By Ross W. Moshier
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Extra resources for Analytical Chemistry of Niobium and Tantalum
Wash the precipitate with a mixed solution containing 5 per cent of ammonium chloride and 1 per cent ammonium oxalate. The completeness of the precipitation and recovery of these three metals should be ascertained by testing the filtrate as follows. 1 g of tannin, and then titrate cautiously with IN ammonium hydroxide until a precipitate appears. If the precipitate is pale orange, titanium or niobium is present (tantalum will always be completely precipitated, even in solutions of higher acidity).
DISSOLUTION OF THE SAMPLE 39 Procedure. A preliminary concentration of the earth acids frees them from a high proportion of the other elements and residual material (zirconia and silica) present. Fuse a weighed sample of the ore with potassium pyrosulfate in a quartz crucible and dissolve the cooled melt in tartaric acid solution. Precipitate the earth acids by the cupferron or tannin method and ignite the impure earth acid precipitate at 600°. The selenous acid procedure is applied to the ignited residue obtained from the preliminary concentration from the ore.
Filter off the residue on a high-retention filter paper, and wash 5 times with 2 per cent sodium hydroxide solution. The filtrate contains chromium, tungsten, molybdenum, tin, silica and aluminum. The residue contains niobium, tantalum, titanium and iron, together with traces of impurities. 3N sulfuric acid solution containing 1 ml of 30 per cent hydrogen peroxide. Discard the filter paper. Add 8 ml of 33 per cent sulfuric acid to the solution and boil to destroy the hydrogen peroxide. Add 1 ml of 1M manganese sulfate solution and 2 g of ammonium persulfate to the cool solution, and dilute to about 200 ml.