A HNO3 -Responsive Aqueous Biphasic System for Metal Separation: Application towards CeIV Recovery.

An acidic aqueous biphasic system (AcABS) presenting a desired and reversible phase transition with HNO3 concentration and temperature was developed herein as an integrated platform for metal separation. The simple, economical, and fully incinerable (C,H,O,N) AcABS composed of tetrabutylammonium nitrate ([N4444 ][NO3 ])+HNO3 +H2 O was characterized and presented an excellent selectivity towards CeIV against other rare earth elements and transition metals from both synthetic solutions and nickel metal hydride (NiMH) battery leachates. The acid-driven self-assembly of AcABS bridges the gap between traditional ABS and liquid-liquid extraction whilst retaining their advantageous qualities, including compatibility with highly acidic solutions, water as the primary system component, the avoidance of organic diluents, rapid mass transfer, and the potential integration of the leaching and separation steps.