Thorium Valorization at the Interface of Technology, Risk, and Sustainability.

Thorium (Th), a naturally occurring actinide, is gaining renewed attention due to its dual role as a strategic nuclear resource and a potential environmental contaminant. This review critically reassesses thorium valorization pathways by integrating extraction technologies, environmental behavior, toxicological risks, and regulatory constraints. While thorium is primarily recovered as a by-product of rare earth element (REE) processing, conventional hydrometallurgical methods-though mature-generate significant secondary waste and pose environmental challenges. Emerging technologies, such as functionalized adsorbents, membrane systems, and biohydrometallurgy, show promise but remain largely confined to laboratory-scale studies due to scalability and stability issues. A key finding is that thorium's environmental mobility and toxicological impact are directly influenced by the extraction processes used, creating species with distinct bioavailability and risk profiles. This work highlights the disconnect between high laboratory efficiencies and real-world applicability, emphasizing the need for integrated approaches that consider lifecycle impacts, waste minimization, and occupational safety. We propose a circular economy framework for sustainable thorium management, connecting green primary processing, secondary recovery from industrial residues, smart environmental stewardship, and supportive policy. The review concludes that successful thorium valorization depends not on incremental efficiency gains but on holistic designs that reconcile technological performance with environmental and health safeguards.