Carbon dioxide (CO2)-aided acidification of aqueous carboxylate solutions and simultaneous reactive extraction of the carboxylic acid is a promising and clean alternative method for the conventional recovery of carboxylic acids. The complexity of the extraction system is endorsed by the presence of three or four coexisting phases (i.e., vapor-liquid-liquid-(solid)) and an aqueous electrolyte solution. Selection of optimal operating conditions in this complex four-phase system requires a robust, yet simple model for description of the phase equilibria. this work, such a simple shortcut model is presented. Although the model parameters are obtained from pure component or infinite dilution data only, the model yields a reasonable description with experimental data. Model predictions were compared with experimental data for the CO2-aided extraction of lactic acid with two different amine extractants from various concentrations of a calcium lactate solution and pressures up to 3.1 MPa. The model is expected to be very useful for equipment and process design.