Study on the Purification Effect and Mechanism of Micro–Nano-Bubble-Based Two-Stage Air Floatation Method on the Raw Sugar Redissolved Syrup

This study explores the purification effect of micro–nano-bubble-based two-stage air flotation on syrup using raw sugar-redissolved syrup as the research object and adopting indicators such as decolourisation and turbidity removal rates. Based on a single-factor experiment, an orthogonal experiment was designed to optimise the process conditions. The optimal process conditions were as follows: magnesium oxide (calculated by magnesium ions), 500 mg/L; pH in the primary air flotation, 11.3; phosphoric acid concentration, 250 mg/L; and pH in the secondary air flotation, 9.0. Under these conditions, the decolourisation rate was 55.83% and the turbidity removal rate was 83.5%. Furthermore, the relevant mechanism is discussed and it is based on the zeta potential of the pure water and syrup systems as well as the infrared absorption spectra of the scum.