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Yttrium oxide with a large specific surface area (SSA) (hereafter called LSSA Y2O3) has high-porosity structure, relatively large interface, and relatively abundant active surface sites, and its optical, chemical and thermal stability properties are greatly improved compared with ordinary yttrium oxide. As a result, LSSA Y2O3 has been applied in various fields as a luminescent, catalytic, and adsorbent material, showing enormous market potential. This study creatively presents a process designed to prepare LSSA Y2O3 powders through moderate carbonation in the presence of CO2. Experimentally, CO2 was used to carbonate a yttrium hydroxide [Y(OH)3] slurry. During the initial stage of carbonation, crystalline yttrium carbonate encapsulated Y(OH)3 through heterogeneous nucleation on its surface. This encapsulation considerably improved the filterability of the carbonation product while allowing it to retain the phase structure and high-porosity morphology of Y(OH)3. Further calcination of the carbonation product produced LSSA Y2O3 with an SSA of approximately 84 m2/g. This Y2O3 powder exhibited a relatively high adsorption capacity for methyl orange and was easy to recycle and reuse, thus showing potential for use as an adsorbent. The process developed in this study for preparing LSSA Y2O3 powders through carbonation in the presence of CO2 is advantageous because it requires only moderate conditions, causes no pollution, produces products with a uniform granularity and morphology, and is easy to scale up to meet industrial demands. Therefore, this process can effectively increase the added value and market competitiveness of Y2O3 powders and provide an experimental basis and theoretical guidance for the synthesis of other rare earth (RE) compounds with large SSAs through carbonation.