Use of O3 and O3/H2O2 for degradation of organic matter from Bayer liquor towards new resource management: Kinetic and mechanism

Since the quality of bauxite resources has decreased and the organic carbon content has increased, different approaches are explored to remove the organic matter in alumina production. Advanced oxidative processes (AOPs) represent a possibility since they are widely used as an alternative for treating wastewaters to degrade organic pollutant molecules and in hydrometallurgy processes. For this reason, the goal of the project was the ozonation of Bayer liquor for organic matter removal. The ozone concentration was evaluated over time, as well as the H2O2 concentration and temperature. Results showed that the total organic carbon (TOC) removal achieved 19% in the most optimized condition with a kinetic rate of 0.0157 h(-1) -21.9 mg/L O-3, 0.05 mol/L H2O2 at 80 degrees C. The colour of the liquor changed from dark brown to white-yellow, indicating that the size of the organic compounds had decreased. Also, 95.4% of degraded TOC formed CO2, and almost 50% of the organic matter was oxalate compounds. The energy required for ozone production versus removed organic matter demonstrated that the technique proposed might be technically and economically feasible to be applied in the Bayer process. The study demonstrates the application of AOP in an extremely alkaline condition.