Study on Chemical Speciation of Uranium in Samples from in-situ Leaching Sandstone-type Uranium Deposit in Xinjiang

This paper presents a method of studying uranium speciation from in-situ leaching sandstone-type uranium deposits by a sequential extraction procedure and demonstrates its application to sandstone uranium exploration. The chemical extraction procedure was modified from Tessier. Uranium in samples was classified into five speciations: exchangeable ions, bound to carbonates, bound to Fe-Mn oxides, bound to sulfide-organic matter and residual speciation. The first four phases consisted of active uranium with the residual uranium being stable uranium. The results show that the uranium distribution characteristics were significantly different whether they were in different samples or in the same sample. The average amounts of residual speciation, carbonates speciation, exchangeable speciation, sulfide-organic matter speciation and Fe-Mn speciation decreased in order as 37.75% (RSD=1.80%), 20.56% (RSD=2.72%), 15.51% (RSD=1.85%), 14.26% (RSD=2.08%) and 11.91% (RSD=1.75%), respectively. According to the present technology of acid dipped processing, the active uranium was leachable and the inert uranium was unleachable. This study indicates that residual speciation is the primary component. The uranium extraction rate for uranium ore with a high proportion of residual uranium (such as the No.4 sample with 57.17% residual uranium in this paper) is lower and the extraction rate does not increase significantly by improving the dissolve acidity and oxidants.