2022
Published online: 31 October 2022

Abstract

Here we present a series of complete phase prisms for water, an organic diluent and di-(2-ethylhexyl) phosphoric acid (HDEHP), one of the most widely used double-branched lipophilic surfactants in hydrometallurgy. Partial or total titration with sodium hydroxide evidence that the mole fraction of the counter-cation “Z” is the variable that controls the packing and spontaneous curvature of the curved film formed by this extractant. Penetrating solvents such as toluene and iso-octane and the non-penetrating solvent dodecane as well as common hydrotropes acting as co-solvents, are considered. The three classical cuts of the phase prism are shown. The regions for which liquid–liquid extraction is possible are determined, as well as the location of the liquid crystals at the origin of the often observed third-phase formation. It is shown that profoundly different trends are obtained when replacing the common solvents currently used in hydrometallurgical processes with hydrotropes.