## 5 Discussions
### Role of Ferric Ions in Uranium Mineralization  
Ferric ion is one of the standard ions in the redox environment of natural water. In temperate, tropical climates, Fe is easily taken out of the weathering crust by surface water as Fe (OH)\({}_{3}\) colloid. Under the protection of an appropriate amount of humic acid or combined with humic acid to form a stable complex, Fe is transported by rivers to the catchment basin, distributed in the shallow sea on the continental margin, parallel to the coastline, and occurs in layers or lenticular. The scanning images of the uranium and ferric  
Figure 10: Synsedimentary and later diagenesis ferruginous sandstone in study area. (**a,b**) Ferruginous concretion formed in the sedimentary period with eU content of 30–40 ppm; (**c**) Uranium anomaly in ferruginous sandstone formed in the sedimentary period, 15–30 cm thick, later transformed with eU content of 341.74 ppm; (**d**) Ferruginous sandstone formed in later diagenesis period, 2–4 cm thick, with eU content of 5.2 ppm.  
ions are consistent with each other, indicating that the ferric ions are closely related to uranium mineralization. The concentration of ferric and uranium ions in water, the acidity and alkalinity of water, chemical composition, temperature, and pressure have effects on the redox reaction between ferric and uranium. Under standard conditions, when the temperature, pressure, uranium, and iron content in the water remain unchanged, Fe\({}^{2+}\) can reduce U\({}^{6+}\) in an alkaline medium, and the electrochemical reaction can be carried out spontaneously. The pitchblende-limonite or hematite-type uranium mineralization in the study area is the product of ferrous ion reduction.  
Figure 11: Uranium metallogenic model of Wajid ferruginous sandstone. **(a)**. Sedimentary and diagenetic period of ferruginous sandstone; **(b)**. Ferruginous sandstone transformation period.  
The paleoclimate of the Wajid sandstone sedimentary period was a temperate climate. The uranium-rich rock of the Arabian shield was oxidized and denuded, and most of the uranium in the rock was oxidized and dissolved, and migrated to the basin in the form of UO\({}_{2}\)\({}^{2+}\), UO\({}_{2}\)(SO\({}_{4}\))\({}_{n}\)\({}^{2(1-n)}\), UO\({}_{2}\)(CO\({}_{3}\))\({}_{n}\)\({}^{2(1-n)}\). The ferruginous sandstone in the sedimentary period contained a mixed colloidal solution of Fe\({}^{3+}\) and Fe\({}^{2+}\), which was generally a weak alkaline environment. When the oxygenated uranium-bearing water encountered the ferric colloidal solution, most of it was adsorbed by Fe(OH)\({}_{3}\), and part of it was reduced and precipitated by Fe\({}^{2+}\), organic carbon, and sulfur, forming the preconcentration of uranium, dispersed in the ferric cementation. During the transformation period of ferruginous sandstone in the early Neogene, the average pH values of the ferruginous sandstone and the surrounding sandstones were 8.98 and 8.49. The alkaline environment caused the dissolution of quartz particles to form a large number of dissolution pores and fissures. When the pH value was greater than 7.5, the uranium adsorbed by early Fe(OH)\({}_{3}\) began to resolve, and the uranium was filled into the corrosion pores and fissures, making the uranium ore further superimposed, transformed, and concentrated.