Abstract: This study investigated re-dissolved red granulated sugar juice and evaluated the feasibility of achieving efficient decolorization using a two-stage flotation process based on in situ formed magnesium hydroxide. The single-factor and orthogonal experiments were used to analyze the effects of magnesium oxide dosage, pH, phosphoric acid dosage, sulfite dosage, temperature, and other variables on the decolorization rate. The mechanism through zeta potential measurements, X-ray diffraction, and scanning electron microscopy were explored. Results showed that, under the optimal conditions, which included a pH level of 11.3, a magnesium oxide concentration of 500 mg/L, a phosphoric acid concentration of 450 mg/L, a sulfurous acid concentration of 150 mg/L, and a temperature of 70 °C, the process achieved a decolorization rate of 91.51%. The in-situ formed magnesium hydroxide exhibited a positive zeta potential, indicating a high positive charge that neutralized and adsorbed negatively charged non-sugar impurities, such as pigments, in sugar juice through electrostatic interactions. During the first air flotation, magnesium hydroxide primarily adsorbed these impurities to achieve decolorization. The air flotation method efficiently separated the pigment-laden magnesium hydroxide from the sugar juice. These findings could provide new evidence for developing green and efficient magnesium-based sugar refining processes.