鉱石中のタングステンの光度定量法

概要

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Thermal decomposition of tungsten ores with hydrochloric, sulfuric, or phosphoric acid, and heating of the resultant product with sulfuric acid to a temperature at which white fumes were evolved produced a solution. The solution was filtered, diluted to a definite volume, and a portion of it was used for photometric determination. Since the coloration by reduction of the sample solution acidified with sulfuric or hydrochloric acid gave a lower value, the solution was made alkaline with NaOH ; but still it was not possible to obtain the coloration as above with an error less than 1 %. Therefore, the sample solution was heated to fuming with sulfuric and phosphoric acids, and the coloration of the product by reduction showed a linear relationship with the amount of tungsten when the amount of tungsten was less than 2.1 mg. Thus, the sample solution in 10 cc H2SO4 and 2 cc H3PO4 was heated to white fuming in 5 minutes, cooled, and 810 cc water and 20 cc HCl were added. The solution was then reduced with 3 g SnCl2, colored with 5 cc water and 10 cc 10 % KSCN, and made up to 100 cc with water. The intensity of color through an S 43 filter plate and a 1 cm layer was estimated. Application of this method to ores containing less than 50 % WO3 and a comparison of the results with the JIS method showed that the maximum error was 0.5 % and the average error was 0.30.02 %.
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