Kinetics of Adsorption in Mercury Removal Using Cassava (Manhiot esculenta) and Lemon (Citrus limonum) Wastes Modified with Citric Acid

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Abstract

The high toxic concentrations of mercury (Hg) in water bodies and its negative impact on the environment has resulted in the need for research on effective and low-cost methods for the treatment of industrial effluents, such as adsorption. This research compares the feasibility and viability of the Hg (II) adsorption abilities of cassava and lemon citric acid-modified peels. The results showed that the modified peel of cassava has a better adsorption ability compared to that of lemon. The kinetics models that best fit the experimental data were a pseudo-second order model and the Elovich model for both modified biomasses. This means that the mechanism that controls the adsorption is a second order reaction, and also shows that the catalytic area of the adsorbent is heterogeneous; whereas the Freundlich isotherm describes better the adsorption process. In conclusion, the use of waste material is possible for Hg (II) removal. The study of chemical modifications is suggested to improve the adsorption percentages.

Translated abstract

Las altas concentraciones tóxicas de mercurio en los cuerpos de agua y su impacto negativo en el medio ambiente han generado la necesidad de estudiar métodos más económicos y eficaces para el tratamiento de los efluentes industriales, como es el caso de la adsorción. Esta investigación realizó un estudio de factibilidad, viabilidad y un comparativo entre las capacidades de adsorción de la cáscara de yuca y la cáscara de limón modificadas con ácido cítrico. Los resultados arrojaron que la cáscara de yuca modificada presenta una capacidad de adsorción mayor, en comparación con la cáscara de limón modificada. Los modelos cinéticos que más se ajustaron a los datos experimentales obtenidos fueron el modelo de seudosegundo orden y el de Elovich para las dos biomasas estudiadas modificadas, lo cual indica que el mecanismo controlante de la adsorción es una reacción de segundo orden y que la superficie catalítica del bioadsorbente es heterogénea; mientras que la isoterma de Freundlich describe mejor el proceso de adsorción. Se concluye que es posible el uso de materiales residuales para la remoción de Hg (II) y se sugiere el estudio de modificaciones químicas que puedan mejorar los porcentajes de adsorción.

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Removal of mercury(II) from aqueous media using eucalyptus bark: Kinetic and equilibrium studies.

Ilhem Ghodbane, Oualid Hamdaoui (2009)

In this study, eucalyptus camaldulensis bark, a forest solid waste, is proposed as a novel material for the removal of mercury(II) from aqueous phase. The operating variables studied were sorbent dosage, ionic strength, stirring speed, temperature, solution pH, contact time, and initial metal concentration. Sorption experiments indicated that the sorption capacity was dependent on operating variables and the process was strongly pH-dependent. Kinetic measurements showed that the process was uniform and rapid. In order to investigate the mechanism of sorption, kinetic data were modeled using the pseudo-first-order and pseudo-second-order kinetic equations, and intraparticle diffusion model. Among the kinetic models studied, the pseudo-second-order equation was the best applicable model to describe the sorption process. Equilibrium isotherm data were analyzed using the Langmuir and the Freundlich isotherms. The Langmuir model yields a much better fit than the Freundlich model. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy, and entropy of sorption. The maximum sorption capacity was 33.11mgg(-1) at 20 degrees C and the negative value of free energy change indicated the spontaneous nature of sorption. These results demonstrate that eucalyptus bark is very effective in the removal of Hg(II) from aqueous solutions.