Biossorção de tório e urânio pela macroalga marinha sargassum filipendula

Abstract

Due to its low cost and ligand properties, the seaweed Sargassum filipendula is highly used as a biosorbent material for metals biosorption processes. In the present work this brown seaweed was used in the kinetic and equilibrium studies of the process of biosorption of thorium and uranium, alone and in combined solutions. Tests were performed in the range of metals concentrations from 1 to 10 mg/L and pH values 1.0 and 4.0 at 25 ±1ºC. The best condition for the biosorption of thorium was found in the low concentration of 1 mg/L at pH 1.0, while uranium was best biosorbed at the concentration of 1 mg/L at pH 4.0. The kinetic study of thorium biosorption indicated that the second-order kinetic model best represented the experimental data for the low concentration of 1 mg/L (R2= 0.9987) and 10 mg/L (R2= 0.9919) at pH 1.0; for 1.0 mg/L R2= 0.9976 at pH= 4.0, while for the most concentrated solution (10 mg/L) R2 value was equal to 09787) at pH= 4.0, following a pseudo-first order kinetics. The biosorption of uranium indicated that both kinetic models fitted the experimental data, under both experimental conditions. Equilibrium study showed an increasing thorium biosorption, for increasing initial metal concentration, reaching 96 and 54% recovery of the metal, at pH 1.0 and 4.0, respectively. The higher individual efficiencies observed were 33% biosorption for a 100 mg/L initial concentration at pH 1.0 and 71% for a 1 mg/L concentration, at pH 4.0. Experimental equilibrium data, for the element thorium, indicated a best fit on Freundlich model, at pH 1.0, while at pH 4.0 the results were best represented by the Langmuir model, due to higher determination coefficient values. Considering the uranium isotherm obtained, Freundlich model best represented experimental data, suggesting the formation of a multilayer adsorption on the surface of the biomass. Equilibrium parameters calculated from the Langmuir (kL, qmax) and Freundlich (kF, n) models, indicated a higher affinity of the biomass for thorium, in comparison to uranium in both conditions tested. The study of the binary system equilibrium showed that the biosorption of thorium was not affected by the presence of uranium in solution, due to the same uptake values observed when thorium was solely present in solution, reaching qmax= 85,95 μmol Th/g (individual) and qmax= 110,1 μmol Th/g (mixture). On the other hand, uranium biosorption was markedly affected by the presence of thorium in solution, reaching low or not significant uranium by the biomass. Key words: Biosorption, Sargassum filipendula, Thorium, Uranium.