Smart Sorption: Novel Applications of Cellulosic Nanomaterials for Selective Critical Metal Recovery from Black Mass Leachates Through Multibatch Processes

Selective critical metal recovery from black mass leachates (BML) is a great challenge for the Li-ion batteries recycling sector. This paper shows the potential of nanocellulose products as green adsorbents for a selective recovery of critical metals through multibatch sorption processes. Cellulose nanocrystals (CNCs) and cellulose nanofibers (CNFs) of 0.4 and 1.5 meq/g cationic demand, respectively, have been produced and used as biosorbents. Metal leaching from non-pyrolyzed black mass with HCl presented the highest critical metal extraction yield, obtaining up to 10 g/L of Co and more than 1 g/L of Cu, Mn and Ni. The adsorbents were tested under different dosages and pH conditions for the treatment of both synthetic multimetal solution (MMS), with Mn, Cu, Co, and Ni, and real BML, through a multiple step batch treatment to increase the selectivity towards each critical metal. For MMS treatments, the lowest pH (1-2) conditions are favorable for Co separation, reaching 135 g/g, while higher pH values (4-5) are better to recover Cu and Ni. Selectivity indexes between metals could reached values above 40 for the optimal conditions. For the treatment of BML, pH around 3 enhanced the selectivity of Al and pH of 5 of the Li. In this case, metal recoveries were higher than 30 g/g. When CNCs were used, more than 4 g/g of Co was adsorbed, recovering more than 99 % of the Co present in the waste. 99 % of Co purity was obtained at the optimal Co selective recovery conditions. Although the studied critical metals were strongly sorbed onto the nanocelluloses, a solution with a concentration of 2.5-5 g/L of these metals could be extracted from desorption tests.