Preparation and characterization of sulfated nanocellulose: From hydrogels to highly transparent films

This study focuses on the production of sulfated cellulose microfibers and nanocellulose hydrogels from native cellulose microfibers (CMF). The process involves using a combination of H2SO4 and urea, resulting in highly sulfated cellulose microfiber hydrogel (SC) with notable properties such as a sulfur content of 7.5 %, a degree of sulfation of 0.49, a surface charge content of 2.2 mmol. g-1, and a high yield of 81 %. The SC hydrogel can be easily fibrillated into sulfated nanocellulose hydrogel (S-NC) with elongated nanocellulose structures having an average diameter of 6.85 ± 3.11 nm, as determined using atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) analysis confirms the presence of sulfate groups on the surface of the nanocellulose material. Transparent films with good mechanical properties can be produced from both cellulose microfiber and nanocellulose hydrogels. The sulfate functionality gives the hydrogel attractive rheological properties and makes S-NC re-dispersible in water, which can be beneficial for various applications. This study demonstrates the potential of this process to address previous challenges related to nanocellulose materials production.

Removal of copper and iron from ethanolic solutions by an anion exchange resin and its implication to rare-earth magnet recycling

In the recycling of end-of-life rare-earth magnets, the recovery of non-rare earth constituents is often neglected. In the present study, strong cation and anion exchange resins were tested batchwise for the recovery of the non-rare-earth constituents of permanent magnets (copper, cobalt, manganese, nickel and iron) from synthetic aqueous and ethanolic solutions. The cation exchange resin recovered most of metal ions from aqueous and ethanolic feeds, whereas the anion exchange resin could selectively recover copper and iron from ethanolic feeds. The highest uptake of iron and copper was found for 80 vol% and 95 vol% multi-element ethanolic feeds, respectively. A similar trend in selectivity of the anion resin was observed in breakthrough curve studies. Batch experiments, UV-Vis, FT-IR and XPS studies were performed to elucidate the ion exchange mechanism. The studies indicate that the formation of chloro complexes of copper and their exchange by the (hydrogen) sulfate counter ions of the resin have an important role in the selective uptake of copper from the 95 vol% ethanolic feed. Iron(II) was largely oxidized to iron(III) in ethanolic solutions and was expected to be recovered by the resin in the form of iron(II) and iron(III) complexes. The moisture content of the resin did not have a significant role on the selectivity for copper and iron.