Decomplexation of Cu(II)-EDTA by heat assisted CuO catalyzed H2O2: Sequential addition of H2O2, kinetics, mechanism and catalyst reutilization

A Cu-Fenton oxidation, heat assisted CuO catalyzed H2O2 (H2O2/CuO/heat), has been successfully combined with alkaline precipitation to remove Cu complexes from wastewater. The decomplexation process of Cu(II)-EDTA by H2O2/CuO/heat involved heterogeneous and homogeneous Cu-Fenton reactions. The acidic reaction condition (pH 2), higher temperature (80 °C), and higher CuO dosage (2 g/L) could improve the rate-limiting step of reduction of Cu(II) to Cu(I) in Cu-Fenton reactions of H2O2/CuO/heat to release more reactive oxygen species (ROS) for the decomplexation of Cu(II)-EDTA. With the sequential addition of H2O2, the Cu removal efficiency of Cu(II)-EDTA (3.14 mM) could reach up to 99.86% after 60 min of treatment of H2O2/CuO/heat. ROS including OH•, O2•-, and 1O2 produced by H2O2/CuO/heat were responsible for the decomplexation of Cu(II)-EDTA. Under attacks of ROS, the structure destruction of Cu(II)-EDTA induced the release of Cu ions and the formation of some small molecule organic acids and inorganic anions. The technical feasibility of Cu complexes decomplexation by H2O2/CuO/heat was further demonstrated on the treatment of real Cu-containing electroplating wastewater. In all 30 cycles of experiments, generated CuO sludge could be reutilized and possessed excellent long-lasting catalytic activity. The Cu residual concentration in all cycles could meet the stringent emission standard of pollutants for electroplating.