The reversible cycling of CaO adsorbents to CaCO3 for high-temperature CO2 capture is substantially improved by mechanical treatment. The mechanical milling intensity and conditions of grinding (e.g., wet vs. dry, planetary vs. vibratory milling) were determined to be the main factors that control the effectiveness of the mechanochemical synthesis to enhance the recycling stability of the sorbents prepared. In addition, MgO was used as an example of an inert binder to help mitigate CaCO3 sintering. Wet planetary milling of MgO into CaCO3 allowed efficient particle size reduction and the effective dispersion of MgO throughout the particles. Wet planetary milling yielded the most stable sorbents during 50 cycles of carbonation–calcination.