Gas Electrode Method for Determination of Azide in Aqueous Samples From the Reprocessing Industry

Abstract

A method has been developed to determine azide (N₃^–) in aqueous samples from the reprocessing industry using a gas electrode with Teflon membrane sensitive to changes in the gaseous hydrazoic acid (HN₃) concentration. The presence of nitrite in mentioned samples gives rise to interferences from gaseous nitrogen oxides, hence nitrite was eliminated by oxidation with hydrogen peroxide prior to determination. As samples from the reprocessing industry have a varying matrix, the method of standard additions was used in combination with a fitting method based on linear least squares regression with Mathcad software. The electrode response was linear with the azide concentration from 3 × 10^–6 to 3 × 10^–3 mol l^–1 and the detection limit was about 10^–7 mol l^–1 azide. Relative standard deviations were between 10 and 20%.

In the reprocessing of ‘spent’ fuel elements, uranium is separated from plutonium and other radioactive fission products. To this end the ‘spent’ fuel elements are dissolved in concentrated nitric acid and the uranium in the resulting solution is extracted, purified and preconcentrated with a tributyl phosphate–kerosene mixture.During reprocessing, sodium azide (NaN₃) may be formed in the raffinate stream and thus introduce a potential hazardous situation (formation of an explosive mixture). To prevent this, azide is destroyed by reaction with nitrite in acidic medium according to the following reaction: HNO₂ + HN₃ → N₂O + N₂ + H₂O. However, it is still necessary to confirm the absence of azide in any given sample.

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