Synthesis and application of plasticized polymer membranes containing Aliquat 336 and D2EHPA as carriers for efficient cobalt ion separation: a sustainable approach for metal resource recovery

The research on cobalt ion extraction using Plasticized Polymer Membranes (PPMs) is pivotal as it introduces an innovative single-step separation process. The aim of this study is to synthesize novel cellulose triacetate (CTA)-based polymer membranes with specific percentages of 2-Nitrophenyl pentyl ether (2NPPE) and two types of carriers (di-(2-ethylhexyl) phosphoric acid (D2EHPA)/methyl trioctylammonium chloride (Aliquat336) to transport and separate Co(II) ions under particular conditions. Plasticized Polymer Membranes characterization using scanning electron microscopy (SEM) and attenuated total reflectance–Fourier-transform infrared spectroscopy (FTIR-ATR) revealed that the introduction of the plasticizer resulted in a dense and smooth membrane structure, with pores filled by plasticizer molecules. This led to a thick membrane, indicating uniformity and strong adhesion among the polymer matrix, carrier, and plasticizer. Various crucial transport parameters, including carrier type, source phase pH, receiving phase type, and the plasticizer amount, were systematically discussed. The CTA/30% D2EHPA membrane yields the highest percentage of cobalt (II) cations extractions (66%) compared to the (CTA)/30% Aliquat 336 (45%). By adding the plasticizer, the prepared membranes demonstrated a high extraction efficiency of over 85% after just 24 h. Furthermore, the prepared PPMs exhibit remarkable stability: the percentage of extraction remains nearly constant after 384 h (8 successive cycles). Then, successful separations of cobalt (II) and nickel (II) were thoroughly investigated. The obtained results revealed that the selection of the appropriate receiving phase has a significant impact for efficient cobalt ions separation. This research presents methodological advancements in the realm of (PPMs), thereby enabling the implementation of more sustainable approaches in cobalt (II) recovery, consequently fortifying the resilience of the critical materials supply chain.