Cobalt extraction from Chloride/Nitrate/Sulfate Media with Phosphonium-based Ionic Liquids.

Room temperature ionic liquids (RTILs) have emerged and attracted increasing interest in the past few years in numerous applications. RTILs are salts generally composed by an organic cation and an inorganic anion in the liquid state at 25 °C. They present high thermal and chemical stability, non-flammability, wide electrochemical window, low volatility and low toxicity [1]. Moreover, these properties can be finely tuned by systematically altering the structure of cations and anions. Due to these attractive features, RTILs have been used as "green" substitutes of volatile organic solvents in a number of applications related to the energy and environmental fields (e.g. separations, extractions, electrochemistry and catalysis). Among these, the use of RTILs for the separation and recycling of “critical” metals deriving from mining or high-tech waste was proposed in the last decade [2]. The recycling of cobalt assumed a growing importance due to the growing demand related to his use in key technologies, such as Li-ion batteries or motors for electric mobility [3]. The current processes for cobalt recovery in the hydrometallurgical route from aqueous solutions have some advantages such as method flexibility, high purity and low energy consumption [4] and some works on the application of RTILs in such process have appeared in the last years [4,5]. Among the available RTILs, those based on phosphonium cation (Figure 1) have been studied for metal extractions in recent years [6]. However, only few works were focused on the nature of the dissolved metals and their speciation in RTILs [7], despite these are fundamental data to understand the separation processes. In this communication, the results on Co(II) extraction in chloride/nitrate/sulfate media using [P66614][Cl], [P66614][Decanoate] and [P66614][Br] are reported, along with the extraction efficiency. The interest in the Co2+ extraction with different media is due to the fact that the liquid samples containing the metal to be recovered usually can give extractions greater than 95%, with different Co(II) coordination. In addition, after stripping, the ionic liquid phase can be regenerated. References: [1] a) K. M. Docherty, C. F. Kulpa, Jr., Green Chem. 2005, 7 (4), 185-189; b) M. Armand, F. Endres, D. R. MacFarlane, H. Ohno, B. Scrosati, Nat. Mater. 2009, 8, 621-629. [2] a) A. P. Abbott, G. Frisch, J. Hartley, K. S. Ryder, Green Chem. 2011, 13 (3), 471-481; b) A.P. Paiva, C.A. Nogueira, Waste Biom.Valoriz. 2021, 12, 1725-1747. [3] J. Piatek, S. Afyon, T. M. Budnyak, S. Budnyk, M. H Sipponen, A. Slabon, Adv. Energy Mater. 2020, 11, 2003456. [4] E. A. Othman, A. G. J van der Ham, H. Miedema, S. R. A Kersten, Sep. Purif. Technol. 2020, 252, 117435. [5] L. Xu, C. Chen, M.-L. Fu, Hydrometallurgy 2020, 197, 105439. [6] K.J. Fraser, D. R. MacFarlane, Austr. J. Chem. 2009, 62 (4) 309-321. [7] M. Busato, A. Lapi, P. D’Angelo, A. Melchior, J. Phys. Chem. B 2021, 125 (24), 6639.