Treatment of chelated iron and copper wastes by chemical oxidation

Abstract

Chelating agents are used commonly to remove deposits from surfaces of industrial equipment and to solubilize metals in electroless plating baths. The destruction of chelate (Ethylenediaminetetraacetic acid, EDTA) in chemical cleaning wastes using hydrogen peroxide and/or ozone as oxidants is described. The experiments were conducted in a batch reactor using simulated wastes containing elevated levels of iron, copper, and EDTA. With hydrogen peroxide as the oxidant, the pH, hydrogen peroxide dose, temperature, and initial composition of the solvent had the greatest effects on chelate destruction. A pH between 4 and 5, a 20:1 molar ratio of hydrogen peroxide to EDTA and a temperature of 40–60 °C consistently produced >95% destruction of the chelate. For ozone, EDTA removal was more dependent on the initial iron and EDTA concentrations than on the pH or ozone flowrate. Overall, hydrogen peroxide alone at above ambient temperatures was judged to be the most effective oxidant for destroying chelates in the cleaning wastes investigated.