Nickel biosorption using Gracilaria caudata and Sargassum muticum

Two seaweeds (Sargassum muticum, S.m. and Gracilaria caudata, G.c.) collected on the coasts of Cuba have been tested and compared for nickel biosorption. The metal was efficiently bound to the biomass at pH 3 for S.m. and pH 5 for G.c. Sorption isotherms, at the optimum pH, showed that S.m. is more efficient than G.c.: maximum sorption capacity reached about 70 mg Ni g−1 and 45 mg Ni g−1 for S.m. and G.c., respectively. The isotherms were modeled using the Langmuir equation (which fits better experimental data than the Freundlich and Temkin equations). Sorption kinetics were also carried out varying metal concentration, sorbent dosage particle size and temperature. The kinetics were modeled using the pseudo-second order rate equation and the intraparticle diffusion equation.