BACKGROUND Previous studies have found that phosphorite deposits in Tongren Bahuang of Guizhou Province is rich in the radioactive element uranium.

BAOBJECTIVES To investigate the distribution regularity of phosphorite type uranium deposits, the metallogenic mechanism, and comprehensive development of uranium resources, by using the stepwise chemical extraction method to analyze the occurrence of uranium.

METHODS The modified Tessier process was used to extract seven different forms of uranium, including water-soluble, exchangeable ion, carbonate-bound, iron-manganese combined, organic-pyrite combined, strong acid and residual.

RESULTS The uranium in the phosphorite deposits occurs mainly in the form of independent uranium minerals and metamorphosed isomorphisms, accounting for 37.83% and 37.21%, respectively, and a small amount of uranium (24.96%) exists in the form of dispersed adsorption. The results show that the content of independent uranium minerals in the P-rich rocks, pyrite veins and specular surface is higher, which indicates that the hydrothermal activity is beneficial to the enrichment of uranium in the form of independent minerals. The isomorphism uranium is positively correlated with the content of phosphorus, and the uranium element may be deposited in the lattice defects of colloidal phosphate in the way of ion-substitution. The content of the adsorbed uranium is affected by the clay mineral content and pyrite vein in the rock. The organic matter pyrite state is the main state of the adsorbed uranium. A small amount of uranium adsorbed on the surface of clay minerals by diffusion.

CONCLUSIONS In addition to the fact that the isomorphous uranium is not easy to extract and utilize due to its existing form, independent uranium minerals and adsorbed uranium have practical significance for optimizing the resource allocation in the future.