Phenol, 2-chlorophenol (2-CP), and 4-chlorophenol (4-CP) biosorption on Sargassum muticum, an invasive macroalga in Europe, has been investigated. The efficiency of this biosorbent was studied measuring the equilibrium uptake using the batch technique. A chemical pre-treatment with CaCl 2 has been employed in this study in order to improve the stability as well as the sorption capacity of the algal biomass. The influence of pH on the equilibrium binding and the effect of the algal dose were evaluated. The experimental data at pH = 1 have been analysed using Langmuir and Freundlich isotherms. It was found that the maximum sorption capacity of chlorophenols, q max = 251 mg g −1 for 4-CP and q max = 79 mg g −1 for 2-CP, as well as that of a binary mixture of both chlorophenols, q max = 108 mg g −1 , is much higher than that of phenol, q max = 4.6 mg g −1 . Moreover, sorption kinetics have been performed and it was observed that the equilibrium was reached in less than 10 h. Kinetic data have been fitted to the first order Lagergren model, from which the rate constant and the sorption capacity were determined. Finally, biosorption of the phenolic compounds examined in the present study on Sargassum muticum biomass was observed to be correlated with the octanol-water partitioning coefficients of the phenols. This result allows us to postulate that hydrophobic interactions are the main responsible for the sorption equilibrium binding.

Methylene Blue adsorption on Sargassum muticum, an invasive macroalga in Europe, has been investigated using visible absorption spectroscopy. Different pre-treatments, protonation and chemical cross-linking with CaCl 2 or H 2 CO, have been tested in order to improve the stability as well as the adsorption capacity of the algal biomass. The equilibrium binding has been described in terms of Langmuir or Freundlich isotherms depending on the algal pre-treatment; from the maximum adsorption capacity values, an estimation of the algal specific surface area was made. Moreover, it has been found that adsorption kinetics can be described according to the first order Lagergren model, from which the rate constant and the adsorption capacity were determined. Finally, simple empirical equations were obtained to evaluate the amount of Methylene Blue removed at any initial concentration and reaction time. The results obtained have shown that this type of material has a high adsorption capacity for Methylene Blue dye, this feature together with the short times needed to reach the equilibrium suggest that Sargassum muticum can be used as a low-cost biosorbent in wastewater treatments.

Sargassum muticum biomass was chemically modified to test its sorption capacity toward a model organic cation: methylene blue. Two different classes of treatments, specifically the esterification of the carboxylic acids and the extraction of the lipid fraction, have been applied. Chemical modification of the biomass increases the sorption capacity, especially if the lipid fraction is removed from the algae. The maximum dye uptake was obtained for biomass obtained after the extraction of the lipid fraction by means of acetone under reflux treatment, with a q e value of 860 mg • g -1 from the Langmuir isotherm. Maximum uptakes were found in the pH range of 4 to 10. The equilibrium was achieved in (30 to 60) min, depending on the algal pretreatment. The pseudo-first-order empirical model can describe the process as a whole. Plots of the sorption capacity q t versus the square root of time, at the initial stages of the sorption process, fit the intraparticle diffusion equation, so an intraparticle diffusion coefficient of 5.46 • 10 -8 cm 2 • s -1 is obtained for methylene blue in chemically modified S. muticum. Specific surface areas of the involved biomaterials are calculated from maximum uptakes at equilibrium and critically analyzed.

A kinetic and equilibrium study of the addition reaction of hydroxide ions to nitroprusside has been carried out in this paper. Rate and equilibrium constants at different salt concentrations (up to 4 mol kg −1 ) were obtained, and the influence of ionic strength was studied by means of Pitzer equations. This model is of special interest because it is able to explain the experimental behavior at high ionic strength, when Debye-Huckel limiting law is no longer valid. C