A New Class of Extractants for Cobalt-Manganese Separation: Synthesis and Physicochemical Properties of α-Hydroxyphosphinic Mono Esters
Résumé
The efficient separation of cobalt(II) and manganese(II) is a major challenge in the recycling of spent lithium-ion batteries and in the processing of resources like laterite ores or sea nodules. Conventional extractants, such as D2EHPA (di(2-ethylhexyl)phosphoric acid) and Cyanex®272 (Bis(2,4,4-trimethylpentyl)phosphinic acid), are limited by their selectivity and efficiency, particularly under acidic pH conditions. To address this, a novel class of extractants was synthesized in a cost-effective, two-step process that requires no purification, and these were then evaluated for the selective liquid-liquid extraction of Co(II), Mn(II), Ni(II), and Li(I) from both acidic sulfate and chloride solutions. Among the twenty derivatives prepared, the α-hydroxyphosphinic mono esters (specifically compounds 2a and 2b) proved to be the most promising. These molecules showed high affinity for manganese(II) extraction, achieving selective recovery while keeping the co-extraction of Co (II), Ni(II), and Li(I) to a minimum. The extraction performance was systematically investigated by studying the influence of pH, extractant concentration, and organic-to-aqueous phase volume ratio (O/ A). Furthermore, the efficiency of stripping Mn(II) was optimized. This research significantly contributes to developing a more simplified and efficient hydrometallurgical flowsheet for cobalt-manganese separation in applications such as battery recycling.
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