Abstract
Tantalum and niobium in heat resistant alloys were precipitated quantitatively by tetraphenylarsonium chloride (TPAC) from, respectively, >1M and >8M hydrofluoric acid solution, and were readily separated from tungsten, molybdenum, titanium and zirconium.
A sample was taken in a polyethylene beaker, and decomposed by heating on a boiling water bath with 30 ml of hydrofluoric acid and 40 ml of aqua regia. The solution was then made up to 130 ml with 30ml of hydrofluoric acid and water. Twenty milliliters of TPAC solution (0.025M) was added, and the mixture was allowed to stand for 30 min. in the water bath drawn from fire. The aged precipitate was filtered with a bit of paper pulp through a filter paper and washed with TPAC washing solution (10 ml of TPAC solution and 1 l of 1M hydrofluoric acid). It was then transferred to a high purity alumina crucible, ignited at 900°C for an hour and weighed as combined pentoxides. If necessary, the oxides were fused to dissolve for respective determinations of Nb and Ta by spectrophotometry. The mutual separation of niobium and tantalum was not possible by this procedure.
