Environmental risk and mobilization of uranium and potentially toxic elements during leaching of the sandstone-type uranium ore.

Six lixiviants (NaNO2, FeCl3, citric acid (CA), oxalic acid (OA), HEDP, and EDDS) were employed in columnar static experiments to systematically investigate the release and migration of uranium and potential toxic elements (PTEs) in sandstone-type deposits and evaluate their associated ecological risks. Element mobilization was driven by the synergy between mineral dissolution and the physicochemical properties of the lixiviants. A dual-criteria evaluation framework, integrating leaching efficiency and the potential ecological risk index (PERI), was developed to optimize sustainable and efficient uranium leaching. The comprehensive performance ranking followed the order of CA > HEDP > OA > NaNO2 > FeCl3 > EDDS, indicating that CA represents a promising, high-efficiency, and eco-friendly leaching agent. In inorganic salts system, fluctuations in ionic strength altered mineral solubility, subsequently promoting PTEs mobilization. In the low-molecular-weight organic acids, acid-induced dissolution of clay minerals significantly elevated elemental concentrations. In the chelating agents system, metal migration was primarily governed by the stability of organo-metal complexes and their interactions with silicates, illite, and Fe-Al oxides. Ecological risk assessment results identified Ni and As, alongside uranium, as the primary contributors to the PERI in the leachates. Leaching significantly enhanced sample permeability but resulted in limited porosity increases, indicating simultaneous occurrence of mineral dissolution and secondary precipitation during water-rock reactions. This phenomenon significantly impacts the elemental migration pathways and subsequent environmental risks.