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 (O3), and persulfate (PS) (HC@PS@O3 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. O3 was also shown to activate PS. For OA oxidation using the HC@PS@O3 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@O3 process as a chemical oxidation technology. The kinetic investigation and economic evaluation of the HC@PS@O3 process can be used as the basis for real wastewater treatment processes in the future.