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Interaction of Mercuric Ions with Different Marine Algal Species

ABSTRACT The use of different seaweeds such as Sargassum sp., Turbinaria conoides, and Ulva sp. in removing mercury(II) from aqueous solutions were investigated. The initial experimental runs, conducted at different equilibrium pH conditions, demonstrated that brown seaweeds outperformed green seaweed in Hg(II) biosorption at all pH conditions. In particular, at pH 5, maximum biosorption capacities of 170.3 and 145.8 mg/g were recorded for the brown seaweeds T. conoides and Sargassum sp., respectively, compared with 138.4 mg/g for the green seaweed Ulva sp. Isotherm data were modeled and interpreted using the Langmuir, Freundlich, Redlich-Peterson, and Toth models, with the latter described the Hg(II) isotherms with high correlation coefficients and low % error values. The kinetic data indicate the rapidity of the biosorption process, with the equilibrium achieved within 90 min. Several models, including the Elovich, pseudo-first-order, and pseudo-second-order models, were examined for their suitability with the present data; the correlation coefficient and % error values, along with better prediction of equilibrium uptake values, favored the pseudo-first-order model. The desorption experiments were highly successful for T. conoides biomass with 0.05 M HCl, whereas for the other two seaweeds, 0.05 M HCl resulted in high biomass weight loss. Reusing T. conoides biomass in three successive sorption-desorption cycles resulted in only 8.8% reduction in Hg(II) biosorption capacity compared with its original uptake.