Recovery of critical raw materials using functional nanocelluloses with high adsorption capacity

The utilization of critical raw materials such as cobalt (Co), antimony (Sb), tungsten (W), and germanium (Ge) is essential in the modern technology industry. However, the supply chain of these materials has been prone to instability due to geopolitical factors, resulting in price volatility and potential supply disruption. In this regard, the development of sustainable and effective methods for the removal of critical raw materials from waste streams such as mining waste is of utmost importance.
Nanocellulose-based materials have been shown to have high adsorption capacity and selectivity for various metal ions, making them promising candidates for the removal of critical raw materials from wastewater. Furthermore, cellulose nanofiber (CNF) is an abundant and renewable resource, which makes it an attractive alternative to conventional adsorbents that rely on non-renewable resources. However, little is known regarding the adsorption capacity of CNFs specifically in Co, Sb, W and Ge. This study aimed to develop various chemically modified nanocelluloses and to determine the potential removal rate of the metal ions.
Six different CNFs were prepared in the study including Native CNF which was produced from hardwood kraft pulp with mechanical treatments and carboxymethylated CNF. In addition, TEMPO-oxidized CNF and further modified the TEMPO CNFs with allylamine, 1,5-diamino-2-methylpentane, or N-methylglucamine by esterification followed by amidation. Chemical characterization of the CNFs was conducted by 1H NMR and SEM-EDX. Adsorption experiments were carried out by contacting metal solutions with a constant amount of dry CNFs under agitation at room temperature. The pH was controlled using standardized solutions, and the adsorbent material was removed after 24 hours. Metal concentration in the aqueous phase was determined by ICP-MS or ICP-AES.
The results showed that some of the CNFs had a high adsorption capacity on either Co (II), Sb (III) or Sb (V), suggesting that nanocellulose-based adsorbents could selectively remove critical raw materials from wastewater. The study also demonstrated their potential as sustainable solutions for critical raw material recovery. Other aspects of nanocellulose materials for metal recovery are also discussed. This work was done as a part of RAWMINA project which has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 958252.