Mechanism of Enhanced Leaching U and Sc by Sulfuric Acid with H3NTA

To address the issues of low leaching efficiency and pore clogging in sandstone-type uranium deposits during conventional sulfuric acid leaching, this study proposes a low-acid synergistic leaching enhancement method using nitrilotriacetic acid (H 3 NTA). The effects of sulfuric acid concentration, organic ligand type, and ligand concentration on the leaching of uranium and scandium were systematically investigated. The enhancement mechanism was elucidated through UV-Vis spectroscopy and first-principles calculations based on CASTEP. The results showed that under the conditions of H 2 SO 4 2.0 g/L, H 3 NTA 1.6 g/L, L/S ratio of 5:1, room temperature, and leaching for 1 day, the leaching of U and Sc reached 75.1% and 13%. Among EDTA and EGTA, H 3 NTA exhibited the best synergistic leaching effect. The red shift of the characteristic peak at 803∼820 nm in the UV-Vis spectrum confirmed the chelation between H 3 NTA and uranyl ions. First-principles calculations revealed that [UO 2 (SO 4 ) (HSO 4 ) 2 (H 2 O)] 2- is the most stable species in the sulfuric acid system, and the introduction of H 3 NTA competes with SO 4 2- for coordination sites, forming stable U-NTA complexes. This study significantly improves the recovery of uranium and scandium by utilizing the chelating synergistic effect of H 3 NTA, providing a new pathway for efficient and clean leaching of low-permeability sandstone uranium deposits.