Method for regenerating alkaline solutions for pickling aluminum

A method for regenerating alkaline solutions for pickling aluminum to recover aluminum hydroxide, comprising:

• a) providing an aqueous pickling solution for pickling aluminum comprising alkali hydroxide and a complexing agent in a pickling bath;
• b) contacting the pickling solution with aluminum to be pickled, so that aluminum is dissolved in the pickling solution as aluminate;
• c) adjusting the concentration of aluminate, alkali hydroxide, and complexing agent in the pickling solution to maintain a concentration of about 30 to 60 g/l aluminate given as equivalents of Al, about 30 to 60 g/l alkali hydroxide given as equivalents of sodium hydroxide, and about 0.1 to 5 g/l complexing agent given as gluconate or equivalents of gluconate, and adjusting the temperature of the pickling solution in the pickling bath to maintain the temperature of the pickling solution between 40.degree. to 90.degree. C., so that the pickling solution in the pickling bath with respect to precipitation of aluminum as aluminum hydroxide is undersaturated or metastably supersaturated;
• d) transferring the pickling solution from the pickling bath to a reactor section, defining an aqueous reactor solution, for precipitating aluminum as aluminum hydroxide from said reactor solution;
• e) cooling the reactor solution by about 5.degree. to 70.degree. C. so that the reactor solution in the reactor section with respect to precipitation of aluminum as aluminum hydroxide is unstably supersaturated;
• f) precipitating aluminum as aluminum hydroxide from the reactor solution in the reactor section, thereby reforming alkali hydroxide;
• and,
• g) recovering the aluminum hydroxide and the reformed alkali hydroxide.