Background and purpose: Adsorption is considered as one of the promising treatment methods for removal of heavy metals from aqueous solutions. The aim of this study was to determine the efficiency of Padina sanctae crucis in removal of manganese (Mn) from aqueous solutions.

Materials and methods: Biosorption was studied in a series of batch experiments at room temperature and the effects of experimental parameters such as biosorbent dose (0.1-10 g/L), contact time (3–120 min), pH (3, 5, 7, 8) and initial Mn concentration (0.5–100 mg/L) were studied.

Results: The highest removal biosorption of Mn was reached at 5 g/L biosorbent dose, 20 min contact time, and 20 mg/L initial Mn concentration (100% removal). Langmuir model was better fitted than Freundlich model that showed homogeneous biosorption surface and the possibility of monolayer biosorption of Mn by biosorbent. The biosorption kinetics was controlled by the pseudo-second order.

Conclusion: According to the results, Padina sanctae crucis could be used as an effective and low-cost biosorbent for Mn removal from aqueous solutions.