Biosorption of fluoride from aqueous phase onto Padina sanctae crucis algae: evaluation of biosorption kinetics and isotherms

Biosorption is considered as one of the favorable treatment technologies for fluoride removal from aqueous solutions. The present study is the first attempt to evaluate the biosorption capability of the Padina sanctae crucis algae in removal of fluoride from aqueous phase. Biosorption was studied in a series of batch experiments at room temperature (25 +/- 1 degrees C). The effects of experimental parameters such as biosorbent dose (0.8-64 g/L), contact time (5-120 min), pH (3, 7, and 11), initial fluoride concentration (2-8 mg/L), and the presence of competing anions (bicarbonate, nitrate, carbonate, sulfate, and chloride) were investigated. The highest removal biosorption was observed at 48 g/L biosorbent dose, 5 min contact time, and initial fluoride concentration at 8 mg/L (97% fluoride removal). Competing anions had no significant effect on the fluoride biosorption by the biosorbent. Freundlich model was better fitted than Langmuir model that showed heterogeneous biosorption surface and the possibility of multilayer biosorption of fluoride by biosorbent. The biosorption kinetics was controlled by the pseudo-second-order and pore diffusion models. It was concluded that the Padina sanctae crucis algae can be used as an effective, low-cost, and environmental friendly biosorbent for fluoride removal from aqueous solutions.