Acid-base properties of brown seaweed biomass considered as a Donnan gel. A model reflecting electrostatic effects and chemical heterogeneity
Issue date
2003Suggested citation
Rey Castro, Carlos;
Lodeiro, Pablo;
Herrero, Roberto;
Sastre de Vicente, Manuel E.;
.
(2003)
.
Acid-base properties of brown seaweed biomass considered as a Donnan gel. A model reflecting electrostatic effects and chemical heterogeneity.
Environmental Science and Technology, 2003, vol. 37, núm. 22, p. 5159-5167.
https://doi.org/10.1021/es0343353.
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Show full item recordAbstract
Brown seaweeds are interesting materials to be used as
biosorbents for heavy metals due to their high binding ability
and low cost. The study of the passive biosorption of
protons on this kind of materials and its dependency on
pH, ionic strength, and medium composition is essential for
the practical application of brown algae in wastewater
treatment. This work reports the results of the study of the
proton binding equilibria of dead biomass from the
seaweeds Sargassum muticum, Cystoseira baccata, and
Saccorhiza polyschides by potentiometric titration with a
glass electrode in the pH range between 2 and 8. Two different
salts, NaCl and KNO3, in concentrations ranging from
0.05 to 2 mol‚L-1
, were used as background electrolytes.
The influence of the ionic strength was accounted for by
means of the Donnan model in combination with the
master curve approach. Different empirical expressions to
describe the swelling behavior of the biosorbent were
tested. On the basis of the intrinsic affinity distribution
analysis a unimodal Langmuir-Freundlich isotherm was
selected to describe the proton binding properties. The
results show very little influence of the type of salt. The ionic
strength dependency of the proton binding is very
similar for the three species, and average empirical
expressions of the Donnan volume are proposed. The
maximum proton binding capacities obtained ranged between
2.4 and 2.9 mol‚kg-1
, with average intrinsic proton
affinity constants between 3.1 and 3.3, and heterogeneity
parameters of ca. 0.5 for S. muticum and C. baccata, and
slightly higher (ca. 0.7) for S. polyschides. The combined
Langmuir-Freundlich equation and Donnan model allowed a
good description of the experimental charge vs pH
curves obtained.