Biocarvão do osso de tilápia: obtenção e aplicação na remoção de poluentes emergentes

Abstract

Tilapia bone is an underutilized and abundant residue in western Paraná, due to the large number of psicultures. Therefore, this work aimed to use the bones as raw material for obtaining biochar, specifically aiming at its application as an alternative adsorbent material. Initially, the conditions for obtaining and activating (chemical and physical) biochar were investigated, then the characterization was carried out in relation to surface area and pore size (N2 physisorption), morphology (scanning electron microscopy - SEM), elementary composition (X-ray dispersive energy - EDX), functional groups (Fourier Transform infrared spectroscopy – FT-IR), crystallographic structure (X-ray dispersion - XRD) and isoelectric point (pHPZC). The adsorptive capacity of the biochar was evaluated in adsorption tests, carried out separately, with the reactive dye blue 5G and with the drug Tetracycline, both considered as emerging pollutants. Batch (kinetics and equilibrium) and fixed bed column adsorption tests were performed. Equilibrium models were adjusted to the equilibrium data widely used in the literature. In addition, three phenomenological kinetic mathematical models were applied to the experimental data in a batch system, seeking a better understanding of the adsorption process by biochar. Each kinetic model considered only one limiting step of the global adsorption process, that is, the mass transfer process (T.M.): (I) the first took into account the resistance to T.M. from the sinus of the liquid phase to the adsorbent surface (RETM model); (II) the second resistance to T.M. intraparticle diffusion (RITM model); and (III) the third considers the adsorption in the active sites and, possibly, the formation of multilayers (AMM model). Using the data and parameters obtained in batch systems (kinetics and equilibrium), a mathematical model for adsorption in a fixed bed column was applied with the intention of simulating and predicting the adsorption process in a continuous system. The results show that the tilapia bone biochar is a biphasic material, consisting of compounds of apatites (pure and carbonated hydroxyapatite) (crystalline phase) and carbon (amorphous phase). It has a complex porous structure with a predominance of mesopores (average pore diameter of 8.9 nm) and 124 m2 g-1 of surface area. The results of the sorption tests show a high capacity to remove the 5G dye (q ≈ 60 mg L-1) and the tetracycline (q ≈ 120 mg L-1). By the estimated removal capacity values of the data obtained in a fixed bed column, it can be said that the biochar has the potential to be used in sorption processes in a continuous system. The fixed bed column model obtained a good forecast of the tendency of the formation of rupture curves for the dye and tetracycline adsorption process, both in low and high concentrations. The ability to predict data from the fixed bed column based on the estimated parameters of the batch system, shows the importance of this tool in the development of projects to increase the scale in adsorption processes. The high adsorption capacity of the pollutants evaluated, both in batch and continuous systems, and the desirable physical and chemical characteristics show the great biocarbon potential obtained from the tilapia bone residue as a possible alternative to commercial adsorbents.