I'd use hydrogen peroxide because after it oxidizes, it becomes water, thus there aren't unwanted cations. I thought commercial peroxide was 3% pure H2O2 stabilized with 0.001% phosphoric acid, if I remember reading the ingridients on an old bottle some years back. But you're saying now it's some urea compound involved? I'm not sure what reactions that would have with a halogen. I know Chl;orine dissolves in water, anyways, all of those compounds work together and reall digest copper.
Would this peroxide-muriatic acid mixture dissolve silver, or gold, if very powerful oxidizing oxychlorides and free Cl2 are dissolved in water?