Extraction of palladium (II) by a silicone ionic liquid-based microemulsion system from chloride medium

• [Si4mim]Cl is first used for the construction of the W/O microemulsion system.
• The [Si4mim]Cl/n-heptane/n-hexanol/NaCl system is applied for Pd (II) extraction firstly.
• The microemulsion shows high extractability of 98% for Pd (II).
• The extraction percentage of several metals is less than 12% by the microemulsion.
• Pd (II) is easily stripped using NaCl from the Pd (II)-loaded microemulsion phase.

The silicone ionic liquid, 1-methyl-3-[tri-(trimethylsiloxy)]silylpropyl-imidazolium chloride ([Si4mim]Cl), was first used for the construction of the W/O microemulsion system and the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system was applied for palladium extraction for the first time. The stability of [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system was characterized by the Turbiscan Lab. For the Pd (II) extraction by the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system, primary parameters (namely, the vibration time, the [Si4mim]Cl concentration, the phase ratio and the additives) affecting the palladium extraction was investigated to optimize the process. Under the optimum conditions, the extraction percentage of Pd (II) is up to 98%. Afterwards, the ionic-exchange mechanism of Pd (II) extraction by the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system was confirmed by the Job Method and analyzed by FT-IR spectra. The stripping of Pd (II) from the microemulsion phase was also studied using the NaCl solutions, indicating a high stripping efficiency. At last, the selectivity of the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system to Pd (II) from other metals (Cu (II), Co (II), Ni (II), Fe (III), Al (III) Zn (II), Ce (III), Li (I), Mg (II) and Sn (IV)) was demonstrated to be quite high. The results of our work indicate that the [Si4mim]Cl/n-heptane/n-hexanol/NaCl microemulsion system is a promising approach for Pd (II) extraction.