High flow-rate pre-leaching of low-grade uranium ore: gypsum reduction

Currently, a widely accepted solution to reduce gypsum precipitation in acid leaching of low-grade uranium ore has not yet been identified. This study aims to delve into the impact of different flow rates on gypsum precipitation in ore through column leaching experiments. Complementary methods such as Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were used to characterize slag samples. The results indicate that as the flow rate surged from 63.69 Lh⁻¹m⁻² to a whopping 254.76 Lh⁻¹m⁻², the gypsum content and types in the slag decreased gradually. This can be attributed to two factors: (1) the elevation of flow rates maintains the ore heap in a lower pH environment, promoting the conversion of SO₄²⁻ to HSO₄⁻; (2) higher flow rates contribute to increased ore heap porosity, providing more migration pathways for solutions containing high concentrations of Ca²⁺, SO₄²⁻, and HSO₄⁻, thus facilitating the separation of gypsum from the ore. This study affirms the feasibility of employing high-flow pre-leaching to address gypsum clogging issues, offering a new perspective for acid pre-leaching.