Process for recovering chromic anhydride from exhausted aqueous chromium plating bath solutions with exploitation of the recovered chromium
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United States of America Patent
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May 12, 1992
Grant Date -
N/A
app pub date -
Nov 7, 1990
filing date -
Mar 23, 1988
priority date (Note) -
Expired
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Abstract
The chromic anhydride contained in soluble form (chromic acid) in exhausted, polluted chromium plating baths is recovered by alkalizing the exhausted chromium plating liquid to a pH comprised between 3 and 7 at a temperature of 70.degree. C. with a commercial sodium hydroxide solution, keeping the mass in reaction at this temperature for an hour and filtration separating the precipitate obtained. The filtered solution having a specific gravity of 1.25 kg/l, contains CrO.sub.3 (22% in weight) which is then reduced with sulphur dioxide to obtain a solution containing basic chromium sulphate and sodium sulphate, suitable for use as a tanning bath; in this manner pollution is avoided and the waste chromium is exploited. The solution containing CrO.sub.3 can also be introduced into a hexavalent chromium salt production cycle.
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