Conchas de Mytella falcata calcinadas como adsorvente alternativo para remoção eficiente do antibiótico rifampicina de soluções aquosas

Abstract

The present work studied the viability of using Mytella falcata shells (sururu, a bivalve mollusk) as an innovative biosorbent for the removal of rifampicin antibiotic from aqueous solutions. The alternative material was tested in natura and after pyrolysis and calcination. Preliminary adsorption tests allowed to choose the calcined form as the most selective for the antibiotic removal. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and X-ray-dispersive energy spectroscopy (EDS) were performed in order to characterize the proposed adsorbent, showing the presence of residual CaCO3, mainly in aragonite and calcite forms, as well as a porous structure with heterogeneous surface characterized by rounded particles. Several assays were carried out to study the influence of the main parameters that could influence the adsorption process, like adsorbent dosage (0.1, 0.2, 0.3 and 0.5 g) and matrix pH (3.0, 7.0 and 13.0). The best adsorption results were obtained for 0.2 g of adsorbent and pH 13.0. Fixed parameters were used in the kinetic, ionic strength and regenerations tests, such as 0.2 g of calcined sururu shells, solution pH 13.0, agitation speed of 140 rpm, adsorbate volume of 0.01 L and temperature of 30°C. The parameters employed in the equilibrium studies were the same mentioned before, but also considering the temperatures of 30°C, 40°C, 50°C e 60°C and equilibrium time of 30 min. Kinetic studies evidenced fast adsorption phenomena, attaining the equilibrium between 30 and 45 min. The experimental data obtained presented the best fit with the pseudo- first order kinetic model, providing adsorption capacities in equilibrium of 3.05, 4.58 and 7.00 mg.g-1and rifampicin removal of 72.37± 0.97, 82.28± 0.19 and 82.26± 1.38 for adsorbate initial concentrations of 50.0, 100.0 and 200.0 mg.L-1, respectively.Equilibrium data showed that the rifampicin adsorption capacity was slightly dependent on the temperature, probably due to the simultaneously increment of water desorption, associated with the temperature increase. The isotherms showed a Redlich-Peterson model behavior, indicating a multilayer adsorption. The analysis of thermodynamic parameters showed that adsorption was spontaneous and lightly endothermic. Additional experimental tests indicated that increasing the ionic strength of the adsorbate solution can help the rifampicin adsorption onto the selected adsorbent. Finally, adsorbent regeneration by sonication revealed a significant decrease in the performance after 5 adsorption/desorption cycles.