The Application of the Radiotracer Techniques in Hydrometallurgy: A Method for Online Monitoring of Solvent Extraction Processes Using 181Hf

The increasing demand for critical metals essential for renewable energy technologies necessitates efficient and environmentally sustainable extraction methods. Ilmenite (FeTiO3) and similar ore deposits serve as abundant sources of primary elements while also incorporating a suite of strategically significant trace elements, including REEs and Hf, among others. Mixer–settler units are extensively utilized in metal purification processes. It is important to develop approaches for tracking the metal’s extraction process online and optimizing flow dynamics. One widely adopted technique for evaluating the flow dynamics of the various components is the residence time distribution (RTD) measurement, which provides insights into the hydrodynamic behavior of process reactors. This study explored the application of radiotracer techniques for online monitoring of solvent extraction processes in hydrometallurgy, focusing on Hf recovery. A mixer–settler system was employed using di(2-ethylhexyl) phosphoric acid (D2EHPA) as the extractant and the 1M HNO3 aqueous phase of Ti ore. The radiotracer 181Hf was synthesized via neutron activation and introduced into the system to track phase distribution and RTD. Real-time monitoring revealed over 95% extraction efficiency within 133 min (8000 s). The RTD studies validated system performance using perfect mixers in series and axial dispersion models. The calculated mean residence time of 100 min (6000 s) closely aligned with the theoretical 104 min (6240 s), confirming the model accuracy. The findings demonstrate the viability of radiotracers in monitoring solvent extraction, offering real-time insights into flow dynamics and extraction efficiency.