Lignocellulosic materials as potential biosorbents of trace toxic metals from wastewater

The potential capability of Arundo donax stems, Brazil nutshells, sugarcane bagasse, and sawdust from a. native wood species (Prosopis ruscifolia) to sequester trace metals from wastewater was comparatively examined using dilute aqueous solutions of Cd(II) or Ni(II) ions as models. Brazil nutshells showed the best effectiveness (>90%) for the uptake of both metals from solutions of 20 mg/L initial concentration for dosages larger than 0.2-0.4 mg/L, even superior to those obtained for a commercial activated carbon and/or red marine algae (Corallinales) used for comparison under identical conditions. Equilibrium isotherms of cadmium on the lignocellulosic and algae samples and of nickel on the nutshells were determined and properly described by the Langmuir model. The highest maximum sorption capacity of Cd(II) ions was obtained for the nutshells (X-m = 19.4 mg/g) among the lignocellulosic samples. The trend in the estimated X-m values was found to be consistent with their contents of lignin and total surface acidic functional groups. Nevertheless, X-m for the nutshells was lower than that for the algae (X = 29.7 mg/g). The nutshells were also found to be less effective at removing Ni(II) ions compared to Cd(II) ions.