Recovery of dysprosium by biosorption onto a biocomposite from sericin and alginate

Dysprosium is a critical rare-earth metal used in high-tech industry. Its recovery from secondary sources is fundamental in the context of circular economy. The use of polymer-based biosorbents is promising for this purpose. In this work, we employ a biocomposite produced from waste protein from silk yarns processing, sodium alginate, and polyvinyl alcohol for dysprosium recovery by batch biosorption in aqueous medium. The pH range between 4.5 and 5.0 for dysprosium biosorption and calcium release by biosorbent beads was defined by chemical equilibrium diagrams. Kinetics assays indicated that the equilibrium times and dysprosium biosorbed amounts at equilibrium were 120 to 390 min and 0.048 to 0.139 mmol/g, respectively. Kinetic data followed the pseudo-first order model and were governed by external diffusion resistance. The kinetics profiles also indicated that the cationic exchange between dysprosium and calcium was stoichiometric. Additionally, calcium nitrate/ nitric acid (0.1 mol/L) was selected for the reuse cyclic assays, due to the higher elution efficiency of dysprosium achieved. Beads reusability and dysprosium recovery were performed for up to four reuse cycles and achieved biosorption and desorption efficiencies above 94 and 98%, respectively. The characterizations of beads loaded with Dy(III) indicated that biosorbent maintained its macroporous structure, low porosity and specific surface area, lower thermal resistance, and amorphous structure. Finally, cationic exchange mechanism was confirmed by techniques of energy-dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. Therefore, the use of crosslinked sericin/alginate beads is the first step towards achieving a sustainable valorization of sericin and recovery of high added value metals.

Automated summary

Dysprosium, a critical rare-earth metal in high-tech industry, was successfully recovered using a biocomposite made from waste protein, sodium alginate, and polyvinyl alcohol. The biosorbent demonstrated high efficiency in dysprosium recovery and excellent reusability.