Basic-dye adsorption in albedo residue: Effect of pH, contact time, temperature, dye concentration, biomass dosage, rotation and ionic strength

This work was aimed at evaluating the efficiency of orange albedo as an adsorbent for the removal of cationic dyes in aqueous solution. The material was characterised by SEM, FTIR and pHZ. In order to verify the influence of the main parameters essential for adsorption, kinetic, equilibrium and thermodynamic studies were carried out, as well as a study regarding the influence of rotation and salinity (ionic strength). For SEM, the material presented a heterogeneous and porous surface, while the FTIR spectra identified bands assigned to hydroxyl and carboxyl groups and a pHZ of 4.61, usually associated to the adsorption on biomass, making it possible to use solutions at the natural pH. The equilibrium was reached at approximately 10 min, with no significant differences between the kinetic models. The best condition in terms of biosorbent saturation was found when 1% of biomass, 100 rpm and 30 °C were applied reaching an experimental q of 70 mg g−1 for 1000 mg L−1. The isothermal model with better adjustment to the experimental data was the Langmuir-Freundlich model, with a qmax of 77.79 mg g−1 at 30 °C. The thermodynamic values demonstrated a spontaneous nature of the process. In terms of the salinity (ionic strength) influence, it could be observed that the adsorptive capacity was reduced in between 20 and 65% when CNaCl varied between 0.1 and 1% (w/v). These results therefore demonstrate the technical potential of orange albedo as an adsorbent, mainly when any activation process is used. © 2019 The Authors