Solvent extraction of La3+ and Ba2+ by an ionic liquid extractant in an imidazolium-based ionic liquid diluent was investigated. Seven protic ionic liquid extractants were examined and these PILs are based on five organic superbases and either 6,6,7,7,8,8,8-heptafluoro-2,2-dimethy1-3,5-octadione (Hfod) or 1,1,1,5,5,5-hexafluoroacetylacetone (Hhfac) beta-diketones as anion. For these PIL extractants, the extraction efficiencies and separation factors were found to be concentration dependent. The effects of aqueous phase acidity, extractant structure, and extractant concentration on separation properties of La3+ and Ba2+ are discussed in this paper. (C) 2014 Elsevier B.V. All rights reserved.