The structure of Fe-containing components of the carbon adsorbent prepared from the residue after carbon dioxide lignin reforming stimulated by microwave radiation was studied before and after the m-cresol sorption. As shown by X-ray photoelectron spectroscopy (XPS), the prevalent state of iron in the samples is Fe3+. The revealed "apparent decrease in the iron content" after the adsorbent treatment with cresol is due to the formation of surface complexes partially absorbing the emitted photoelectrons. The Mossbauer spectra show that the iron-containing phase of the initial adsorbent contains a fraction of Fe-0 atoms (approximate to 7%), which are oxidized from 0 to 3+ oxidation state upon m-cresol adsorption. This result can be attributed to the occurrence of reactions yielding surface iron alcoholates.