Studies On The Determination Of Trace Neptunium By Replacement Fluorometric Analysis

Neptunium is a very poisonous long-lived transuranium element. In the spent fuel reprocessing process and for the environmental concerns, very strict control is required for determination of neptunium.All the methods used now have a common technical difficulty: The presence of large amount of uranium makes unacceptable interferences to the determination of neptunium. A separation procedure is absolutely necessary to separate neptunium from uranium completely. Owing to the fact that uranium is 106~107 higher than that of neptunium ,it is extremely difficult to remove uranium from neptunium without any loss of neptunium ,either from the theoretical calculation or from practical experience . But this case is a common problem that often meets in samples of reprocessing.In this dissertation, an indirect fluorescence analysis method to analyze trace neptunium is discussed. Tb3+ in DTPA-Tb is replaced by Np4+ giving DTPA-Np and Tb3+, then the free Tb3+ complex with Tiron producing Tiron-Tb which is a strong fluorescence substance. We use the fluorescence signal of the ligand to measure Np4+ in the system. The high sensitivity of Tiron-Tb makes the method for neptunium sensitive.Main research work is as follows:(1) By choosing the working condition of instrument, consumption of ligand, optimal pH, buffer solution consumption and reaction time, etc, fluorescence signal of ligand of Tiron-Tb is improved and the background is reduced. The detection limit is 4.8 10-12g/ml, it is in accordance with the value reported.(2) High sensitivity was used to judge whether DTPA reaction with Tb3+ is complete or not, and whether the ratio between quantity of DTPA and Tb3+is 1:1 or not. A solution of DTPA-Tb is prepared by repeated experiments. Free Tb3+ in the solution is 2.53 10-10g/ml.This value is less than Tb3+ 's lower limit actually and show the prepared DTPA-Tb solution meeting the experimental request.(3) A procedure to analysis of Th4+ is established by selecting the acidity of the system, the temperature of replacement and the reaction time etc. The range of determination is 4 10-8~6 10-9g/ml, the minimum detection limit is 1.95 10-10g/ml.(4) At 45 , 90min, pH = 3, Np (V) can be reduced to Np (IV) with hydrazine nitrate.(5)We established a test method for the quantitative determination of trace neptunium by fluorescence of replacement. Within the range of 1 X 10-8~9.72 10-10 g/ml, the concentration of Np and intensity to the fluorescence of Tiron-Tb present relations of linearity, the detection limit for Np is 0.127ng/ml, nearly 1000 times high of uranium does not interfere the determination of the neptunium.The result obtained has high sensitive and the operation is simple to use this method. Especially it has strong anti-interference ability to uranium that will greatly reduce the separation difficulty.