A method is given for the regeneration of cr6+ while substantially reducing the quantity of impurity metal ions in solution. Thus, spent cr6+ etching solution was filtered through a polypropylene cartridge. A pb-based anode and cu cathode were used with a catholyte containing h2so4 180 g/l. A current density of 2.15 A/dm2 was used. The composition of a typical spent etchant for brass was: cr3+ 45, cr6+ 42, cu 36, zn 22, na 35, ni 1.2 and so42- 270 g/l, with al, ca, CO, fe, k, mg, and mn present in trace amounts. The cr3+ was oxidized at 90 pct efficiency and the cu and zn were removed in amounts of 47 and 41 pct respectively. The cr lost to the catholyte was 5.8 pct.
U.S. Pat. 4,337,129, June 29, 1982; Chem. Abstr. 95:177,698W