Wet-process phosphoric acid brightening reagent for aluminum

Claim 1

A process for brightening aluminum using a wet process acid which consists essentially of (a) diluting with water a wet process polyphosphoric acid, said wet process polyphosphoric acid comprising a phosphoric acid concentration of about 80% by weight, flouride ions, a phosphorus to flouride ion ratio of about 35:1 and further comprising iron, aluminum and magnesium contaminates so that said phoshoric acid concentration is reduced to about 50% by weight and said phosphorus to flouride ion ratio is increased to about 100:1 and filtering to remove a formed fluoride precipitate; (b) adding to the diluted polyphosphoric acid mixture copper, nitric acid, and fume inhibitor forming an aluminum brightening bath; (c) maintaining the total concentration of said iron, aluminum, and magnesium ion contaminants in said bath below about 3% as expressed in aluminum equivalents; (d) maintaining the purity of said bath to below about 500 ppm organic substances oxidizable in nitric acid; (e) maintaining said bath's temperature between about 90° C. and about 120° C.; and (f) immersing the aluminum to be brightened in the bath for about 0.5 to about 4.0 minutes.