The marine macroalga Cystoseira baccata as biosorbent for cadmium(II) and lead(II) removal: Kinetic and equilibrium studies

This work reports kinetic and equilibrium studies of cadmium(II) and lead(II) adsorption by the brown seaweed Cystoseira baccata. Kinetic experiments demonstrated rapid metal uptake. Kinetic data were satisfactorily described by a pseudo-second order chemical sorption process. Temperature change from 15 to 45 °C showed small variation on kinetic parameters. Langmuir–Freundlich equation was selected to describe the metal isotherms and the proton binding in acid–base titrations. The maximum metal uptake values were around 0.9 mmol g−1 (101 and 186 mg g−1 for cadmium(II) and lead(II), respectively) at pH 4.5 (raw biomass), while the number of weak acid groups were 2.2 mmol g−1 and their proton binding constant, KH, 103.67 (protonated biomass). FTIR analysis confirmed the participation of carboxyl groups in metal uptake. The metal sorption was found to increase with the solution pH reaching a plateau above pH 4. Calcium and sodium nitrate salts in solution were found to affect considerably the metal biosorption.