process for recovery of chromanhydrid from erschoepften waessrigen chromplattierungsbaedern using of the recovered chromium.

摘要

PCT No. PCT/IT88/00038 Sec. 371 Date Nov. 7, 1990 Sec. 102(e) Date Nov. 7, 1990 PCT Filed May 24, 1988 PCT Pub. No. WO89/09188 PCT Pub. Date Oct. 5, 1989.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 DEG 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 CrO3 (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 CrO3 can also be introduced into a hexavalent chromium salt production cycle.