Biosorption of cadmium by the protonated macroalga Sargassum muticum: Binding analysis with a nonideal, competitive, and thermodynamically consistent adsorption (NICCA) model
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Date
2005
Authors
Rey Castro, Carlos
Lodeiro, Pablo
Herrero, Roberto
Sastre de Vicente, Manuel E.
Barriada, José L.
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Abstract
Protonated biomass of the seaweed Sargassum muticum was investigated for its ability to remove cadmium(II) from aqueous solutions. In
this work, a nonideal, semiempirical, thermodynamically consistent (NICCA) isotherm was proposed to fit the experimental ion binding data
obtained in NaNO3 0.05 mol L−1. This model describes the competition between protons and metal ions satisfactorily. Moreover, it reflects
the complexity of the macromolecular systems that take part in biosorption considering the heterogeneity of the sorbent. It was demonstrated
in this work that the NICCA isotherm constitutes a great improvement with respect to a simpler Langmuir competitive equation, which
was not able to describe all the experimental data satisfactorily. Potentiometric acid–base titrations in the absence of cadmium were made
to estimate the maximum amount of acid functional groups (2.61 mmol g−1) and the conditional proton binding parameters, logK˜H (3.8)
and mH (0.54). The values of the binding parameters for the cadmium ion were chosen to provide the best simultaneous description of the
isotherm at pH 4.5, as well as the dependence of cadmium adsorption on pH. Values of logK˜Cd (3.1), nCd (1.8), and p (0.19) in the case
of the NICCA isotherm or logKCd (2.94–3.4) for Langmuir competitive models were obtained. Kinetic experiments were performed at two
different pH values (3.0 and 4.5), establishing the time dependence that represents the sorption of cadmium with a pseudo-second-order
kinetic model. It was observed that 4 h is enough to ensure that the equilibrium uptake was reached.
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Journal of Colloid and Interface Science, 2005, vol. 289, núm. 2, p. 352-358