Browsing by Author "Freitas, Olga"
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- Accumulation and release of Pb(II) in aqueous solution by aquatic mosses (Fontinalis antipyretica)Publication . Martins, Ramiro; Freitas, Olga; Vilar, Vítor J.P.; Boaventura, RuiThe uptake and release of Pb(II) by Fontinalis antipyretica was studied in laboratory, by exposing the plants to different lead concentrations for 144 h and 335 h contamination and decontamination periods, respectively. A first order kinetic model was fitted to the experimental data to determine the uptake and release constants, k1 and k2, and other relevant parameters. The metal accumulation capacity, at equilibrium, follows the order: Pb(II) > Zn(II) > Cd(II) > Cr(VI). A Bioconcentration Factor (BCF) and a Biological Elimination Factor (BEF) were also determined; for 0.9–2.2 mg Pb l–1, BCF decreases from about 30748 to 21296.
- Cr(III) uptake by marine algal biomass: equilibrium and kineticsPublication . Vilar, Vítor J.P.; Freitas, Olga; Costa, Pedro; Botelho, Cidália; Martins, Ramiro; Boaventura, RuiIn this work, biosorption of trivalent chromium by the marine brown algae Sargassum muticum was 37 studied in a batch system. The effect of the solution pH on Cr(III) uptake by Sargassum was 38 investigated. Kinetics and equilibrium experiments were conducted at different pH values (3.0, 4.0 and 39 5.0). Equilibrium data are well described by the Langmuir and Langmuir-Freundlich isotherms and 40 kinetics follows the pseudo-second-order model, at different pH values. The two mass transfer models 41 give comparable results, but they did not provide a perfect representation of the sorption data. The 42 homogeneous diffusivity, Dh, was found to be around 1.6´10-8 cm2 s-1 for 100 mg l-1 Cr(III) 43 concentration. 44 Sargassum muticum was compared with the brown algae Laminaria hyperborean and the red algae 45 Gelidium sesquipedale in terms of uptake capacity. The maximum uptake capacities for Sargassum, 46 Laminaria and Gelidium were, respectively, 56 ± 3, 70 ± 4 and 18 ± 1 mg Cr(III) g-1, at pH = 5.
- Removal of Cd(II), Zn(II) and Pb(II) from aqueous solutions by brown marine macro algae: kinetic modellingPublication . Freitas, Olga; Martins, Ramiro; Matos, Cristina; Boaventura, RuiSpecific marine macro algae species abundant at the Portuguese coast (Laminaria hiperborea, Bifurcaria bifurcata, Sargassum muticum and Fucus spiralis) were shown to be effective for removing toxic metals (Cd(II), Zn(II) and Pb(II)) from aqueous solutions. The initial metal concentrations in solution were about 75-100 mg L-1. The observed biosorption capacities for cadmium, zinc and lead ions were in the ranges of 23.9-39.5 mg g-1, 18.6-32.0 mg g-1 and 32.3-50.4 mg g-1, respectively. Kinetic studies revealed that the metal uptake rate was rather fast, with 75% of the total amount occurring in the first 10 min for all algal species. Experimental data were well fitted by a pseudo-second order rate equation. The contribution of internal diffusion mechanism was significant only to the initial biosorption stage. Results indicate that all the studied macro algae species can provide an efficient and cost-effective technology for eliminating heavy metals from industrial effluents.