Original Articles
Da-Zhi Li and Bin Xu
Abstract
Saponified 2-ethylhexylphosphoric acid mono-2-ethylhexyl ester (P507)/ /n-hexanol/n-heptane salting out agent free microemulsion is found to be a promising efficient system for separating Co (II) and Li (I). In this microemulsion system, the volume ratio of saponified P507, n-hexanol and n-heptane is 1:6:14. The concentration of the external aqueous Co (II) and Li (I) was 100 and 40 mg/L, respectively. The optimum condition is assured as follows: water bath temperature of 298.15 K, vibration time for 7 min, molar ratio of P507 and NaOH 1.5:1, volume ratio of aqueous phase and microemulsion 8. Under the optimum condition, the extraction yield of cobalt and lithium is 99.1% and 14.4%, respectively. The average reverse extraction yield of colbat is 97.2% when 1.0 mol/L HCl is used as reverse extraction experiments on the organic phase. The organic phase after stripping can be reused. The results show that: the saponified P507 microemulsion system is not only thermodynamic stability, but also has a broad application prospect in the extraction and separation of Co (II) and Li (I) with strong selectivity and high efficiency. Density functional theory (DFT) based calculations have been carried out on the structures and relative binding energies of Co (II) and Li (I) with the surfactant sponified P507 in n-heptane and water solution, respectively. The calculated results suggest that the different interaction between the ions with surfactant saponified P507 is responsible for the preferential complexation of saponified P507 to Co (II) and Li (I) ions. The combined experimental and theoretical studies help us to understand the superior complexation behavior of Co (II) over Li (I) within saponified P507/n-hexanol/n-heptane microemulsion.