The Impact of Alginate Physiochemical Properties on the Adsorption Performance and Reusability of Calcium Alginate Beads.

The establishment of a rigorous formulation methodology considering physiochemical properties of alginate systems has been widely overlooked within current biosorption research utilizing calcium alginate beads. Here, we present for the first time, the effects of molecular weight and viscosity on bead sphericity and its impacts on adsorption and regeneration efficiency using different calcium alginate sorbents. Findings show an increase in molecular weight (MW) results in increased viscosifying properties, which correlates closely to sphericity of the alginate bead. The relationship between sphericity and concentration followed a 2^nd order polynomial, where maximum sphericity was maintained over an ideal concentration range of 2-6% (w/v) for respective brands of sodium alginate (MW 300-670 kDa). This increase in sphericity resulted in adsorption enhancement; 1-15%, 81-93% and 88-95% for Pb²⁺, Cu²⁺ and Cd²⁺ respectively over non-spherical counterparts. Furthermore, compared to a commercial resin (Amberlite), the beads showed similar adsorption performance for Pb²⁺ with reductions of up to 40% and 70% observed for Cu²⁺ and Cd²⁺ respectively. This decline was attributed to the opposing affinity of the resin (Cd>Cu>Pb), whereas the alginate beads had an affinity following Pb>Cu>Cd. These results aligned well with the findings for sorbent regeneration, with subsequent adsorption efficiency largely decreasing (>20% reduction), ascribed by the alginate mass loss due to chemical and mechanical instability. Thus, future work is needed to further optimize the formulation methodology to promote greater adsorption and regeneration considering key performance indicators established in this study.