Determination of stability constants of U(VI), Np(VI) and Pu(VI) with chloride ions by extraction chromatography

The complex formation of U(VI), Np(VI) and Pu(VI) with chloride ions was studied in HClO4-HCl solutions at ionic strength of 2.0 and [H+] = 2.0M by the method of extraction chromatography using dilute HDEHP as the stationary phase. The columns were dry packed with silicone treated Hyflo Super Cell. The amount of kieselguhr was 0.36-0.38 g. The stationary phase consisted of the 0.2 M HDEHP is mesitilene in the case of experiments with uranium and neptunium and, of 0.4 M HDEHP in mesitilene in the case of experiments with plutonium. About 100 μl of organic phase was introduced into the dry column. Oxidation of neptunium and plutonium was performed by means of ozone in 1 M HCl. No catalizing reagent was used. Elutions were performed at 25 +- 0.1 deg C, using 2 M HClO4, 2 M HCl or their mixtures, always pre-equilibrated with the organic phase used. The total concentration of the hydrogen ions was 2M. Before each elution the column was pre-equilibrated with about 5 ml of the mobile phase. The flow rate of mobile phase was controlled by means of a pressure device, and was equal to about 0.5 cmxmin-1. Drops of the eluate were collected on watch glasses, evaporated under the infrared lamp, and measured in γ or α solid scintillation counters. (T.G.)