Cadmium biosorption by alginate extraction waste and process overview in Life Cycle Assessment context

This work evaluated the cadmium biosorption capacity by the alginate extraction residue from brown seaweed Sargassum filipendula, an industry waste which is often discharged into the sea. The biosorption kinetics and equilibrium were investigated, with further analysis of the process thermodynamics. The Mass Transfer in External Film model best described the kinetic data and the rate controlling step is the diffusion through the boundary layer. The kinetic constant values of the model were 0.129, 0.064 and 0.066 1/min for initial concentrations of 1.0, 1.5 and 2.0 mmoL/L, respectively. The isotherms were obtained at four temperatures (293, 303, 313 and 323 K) and were analyzed by Langmuir, Freundlich and Dubinin-Radushkevich models. The system was better described by Freundlich model, and the Dubinin-Radushkevich model suggested that the cadmium uptake is of physical nature. The maximum biosorption capacity obtained at 293 and 303 K were 0.394 and 0.429 mmoL/g, respectively. The thermodynamic parameters indicated that the biosorption of cadmium is spontaneous and exothermic. The simplified LCA showed that the use of dealginated residue would lead to lower environmental impacts for Acidification, Climate Change, Eutrophication, Human Toxicity and Photochemical Oxidation.