No abstract

The golden trumpet tree bark (GTB), a wood-processing residue, was tested as adsorbent material for decontamination of wastewaters containing methylene blue dye (MB). The powdered material was preponderantly amorphous, containing an irregular surface with the presence of lignin and holocellulose. The adsorption was favorable at basic pH of 10 and adsorbent dosage of 0.5 g L −1. The kinetics has finished in only 30 min and fitted by the general order model (GO). The isotherm behaviors were successfully represented by the Langmuir model. The value found for the maximum adsorption capacity was 232.25 mg g −1 , being obtained at 328 K. The standard variation of Gibbs free energy (ΔG 0) ranged from − 10.77 to − 8.09 kJ mol −1 , indicating a spontaneous and favorable adsorption. A variation of standard enthalpy (ΔH 0) of 18.58 kJ mol −1 revealed an endothermic adsorption. A sloped forward curve was found in the continuous operation, with breakthrough time (t b) of 325 min. The stoichiometry capacity of the column (q eq) and the length of mass transfer zone (Z m) were, respectively, 23.57 mg g −1 and 11.28 cm. The GTB was efficient in the treatment of a simulated effluent, obtaining color removal of 96%. These results show that GTB can be applied as adsorbent for decontamination of wastewaters containing methylene blue.

Bark residues of the forest species Cedrela fissilis were physically and chemically modified with zinc chloride (ZnCl 2 ) as an activating agent. The two modified materials were analyzed as adsorbents in removing atrazine and 2,4-D herbicides from effluents. Firstly, the precursor material and the modified ones were characterized by different techniques to identify the structural changes that occurred in the surfaces. Through TGA, it was observed that both modified materials have thermal stability close to each other and are highly superior to the precursor. X-ray diffractions proved that the amorphous structure was not altered, the three materials being highly heterogeneous and irregular. The micrographs showed that the treatments brought new spaces and cavities on the surface, especially for the material carbonized with ZnCl 2 . The pH PZC of the modified materials was close to 7.5. The physically modified material had a surface area of 47.31 m 2 g −1 and pore volume of 0.0095 cm 3 g −1 , whereas the carbonized material had a surface area of 98.12 m 2 g −1 and pore volume of 0.0099 cm 3 g −1 . Initial tests indicated that none of the adsorbents were efficient in removing 2,4-D. However, they showed good potential for removing atrazine. The Koble-Corrigan isothermal model best fits the experimental data, with a maximum capacity of 3.44 mg g −1 and 2.70 mg g −1 for physically modified and with ZnCl 2 , respectively. The kinetic studies showed that the system tends to enter into equilibrium after 120 min, presenting good statistical indicators to the linear driving force model (LDF). The surface diffusion coefficients were 2.18×10 −9 and 2.37×10 −9 cm 2 s −1 for atrazine adsorption on the physically and chemically modified materials. These results showed that the application of residues from the processing of cedar bark is promising. However, new future studies must be carried out to improve the porous development of the material and obtain greater adsorption capacities.