Adsorptive recovery of rare earth elements from aqueous solution by citric acid crosslinked carboxymethylated cellulose nanofibril aerogel

Rare earth elements (REEs) have become crucial resources in the electric vehicle industry; however, their recycling remains challenging. In this study, we developed a carboxymethylated cellulose nanofibril aerogel crosslinked with citric acid (CMCNF-CA aerogel) through thermal treatment and employed it as an adsorbent for REE recovery. The CMCNF-CA aerogel possesses a substantial amount of free -COOH groups, resulting in a strong negative charge. This unique characteristic enables the aerogel to exhibit excellent adsorption capacities of 200 mg/g for lanthanum(La3+) and 170 mg/g for cerium(Ce3+). The findings from FTIR and XPS analyses provide insights into the adsorption mechanism. It is revealed that hydroxo-complexes, such as La-(OH)x and Ce-(OH)x, are adsorbed onto the CMCNF-CA aerogel through strong electrostatic interactions with the -COOH groups. This leads to the formation of metal ionic crosslinking. Remarkably, the CMCNF-CA aerogel maintains its high adsorption performance even after undergoing five consecutive adsorption-desorption cycles. Based on these results, we demonstrate that the CMCNF-CA aerogel is an efficient and reusable adsorbent for the sustainable recovery of La3+ and Ce3+ from aqueous solutions. This study offers promising prospects for addressing the challenges in the recycling of REEs, highlighting the potential of the CMCNF-CA aerogel as a practical solution in the field of REE recovery.