Crosslinked alginate/sericin particles for bioadsorption of ytterbium: Equilibrium, thermodynamic and regeneration studies

Sericin is a soluble globular protein, present in Bombyx mori silkworm cocoons. Sericin's properties can be improved to expand its application by producing blends with other substances, such as alginate polysaccharide and crosslinking agent poly(vinyl alcohol). This study evaluates the use of alginate and sericin particles chemically crosslinked with poly(vinyl alcohol) (SAPVA) for batch bioadsorption of rare-earth element ytterbium from aqueous medium. The equilibrium study showed that the maximum bioadsorption capacity for ytterbium was 0.642 mmol/g at 55 °C. Equilibrium data fit both Langmuir and Dubinin-Radushkevich models. The estimation of thermodynamic parameters showed that there was an increase in the entropy change, and that the bioadsorption process is endothermic and spontaneous. Characterization analyzes revealed that SAPVA particles, even after ytterbium bioadsorption, showed spherical shape, homogeneous composition, amorphous structure, low surface area, macropores, and low porosity. After the first regeneration cycle, the amount of captured ytterbium ions showed a slight increase (about 0.01 mmol/g) and calcium ions were completely released by SAPVA particles. Bioadsorbent particles separated selectively ytterbium from synthetic effluent containing different toxic metal ions. These results show that the SAPVA particles can be used as an effective bioabsorbent to remove and recover ytterbium from wastewater.