Valorization of Agar extraction residues from the red algae Gelidium sesquipedale as biosorbents for organic and inorganic pollutants

The aim of this research is to study the adsorption capacity of methylene blue and methyl orange by Gelidium sesquipedale (GS), Gelidium sesquipedale residues (GSR) and an equal mixture of algae residues and diatomaceous earth (GRD). To this end, we have carried out a physico-chemical and structural characterization of the three samples (GS, GSR and GRD). Gelidium sesquipedale and its residues are rich in lignin (33.22% and 28.60%, respectively) and cellulose (20.29% and 13.31%, respectively). X-ray fluorescence analysis has showed that the mixture of algae residues and diatomaceous earth is rich in silica (72.23%). The equilibrium adsorption capacity of GSR is comparable to that of GS, both higher than GRD, with rapid retention for methylene blue. Methylene blue adsorption follows the Freundlich model. It is described by the pseudo-second-order kinetic model and is minimally influenced by pH variations. These biomaterials have showed potential for various wastewater treatment applications.