Selective separation of sodium with citric acid leaching from red mud has been put forward. The main factors and dealkalization mechanism by using inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, and shrinking core model were studied. The results show that the dealkalization rate reached more than 95% under the following conditions: citric acid dosage of 15%, liquid-to-solid ratio of 7 mL/g, leaching temperature of 100 degrees C, stirring speed of 300 rpm, and leaching time of 120 min. Sodium easily dissolved in the solution by citric acid leaching. The dealkalization process was controlled by internal diffusion and the apparent activation energy (E-a) was 19.43 kJ/mol.