Effect of liquid nitrogen cold soaking on the pore structure and fractal characteristics during in situ leaching of sandstone uranium ores

In this study, a green and efficient liquid nitrogen fracturing method was explored. Sandstone uranium ore was first treated with liquid nitrogen cold soaking, followed by an analysis of the evolution of its pore and fracture structure using Low temperature nitrogen adsorption(LTNA), Nuclear magnetic resonance (NMR), and Scanning electron microscopy (SEM). The fractal characteristics of the pore structure and its evolution mechanism were also examined.The results show that gas adsorption in the ore increased with longer cold soaking times and more cycles.The highest nitrogen adsorption capacity was observed at a soaking time of 180 min, reaching 15.8556 cm³/g. Additionally, after 15 freezing cycles, the nitrogen adsorption capacity reached 14.8818 cm³/g. The proportion of micropores decreased, while mesopores and macropores increased. Specifically, after 180 min of liquid nitrogen soaking, micropores decreased by 9.59 %, mesopores increased by 7.79 %, and macropores increased by 1.8 %. After 15 cycles, micropores decreased by 10.55 %, mesopores increased by 6.38 %, and macropores increased by 4.17 %. SEM observations confirmed that the liquid nitrogen treatment expanded existing pores and cracks, and generated new fractures.Fractal dimension analysis revealed that liquid nitrogen treatment reduced the fractal dimension of the ore.This study effectively improves permeability and promotes uranium leaching in sandstone ores.