Rapid volumetric determination of niobium in the presence of titanium and zirconium by hydrogen peroxide complex formation

Abstract

Complexes of titanium and niobium with hydrogen peroxide are similarly formed in a dilute sulfuric acid solution, but their reactivities with potassium permanganate are distinctly different from each other against the concentration of sulfuric acid. Titaniumhydrogen peroxide complex readily reacts with potassium permanganate. Niobium complex (Nb : H₂O₂= 1 : 1) does not react in the sulfuric acid concentration less than 3 M, but does completely in that more than 8 M. On the other hand, no complex of zirconium is formed with hydrogen peroxide.
The recommended procedure for determination of niobium is as follows. One gram of sample (mixture of oxides of titanium, niobium and zirconium) is heated to dissolve in the mixture of 5 ml of 98% sulfuric acid and 3 g of ammonium sulfate, and diluted to 100 ml with distilled water. An aliquot of this solution is mixed with 5 ml of 0.1 M hydrogen peroxide, and titrated with 0.04 M potassium permanganate solution. The amount of niobium is calculated from the difference of the added and titrated volumes of hydrogen peroxide. To the above titrated solution is then added gradually the same volume of 98% sulfuric acid in an ice-water bath, and the titration is carried out at below 20°C. The amount of niobium is also calculated from this titer. One ml of 0.04 M KMnO₄ corresponds to 9.29 mg of niobium.
A number of samples can be analyzed by the proposed method rapidly and conveniently without any special equipment or chemicals.