Analytical Chemistry of Niobium and Tantalum by Ross W. Moshier

By Ross W. Moshier

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TARTRATE HYDROLYSIS FOR PRECIPITATION OF THE MAJOR FRACTION OF THE TANTALIC, NIOBIC AND TUNGSTIC ACIDSd'2) Treat the filtrate after removal of the metals of the hydrogen sulfide group with more hydrogen sulfide to reduce iron to the ferrous condition. This should be done on the filtrate evaporated to 150 ml. Bring the solution to the boil and stir in 25 ml of concentrated hydrochloric acid and continue to boil for 5 min. Niobic acid precipitates immediately but tantalic acid requires a little longer for precipitation.

The tantalum precipitate is not of definite composition. The precipitate therefore cannot be dried and weighed as such, and must be ignited to the oxide. 46 per cent niobium. It dries to constant weight at 110° and can be weighed as such if desired/33^ Procedure III. ^® The combined filtrates and washings from Procedure I contain all of the titanium and zirconium. Evaporate the solution almost to dryness and destroy the pyrogallol by digesting first with fuming nitric acid and then with a mixture of perchloric acid and sulfuric acid.

Cool the melt on the sides of the crucible, dissolve it in 1 g of tartaric acid in 20 ml of water, and dilute with water to volume in a 100 ml volumetric flask. Samples containing 4 per cent or 15 per cent niobium pentoxide are dissolved using 2 g and 5 g of tartaric acid respectively. The solution is now ready for colorimetric analysis. Recommended is the homogenous solution (with acetone) thiocyanate method of Freund and Levitt, with suitable corrections for the interference of iron, titanium and tungsten.

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