Solvent extraction is widely used for the recovery and separation of metals from acidic,aqueous solutions of raw ore.The recycling of the solvent and diluents and also modifiers is a crucial step in the development of clean molybdenum (Mo) separation technologies.In addition to reducing the volume of liquid waste,the recycling of used extractant solutions reduces chemical costs.[1,2] Although several researchers have developed methods for recycling of used extractant solutions,a scalable practical approach has yet to be proposed.Crystallization could be one of the key steps in recovering solvent from the used solutions after extraction.To design a crystallization process,a reliable solid–liquid equilibrium (SLE) data for the system involved must be obtained and represented in the form of a phase diagram.The commonly used solvents for theMo extraction industry are organic amine-type extractant,such as trioctyl amine,Alamine 336 and Alamine 304-1.[3,4] In this work,the SLE for binary system ofsolvent-diluents,widely used for extraction of Mo was determined by synthetic method.The experimental data have been correlated by Non Random Two Liquid (NRTL) and UNIversal QUAsi Chemical (UNIQUAC) models.In addition,excess molar volumes (VE) and deviations in molar refractivity (ΔR) data were reported at 298.15 K under atmospheric pressure for the binary systems.Densities (?) and refractive indices (nD) at 298.15 K for the binary systems have been measured using a digital vibrating tube densimeter and a precision digital refractometer.Then VE and ?Rwere derived from the measured densities and refractive indices.The measured VE and ΔR data were correlated well with the Redlich-Kister equation.The SLE determination apparatus consisted of a triple-jacket glass still,a low-temperature cryostat and a temperature measuring system.The cryostat medium flowed through the outside of the equilibrium cell in the glass still.In the equilibrium cell,the chemicals were exposed to nitrogen gas to avoid humidification.The temperature was determined with a platinum resistance thermometer,and a digital temperature readout box (ASL F250,UK).To calculate VE in this study,the ρ of pure solvents and binary mixtures was measured using a digital vibrating glass tube densimeter (Anton Paar,model DMA 5000,Austria) was used.The following figures illustrate SLE data for Alamine 336 contained systems.