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

High content sulfur (S 2− ) in Bayer liquor can increase alkali consumption, accelerate equipment corrosion, especially seriously affect alumina production. The removal of S 2− 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 S 2− is 25.34 % higher than that of ozone (O 3 ) system after introducing ultrasound (US), indicating that US accelerates the mass transfer process of O 3 and increases the hydroxyl radicals ( OH) content. For further explanation of the mechanism of US/O 3 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/O 3 system is more than US and O 3 systems, and all sulfur is converted to SO 4 2− after full oxidation.