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.

Green separation of lanthanum, cerium and nickel from waste nickel metal hydride battery.

In a circular economy context, there is a growing need for more sustainable waste management options to recover elements from end-of-life materials. These "secondary ores" represent a source of critical elements that are often present in higher concentration compared to their primary ore. In this work, the recovery of lanthanum (La) from waste nickel metal hydride battery (NiMH) leachate is investigated using an aqueous biphasic system (ABS) process based on a pluronic triblock copolymer (L35). An initial screening is performed to determine the influence of the ABS phase forming salt anion and alizarin red extractant on the La extraction efficiency and selectivity. From these results, a three-step ABS process is developed, varying only the nature of the salt and requiring no additional extractant. In a first step, the ABS composed of L35 + thiocyanate ammoniun + H2O efficiently extracts iron, manganese, and cobalt leaving La, cerium, and Ni in solution. Nickel is subsequently recovered by precipitation using dimethylglyoxime. Finally, La is separated from cerium using the L35 + ammonium nitrate + H2O ABS, recovering 62 g of La with 94% purity per kilogram of black mass of NiMH battery. This work highlights the applicability of ABS for the treatment of raw and complex matrices, potentially allowing for a greener hydrometallurgical treatment of wastes.

Integrated Leaching and Separation of Metals Using Mixtures of Organic Acids and Ionic Liquids.

In this work, the aqueous phase diagram for the mixture of the hydrophilic tributyltetradecyl phosphonium ([P44414]Cl) ionic liquid with acetic acid (CH3COOH) is determined, and the temperature dependency of the biphasic region established. Molecular dynamic simulations of the [P44414]Cl + CH3COOH + H2O system indicate that the occurrence of a closed "type 0" biphasic regime is due to a "washing-out" phenomenon upon addition of water, resulting in solvophobic segregation of the [P44414]Cl. The solubility of various metal oxides in the anhydrous [P44414]Cl + CH3COOH system was determined, with the system presenting a good selectivity for CoO. Integration of the separation step was demonstrated through the addition of water, yielding a biphasic regime. Finally, the [P44414]Cl + CH3COOH system was applied to the treatment of real waste, NiMH battery black mass, being shown that it allows an efficient separation of Co(II) from Ni(II), Fe(III) and the lanthanides in a single leaching and separation step.