Antonio Wilson Macedo Carvalho Costa

Herein, the biosorption of Cr(VI) by magnetized coconut fibers obtained from agricultural waste has been described. Magnetization was achieved by incorporating magnetite nanoparticles into the fibers by a coprecipitation reaction in alkaline media. The biosorption capacity of the fibers was evaluated by two series of experiments. In the first series, 500 mg L^-1 of the biosorbent was added to a 50 mg L^-1 K₂Cr₂O₇ solution at 28 °C and stirred at 200 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 fibers at the optimum pH, under the same agitation speed and temperature but with an adsorbate concentration of 100 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 87.38 mg g^-1 for the magnetized fiber and 23.87 mg g^-1 for the natural fiber, with an equilibrium time of less than 20 min.