Biochars obtained from arabica coffee husk by a pyrolysis process: characterization and application in the Fe(II) removal in aqueous systems.

In this work biochars were synthetized from arabica coffee husks and were used for Fe (II) adsorption by a pyrolysis process at 350 and 600 °C. The in natura material before and after pyrolysis exhibited amorphous structure, showing levels of C, H, and N, for both biochars, around 70; 0.25; and 2.5% (m/m), respectively. The Point of Zero Charge (PZC) was 9.5 and 10.2 for BIO350 and BIO600, respectively. FTIR spectra and thermogravimetric analyses confirmed the presence of OH, COOH, and SO3H groups on the coffee husks surface as well as the loss of these groups on biochars, being the biochars more stable if compared with the coffee husks. The synthetized biochars presented amorphous characteristics before the adsorption process of iron(II), turning to a structure in nail form after the Fe(II) adsorption studies. Langmuir isotherm model and pseudo-second order kinetic model were the best models fitted to the experimental data and were evaluated based on the coefficient of determination. Both biochars demonstrated similar efficiencies in Fe(II) removal, with a maximum absorption capacity about 110 mg of Fe(II) per gram of biochar. The adsorption thermodynamic indicates a spontaneous and favorable process, thus justifying the use of biochars for Fe(II) adsorption in aqueous solution.