Combining ozone and ultrasound technology to remove S2− in Bayer liquor

High content sulfur (S2-) in Bayer liquor can increase alkali consumption, accelerate equipment corrosion, especially seriously affect alumina production. The removal of S2- in Bayer liquor is studied using ultrasonic enhanced ozone method, which significantly improves the removal efficiency. Results indicate that the best removal efficiency of 93.83 % is obtained with reaction duration of 20 min, oxygen flow rate of 80 L/h, ultrasonic power of 60 W and reaction temperature of 60 °C. The comparative analysis shows that the removal efficiency of S2- is 25.34 % higher than that of ozone (O3) system after introducing ultrasound (US), indicating that US accelerates the mass transfer process of O3 and increases the hydroxyl radicals (OH) content. For further explanation of the mechanism of US/O3 system, EPR and XPS spectra are applied to analyze the content of free radical and the form of sulfur in Bayer liquor, indicating that the content of free radical in US/O3 system is more than US and O3 systems, and all sulfur is converted to SO42- after full oxidation.