Conversion of the forest species Inga marginata and Tipuana tipu wastes into biosorbents: Dye biosorption study from isotherm to mass transfer

Abstract Residual seed pods from the forest species Inga marginata and Tipuana tipu were used as biosorbents to remove the cationic dye gentian violet from diluted aqueous solutions. It was observed that the materials presented heterogeneous structural characteristics, with a predominance of amorphous regions formed by functional groups typical of hemicellulose, cellulose, and lignin. The dosages of 0.80 and 0.72 g L−1 for the Inga marginata and Tipuana tipu, respectively, were sufficient for good biosorption performance. The isothermal studies for both biosorbents were best described by the Langmuir model, with a maximum biosorption capacity of 448.1 and 376.1 mg g−1 for the Inga marginata and Tipuana tipu, respectively. Thermodynamic parameters showed that both biosorbents possess a spontaneous and endothermic nature in the presence of gentian violet. The PVSDM (pore volume and surface diffusion model) model successfully described the concentration decay curves. It was found that the surface diffusion coefficient ranged from 1.00 × 10−6 to 6.97 × 10−6 cm 2 s−1. However, Biot numbers indicate that the external mass transfer is a rate-controlling step. The application of the biosorbents in the treatment of simulated effluent showed that they were able to remove up to 77.65% (Inga marginata) and 68.71% (Tipuana tipu) of the dye. Thus, the forest species’ pods showed great potential for removing the gentian violet dye from diluted solutions.