In this work, we report that the addition of lactic acid (HLa) can make irreversible desulfurization processes [such as using NaOH and Ca(OH)(2)] reversible. A universal method to save energy for any reversible flue gas desulfurization process using HLa is reported. It is found that adding HLa to existing absorbents (such as ionic liquids and deep eutectic solvents) has two benefits: accelerating the desorption rate and reducing the energy use of SO2 desorption processes. Furthermore, as a result of the addition of HLa, the residual contents of SO2 in absorbents after regeneration are reduced, which can significantly decrease the SO2 concentration in the emitted flue gas.