Phenomenological modeling of reactive dye adsorption onto fish scales surface in the presence of electrolyte and surfactant mixtures.

The aim of this work was an experimental and theoretical investigation of the influence of electrolyte (NaCl) and surfactant (SP), as textile auxiliary agents (TAAs), onto reactive blue 5G (RB5G) dye removal by applying untreated fish scales (FS) in batch system. Kinetic and equilibrium studies were performed, aiming at the comprehension of the mass transfer mechanisms through phenomenological modeling. The biosorbent was texturally characterized, to investigate the adsorbent's characteristics and to support the models' assumptions. Hence, a 'physically meaningful' modeling to assess different systems containing dye-TAA mixtures was employed. The experimental results indicated that despite the FS nonporous characteristics, it showed remarkable adsorption capacities (≈291 mg g-1), which may be ascribed to the adsorbent-adsorbate affinity and to dye-aggregates adsorption onto the FS surface. Those results evidence a potential use of FS as an alternative biosorbent material. The mathematical model was able to identify the rate-limiting step of the process; to predict the adsorption kinetics and equilibrium condition, comprising the description of aggregates formation; and to successfully predict kinetic behavior of independent data in simulated real effluent. Those results indicate that the model can be used to simulate operating conditions and, therefore, support the design, optimization, and scale-up of adsorption processes.