Time-dependent citrate-mediated precipitation inhibition in uranium column leaching: Mechanistic insights into pore...

Uranium is a critical resource for clean nuclear energy, but its extraction efficiency is severely hindered by pore blockages caused by secondary precipitates from dissolved associated ions during acidic leaching. This study explored the pore-structure evolution, calcium sulfate precipitation, and solute transport behavior during uranium column leaching with timing-controlled citric acid dosing, elucidating temporal regulation mechanism of complexing agent to uranium transformation and migration in ore media. The results showed that acidification-stage dosing achieved a peak uranium leaching rate of 5.54%·d^-1 at an effluent pH of 6.27 and Eh of -80 mV, and yielded a final uranium recovery of 92.73% (14.86% higher than the control) with the most longitudinal recovery uniformity. XRD, FT-IR, BET, and SEM-EDS characterization indicated that this improvement was associated with citrate-involved surface interactions on mineral surfaces, as evidenced by the appearance of a carboxyl-related CO band at ∼1685 cm^-1. This dosing strategy reduced gypsum accumulation and preserved a high specific surface area of 14.47 ± 0.09 m²·g^-1 in the leaching residues. Conversely, continuous dispersed dosing promoted denser pore-filling calcium sulfate deposits, resulting in a lower residue specific surface area of 7.98 ± 0.02 m²·g^-1 and less favorable uranium recovery. These findings highlight the crucial role of complexing agent timing-controlled regulation on uranium transformation and recovery, also providing significant insights into elucidating the uranium fate in environment.