Synthesis of biochar using brewery waste for efficient adsorption of ionic iron species

Biochar from agro-industrial residues has been reported as an excellent adsorbent material for metal ions due to its physical-chemical characteristics and he low cost of raw material. In this work, the synthesis and activation pathways of biochar produced from brewery waste and its capacity to adsorb iron ions in aqueous solutions were investigated. The synthesis was performed by pyrolysis in an oxygen deficient atmosphere. Biochar was chemically activated using solutions of sodium hydroxide, hydrochloric acid, and calcium chloride. The biochar samples as well as the raw material were characterized by Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and determination of the surface area and total pore volume by adsorption of N-2 (BET) with the aim of evaluating the physicochemical changes in the material. The biochar activated by NaOH (B-NaOH) had the highest Fe adsorption capacity, followed by B-CaCl2, brewery waste (BW), raw biochar (RB), and B-HCl. Pyrolysis increased the surface area and pore volume of all biochar compared to the in natura sample (0.108 m(2)/g), with emphasis on the RB (0.832 m(2)/g) and B-NaOH samples (1067 m(2)/g). The maximum adsorption capacity of Fe2+ was obtained for B-NaOH (q = 21.5 mg/g) with 2 g/L of sample, 16 h of contact, and neutral pH. The Langmuir and Freundlich models fitted the experimental equilibrium data obtained for B-NaOH sample (R-2 > 0.960). The kinetic curves showed equilibrium conditions after 300 min, and the pseudo-second-order model presented a better correlation with the data for all curves (R-2 > 0.998). Biochars produced in this study can be effectively applied in processes involving iron ion removal.