Algal biosorbents for gold and cobalt

Different types of biomass samples including fungi and algae were treated for their gold and cobalt uptake capacity. The performance of activated carbon and ion-exchange resins were compared with the metal uptake capacity of the biosorbents. Sargassum natans, a brown seaweed, exhibited a high gold uptake capacity outperforming the ion-exchange resin and equalling activated carbon. Algal biomass of Ascophyllum nodosum proved to be a very potent biosorbent for cobalt. While the temperature, agitation and biomass particle size did not affect the metal uptake process, the effect of pH was significant for both gold and cobalt uptakes. The optimum pH for gold uptake was 2.5 and for cobalt, was 4-5. The kinetics of cobalt biosorption was relatively rapid (5 min) at the initial concentration of the metal in solution, 100 mg/L. The biosorptive uptake of gold required 2 h to reach equilibrium when the initial concentration of gold was 100 mg/L. None of the tested cations, such as K$ sp+$, Ca$ sp{2+}$, Fe$ sp{2+}$, Cr$ sp{3+}$, UO$ sbsp{2}{2+}$, Ni$ sp{2+}$, Zn$ sp{2+}$, Ag$ sp+$, affected the gold uptake capacity of S. natans biomass under the optimum conditions. Anions, such as NO$ sbsp{3}{-}$, SO$ sbsp{4}{2-}$, CO$ sbsp{3}{2-}$, PO$ sbsp{4}{3-}$, and Pb$ sp{2+}$ suppressed the gold uptake somewhat. Under the optimum process conditions cations, except K$ sp+$ and Fe$ sp{2+}$, and anions, NO$ sbsp{3}{-}$ in particular, exhibited a pronounced negative effect on the cobalt uptake by A. nodosum biomass.Sequestered gold was eluted with a mixture of thiourea and ferric ammonium sulphate solution. Approximately 98% of sequestered gold was eluted with 17 h in a batch contacting system at the optimum solids (biomass)-to-liquid ratio of 5 and pH of 5. At increased temperatures, the gold elution rate increased only slightly. Efficient desorption of cobalt was achieved using CaCl$ sb2$/HCL solution at pH 3. Cobalt elution time was quite short. Temperature affected neither desorption rate nor the equilibrium. The optimum solid-to-liquid ratio was 12 for desorption of cobalt from A. nodosum biomass.The gold taken up by the biosorbent was deposited in its elemental form.Available mathematical models, including the REDEQL2 chemical equilibrium model, were tested for theoretical predictions of co-ion competition in attempt to better understand the biosorption mechanism. (Abstract shortened with permission of author.