Hybrid reactor based on hydrodynamic cavitation, ozonation, and persulfate oxidation for oxalic acid decomposition during rare-earth extraction processes

Abstract

A cost-effective method for treating oxalic acid (OA) during rare-earth extraction was developed using hydrodynamic cavitation (HC), ozone (O-3), and persulfate (PS) (HC@PS@O-3 process). The results showed that the optimal inlet pressure during HC was 5.10 kg cm(-2) with an orifice plate diameter of 2 mm. Moreover, HC was shown to activate PS, providing an alternative activation method to base or heat as an ultrasound activation method for chemical oxidation. O-3 was also shown to activate PS. For OA oxidation using the HC@PS@O-3 process, the optimum pH was 3 and the reaction rate increased with increasing temperature. Further, the activation energy was 36.69 kJ mol(-1). The mechanisms unveiled in this study will allow optimization of the HC@PS@O-3 process as a chemical oxidation technology. The kinetic investigation and economic evaluation of the HC@PS@O-3 process can be used as the basis for real wastewater treatment processes in the future.