Selective separation of manganese, cobalt, and nickel in a fully aqueous system

Abstract

The continued electrification of society and the related growing demand for rechargeable batteries require in turn the elaboration of efficient and sustainable recycling strategies for their recovery and valorization. An important separation relevant to nickel metal hydride (NiMH) and lithium-ion battery recycling is the intertransition element separation between Ni(II), Co(II), and Mn(II). In this work, a fully aqueous process for the recovery of Mn(II) and Co(II) from concentrated Ni(II) effluents typical of NiMH battery leachate is disclosed consuming only Na2CO3. In the first instance, Mn is selectively precipitated as Mn(IV) by oxidation using ozone as an oxidant, resulting in a significant enrichment of Mn in the precipitate relative to its original solution concentration. Second, a thermo- and acid-responsive aqueous biphasic system (ABS) based on the ionic liquid (IL) tributyltetradecylphosphonium chloride ([P44414]Cl) and NiCl2 was used to recover Co(II). By using the high NiCl2 content found in NiMH leachates both as the ABS phase former and salting-out agent, no additional salt is required. Through careful manipulation of the Co(II) to Ni(II) and the IL to Co(II) molar ratios, an effective and selective separation of Co(II) from Ni(II) was achieved. Finally, Co(II) is precipitated from the IL-rich phase and the IL is regenerated in one step by the addition of Na2CO3 to induce a new phase separation.