Adsorbents obtained from black liquor residues: synthesis, characterization, and evaluation in the removal of textile dyes

In this work, charcoal-type adsorbents were prepared from black liquor, a cellulose and paper industry residue rich in lignin and containing inorganic salts. During the preparation of adsorbent materials, black liquor was dried at 120 °C and then pyrolyzed at different temperatures (600 °C, 700 °C, and 800 °C) under a nitrogen atmosphere. The samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), measurement of specific surface area (BET), point of zero charges (PZC) determination, and evaluating of removal capacity of methylene blue dye. DRX results indicated the presence of crystalline phases of different salts, mainly sodium carbonate, on the surface of the produced carbonaceous materials from black liquor waste. Besides, a significant effect of the pyrolysis temperature on the charcoal crystallinity was observed. Materials presented low values of porosity and specific surface area, and similar morphologies. Solids' surface character was predominantly alkaline, according to PZC curves. All solids were efficient in removing 70 to 85% of the methylene blue's color.