Pore Structure of Carbonized Lignite Modified by Ferric Nitrate

Abstract

The influence of added ferric nitrate on the pore structure of carbonized lignite is studied. The ferric nitrate Fe(NO₃)₃ is added by steeping in terms of the moisture capacity, with the following ratios of the anhydrous salt and the carbonizate: 0.20, 0.25, 0.33, and 0.50 g/g. (The ferric nitrate is first dissolved in dilute nitric acid solution.) The texture of the modified carbonizates is studied by analysis of the N₂ adsorption–desorption isotherms at 77 K (–195.97°C) on an ASAP-2020 system. The addition of ferric nitrate is found to produce carbon materials with higher specific surface and pore volume. The greatest increment in specific surface (by 30%) and pore volume (by 40%) is observed in samples with ratios of 0.20 and 0.25 g/g. With increase in the added ferric nitrate, the proportion of mesopores increases; it is greatest (54.6%) for the sample with a ratio of 0.50 g/g. According to energy-dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction, the addition of ferric nitrate results in the formation of small magnetic Fe, γ-Fe₂O₃, and Fe₃O₄ particles on the surface of the carbon materials. Consequently, those materials may be retained by means of the field created by neodymium permanent magnets.