Rapid titrimetric determination of free acidity in process samples of uranyl nitrate

Abstract

A simple titrimetric method for the rapid determination of free nitric acid associated with process stream samples of uranyl nitrate is described. The hydrolysable ions present in the samples are protected from interference by complexing them with sodium fluoride or potassium oxalate. Sodium hydroxide is used as the titrant for the free acid. A mixed indicator of Bromothymol Blue and Neutral Red with a transformation point at pH 7.2 is used for the detection of the end-point when sodium fluoride is the complexant. Another mixed indicator of Methyl Red and Methylene Blue with a transformation point at pH 5.4 is used when potassium oxalate is used as the complexant. A precision of 0.02 mol l^–1 is attainable in both cases. The results obtained compared well with those obtained using potassium hexacyanoferrate(II) as the complexant. For samples containing larger amounts of soluble silica, potassium oxalate is preferred over sodium fluoride as the latter reacts with silica, releasing hydroxyl ions and leading to lower values of free acidity. Also, potassium oxalate is superior to sodium fluoride as it generates no corrosive analytical waste.