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Commercially available oxidized (carboxylic groups) and nonoxidized multiwalled carbon nanotubes were studied as adsorbents of cerium(III) in batch operation mode. Several variables affecting the rare earth adsorption were investigated, including: the stirring speed applied to the system, the pH of the solution, and the metal concentration and carbon dosages. Although the removal of cerium from the solution is different and dependent upon the adsorbent type—(i) adsorption in nonoxidized multiwalled carbon nanotubes, (ii) cation exchange in the case of using oxidized multiwalled carbon nanotubes—the adsorption kinetics, the rate law and the isotherm models are the same for both adsorbents: pseudo-second order, film diffusion, and Langmuir Type-1, respectively. Cerium is desorbed from loaded adsorbents using acidic solutions.