10The Caribbean has seen the influx of Sargassum, affecting the livelihood of communities. Sodium 11 alginate extracted from Sargassum is known for its cross-linking properties, making the seaweed 12 attractive as an adsorbent. Hence, the use of calcium alginate thin films can decrease the mass 13 transfer resistance found in commonly used alginate beads, resulting in increased adsorption 14 efficiency. This article discusses the adsorption potential of calcium alginate thin films for Pb 2+ , 15 Cu 2+ and Cd 2+ adsorption. Pb 2+ , Cu 2+ and Cd 2+ adsorption fitted the Langmuir isotherm well with 16 capacities of 0.80, 0.10 and 0.02 mmol of metal/g of beads respectively for Sargassum. Kinetic 17 studies showed that the ions followed the pseudo-second-order model, elucidating that ion 18 exchange governed adsorption. Furthermore, NMR characterization showed that G-block 19 monomers influenced kinetic parameters and selectivity in the order: Pb 2+ > Cu 2+ > Cd 2+ . 20 Keywords 21Calcium alginate; Thin film; Biosorption; Heavy metal ions; M:G ratio, Sargassum natans 22 chemical precipitation, 6 ion exchange, 7 adsorption, cementation and electrolysis. 8 These methods 33 often involve chemicals, which may be energy intensive processes and in some cases, ineffective 34 at high concentrations. 9, 10 The use of biomass as a potential adsorbent for the removal of these 35 heavy metal ions could serves as an inexpensive and effective means of water treatment. 11 36 Alginate, which can be extracted from the walls of brown seaweed, is a natural linear 37 polysaccharide copolymer. It consists of two uronic acids; β-D-mannuronic acid (M) and α-L-38 guluronic acid (G). 12 The presence of these blocks in various ratios and molecular weight alters 39 the physiochemical properties. The alginates that are rich in L-guluronate form strong but brittle 40 gels and those rich in D-mannuronate are weaker but more flexible. 13 These physiochemical 41 properties vary depending on the type of seaweed and the geographical location. Sargassum natans 42 (S.natans) is an invasive brown seaweed which has besieged Caribbean coastlines. S.natans has 43 negatively impacted marine ecosystems resulting in a decrease in economic activities such as 44 tourism and fishing. 14 Due to its abundance and invasive nature, there is an urgent need for its 45 3 utilization as a possible beneficial raw material. Commercial alginates are usually extracted from 46 brown seaweed such as kelps or Laminariales. These alginophytes are usually cultivated for the 47 °C for 2 h until a thin sodium alginate film (<100 µm in thickness) was formed. The thin sodium 108 alginate film was then cooled to room temperature prior to immersing into 3L of 7% (w/v) CaCl2 109 bath for 15 min. The calcium alginate film was then washed with deionized water, cut into discs 110 of 3.5 cm in diameter using a surgical scalpel and fixed onto Whatman Filter paper (Grade 1) as a 111 support for subsequent use. 112 113 336 3. Satarug, S.; Garrett, S. H.; Sens, M. A.; Sens, D. A. Cadmium, ...