Elena Torres

Gold(III) biosorption and bioreduction with the brown alga Fucus vesiculosus

In this paper, the bioreduction of Au(III) to Au(0) using biomass of the brown alga Fucus vesiculosus was investigated. The recovery and reduction process took place in two stages with an optimum pH range of 4-9 with a maximum uptake obtained at pH 7. In the first stage, an induction period previous to gold reduction, the variation of pH, redox potential and gold concentration in solution was practically negligible and no color change was observed. In the second stage, the gold reduction was followed by a sharp decrease of gold concentration, pH and redox potential of solution and a color change from yellow to reddish purple. Hydroxyl groups present in the algal polysaccharides were involved in the gold bioreduction. Metallic gold was detected as microprecipitates on the biomass surface and in colloidal form as nanoparticles in the solution. Bioreduction with F. vesiculosus could be an alternative and environmentally friendly process that can be used for recovering gold from dilute hydrometallurgical solutions and leachates of electronic scraps, and for the synthesis of gold nanoparticles of different size and shape.

Lead and Gold Removal Using Sugar-Beet Pectin Gels With and Without Immobilized Fucus vesiculosus

Sugar-beet pectin gels are a novel material with applications in heavy and precious metal removal and biomass immobilization which are similar to those of alginate. This paper presents the experimental results of the kinetics of Pb(II) and Au(III) batch removal with these gels, with and without immobilized biomass of the brown algae Fucus vesiculosus. The evolution of the metal concentration, solution pH and Ca2+ liberation was determined. The biomass was characterized before and after the metal removal using SEM-EDX, FESEM, FETEM, XRD and FTIR techniques. The Pb(II) removal followed a typical biosorption kinetics with a final equilibrium metal concentration. The immobilized algae had different biosorptive behaviour than both the original sugar-beet pectin gels and the free biomass. There was no Au(III) removal with the pectin gels without algae. In the case of the immobilized biomass, the Au(III) recovery occurred in two stages, where the biosorption was followed by the reduction of the Au(III) to Au(0) due to the presence of the own algae. The Au(0) precipitated preferably on the surface of the algal biomass and in the form of colloidal gold in the solution and entrapped within the pectin gel matrix.