Removal of Copper Ions from Rinse Water Using TIO(2) Photocatalysis

The switch to copper in the manufacture of circuitry for advance microchips has raised concern in the semiconductor industry about the status of wastewater discharges containing copper and the uncertainty of how the Environmental Protection Agency (EPA) will regulate these discharges. Regardless of how the EPA will regulate discharges each facility will still need to meet the requirements of its publicly owned treatment works (POTW). As an example, the city of Sunnyvale limits discharges of copper to 0.7 mg/L for a grab sample, and 0.5 mg/L for a 24 hour composite. As the industry implements copper interconnect processing it will also need to develop new, efficient methods for removing and recovering copper from aqueous waste streams. This paper demonstrates how copper ions can be effectively removed and concentrated from effluent waste streams with the use of Titanium Dioxide (TiO2) Photocatalysis. In the TiO2 photocatalytic process a photo-generated electron, in the absence of dissolved oxygen, is used to reduce copper (II) to copper (I) creating Cu2O, Which is bound on the TiO2 surface. After the copper ions have been removed from the original solution, a reverse process that re-oxidizes the copper can be used to regenerate the TiO2 and concentrate the copper ions in a separate solution for recovery or reuse. The aqueous copper waste used in thses experiments was derived from an electroless plating bath used to study copper deposition on silicon-based microchips. Under oxygen free conditions at an initial pH of 5.0 a solution with 12 ppm copper (II) ions was reduced to below detection levels within 30 minutes. After subsequent re-oxidation and concentration the copper ions were recovered in one-tenth the original solution volume.