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 m ) 29.7 mg/g). The nutshells were also found to be less effective at removing Ni(II) ions compared to Cd(II) ions.

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Canes from Arundo donax, a rapid-growing plant, were converted to activated carbons by phosphoric acid activation under four different activation atmospheres, to develop carbons with substantial capability to adsorb Cd(II) and Ni(II) ions from dilute aqueous solutions. The carbons showed surface areas and total pore volumes of around 1100 m2/g and 1 cm3/g, respectively. The content of carbons' polar or acidic surface oxygen functional groups, with their development depending on the atmosphere used, influenced predominantly metal adsorption. Carbons derived under flowing air, possessing the largest total content of these groups (3.3 mequiv/g), showed the best adsorption effectiveness (>90%) for both ions, even superior to that determined for a commercial sample used as a reference. A pseudo-second-order rate model properly described adsorption kinetic data obtained for this sample. Equilibrium isotherms using the same carbon were also determined and modeled by the Langmuir isotherm. The influence of the solutions' pH on metal uptake, adsorption competitive effects between Cd(II) and Ni(II) ions, and desorption from the selected metal-loaded carbon for recovery purposes were additionally investigated.

Activated carbons from two different types of sugar cane wastes, agricultural residues and bagasse, were prepared by phosphoric acid activation varying the carbonization temperature (300-600 °C), the weight ratio of phosphoric acid to precursor (R ) 1-2.5), and carbonization time (0-3 h). Surface properties of the resulting carbons were markedly dependent on the precursor and a combined effect of the conditions employed. Bagasse carbons showed higher surface area and pore volume than those from agricultural residues. Maximum surface areas of around 1100 and 780 m 2 /g were respectively attained. Temperature above 500 °C, impregnation ratio higher than 2, or prolonged carbonization beyond 1 h led to reduction in porosity development. Selected carbons from both wastes with relatively large mean pore radius showed good ability to decolorize a diluted solution of synthetic melanoidin, used as a model of molasses wastewater. Iodine number between 608 and 746 and methylene blue uptake of 213-261 (mg/g) were determined for the selected samples.

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SynopsisPermeability coefficients and activation energy values for the transport of water through asymmetric cellulose acetate membranes were determined in order to establish the mechanism of the process when different driving forces are applied. A stirred Lucite cell with controlled temperature was used to measure the membrane transport properties under hydraulic and osmotic pressure differences and also in the presence of a tracer concentration gradient across the membrane. The experimental results based on the temperature dependence of water flow show that the controlling step for water transport is diffusion with net flux in the dense zone of the membrane under hydraulic or osmotic pressure gradients. When a tracer concentration gradient is used, equimolar diffusion of water in the thicker, porous zone of the membrane is the controlling mechanism. A mass transport model based on the composed structure of the membrane is presented to provide a general framework for treating the particular cases. Finally, the difference in the controlling barriers, in agreement with a previous work by Hays,Is is shown to account for the much higher absolute values of osmotic than tracer water permeabilities determined here and frequently reported in the literature.