RESUMO
Herein, the biosorption of Cr(VI) by magnetized coconut fibres obtained from agricultural waste has been described. Magnetization was achieved by incorporating magnetite nanoparticles into the fibres by a coprecipitation reaction in alkaline media. The biosorption capacity of the fibres was evaluated by two series of experiments. In the first series, 500â mg L-1 of the biosorbent was added to a 50â mg L-1 K2Cr2O7 solution at 28 °C and stirred at 200â rpm and the pH was varied from 1 to 13 to determine the optimum pH value. The second series of experiments evaluated the sorption capacity of the fibres at the optimum pH, under the same agitation speed and temperature but with an adsorbate concentration of 100â mg L-1. The biosorbents were characterized using Fourier transform-infrared spectroscopy, inductively coupled plasma-atomic emission spectroscopy, scanning electron microscopy, dispersive X-ray fluorescence, and X-ray powder diffraction. The biosorption experiments demonstrated that the magnetization process increased the biosorption capacity of the material. Optimum biosorption occurred at pH 2, and at optimal conditions, the best adsorptive efficiency exceeded 90%, reaching a biosorption capacity of 87.38â mg g-1 for the magnetized fibre and 23.87â mg g-1 for the natural fibre, with an equilibrium time of less than 20â min.
