Green approach for separating iron and rare earths from complex polymetallic solid residues via hydrogen-based mineral phase transformation: A pilot-scale study

The Bayan Obo low-grade polymetallic ore (BOLPO) has been abandoned for many years owing to its difficult beneficiation and remains as a solid residue. This is causing significant ecological damage to the surrounding environment. In this pilot-scale study, hydrogen-based mineral phase transformation (HMPT) technology and associated equipment were used to successfully separate iron and rare earths from BOLPO, demonstrating stable operation for 48 h. Optimal HMPT conditions included a feed rate of 120 kg/h, HMPT temperature of 500 °C, gas flow rate of 3.5 m3/h and gas concentration of 22.5 vol%. After grinding and flotation defluorination, the obtained iron concentrate had a TFe grade of 65.26 wt%, a recovery of 85.29 wt%, and a low F grade of 0.28 wt%. Product analysis revealed phase transformations of iron and rare earths during the HMPT process, which increased the magnetic difference between the magnetic and non-magnetic products. The formation of pores and cracks during this process also facilitates the subsequent separation of iron and rare-earths. This study paves the way for clean and efficient iron and rare earth separation with regional mineral recovery potential.