On the binding affinity and thermodynamics of sodium alginate-heavy metal ion interactions for efficient adsorption

Alginate is a versatile polymer with gelling properties facilitating many applications, such as adsorption. To promote efficient adsorption, guidance is needed on the reactivity and coordination of the alginate-metal binding process. This study presents a novel approach utilizing Isothermal Titration Calorimetry (ITC) to elucidate the interaction between Pb 2+, Cu 2+, and Cd 2+ ions; and alginates of various monomeric compositions. A 2-step binding process was observed during gelation, with the first driving the gelation process at low temperatures. Furthermore, Pb 2+ and Cu 2+ binding parameters were enhanced over lower Cd 2+ affinity with decreasing M:G ratios. Our results support these findings, showing high removal rates for Pb 2+ and Cu 2+ of 85 and 65% respectively at low M:G ratios and low molecular weight and 75% for Cd 2+ at high M:G ratios. Thus, alginate monomeric composition plays an integral role in the binding process and should be considered for efficient adsorption.