On the Performance of Sargassum derived Calcium Alginate Ion Exchange Resins for Pb2+ Adsorption: Batch and Packed Bed Applications

Abstract

Driven by climate change and human activity, Sargassum blooming rates have intensified, producing copious amount of the invasive, pelagic seaweed across the Caribbean and Latin America. Our study details a comprehensive investigation into the use of Sargassum (S. natans), as a potential resource-circular feedstock for the synthesis of calcium alginate beads utilized in heavy metal adsorption, both in batch and column experiments. Given the low quality of alginates extracted from Sargassum which produce poor morphological beads, composite beads in conjunction with graphene oxide and acrylamide were used to improve fabrication. Results from batch experiments showed that compared to composite as well as commercial resins (Amberlite), stand-alone calcium alginate beads outperformed all other adsorbents, with an adsorption capacity of 2123 mg Pb2+ g− 1 tested at 20°C and a pH of 3.5. Furthermore, its performance was within the range for other seaweed and polysaccharide based adsorbents, thus indicating its efficacy as a bio-based alternative to synthetic resins. For composite alginate resins, incorporation of additives such as acrylamide and graphene oxide, resulted in a 21–40% reduction in Pb2+ adsorption – with characterisation revealing a reduction in active sites as the main indicator to inferior performance. Analysis of column operations confirms the practicality of Alginate systems over commercial counterparts, with 20–24% longer operating times, 15 times lower adsorbent mass on scale up and 206% smaller column diameters. Ultimately, our results provide evidence supporting the use of Sargassum as a resource-circular feedstock for the fabrication of Alginate ion-exchange beads, with superior heavy metal adsorption performance.