Leaching of Rhenium from Secondary Resources: A Review of Advances, Challenges, and Process Optimisation

Rhenium is one of the rarest and most strategically important metals, indispensable in high-temperature superalloys and platinum–rhenium catalysts used across the aerospace and petrochemical industries. Owing to its limited primary reserves, recovering rhenium from secondary sources, such as spent catalysts, superalloy residues, and metallurgical dusts, has become vital to ensuring supply security. This review examines technological developments between 1998 and 2025, focusing on how operational parameters, including temperature, leaching time, reagent concentration, and solid-to-liquid ratio, govern dissolution kinetics and overall process efficiency. Comparative evaluation of hydrometallurgical, alkaline, and hybrid processes indicates that modern systems can achieve recovery rates exceeding 98% through selective oxidation, alkaline activation, or combined pyro and hydrometallurgical mechanisms. Acid–chlorine leaching facilitates rapid, low-temperature dissolution; alkaline sintering stabilises rhenium as soluble perrhenates; and hybrid smelting routes enable the concurrent separation of rhenium and osmium. Sustainable aqueous systems employing nitric and ammonium media have also demonstrated near-complete recovery at ambient temperature under closed-loop recycling conditions. Collectively, these findings highlight a technological transition from energy-intensive, acid-based pathways towards low-impact, recyclable, and digitally optimised hydrometallurgical processes. The integration of selective oxidants, phase engineering, circular reagent management, and artificial intelligence-assisted modelling is defining the next generation of rhenium recovery, combining high extraction yields with reduced environmental impact and alignment with global sustainability goals.