Ionic liquid-containing polymer including membrane for the removal of cobalt: Synthesis, adsorption, transport, and modeling studies

This work describes synthesis of polymer inclusion membranes (PIMs), which is prepared by using varying ratios of polyvinylidene fluoride co-hexafluorophosphate (PVDF-HFP) as the base polymer and trioctyldodecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate) (P₈₈₈₁₂BTMPP) as extractant carrier, and its utilization for the Co(II) sorption and transport. PIM with 40 wt% ionic liquid content showed a high sorption efficiency (>95 %) for 100 mg/L Co(II) feed with 0 and 5 mol/L HCl. Likewise, the transport experiment was achieved with Co(II) in 5 mol/L HCl as feed solution and 2 mol/L H₂SO₄, which exhibited excellent performance with a recovery factor of more than 85 %. The effect of various parameters on the efficiency of Co(II) sorption and transport was examined systematically. The kinetic and thermodynamic studies revealed that Co(II) sorption onto PIM was chemisorption in nature. Interestingly, the adsorption mechanism of Co(II) was found to be dependent upon the HCl concentration, resulting in two different mode of sorption mechanisms. Moreover, Co(II) desorption (>95 %) was achieved effectively, using 2 mol/L H₂SO₄. The recycling experiments suggested that PIM could be reused effectively without significant performance loss after six consecutive sorption-stripping cycles. Therefore, the reported PIM holds a good potential as a sorbent of critical metals, such as cobalt, due to its cost-effectiveness, excellent performance in batch-sorption and continuous transport processes, as well as good regeneration properties. To the best of our knowledge, this is the first report on Co(II) transport, employing a membrane transport system with a novel phosphonium-based ionic liquid.