This study proposes the use of multi-acidification to reactivate CaO-based sorbents and investigates the feasibility of this process under N-2 or oxy-fuel (with and without SO2) calcination conditions. The multi-acidification process involves the repeated modifications of CaO-based sorbents using acid, such as the waste acid from industrial chemical processes. Under pure N-2 or oxy-fuel (without SO2) calcination conditions, the multi-acidification can completely improve the adsorption capacity and capture rate of the sorbents to its original value, owing to the significantly improved physicochemical characteristics such as the grain size and surface area. Under oxy-fuel (with SO2) calcination conditions, the effectiveness of multi-acidification is limited due to the formed insoluble CaSO4. However, the introduction of filtration during multi-acidification can effectively remove CaSO4, thus recovering the adsorption capacity to its initial values.