Kompleksometryczna półmikroanaliza spinelu z Gierczyna

Wojciech Narębski



The author describes his method of semimicrochemical analysis of the zinc-magnesium spinel from Gierczyn in the Sudeten, by which method the quantitative determination of iron, aluminium, magnesium and zinc (and manganese if present), became possible using a very small specimen of this mineral (0.025-0.050 g). He used the powdered spinel in a quartz crucible with pyrosulphate, and dissolved the fused material in water slightly acidified with hydrachloric acid. In this manner; iron and aluminium were separated from magnesium and zinc by a single precipitation with pyridine, after adding 10 g ammonium chloride (due to the high content of sulphate in the solution). The washed precipitate is dissolved in weak hydrochloric acid and the iron content is determined by complexometric titration with salicylic acid as indicator, after the acidity has been adjusted very accurately to pH = 2. Aluminium is subsequently determined in the same solution by titrating excess of EDTA added with zinc salt in the presence of ferro- and ferricynide and dimethylnaphtidine (Sajo 1955). It 16 recommended to carry out the alkalization of the solution by means of an acetic buffer very carefully in order to avoid the formation of hydroxycomplexes of aluminium. For determining the iron content it is advisable to titrate photometrically; extremely small amounts of iron should be determined by the photocolorimetric method with the use or sulphosalicylic acid. From the filtrate containing large amounts of sulphates and ammonium salts, magnesium and zinc are precipitated by means of 8-oxychinoliine. The precipitate is carefully calcined, and the oxides obtained are dissolved in weak hydrochloric acid. In this solution, zinc i8 complexed by cyanide, and the magnesium la titrated with an EDTA solution .In the presence of Eriachrome Black. Subsequently, zinc is analogically determined in the same solution, after decomposition of its cyanide complex by means of formaldehyde.

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