The absorptiometric determination of niobium and tantalum with pyrogallol

Abstract

Absorptiometric procedures are described for the determination of niobium and tantalum in mixtures of their oxides. The method is applied to the determination of the two metals in mixtures obtained by their chromatographic extraction from minerals and ores. The determinations depend on the formation of a coloured complex between tantalum and pyrogallol in acid solution and between niobium and pyrogallol in alkaline solution. Both systems obey Beer's law, and, with 1-cm cells, the optimum limits of concentration are 0 to 20 p.p.m. for niobium and 0 to 80 p.p.m. for tantalum. The effect of variation in pH and the interference of a number of cations and anions are recorded.

Determination of Niobium and Tantalum in Minerals, Ores and Concentrates Using Ion Exchange.

“…The determination of niobium and tantalum in ores based on cellulose chromatography (3,4,22,38) has become popular in Europe, less so in the United States. A shortened chromatographic procedure is also available (15,21).…”

Determination of Tantalum in Niobium

“…Although methods have been published in which Rhodamine B (3) and hydrogen peroxide (11) have been used for the photometric determination of tantalum, pyrogallol is the most widely used color-developing reagent for this element. Previous methods in which the tantalum-pyrogallol color was measured in sulfuric or phosphoric acid solution (5,6,10) wrere subject to strong interference from niobium, titanium, and tungsten, and some corrections had to be applied. By measuring the tantalum color in hydrochloric acid solution at 325 µ, Dinnin (2) found that the interference caused by niobium and titanium could be greatly diminished.…”

Separation and Determination of Tantalum

“…1 Uranium, 92.0 mg.; tungsten, 0.5 mg. 8 Uranium, 105 mg.; tungsten, 0.5 mg. 4 Molybdenum, 0.5 mg.; zirconium, 2.0 mg.; cobalt, 6.0 mg. * Cerium, 1.0 mg.; neodymium, 1.0 mg. ' Cobalt, 3.0 mg.; neodymium, 2.0 mg.; zirconium, 1.0 mg.; cerium, 1.0 mg.; ruthenium, 0.5 mg. 4 Cobalt, 3.0 mg.; cerium, 1.0 mg.; zirconium, 1.0 mg.; molybdenum, 0.5 mg.; ruthenium, 0.5 mg.…”

“…For determination of small amounts of tantalum after separation, colorimetric methods seemed to offer the sensitivity required. The pyrogallol (4,5,10), perhydrol (8), and chromotropic acid reactions (1) have been adapted for colorimetric procedures.…”