Room Temperature Ionic Liquids as Novel Media for Zn Ions Extraction from Aqueous Solutions
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Room Temperature Ionic Liquids as Novel Media for Zn Ions Extraction from Aqueous Solutions Leticia E. Hernández Cruz, Felipe Legorreta García and Ana M. Herrera González Área Académica de Ciencias de la Tierra y Materiales, Universidad Autónoma del Estado de Hidalgo, Carretera Pachuca – Tulancingo, Km 4.5 s/n, Mineral de la Reforma, Hgo. México, C.P. 42184. ABSTRACT Wastewaters often contain offensive cations. Because of their high affinity for water, it is difficult to remove those using conventional solvents for liquid- liquid extraction [1]. Hydrophobic ionic liquids may provide a useful extraction process. Because the properties of ionic liquids are turnable, it may be possible to identify some ionic liquids that have low viscosity, very low solubility in water, and high affinity for select metal ions [2]. In this sense in this work liquid- liquid extraction of dilute Zn ions from water was performed near room temperature with two ionic liquids (IL). Distribution coefficients are reported for Zn ions extracted with bromide 1-hexyl-pyridinium and bromide 1-octyl-pyridinium diluted in decanol. The extraction has been studied, and these confirmed that the metal extraction proceeds via a cation – exchange mechanism. Furthermore, stripping of Zn (II) from ILs into an aqueous phase by sulfuric acid (1 M) and recycling of the extracting ILs phase was successfully accomplished. INTRODUCTION Liquid – liquid extraction has often been a favored choice of the process engineer for the development of separation processes [1-2]. Traditional solvent extraction [2], however, employs an organic solvent and an aqueous solution as the two immiscible phases and the increasing emphasis on the adoption of clean manufacturing processes and environmentally benign technologies may make such processes seem increasingly anachronistic because of their high usage of toxic, flammable, volatile organic compounds (VOCs). The costs of solvents are high and their safe engineering attracts significant capital costs over and above simple containment. Disposal of spent extractants and diluents will also attract increasing costs through the impact of environmental protection regulations. So much are VOCs the normal media for organic synthetic processes, that current worldwide usage of these materials has been estimated at over 5 billion dollars per year [3-8]. The design of safe and environmentally benign separation processes has an increasingly important role in the development of clean manufacturing processes and in the remediation of sites contaminated by an older generation of manufacturing technology. Recently, considerable interest has been manifest in the use of room temperature ionic liquids as solvents for industrial catalytic reactions [9-15]. This approach appears to allow the controlled production of desired products from reactants with a minimum of waste production through side reactions due to the tendency of ionic liquids to suppress conventional solvation and solvolysis phenomena [3]. IL´s are usually composed of heterocyclic organic
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