Detoxification of Ion-Adsorption Rare Earth Elements Low-Level Radioactive Residues via Mild Alkali–Carbonate: Uranium Extraction and Multi-Metal Recovery

Abstract Impeded by the harsh high-temperature/pressure conditions and persistent uranium (U) radioactivity, industrial scalability of the stepwise alkaline disposal for ion-adsorption rare earth elements (REEs) low-level radioactive residues (IAREEs-LLRRs) faced challenges. This work presented a mild atmospheric-pressure process for deep U(VI) extraction. After initial Al(III) leaching from IAREEs-LLRRs with dilute NaOH at atmospheric pressure, U(VI) was selectively leached using a NaHCO3–Na2CO3 buffer (pH 9–10, ≤90 °C), achieving 95.8% U(VI) extraction and reducing residue’s U-specific activity from 13.9 to 0.72 Bq·g–1 (<1 Bq·g–1 regulatory limit). The stepwise mild alkaline process cumulatively leached ∼88 wt% Al and ∼97 wt% U, achieving a weight reduction of ∼77 wt%, and enriched the REEs grade from 0.88 to 2.23 wt%. The U(VI) deep leaching mechanism proceeded via stabilization of soluble [UO2(CO3)3]4– while suppressing Na2U2O7 precipitation in the NaHCO3–Na2CO3 buffer at atmospheric pressure. Techno-economic assessment confirmed that this approach offered a viable and compliant route for sustainable residue detoxification and resource recovery.