A cobalt-based forward osmosis draw solute synthesized from lithium-ion battery wastes for cobalt-containing wastewater purification

The demand to remove Co2+ ions from industrial wastewater is escalated due to the rapid growth of lithium-ion batteries (LIB) as power storage in personal electronic devices. Herein we report a novel cobalt-based draw solute, Co-Bet-Tf2N, synthesized from lithium-ion battery (LIB) wastes, in a forward osmosis (FO) process to purify Co2+-containing wastewater discharged from the LIB industry. Co-Bet-Tf2N possesses abundant –NMe3+ groups and releases multiple ionic species in water, allowing it to produce a high osmotic pressure to drive FO separation efficiently; meanwhile its three-dimensional structure prevents the reverse Co-Bet-Tf2N diffusion in FO experiments. Consequently, a dilute Co-Bet-Tf2N solution (0.2 mol/L) generates a water flux as high as 14.7 LMH along with a negligible solute loss (< 0.02 g/L), outperforming other reported draw solutes. Moreover, Co-Bet-Tf2N extracts water from the Co2+-containing wastewater more efficiently with a water flux 232 % and 174 % higher than those of the conventional NaCl and MgCl2 draw solutes, respectively. Particularly, Co-Bet-Tf2N is easily regenerated via the [Hbet][Tf2N]-based extraction without energy input, thus more practical than the recycling of other draw solutes reported elsewhere. This study not only demonstrates the superiority of Co-Bet-Tf2N as a novel draw solute, but achieves effective waste reuse and wastewater reclamation.