The Caribbean has seen the influx of Sargassum, affecting the livelihood of communities. Sodium alginate extracted from Sargassum is known for its cross-linking properties, making the seaweed attractive as an adsorbent. Hence, the use of calcium alginate thin films can decrease the mass transfer resistance found in commonly used alginate beads, resulting in increased adsorption efficiency. This Article discusses the potential of calcium alginate thin films for Pb2+, Cu2+, and Cd2+ ion adsorption. Pb2+, Cu2+, and Cd2+ adsorption fitted the Langmuir isotherm well with capacities of 0.80, 0.10, and 0.02 mmol of metal/g, respectively, for Sargassum. Kinetic studies showed that the ions followed the pseudo-second-order model, elucidating that ion exchange governed adsorption. Furthermore, NMR characterization showed that G-block monomers influenced kinetic parameters and selectivity in the following order: Pb2+ > Cu2+ > Cd2+