Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 447 of 707

A - ml 0.02M EDTA (20ml); B - ml MgCl2, used for titration the excess of EDTA 0.02M; C - ml of sample, used; K= X , whereY X - 20ml 0.02M EDTA; Y - ml MgCl2, corresponding 20 ml 0.02 M EDTA One ml 0.02M EDTA corresponds 1.9212mg of sulfate. RESULTS AND DISCUSSION The obtained results summarized in Table 1, which represents a comparison of results the determination of sulfate in two working chromium plating baths and synthetically prepared chromium–sulfate solution, using gravimetric method and EDTA titration method. A number of samples were analyzed using the method of standard additions. Table 1 shows that the proposed volumetric EDTA method can be applied successfully for the simple and accurate determination of sulfate in chromium plating baths without a significant systematic error even in presence of 100 - fold excess of chromium (VI) and other of metals (iron, chromi- um (III), cupper, nickel), which usually are observed in chromium plating baths. The method involves the use of glycerin in presence of HCl (1:1) to rapidly and effectively reduce the valence state of chromium (VI) to chromium (III). Hydrochloric acid provides the environment for complete precipitation of BaSO4 in the presence of chromium (III) and other ions. Barium sulfate is separated from the mother solution by centrifuging. Next, the solution is separated from pre- cipitated BaSO4, after washing the precipitate with deionized water via a vacuum device. Aluminum alloys heating block is used for full and rapid dissolving pre- cipitate BaSO4 into EDTA + NH4OH mixture, providing accurate EDTA volu- metric method determination of sulfate in chromium plating bath. The volumetric EDTA method are most simple, rapid, sensitive and have sat- isfactory precision and accuracy in range 2.5–3 g/l sulfate and 232–262g/l of chromic acid. REFERENCES 1. Kenneth E., Langford, Janet E. Parker "Analysis of electroplating and relat- ed solutions", Fourth Edition, 1971. 2. Frank J. Welcher, "The analytical uses of Ethylenediamine tetraacetic acid", Toronto-London-New York, 1961. 3. Lurie Y.Y., Ribnikova A.I., "Chemical analysis of Wastewater", M, 1974, p.85. 4. White W., W., Henry M.C., "The determination of sulfate in chromium plating baths by EDTA titration" Plating, May, 1972, p.429-430. 446

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