Time-resolved Fluorescence Method For The Determination Of Trace Uranium Sample Pretreatment Methods

Uranium is an important nuclear material, so the analysis of uranium is of great importance in every step of nuclear industry. The quantitative analysis of uranium is necessary in uranium's prospecting, smelting, purifying, transforming and concentrating, especially in nuclear fuel reprocessing and treatment of "three wastes". All of these analyses belong to trace uranium analysis in complex system analysis.Uranyl cations have the capability of fluorescent luminescence in a variety of medium while other metallic ions seldom have this characteristic. Hence, the fluorescent analysis method on uranium is provided with a specific property-selectivity. Time-resolved fluorescent (TRF) method is characterized with high sensitivity, easy operation, simple apparatus and small volume. As a result, it can be used for mining on-site analysis and can be placed in the glove box such that harm to analysts can be reduced. TRF method is the most important method in trace uranium analysis.Interfering ions are the main influencing factors to trace uranium's TRF analysis. The influence of H⁺, Fe³⁺ and NO₃^- are studied in this paper. The fluorescence intensity of uranyl cations is greatly affected by nitric acid. The fluorescence of uranyl cations are completely quenched when the concentration of nitric acid is 0.075mol/L. The concentration and lifetime of fluorescent complex are reduced by the addition of H⁺. The fluorescence intensity of uranyl cations are also affected by Fe³⁺ and NO₃^- because of the absorption of exciting light.A rapid and simple method that can eliminate the influence by interfering ions is established. The easy hydrolysis characteristic of Fe³⁺ and Pu⁴⁺ are used to precipitate them by addition of carbonate while the complex anions of uranyl cations and carbonate ions can be formed, thus the influence of H⁺, Fe³⁺ and Pu⁴⁺ to trace uranium's TRF analysis could be eliminated. Precipitation-baking-leaching method is chosen as the sample pretreated method. Ammonium carbonate is chosen as the precipitator after compared with other carbonates. The dosage of ammonium carbonate is also studied. The baking temperature and time of the samples are compared after addition of ammonium carbonate. The ammonium carbonate solution is chosen as the leaching solvent, and the dosage of leaching solvent and leaching time are studied.The actual samples are analyzed in the method after the conditions of which are optimized. The pretreated samples are analyzed by TRF in which the content of Fe³⁺ are different. The samples of trace uranium in large quantity of plutonium are pretreated by the method, and then the pretreated samples were analyzed by TRF with the recovery of 30%. The samples are pretreated in the method after addition of certain quantity Fe³⁺ and then uranium content is determined by TRF with the recovery of uranium increase to 60%～70%. The steady recovery can be used to calibrate the content of trace uranium. The method is simple and rapid.