Comparison of acidic leaching using a conventional and ultrasound-assisted method for preparation of magnetic-activated biochar

Four magnetic biochars (MBs) were prepared from two mixtures of Sappeli sawdust with NiCl₂ solution or Sappeli sawdust with NiCl₂ plus ZnCl₂ solutions. These mixtures formed two pastes that were dried and further pyrolyzed at 700 °C under nitrogen flow. The pyrolyzed material was leached out with 0.1 M HCl under conventional reflux (AL- 80 °C, 2 h) or assisted by ultrasound-leaching (US- 15 min, 600 W), obtaining four biochars: SNiAL, SNiUS, SNiZnAL, SNiZnUS. The biochars were characterized by VSM, XRD, FTIR, isotherms of adsorption and desorption of nitrogen, pH_pzc, hydrophobically characteristics (HI), TGA, elemental analysis (CHN/O). The data show that using the leaching process assisted by ultrasound can obtain biochars that present good magnetization saturation, with a lower leaching time than conventional leaching. The four biochar were tested as adsorbents to remove ten emerging contaminants and four dyes of aqueous effluents. It was observed that the impregnation of zinc chloride in the samples led to an increase in the surface areas of the magnetic biochars, which influenced the most of sorption capacities of the adsorbents for the different sorbing species. Making a ratio of sorption capacities of SNiAL/SNiZnAL and SNiUS/SNiZnUS, it was obtained the values, respectively, of 0.9761, and 0.9710 (Acid Red 1), 2.057, and 3.030 (Reactive Blue 4), 4.192, and 1.971 (Basic Violet 3), 3.359, and 1.129 (Basic Green 1), 1.673, and 1.835 (Paracetamol), 3.612, and 3.779 (Propranolol), 5.871, and 5.171 (Sodium Diclofenac), 1.457, and 1.607 (Nicotinamide), 1.094 and 1.093 (Caffeine), 1.167, and 2.398 (4-chloroaniline), 1.009 and 0.9965 (2-nitrophenol), 1.156 and 1.341 (Resorcinol), 1.299 and 1.331 (Hydroquinone), 0.9975 and 1.019 (4-bromophenol).