This paper collects experimental data and mathematical modelling of Nd(III), Tb(III) and Dy(III) solvent extraction with an ionic liquid prepared from Aliquat 336 (Methyl-tri(octyl/decyl)ammonium chloride) and Oleic Acid (AliOle). Extraction experiments were carried out to evaluate the effect of chloride anion in aqueous phase, AliOle and REE concentrations over the extraction extension. Mathematical models computed with Matlab software were derived from the mass balances and chemical equilibria involved in the extraction system of Neodymium(III), Terbium(III) and Dysprosium(III) individually. The optimized equilibria parameters proposed fit accurately the experimental data and allowed us to predict the extraction extension of each metal from an aqueous mixture.Postprint (author's final draft