Recycling of metals in hydrometallurgy is based on liquid-liquid extraction and desextraction between complex fluids [1]. These are concentrated acidic or basic aqueous solutions in contact with organized organic phases containing extractant molecules (which selective affinity to extracts metal ions) in the form of water-poor microemulsions. Winsor II regime with excess aqueous solution is required for efficient electrolyte transfer. The free energy of electrolyte transfer between phases is much lower than the free energy of complexation in all industrially cases. Here, we combined a general model based on thermodynamics equations [2] taking into account the microemulsion structures for which the free energy is calculated using a Gaussian random fields model [3-4] in order to calculate the ion free energy of transfer between an aqueous reservoir and an organized organic phase. We show that taking into account extensive values for the complexation, the extractant adsorption at the interface, and the active area variation allows for predicting the free energy of extraction. This is also confirmed by small angle scattering as a signature of the type of water-poor self-assembly. Furthermore, we demonstrate that the apparent selectivity is really different from the complexation energy differences between ions. To our best knowledge, this is the first theory proposed to link complexation with nearest neighbour and free energy of phase equilibria from first principles. We will show the strength as well as the weaknesses of this emerging modelling method using Gaussian random waves. Acknowledgements: The authors acknowledge financial support from the European Research Council under the ERC Grant Agreement no. [320915] REE-CYCLE: Rare Earth Element reCYCling with Low harmful Emissions. [1] Th. Zemb, C. Bauer, P. Bauduin, L. Belloni, Ch. Déjugnat, O. Diat, V. Dubois, J.-F. Dufrêche, S. Dourdain, M. Duvail, Ch. Larpent, F. Testard and S. Pellet-Rostaing, Colloid Polym. Sci., 2015, 293, 1. [2] J.-F. Dufrêche and T. Zemb, Chem. Phys. Lett., 2015, 622, 45. [3] M. Duvail, J.-F. Dufrêche, L. Arleth and T. Zemb, Phys. Chem. Chem. Phys., 2013, 15, 7133. [4] M. Duvail, L. Arleth, Th. Zemb and J.-F. Dufrêche, J. Chem. Phys., 2014, 140, 164711.