PROCESS OF REJUVENATION OF CHROMIUM ELECTROLYTES ( VARIANTS ) Russian patent published in 2003 - IPC

FIELD: technology of electrocoloring processes which can be employed in mechanical and radio engineering for rejuvenation of chromium electrolytes contaminated with ion impurities of metals. SUBSTANCE: technical result of invention consists in expansion of range of existing methods of rejuvenation of chromium electrolytes, reduction of chromium electrolytes for deposition of coats with any degree of rejuvenation, recovery of chromium anhydride and its injection into technological process without any additional consumption of high-toxicity hexavalent chromium, prevention of disposals of concentrated high-toxicity chromium solutions, wasteless rejuvenation technology. Process of rejuvenation of chromium electrolytes includes injection of potassium hydroxide or potassium carbonate into electrolyte to form complex compounds of ions of metal-impurities and transfer of metal-impurities to precipitate with control over pH value corresponding to formation of complex compound of ions of metals easily dissolved in rejuvenated medium, curing of mixture in the course of 15-20 h, filtration of mixture to separate precipitate and return of electrolyte to technological process. Electrolyte solution is diluted in ratio 1:3 prior to injection of potassium hydroxide or potassium carbonate. Filtrate is evaporated, cooled with crystallization of potassium bichromate contained in it, it is separated from evaporated solution, then saturated aqueous solution of potassium bichromate is obtained. Chromium anhydride is formed by treatment of saturated aqueous solution of potassium bichromate with the aid of concentrated sulfuric acid with subsequent curing of obtained solution and crystals of chromium anhydride precipitated out of solution are separated. Precipitate obtained after injection of potassium hydroxide or potassium carbonate is washed with water and filtrate is evaporated together with washing water with concentration of potassium bichromate within limits of 15-46 per cent by mass. Electrolyte is returned to technological process in accord with two variants. In compliance with first variant electrolyte is returned to technological process by injection of chromium anhydride. In agreement with second variant return to technological process is carried out by preparation of fresh electrolyte based on chromium anhydride. EFFECT: expanded range of existing methods of rejuvenation of chromium electrolytes, wasteless technology of electrolyte rejuvenation. 6 cl